Philips Heartstart HSI Service manual

H e a r t S t a r t H S 1 D e f i b r i l l a t o r s

T E C H N I C A L R E F E R E N C E M A N U A L

Introductory Note

Heartstream, Inc., was founded in 1992. Its mission was to design and produce an automated external defibrillator (AED) that could be successfully used by a layperson responding to sudden cardiac arrest and that was:

•small

•light-weight

•low-cost

•rugged

•reliable

•safe

•easy-to-use, and

•maintenance-free.

Heartstream introduced its first AED, the ForeRunner, in 1996. The Heartstream ForeRunner AED marked the first widespread commercial use of a biphasic waveform in an external defibrillator.

Hewlett-Packard (HP) purchased Heartstream in 1997. Heartstream then added a relabeled version of the ForeRunner for Laerdal Medical Corporation called the Heartstart FR.

In 1999, Hewlett-Packard spun off its Medical Products Group, including the Heartstream Operation, into Agilent Technologies. While part of Agilent, Heartstream introduced a new AED, the Agilent Heartstream FR2. Laerdal Medical marketed this device as the Laerdal Heartstart FR2. The FR2 evolved into the FR2+, with the addition of an enhanced feature set, in 2001.

Heartstream became part of Philips Medical Systems in 2001, when Philips purchased the entire Medical Group from Agilent Technologies. The following year, all Philips defibrillators were rebranded as HeartStart Defibrillators, and Philips introduced the HeartStart HS1 family of AEDs, including the Philips and Laerdal HeartStart, and Philips HeartStart Home, and Philips HeartStart OnSite defibrillators.

The Philips HeartStart FRx AED was brought onto the market in 2005, along with a Laerdal version.

This manual is intended to provide technical and product information that generally applies to the Philips HeartStart OnSite, the Laerdal HeartStart HS1, and the Philips HeartStart Home Defibrillators, models M5066A, M5067A, and M5068A, respectively. To simplify the discussion, these defibrillators will be referred to as the HeartStart HS1 in this manual.

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October 2007

Philips Medical Systems

CONTENTS

1 The HeartStart HS1 Defibrillator

	Sudden cardiac arrest and the automated external defibrillator .........	1-1
	Design philosophy for the HS1 Defibrillators ..........................................	1-1
	Design features of the HS1 Defibrillators .................................................	1-2
	Reliability and Safety ................................................................................	1-2
	Ease of Use ................................................................................................	1-3
	No Maintenance .......................................................................................	1-5
2	Defibrillation and Electricity
	The Heart’s Electrical System .......................................................................	2-1
	Simplifying Electricity ......................................................................................	2-4
3	SMART Biphasic Waveform
	A Brief History of Defibrillation ..................................................................	3-1
	SMART Biphasic ...............................................................................................	3-4
	Understanding Fixed Energy ..................................................................	3-5
	Evidence-Based Support for the SMART Biphasic Waveform ......	3-6
	SMART Biphasic Superior to Monophasic .........................................	3-6
	Key Studies ................................................................................................	3-7
	Frequently Asked Questions ........................................................................	3-8
	Are all biphasic waveforms alike? .........................................................	3-8
	How can the SMART Biphasic waveform be more effective at
	lower energy? ...........................................................................................	3-9
	Is escalating energy required? ...............................................................	3-10
	Is there a relationship between waveform, energy level,
	and post-shock dysfunction? .................................................................	3-13
	How does SMART Biphasic compare to other
	biphasic waveforms? ................................................................................	3-14
	Is there a standard for biphasic energy levels? ..................................	3-14
	Commitment to SMART Biphasic ........................................................	3-15
	References ........................................................................................................	3-16
4	SMART Analysis
	Pad Contact Quality .......................................................................................	4-1
	Artifact Detection ...........................................................................................	4-1
	Overview ...................................................................................................	4-1
	CPR at High Rates of Compression ....................................................	4-2
	Pacemaker Detection .............................................................................	4-2

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Arrhythmia Detection ....................................................................................	4-4
Rate .............................................................................................................	4-5
Conduction ...............................................................................................	4-5
Stability .......................................................................................................	4-6
Amplitude ..............................................................................................................	4-7
Specific Analysis Examples .....................................................................	4-7
Sensitivity and Specificity ........................................................................	4-10
Shockable Rhythms .........................................................................................	4-11
Validation of Algorithm ..................................................................................	4-14
Specific Concerns for Advanced Users of HeartStart AEDs ................	4-16
HeartStart AED vs. HeartStart ALS Defibrillator Algorithms .......	4-16
Simulator Issues with SMART Analysis ...............................................	4-16
Use of External Pacemakers with Internal Leads .............................	4-17

5 Other Features of the HeartStart HS1 Defibrillator

Overview ...........................................................................................................	5-1
Self-Tests ...........................................................................................................	5-1
Battery Insertion Test .............................................................................	5-1
Ready Light ................................................................................................	5-1
Periodic Self-Tests ...................................................................................	5-2
“Power On” and “In Use” Self-Tests ..................................................	5-4
Cumulative Device Record ...........................................................................	5-5
Supplemental Maintenance Information for Technical Professionals ..	5-5
Background ................................................................................................	5-5
Calibration requirements and intervals ..............................................	5-5
Maintenance testing .................................................................................	5-5
Verification of energy discharge ...........................................................	5-6
Service/Maintenance and Repair Manual ............................................	5-6
CPR Coaching ..................................................................................................	5-6
Quick Shock .....................................................................................................	5-6
Pediatric Defibrillation ...................................................................................	5-7
HeartStart Trainer ..........................................................................................	5-8
Training Scenarios ....................................................................................	5-8

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	iii
6 Theory of Operation
Overview ...........................................................................................................	6-1
User interface ...................................................................................................	6-3
Operation ..................................................................................................	6-3
Maintenance ..............................................................................................	6-3
Troubleshooting .......................................................................................	6-3
Control Board ..................................................................................................	6-3
Battery ........................................................................................................	6-4
Power Supply ............................................................................................	6-4
ECG Front End .........................................................................................	6-4
Patient Circuit ...........................................................................................	6-4
Data Recording .........................................................................................	6-5
Temperature Sensor ...............................................................................	6-5
Real-Time Clock ......................................................................................	6-6
IR Port ........................................................................................................	6-6
7 HeartStart Data Management Software
Overview ...........................................................................................................	7-1
System Requirements .....................................................................................	7-3
Comparison of Event Review and Event Review Pro .............................	7-3
Data Management Software Versions ........................................................	7-5
System Annotations ........................................................................................	7-6
Technical Support for Data Management Software ................................	7-6
Configuration Software ..................................................................................	7-8

CONTENTS

iv

	APPENDICES
A	Technical Specifications
	Standards Applied ............................................................................................	A-1
	HS1 AED Specifications .................................................................................	A-2
	Electromagnetic Conformity ........................................................................	A-6
	Accessories Specifications .............................................................................	A-9
	Environmental considerations ......................................................................	A-11
B	Troubleshooting Information
	Troubleshooting the Heartstart HS1 Defibrillator .................................	B-1
	Verification of Energy Delivery ....................................................................	B-3
C	Pads and Battery
	Defibrillator Pads for the HeartStart HS1 AED .......................................	C-1
	Defibrillator Pads Placement with HS1 AED ............................................	C-2
	Batteries for HS1 AED ...................................................................................	C-3
D	Use Environment
	Defibrillation in the Presence of Oxygen ..................................................	D-1
	Defibrillation on a Wet or Metal Surface ..................................................	D-1
	Protection against Water and Particles .....................................................	D-4
	Effects of Extreme Environments ................................................................	D-6
	Self-Test Aborts Due to Temperature Extremes ....................................	D-8
E	Guidelines 2005
F	Literature Summary for HeartStart AEDs
	Introduction ......................................................................................................	F-1
	References ........................................................................................................	F-2
	Selected Study Summaries .............................................................................	F-15
	HeartStart Low-Energy, High-Current Design .................................	F-15
	HeartStart Quick Shock Feature ..........................................................	F-17
	HeartStart’s Human Factors Design ....................................................	F-20
	HeartStart Defibrillation Therapy Testing in Adult
	Victims of Out-of-Hospital Cardiac Arrest .......................................	F-23
	HeartStart Patient Analysis System Testing with
	Pediatric Rhythms ....................................................................................	F-25
	HeartStart Defibrillation Therapy Testing in a Pediatric
	Animal Model ............................................................................................	F-28

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HEARTSTART HS1 DEFIBRILLATORS TECHNICAL REFERENCE MANUAL

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1 The HeartStart HS1 Defibrillators

Sudden cardiac arrest and the automated external defibrillator

Each year in the United States alone, approximately 340,000 people suffer sudden cardiac arrest (SCA).1 Fewer than 5% of them survive. SCA is most often caused by an irregular heart rhythm called ventricular fibrillation (VF), for which the only effective treatment is defibrillation, an electrical shock. Often, a victim of SCA does not survive because of the time it takes to deliver the defibrillation shock; or every minute of VF with cardiopulmonary resuscitation (CPR), the chances of survival decrease by 7% to 10%.2

Traditionally, only trained medical personnel were allowed to use a defibrillator because of the high level of knowledge and training involved. Initially, this meant that the victim of SCA would have to be transported to a medical facility in order to be defibrillated. In 1969, paramedic programs were developed in several communities in the U.S. to act as an extension of the hospital emergency room. Paramedics went through extensive training to learn how to deliver emergency medical care outside the hospital, including training in defibrillation. In the early 1980s, some Emergency Medical Technicians (EMTs) were also being trained to use defibrillators to treat victims of SCA. However, even with these advances, in 1990 fewer than half of the ambulances in the United States carried a defibrillator, so the chances of surviving SCA outside the hospital or in communities without highly developed Emergency Medical Systems were still very small.

The development of the automated external defibrillator (AED) made it possible for the first responders (typically lay persons) at the scene to treat SCA with defibrillation. People trained to perform CPR can now use a defibrillator to defibrillate a victim of SCA. The result: victims of sudden cardiac arrest can be defibrillated more rapidly than ever before, and they have a better chance of surviving until more highly trained medical personnel arrive who can treat the underlying causes.

Design philosophy for the HS1 Defibrillators

The Philips HeartStart HS1 family of automated external defibrillators (AEDs) include the HeartStart HS1, the HeartStart OnSite, and the HeartStart Home.

The Philips HeartStart HS1 automated external defibrillator (AEDs) are designed specifically for use by the first people responding to an emergency. They are reliable, easy to use, and virtually maintenance free. The design allows these AEDs to be used by people with no medical training in places

1American Heart Association. Heart Disease and Stroke Statistics - 2005 Update. Dallas, TX.:American Heart Association;2005.

22005 American Heart Association Guidelines for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care. Circulation. 2005;112 Supplement IV

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where defibrillators have not traditionally been used. In fact, the HeartStart Home was the first AED cleared by the United States Food and Drug Administration for sale without a prescription.

Factors that had to be considered in their design included the fact that an AED might not be used very often, might be subjected to harsh environments, and probably would not have personnel available to perform regular maintenance.

The HS1 AEDs were not designed to replace the manual defibrillators used by more highly trained individuals. Instead, they are intended to complement the efforts of medical personnel by allowing the initial shock to be delivered by the first person to arrive at the scene.

Design features of the HS1 AEDs

Reliability and Safety

•FAIL-SAFE DESIGN — The HS1 AEDs are intended to detect a shockable rhythm and instruct the user to deliver a shock if needed. They will not allow a shock if one is not required.

•DAILY AUTOMATIC SELF-TEST — The HS1 AEDs perform daily as well as weekly and monthly self-tests to help ensure they are ready to use when needed. An active LED Ready light serves as a status indicator and demonstrates at a glance that the unit has passed its last self-test and is therefore ready to use.

•ENVIRONMENTAL PARAMETERS — Environmental tests were conducted to prove the HS1 AEDs’ reliability and ability to operate in conditions relevant to expected use.

•NON-RECHARGEABLE LITHIUM BATTERY — The HS1 long-life battery pack M5070A was designed for use in an emergency environment and is therefore small, lightweight, and safe to use. The battery pack contains multiple 2/3A size, standard lithium camera batteries. These same batteries can be purchased at local drug stores for use in other consumer products. These batteries have been proven to be reliable and safe over many years of operation. The HS1 battery pack uses lithium

manganese dioxide (Li/MnO2) technology and does not contain pressurized sulfur dioxide. The battery pack meets the U.S.

Environmental Protection Agency's Toxicity Characteristic Leaching Procedure. All battery cells contain chemicals and should be recycled at an appropriate recycling facility in accordance with local regulations.

•QUICK SHOCK — The HS1 can deliver a defibrillation shock very quickly – typically within 8 seconds – after the end of a patient care pause.

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Ease of Use

•SMALL AND LIGHT — The biphasic waveform technology used in the HS1 AEDs has allowed them to be small and light. They can easily be carried and operated by one person.

•SELF-CONTAINED — Both the standard and hard-shell carry cases for the HS1 have room for an extra defibrillator Pads Cartridge and an extra battery.

•VOICE PROMPTS — The HS1 AEDs provide clear, calm, audible prompts that guide the user through the process of using the device.

•CPR COACHING — In its default configuration, the HS1 AEDs provide basic verbal instructions for performing cardiopulmonary resuscitation, including hand placement, rescue breathing, compression depth and timing, provided by the HS1 when the flashing blue i-button is pressed during the first 30 seconds of a patient care pause. If the Infant/Child Pads Cartridge is inserted in the HS1, the CPR Coaching provided will be for infant/child CPR.

•PRE-CONNECTED PADS — The HS1 uses a pre-installed HeartStart SMART Pads Cartridge. The HeartStart Infant/Child Pads Cartridge is designed for use in the event defibrillation is required for an infant or child under 55 pounds and 8 years old. The AED can be turned on by pulling the green Pads Cartridge handle, as well as by using the green On/Off button.

•CAUTION LIGHT — When the HS1 is in use and is analyzing the patient’s heart rhythm, a triangular Caution light on the front of the HS1 flashes to alert the user not to touch the patient. When the HS1 advises a shock, the

Caution light stops flashing and stays on as a reminder not to touch the patient during shock delivery.

•I-BUTTON — The HS1 has a blue information button

(i-button) on the front. When it is on solid (without flashing), it is an indicator that it is safe to touch the patient.

When the button flashes the user can press it to get

information such as summary data about the last use or (default) CPR Coaching.

•SHOCK BUTTON — The orange Shock button on the front of the HS1 bears a lightning bolt symbol to identify it. It flashes when the unit has charged for a shock and directs the user to press the button to deliver a shock by pressing the Shock button.

INTRODUCTION TO THE HEARTSTART HS1 AED

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•CLEAR LABELING AND GRAPHICS — The HS1 AEDs are designed to enable fast response by the user. The 1-2-3 operation guides the user

to: 1) turn the unit on, 2) follow the prompts, and 3) deliver a shock if instructed. A Quick

Reference Card stored inside the carry case reinforces these instructions. The pads placement icon on the pads cartridge indicates

clearly where pads should be placed, and the

pads themselves are labeled to specify where each one should be placed. The polarity of the pads does not affect the operation of the AED,

but user testing has shown that people apply the pads more quickly and accurately if a specific position is shown on each pad.

•PROVEN ANALYSIS SYSTEM — The SMART rhythm analysis system used in the HS1 AEDs analyzes the patient’s ECG rhythm and determines whether or not a shock should be administered. The algorithm’s decision criteria allow the user to be confident that the HS1 will advise a shock only when it is appropriate treatment for the patient.

•ARTIFACT DETECTION SYSTEM — An artifact detection system in the HS1 AEDs senses if the ECG is being corrupted by some form of artifact from electrical “noise” in the surrounding environment, patient handling, or the activity of an implanted pacemaker. Because such artifact might inhibit or delay a shock decision, the HS1 filters out the noise from the ECG, prompting the user to stop patient handling, or determining that the level of artifact does not pose a problem for the algorithm.

•PADS DETECTION SYSTEM — The HS1 AEDs’ pads detection system provides a voice prompt to alert the user if the pads are not making proper contact with the patient's skin.

No Maintenance

•AUTOMATIC DAILY/WEEKLY/MONTHLY SELF-TESTS — There is no need for calibration, energy verification, or manual testing with the HS1 AEDs. Calibration and energy verification are automatically performed once a month as part of the HS1 self-test routine.

•ACTIVE STATUS INDICATOR — The green LED Ready light in the upper right-hand corner of the HS1 AED shows whether or not the device has passed its last self-test. When the Ready light is blinking, you can confident that the device has passed its last self-test and is ready for use. A solid Ready light means the defibrillator is being used

•BATTERY LEVEL INDICATOR — The HS1 AEDs prompt the user with an audible alarm when the battery needs to be replaced.

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HEARTSTART HS1 DEFIBRILLATORS TECHNICAL REFERENCE MANUAL

2 Defibrillation and Electricity

The Heart’s Electrical System

The heart muscle, or myocardium, is a mass of muscle cells. Some of these cells (“working” cells) are specialized for contracting, which causes the pumping action of the heart. Other cells (“electrical system” cells) are specialized for conduction. They conduct the electrical impulses throughout the heart and allow it to pump in an organized and productive manner. All of the electrical activity in the heart is initiated in specialized muscle cells called “pacemaker” cells, which spontaneously initiate electrical impulses that are conducted through pathways in the heart made up of electrical system cells. Although autonomic nerves surround the heart and can influence the rate or strength of the heart’s contractions, it is the pacemaker cells, and not the autonomic nerves, that initiate the electrical impulses that cause the heart to contract.

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Relation of an ECG to the anatomy of the cardiac conduction system

The heart is made up of four chambers, two smaller, upper chambers called the atria, and two larger, lower chambers called the ventricles. The right atrium collects blood returning from the body and pumps it into the right ventricle. The right ventricle then pumps that blood into the lungs to be oxygenated. The left atrium collects the blood coming back from the lungs and pumps it into the left ventricle. Finally, the left ventricle pumps the oxygenated blood to the body, and the cycle starts over again.

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The electrocardiogram (ECG) measures the heart's electrical activity by monitoring the small signals from the heart that are conducted to the surface of the patient’s chest. The ECG indicates whether or not the heart is conducting the electrical impulses properly, which results in pumping blood throughout the body. In a healthy heart, the electrical impulse begins at the sinus node, travels down (propagates) to the A-V node, causing the atria to contract, and then travels down the left and right bundle branches before spreading out across the ventricles, causing them to contract in unison.

The “normal sinus rhythm” or NSR (so called because the impulse starts at the sinus node and follows the normal conduction path) shown below is an example of what the ECG for a healthy heart looks like.

Normal sinus rhythm

Sudden cardiac arrest (SCA) occurs when the heart stops beating in an organized manner and is unable to pump blood throughout the body. A person stricken with SCA will lose consciousness and stop breathing within a matter of seconds. SCA is a disorder of the heart’s electrical conduction pathway that prevents the heart from contracting in a manner that will effectively pump the blood.

Although the terms “heart attack” and “sudden cardiac arrest” are sometimes used interchangeably, they are actually two distinct and different conditions. A heart attack, or myocardial infarction (MI), refers to a physical disorder where blood flow is restricted to a certain area of the heart. This can be caused by a coronary artery that is obstructed with plaque and results in an area of tissue that doesn't receive any oxygen. This will eventually cause those cells to die if nothing is done. A heart attack is typically accompanied by pain, shortness of breath, and other symptoms, and is usually treated with drugs or angioplasty. Although sudden death is possible, it does not always occur. Many times, a heart attack will lead to SCA, which does lead to sudden death if no action is taken.

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The most common heart rhythm in SCA is ventricular fibrillation (VF). VF refers to a condition that can develop when the working cells stop responding to the electrical system in the heart and start contracting randomly on their own. When this occurs, the heart becomes a quivering mass of muscle and loses its ability to pump blood through the body. The heart “stops beating”, and the person will lose consciousness and stop breathing within seconds. If defibrillation is not successfully performed to return the heart to a productive rhythm, the person will die within minutes. The ECG below depicts ventricular fibrillation.

Ventricular fibrillation

Cardiopulmonary resuscitation, or CPR, allows some oxygen to be delivered to the various body organs (including the heart), but at a much-reduced rate. CPR will not stop fibrillation. However, because it allows some oxygen to be supplied to the heart tissue, CPR extends the length of time during which defibrillation is still possible. Even with CPR, a fibrillating heart rhythm will eventually degenerate into asystole, or “flatline,” which is the absence of any electrical activity. If this happens, the patient has almost no chance of survival.

Defibrillation is the use of an electrical shock to stop fibrillation and allow the heart to return to a regular, productive rhythm that leads to pumping action. The shock is intended to cause the majority of the working cells to contract (or “depolarize”) simultaneously. This allows them to start responding to the natural electrical system in the heart and begin beating in an organized manner again. The chance of survival decreases by about 10% for every minute the heart remains in fibrillation, so defibrillating someone as quickly as possible is vital to survival.

An electrical shock is delivered by a defibrillator, and involves placing two electrodes on a person's chest in such a way that an electrical current travels from one pad to the other, passing through the heart muscle along the way. Since the electrodes typically are placed on the patient's chest, the current must pass through the skin, chest muscles, ribs, and organs in the area of the chest cavity, in addition to the heart. A person will sometimes “jump” when a shock is delivered, because the same current that causes all the working cells in the heart to contract can also cause the muscles in the chest to contract.

DEFIBRILLATION AND ELECTRICITY

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Simplifying Electricity

Energy is defined as the capacity to do work, and electrical energy can be used for many purposes. It can drive motors used in many common household appliances, it can heat a home, or it can restart a heart. The electrical energy used in any of these situations depends on the level of the voltage applied, how much current is flowing, and for what period of time that current flows. The voltage level and the amount of current that flows are related by impedance, which is basically defined as the resistance to the flow of current.1

If you think of voltage as water pressure and current as the flow of water out of a hose, then impedance is determined by the size of the hose. If you have a small garden hose, the impedance would be relatively large and would not allow much water to flow through the hose. If, on the other hand, you have a fire hose, the impedance would be lower, and much more water could flow through the hose given the same pressure. The volume of water that comes out of the hose depends on the pressure, the size of the hose, and the amount of time the water flows. A garden hose at a certain pressure for a short period of time works well for watering your garden, but if you used a fire hose with the same pressure and time, you could easily wash your garden away.

Electrical energy is similar. The amount of energy delivered depends on the voltage, the current, and the duration of its application. If a certain voltage is present across the defibrillator pads attached to a patient's chest, the amount of current that will flow through the patient's chest is determined by the impedance of the body tissue. The amount of energy delivered to the patient is determined by how long that current flows at that level of voltage.

In the case of the biphasic waveforms shown in the following pages, energy (E) is the power (P) delivered over a specified time (t), or E = P x t.

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1Voltage is measured in volts, current is measured in amperes (amps), and impedance is measured in ohms. Large amounts of electrical energy are measured in kilowatt-hours, as seen on your electric bill. Small amounts can be measured in joules (J), which are watt-seconds.

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2-5

	Electrical power is defined as the
	voltage (V) times the current (volts=	P = V x I
	joules/coulomb, amps = coulombs/sec):
	From Ohm's law, voltage and	V = I x R or
	current are related by resistance (R)
		I = V/R
	(impedance):
	Power is therefore related to voltage	P = V2/R or
	and resistance by:	P = I2R
	Substituting this back into the equation	E = V2/R x t or
	for energy means that the energy
	delivered by the biphasic waveform is	E = I2R x t
	represented by:

In determining how effective the energy is at converting a heart in fibrillation, how the energy is delivered -- or the shape of the waveform (the value of the voltage over time) -- is actually more important than the amount of energy delivered.

For the SMART Biphasic waveform, the design strategy involved starting with a set peak voltage stored on the capacitor that will decay exponentially as current is delivered to the patient. The SMART Biphasic waveform shown here is displayed with the voltage plotted versus time, for a patient with an impedance of 75 ohms. By changing the time duration of the positive and negative pulses, the energy delivered to the patient can be controlled.

SMART Biphasic waveform

Although the relationship of voltage and energy is of interest in designing the defibrillator, it is actually the current that is responsible for defibrillating the heart.

DEFIBRILLATION AND ELECTRICITY

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The following three graphs demonstrate how the shape of the current waveform changes with different patient impedances. Once again, the SMART Biphasic waveform delivers the same amount of energy (150 J) to every patient, but the shape of the waveform changes to provide the highest level of effectiveness for defibrillating the patient at each impedance value.

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With the SMART Biphasic waveform, the shape of the waveform is optimized for each patient. The initial voltage remains the same, but the peak current will depend on the patient’s impedance. The tilt (slope) and the time duration are adjusted for different patient impedances to maintain approximately 150 J for each shock. The phase ratio, or the relative amount of time the waveform spends in the positive pulse versus the negative pulse, is also adjusted depending upon the patient impedance to insure the waveform remains effective for all patients. Adjusting these parameters makes it easier to control the accuracy of the energy delivered since they are proportionally related to energy, whereas voltage is exponentially related to energy.

The HeartStart Defibrillator measures the patient's impedance during each shock. The delivered energy is controlled by using the impedance value to determine what tilt and time period are required to deliver 150 J.

The average impedance in adults is 75 ohms, but it can vary from 25 to 180 ohms. Because a HeartStart Defibrillator measures the impedance and adjusts the shape of the waveform accordingly, it delivers 150 J of energy to the patient every time the shock button is pressed. Controlling the amount of energy delivered allows the defibrillator to deliver enough energy to defibrillate the heart, but not more. Numerous studies have demonstrated that the waveform used by HeartStart Defibrillator is more effective in defibrillating out-of-hospital cardiac arrest patients than the waveforms used by conventional defibrillators. Moreover, the lower energy delivered results in less post-shock dysfunction of the heart, resulting in better outcomes for survivors.

DEFIBRILLATION AND ELECTRICITY

Notes

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3 SMART Biphasic Waveform

Defibrillation is the only effective treatment for ventricular fibrillation, the most common cause of sudden cardiac arrest (SCA). The defibrillation waveform used by a defibrillator determines how energy is delivered to a patient and defines the relationship between the voltage, current, and patient impedance over time. The defibrillator waveform used is critical for defibrillation efficacy and patient outcome.

A Brief History of Defibrillation

The concept of electrical defibrillation was introduced over a century ago. Early experimental defibrillators used 60 cycle alternating current (AC) household power with step-up transformers to increase the voltage. The shock was delivered directly to the heart muscle. Transthoracic

(through the chest wall)	alternating current (AC) waveform
defibrillation was first used in
the 1950s.

The desire for portability led to the development of battery-powered direct current (DC) defibrillators in the 1950s. At that time it was also discovered that DC shocks were more effective than AC shocks. The first “portable” defibrillator was developed at Johns Hopkins University. It used a biphasic waveform to deliver 100 joules (J) over 14 milliseconds. The unit weighed 50 pounds with accessories (at a time when standard defibrillators typically weighed more than 250 pounds) and was briefly commercialized for use in the electric utility industry.

Defibrillation therapy gradually gained acceptance over the next two decades. An automated external defibrillator (AED) was introduced in the mid-1970s, shortly before the first automatic internal cardioverter-

defibrillator (AICD) was implanted in a human.

Historically, defibrillators used one of two types of monophasic waveforms: monophasic damped sine (MDS) or monophasic truncated exponential (MTE). With monophasic waveforms, the heart receives a single burst of electrical current that travels from one pad or paddle to the other.

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monophasic truncated exponential (MTE) waveform

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biphasic damped sine (MDS) waveform

The MDS waveform requires high energy levels, up to 360 J, to defibrillate effectively. MDS waveforms are not designed to compensate for differences in impedance — the resistance of the body to the flow of current — encountered in different patients. As a result, the effectiveness of the shock can vary greatly with the patient impedance.

Traditional MDS waveform defibrillators assume a patient impedance of 50 ohms, but the average impedance of adult humans is between 70 and 80 ohms. As a result, the actual energy delivered by MDS waveforms is usually higher than the selected energy.

The monophasic truncated exponential (MTE) waveform

also uses energy settings of up to 360 J. Because it uses a

lower voltage than the MDS waveform, the MTE waveform requires a longer duration to

deliver the full energy to patients with higher

impedances. This form of impedance compensation

does not improve the efficacy of defibrillation, but simply

allows extra time to deliver the selected energy. Long-duration shocks (> 20 msec) have been associated with refibrillation.1

Despite the phenomenal advances in the medical and electronics fields during the last half of the 20th century, the waveform technology used for external defibrillation remained the same until just recently. In 1992, research scientists and engineers at Heartstream (now part of Philips Medical Systems) began work on what was to become a significant advancement in external defibrillation waveform technology. Extensive studies for implantable defibrillators had shown biphasic waveforms to be superior to monophasic waveforms.2,3,4 In fact, a biphasic waveform has been the standard waveform for implantable defibrillators for over a decade. Studies have demonstrated that biphasic waveforms defibrillate at lower energies and thus require smaller components that result in smaller and lighter devices.

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defibrillation current flow

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Heartstream pursued the use of the biphasic waveform in AEDs for similar reasons; use of the biphasic waveform allows for smaller and lighter AEDs. The SMART Biphasic waveform has been proven effective at an energy level of 150 joules and has been used in HeartStart AEDs since they were introduced in 1996.

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biphasic truncated exponential (BTE) waveform

The basic difference between monophasic and

biphasic waveforms is the

direction of current flow

between the defibrillation pads. With a monophasic

waveform, the current flows in only one direction.

With a biphasic waveform, the current flows in one direction and then reverses and flows in the opposite direction. Looking at the

waveforms, a monophasic waveform has one positive pulse, whereas a biphasic starts with a positive pulse that is followed by a negative one.

In the process of developing the biphasic truncated exponential waveform for use in AEDs, valuable lessons have been learned:

1.Not all waveforms are equally effective. How the energy is delivered (the waveform used) is actually more important than how much energy is delivered.

2.Compensation is needed in the waveform to adjust for differing patient impedances because the effectiveness of the waveform may be affected by patient impedance. The patient impedance can vary due to the energy delivered, electrode size, quality of contact between the electrodes and the skin, number and time interval between previous shocks, phase of ventilation, and the size of the chest.

3.Lower energy is better for the patient because it reduces post-shock dysfunction. While this is not a new idea, it has become increasingly clear as more studies have been published.

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The characteristics for the monophasic damped sine and monophasic truncated exponential waveforms are specified in the AAMI standard DF80:2003; the result is that these waveforms are very similar from one manufacturer to the next.

There is no standard for biphasic waveforms, each manufacturer has designed their own. This has resulted in various wave-shapes depending on the design approach used. While it is generally agreed that biphasic waveforms are better than the traditional monophasic waveforms, it is also true that different levels of energy are required by different biphasic waveforms in order to be effective.

SMART Biphasic

SMART Biphasic is the patented waveform used by all HeartStart AEDs. It is an impedance-compensating, low energy (<200 J), low capacitance (100 µF), biphasic truncated exponential (BTE) waveform that delivers a fixed energy of 150 J for defibrillation. Heartstream was the first company to develop a biphasic waveform for use in AEDs.

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SMART Biphasic waveform

The SMART Biphasic waveform developed by Heartstream compensates for different impedances by measuring the patient impedance during the discharge and using that value to adjust the duration of the waveform to deliver the desired 150 joules. Since the starting voltage is sufficiently large, the delivered energy of 150 joules can be accomplished without the duration ever exceeding 20 milliseconds. The distribution of the energy between the positive and negative pulses was fine tuned in animal studies to optimize defibrillation efficacy and validated in studies conducted in and out of the hospital environment.

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Different waveforms have different dosage requirements, similar to a dosage associated with a medication. “If energy and current are too low, the shock will not terminate the arrhythmia; if energy and current are too high, myocardial damage may result.” (I-63)5 The impedance compensation used in the SMART Biphasic waveform results in an effective waveform for all patients. The SMART Biphasic waveform has been demonstrated to be just as effective or superior for defibrillating VF when compared to other waveforms and escalating higher energy protocols.

Understanding Fixed Energy

The BTE waveform has an advantage over the monophasic waveforms related to the shape of the defibrillation response curve. The following graph, based on Snyder et al., demonstrates the difference between the defibrillation response curves for the BTE and the MDS waveform.

Philips Medical Systems

With the gradual slope of the MDS waveform, it is apparent that as current increases, the defibrillation efficacy also increases. This characteristic of the MDS response curve explains why escalating energy is needed with the MDS waveform; the probability of defibrillation increases with an increase in peak current, which is directly related to increasing the energy.

For a given amount of energy the resulting current level can vary greatly depending on the impedance of the patient. A higher-impedance patient receives less current, so escalating the energy is required to increase the probability of defibrillation.

The steeper slope of the BTE waveform, however, results in a response curve where the efficacy changes very little with an increase in current, past a certain current level. This means that if the energy (current) level is chosen appropriately, escalating energy is not required to increase the efficacy. This

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fact, combined with the lower energy requirements of BTE waveforms,16,18 means that it is possible to choose one fixed energy that allows any patient to be effectively and safely defibrillated.

Evidence-Based Support for the SMART Biphasic Waveform

Using a process outlined by the American Heart Association (AHA) in 1997,6 the Heartstream team put the SMART Biphasic waveform through a rigorous sequence of validation studies. First, animal studies were used to test and fine-tune the waveform parameters to achieve optimal efficacy. Electrophysiology laboratory studies were then used to validate the waveform on humans in a controlled hospital setting. Finally, after receiving FDA clearance for the Heartstream AED, post-market studies were used to prove the efficacy of the SMART Biphasic waveform in the out-of-hospital, emergency-resuscitation environment.

Even when comparing different energies delivered with a single monophasic waveform, it has been demonstrated that lower-energy shocks result in fewer post shock arrhythmias.7 Other studies have demonstrated that the biphasic waveform has several clinical advantages. It has equivalent efficacy to higher energy monophasic waveforms but shows no significant ST segment change

from the baseline.8 There is also evidence of less post shock dysfunction when the biphasic waveform is used.9,10,11,29 There is evidence that the

biphasic waveform has improved performance when anti-arrhythmic drugs are present,12,13 and with long duration VF.14,20 A more recent study has also

demonstrated improved neurological outcomes for survivors defibrillated with SMART Biphasic when compared to patients defibrillated with monophasic waveforms.15

The bottom line is that the SMART Biphasic waveform has been demonstrated to be just as effective or superior to monophasic waveforms at defibrillating patients in VF. In addition, there are indications that patients defibrillated with the SMART Biphasic waveform suffer less dysfunction than those defibrillated with conventional escalating-energy monophasic waveforms. SMART Biphasic has been used in AEDs for over a decade, and there are numerous studies to support the benefits of this waveform, including out-of-hospital data with long-down-time VF.

SMART Biphasic Superior to Monophasic

Researchers have produced over 20 peer-reviewed manuscripts to prove the efficacy and safety of the SMART Biphasic waveform. Thirteen of these are out-of-hospital studies that demonstrated high efficacy of the SMART Biphasic waveform on long-down-time patients in emergency environments. No other waveform is supported by this level of research.

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Using criteria established by the AHA in its 1997 Scientific Statement,27 the data from the ORCA study15,34 demonstrate that the 150J SMART Biphasic

waveform is superior to the 200J - 360J escalating energy monophasic waveform in the treatment of out-of-hospital cardiac arrest. This is true for one-shock, two-shock, and three-shock efficacy and return of spontaneous circulation.

Key Studies

	year	waveforms studied	results
	1992	low-energy vs.	249 patients (emergency resuscitation). Low-energy and high-energy
		high-energy damped sine	damped sine monophasic are equally effective. Higher energy is
		monophasic	associated with increased incidence of A-V block with repeated shocks.7
	1994		19 swine. Biphasic shocks defibrillate at lower energies, and with less
		biphasic vs. damped sine	post-shock arrhythmia, than monophasic shocks.16
	1995		171 patients (electrophysiology laboratory). First-shock efficacy of
		monophasic
			biphasic damped sine is superior to high-energy monophasic damped
			sine.17
	1995	low-energy truncated	30 patients (electrophysiology laboratory). Low-energy truncated
		biphasic vs. high-energy	biphasic and high-energy damped sine monophasic equally
		damped sine monophasic	effectiveness.18
	1996	115 J and 130 J truncated	294 patients (electrophysiology laboratory). Low-energy truncated
		biphasic vs. 200 J and 360	biphasic and high-energy damped sine monophasic are equally effective.
		J damped sine	High-energy monophasic is associated with significantly more
		monophasic	post-shock ST-segment changes on ECG.8 This study of a 115 J and 130
			J waveform contributed to the development of the 150 J, nominal,
			therapy that ships with Philips AEDs.
	1997		18 patients (10 VF, emergency resuscitation). SMART Biphasic
			terminated VF at higher rates than reported damped sine or truncated
			exponential monophasic.19
	1998		30 patients (electrophysiology laboratory). High-energy monophasic
			showed significantly greater post-shock ECG ST-segment changes than
		SMART Biphasic vs.	SMART Biphasic.9
		standard high-energy
	1999		286 patients (100 VF, emergency resuscitation). First-shock efficacy of
		monophasic
			SMART Biphasic was 86% (compared to pooled reported 63% for
			damped sine monophasic); three or fewer shocks, 97%; 65% of patients
			had organized rhythm at hand-off to ALS or emergency personnel.20
			116 patients (emergency resuscitation). At all post-shock assessment
			times (3 - 60 seconds) SMART Biphasic patients had lower rates of VF.
			Refibrillation rates were independent of waveform.10
	1999	low-energy (150 J) vs.	20 swine. Low-energy biphasic shocks increased likelihood of
		high-energy (200 J)	successful defibrillation and minimized post-shock myocardial
		biphasic	dysfunction after prolonged arrest.21

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	year	waveforms studied	results
	1999	low-capacitance biphasic	10 swine. Five of five low-capacitance shock animals were resuscitated,
		vs. high-capacitance	compared to two of five high-capacitance at 200 J. More cumulative
		biphasic	energy and longer CPR were required for high-capacitance shock
			animals that survived.22
	1999		10 swine. Stroke volume and ejection fraction progressively and
			significantly reduced at 2, 3, and 4 hours post-shock for monophasic
			animals but improved for biphasic animals.11
			338 patients (115 VF, emergency resuscitation). Demonstrated
	2000		superior defibrillation performance in comparison with escalating,
		SMART Biphasic vs.	high-energy monophasic shocks in out-of hospital cardiac arrest
		escalating high-energy	(average time from call to first shock was 8.9 minutes). SMART Biphasic
		monophasic	defibrillated at higher rates than MTE and MDS (96% first-shock efficacy
			vs. 59%), with more patients achieving ROSC. Survivors of SMART
			Biphasic resuscitation were more likely to have good cerebral
			performance at discharge, and none had coma (vs. 21% for monophasic
			survivors).15
	2001		338 patients (115 VF, emergency resuscitation). Use of a low-energy
			impedance-compensating biphasic waveform device resulted in superior
			first-shock efficacy, in the first set of two or three shocks, time to
			shock, and first successful shock compared to traditional defibrillators
			using escalating energy monophasic truncated exponential and
			monophasic damped sine waveforms.34
	2004		62 patients (shockable rhythms; 41% of patients were classified as
			overweight, 24% as obese, and 4% as extremely obese). Overweight
			patients were successfully defibrillated by the 150 J SMART Biphasic
		SMART Biphasic	waveform, without energy escalation.35
	2005		102 patients (all presenting with shockable rhythms). SMART Biphasic
			successfully defibrillated high-impedance patients without energy
			escalation. Rapid defibrillation rather than differences in patient
			impedance accounted for resuscitation success.36

Frequently Asked Questions

Are all biphasic waveforms alike?

No. Different waveforms perform differently, depending on their shape, duration, capacitance, voltage, current, and response to impedance. Different biphasic waveforms are designed to work at different energies. As a result, an appropriate energy dose for one biphasic waveform may be inappropriate for a different waveform.

There is evidence to suggest that a biphasic waveform designed for lowenergy defibrillation may result in overdose if applied at high energies (the Tang AHA abstract from 1999 showed good resuscitation performance for the SMART Biphasic waveform, but more shocks were required at 200 J than at 150 J21). Conversely, a biphasic waveform designed for high-energy defibrillation may not defibrillate effectively at lower energies. (The Tang

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AHA abstract from 1999 showed poor resuscitation performance for the 200 µF capacitance biphasic waveform at 200 J compared to the 100 µF capacitance biphasic waveform [SMART Biphasic] at 200 J.22 The Higgins manuscript from 2000 showed that the 200 µF capacitance biphasic waveform performed better at 200 J than at 130 J.23)

It is consequently necessary to refer to the manufacturer's recommendations and the clinical literature to determine the proper dosing for a given biphasic waveform. The recommendations for one biphasic waveform should not be arbitrarily applied to a different biphasic waveform. “It is likely that the optimal energy level for biphasic defibrillators will vary with the units' waveform characteristics. An appropriate energy dose for one biphasic waveform may be inappropriate for another.”24

SMART Biphasic was designed for low-energy defibrillation, while some other biphasic waveforms were not. It would be irresponsible to use a waveform designed for high energy with a low-energy protocol.

How can the SMART Biphasic waveform be more effective at lower energy?

The way the energy is delivered makes a significant difference in the efficacy of the waveform. Electric current has been demonstrated to be the variable most highly correlated with defibrillation efficacy. The SMART Biphasic waveform uses a 100 µF capacitor to store the energy inside the AED; other biphasic waveforms use a 200 µF capacitor to store the energy. The energy

(E) stored on the capacitor is given by the equation:

E = ½ C V2

The voltage (V) and the current (I) involved with defibrillating a patient are related to the patient impedance (R) by the equation:

V = I R

Peak Current Levels

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For the 200 µF capacitance biphasic waveform to attain similar levels of current to the SMART Biphasic (100 µF) waveform, it must apply the same voltage across the patient's chest. This means that to attain similar current levels, the 200 µF biphasic waveform must store twice as much energy on the capacitor and deliver much more energy to the patient; the graph at right demonstrates this relationship. This is the main reason why some biphasic waveforms require higher energy doses than the SMART Biphasic waveform to attain similar efficacy.

The illustrations to the left show the SMART Biphasic waveform and another biphasic waveform with a higher capacitance, similar to that used by another AED manufacturer. The low capacitance used by the patented SMART Biphasic waveform delivers energy more efficiently. In an animal study using these two waveforms, the SMART Biphasic waveform successfully resuscitated all animals and required less cumulative energy and shorter CPR time than the other biphasic waveform, which resuscitated only 40% of the animals.22

The amount of energy needed depends on the waveform that is used. SMART Biphasic has been demonstrated to effectively defibrillate at 150 J in out-of-hospital studies.15 Animal studies have indicated that the SMART Biphasic waveform would not be more effective at higher energies21 and this

seems to be supported with observed out-of-hospital defibrillation efficacy of 96% at 150 J.15

Is escalating energy required?

Not with SMART Biphasic technology. In the “Guidelines 2005,”5 the AHA states, “Energy levels vary by type of device.” (IV-37) The SMART Biphasic waveform has been optimized for ventricular defibrillation efficacy at 150 J. Referring to studies involving the SMART Biphasic waveform, it states, “Overall this research indicates that lower-energy biphasic waveform shocks have equivalent or higher success for termination of VF than either damped sinusoidal or truncated exponential monophasic waveform shocks delivering escalating energy (200 J, 300 J, 360 J) with successive shocks.” (IV-37)

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All HeartStart AEDs use the 150 J SMART Biphasic waveform. Two ALS defibrillator products, the HeartStart XL and MRx, provide an AED mode as well as ALS features such as manual defibrillation, synchronized cardioversion, etc. Selectable energy settings (from 2 to 200 J for the XL or

1 to 200 J for the MRx) are available in the XL and MRx only in the manual mode. A wider range of energy settings is appropriate in a device designed for use by advanced life support (ALS) responders who may perform manual pediatric defibrillation or synchronized cardioversion, as energy requirements may vary depending on the type of cardioversion rhythm.25,26 For treating VF in patients over eight years of age in the AED mode, however, the energy is preset to 150 J.

Some have suggested that a patient may need more than 150 J with a BTE waveform when conditions like heart attacks, high-impedance, delays before the first shock, and inaccurate electrode pad placement are present. This is not true for the SMART Biphasic waveform, as the evidence presented in the following sections clearly indicates. On the other hand, the evidence indicates that other BTE waveforms may require more than 150 J for defibrillating patients in VF.

Heart Attacks

One manufacturer references only animal studies using their waveform to support their claim that a patient may require more than 200 J for cardiac arrests caused by heart attacks (myocardial infarction) when using their waveform. The SMART Biphasic waveform has been tested in the real world with real heart attack victims and has proven its effectiveness at terminating ventricular fibrillation (VF). In a prospective, randomized, out-of-hospital study, the SMART Biphasic waveform demonstrated a first shock efficacy of 96% versus 59% for monophasic waveforms, and 98% efficacy with 3 shocks as opposed to 69% for monophasic waveforms.15 Fifty-one percent of the victims treated with the SMART Biphasic waveform were diagnosed with acute myocardial infarction. The published evidence clearly indicates that the SMART Biphasic waveform does not require more than 150 J for heart attack victims.

High-Impedance or Large Patients

High impedance patients do not pose a problem with the low energy SMART Biphasic waveform. Using a patented method, SMART Biphasic technology automatically measures the patient's impedance and adjusts the waveform dynamically during each shock to optimize the waveform for each shock on each patient. As demonstrated in published, peer-reviewed clinical literature, the SMART Biphasic waveform is as effective at defibrillating patients with high impedance (greater than 100 ohms) as it is with low-impedance patients.19 The bottom line is that the SMART Biphasic waveform does not require more than 150 J for high-impedance patients.

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Data collected from a group of patients defibrillated by the Rochester, Minnesota, EMS organization during actual resuscitation attempts was examined to determine if patient weight affected the defibrillation effectiveness of the 150 J non-escalating SMART biphasic shock that was used. Of the patients for whom both weight and height data were available, 41% were overweight, 24% were obese, and 4% were extremely obese by BMI (Body Mass Index) standards. As shown in the graph below, the success and failure distributions were identical for the three groups. Thus, defibrillation effectiveness on the first shock was in no way related to the weight of the patient. The cumulative two-shock success rate was 99%, and all patients were defibrillated by the third shock.

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Delays before the First Shock

The SMART Biphasic waveform is the only biphasic waveform to have extensive, peer-reviewed and published emergency resuscitation data for long-duration VF. In a randomized out-of-hospital study comparing the low-energy SMART Biphasic waveform to high-energy escalating monophasic waveforms, the average collapse-to-first-shock time was 12.3 minutes. Of the 54 patients treated with the SMART Biphasic waveform, 100% were successfully defibrillated, 96% on the first shock and 98% with three or fewer shocks. With the monophasic waveforms, only 59% were defibrillated on the first shock and only 69% with three or fewer shocks. Seventy-six percent of the patients defibrillated with the SMART Biphasic waveform experienced a return of spontaneous circulation (ROSC), versus only 55% of the patients treated with high-energy monophasic waveforms.15 In a post-market, out-of-hospital study of 100 VF patients defibrillated with the SMART Biphasic waveform, the authors concluded, “Higher energy is not clinically warranted with this waveform.”20 SMART Biphasic does not require more than 150 J when there are delays before the first shock.

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