Philips Heartstart s Technical Reference Manual

POWER TO SAVE A LIFE

DEFIBRILLATORS

HEARTSTART

AUTOMATED EXTERNAL DEFIBRILLATORS

TECHNICAL REFERENCE MANUAL

Edition 3

Introductory Note

In 1992, Heartstream, Inc. was founded with the mission to develop a small, low-cost, rugged, reliable, safe, easy-to-use, and mainte nance-free automated external defibr il lator (AED) that could be successfully used by a layperson responding to sudden cardiac arrest. Heartstream introduc ed its first AED, the Fo reRunner, 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 ForeRun ner for Laerd al Medical Corporation called the Heartstart FR.

In 1999, Hewlett-Packard spun off the 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.

Heartstream beca me part o f Ph ili ps Med ica l Sys t ems in 2001 when Philips purc hased the entire Medical Group from Agilent Technologies. In 2002, Philips re-branded all of their defibrillat ors as HeartStart Defibrillator s. In the same year, Philips introd uced a new family of defibrillat ors, including the HeartStart Home and HeartStart OnSite AEDs.

This manual i s inten ded to p rovide technical and pr oduct infor mation t hat generally appli es to the following AEDs:

ForeRunner and FR AEDs:

Heartstream ForeRunner Laerdal Heartstart FR

FR2 series AEDs:

Agilent Technologies FR2 Laerdal Heartstart FR2 Philips HeartStart FR2+ Laerdal Heartstart FR2+

HS1 family of AEDs:

Philips HeartStart OnSite Laerdal HeartStart Philips HeartStart Ho me

To help simplify the information presen ted, the Hea rtStart FR2 is us ed as a n example in ma ny parts of this manual. W here the discussion involv es features r elated to a speci fic product, it is so noted.

Philips Medical Systems

CONTENTS

1 HeartStart Automated External Defibrillators

Design Philosophy for H eartStart A EDs .............................. 1-1

Design Features of HeartStart AEDs .................................... 1-2

Reliability and Safety ...................................................... 1-2

Ease of Use ...................................................................... 1-3

No Maintenance .............................................................. 1-4

2 Defibrillation and Elect ricity

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

Understan d ing Fixed Energy ........................................ 3-5

Evidence-Based Support for the SMART

Biphasic Wave form ............................ .... .... ... .... .... .... ..... 3-6

SMART Biphasic Superior to Monophasic ............... 3-7

Key Studies ......................................................... ............. 3-8

Frequently Asked Questions ................................................... 3 -9

Are all biphasic waveforms alike? ............................... 3-9

How can the SMART Biphasic waveform be more

effective at lower energy? ............................................. 3-9

Is escalating energy required? ..................................... 3-11

Is there a relationship between waveform, energy

level, and po st-shock dysfunct ion? ............................. 3-13

How does SMART Biphasic compare to other

biphasic w a veforms? ..................................................... 3-15

Is there a standard for biphasic energy levels? ....... 3-15

Commitment to SMART Biphasic ...................... ......... 3-16

4SMART Analysis

Pad Contact Quality ............................................................ ...... 4-1

Artifact Detection ....................................................................... 4-1

Arrhythmia Detection ................................................................ 4-4

Philips Medical Systems

Shockable Rhythms ..................................... ............................. 4-6

Validation of Algorithm .............................................................. 4-9

ECG Analysis Performance .......................................... 4-9

5Self-Tests

Battery Insertion Test ................................................................ 5-1

ForeRunner and FR2 Series AED s ............................. 5-2

HeartStart HS1 Family of AEDs .. ................................ 5-2

Periodic Self-Tests ................ .................................................... 5-3

“Power On” and “In Use” Self-Tests .......................... 5-5

Cumulative Device Record ........................................... 5-6

Supplemental Maintenance Information for

Technical Professionals ........................... ................................. 5-7

Backgroun d .............................. ........................... ............. 5-7

Calibration requirements and intervals .............. ......... 5-7

Maintenance testing ....................................................... 5-7

Verification of energy discharge .................................. 5-7

Service/Maintenance and Repair Manual ............. ..... 5-7

6 Theory of Operation

Overview .................. ............................... ..................................... 6-1

User interface ........................................................ ..................... 6-3

Operation ... ........................... ........................... ................. 6-3

Maintenan ce .................. ................... ................... ............. 6-3

Troublesho ot in g .... ........ .... ... .... .... .... .... .... .... ....... .... .... .... . 6-3

Configuration ................................................................... 6-4

Control Bo ard ............................................................................. 6-4

Battery .......................................................................................... 6-4

Power Supply ............................................................................. 6-4

ECG Front End ... .... .... ........ .... .... ... .... .... .... .... .... ....... .... .... .... .... .. 6-5

Patient Circuit ............................................................................. 6-5

Recording .................................................................................... 6-5

Temperatu re Sensor ............................................................... .. 6-6

Real-Time Clock ............. ............................................................ 6-6

IR Port ......................................................................... .................. 6-6

TECHNIC AL REFERENCE GU ID E

Philips Medical Systems

7 Literature Summary for HeartStart

AEDs

References .................................................................................. 7-1

Animal Studies (peer-reviewed manuscripts) ........... 7-1

Electrophysiology Laboratory and other studies

(peer-reviewed manuscripts) ........................................ 7-2

Sudden Cardiac Arrest

(peer-reviewed manuscripts) ........................................ 7-3

Animal Stu dies (abstracts) ............................................ 7-4

Out-of-H ospital Study (abstract) ................................. 7-4

Related Papers and Publications ................................ 7-4

Study Sum maries .......................................... ............................. 7-6

HeartStart Defibrillation Therapy Testing in Adult

Victims of Out-of-Hospital Cardiac Arrest ................ 7-6

HeartStart Patient Analysis System Testing with

Pediatric Rhythms ........................................................... 7-8

HeartStart Defibrillation Therapy Testing in a Pediatric

Animal Model ................................... ................................ 7-10

iii

8 Condensed Applicati on Notes

Defibrillation on Wet or Metal Surfaces ............................... 8-2

Defibrillating in the Presence of Oxygen ................ .............. 8-2

Value of an ECG Display on HeartStart AE Ds ................... 8-3

Defibrillation Pad Placement with HeartStart

AEDs .......... ............... ................ ............... ................ ............... ...... 8-4

SMART Analysis - Classification of Rh ythms ...................... 8-5

Artifact Detection in HeartStart AEDs .................................. 8-6

Use of Automated External Defibrillators (AEDs)

in Hospitals ..................................................... ............................. 8-7

Manual Mode of Operation with HeartStart

AEDs ........... ........................... ........................... ................. 8-7

Analysis System in Hear tStart AEDs .......................... 8-8

Shockable/Non-Sho ckable Rhythms .......................... 8-9

Defibrillation Electrode Pads for HeartStart

AEDs ........... ........................... ........................... ................. 8-10

CPR Performed at High Rates of Compressio n ...... 8-10

HeartStart A ED Batte ry Safety ..................................... ..........8-11

Philips Medical Systems

Differences in Battery Chemistries Utilized by

Automated External Defibrillators ............ ... .... ........ .... . 8 -11

Additional Advantages of the HeartStart AEDs

Battery: D isposable vs. Rechargeable ....................... 8-12

Contents

9 Technical Specificat ions

Standards Applied ............................................................... ...... 9-1

AED Specifications ................................................................... 9-2

Physical ............................................................................. 9-2

Environme ntal ........ .... .... .... ... .... .... .... .... ........ ... .... .... .... .... . 9-3

AED (Hea rtStart HS1 Family) ...................................... 9-4

ECG Analysis System .................................................... 9-5

Display ............................................... ............................... . 9-6

Controls and Indicators ............................. .................... 9-7

Data Management Sp ecificatio ns ............................... 9-8

Accessor ies Speci fic a tions ..................................................... 9-9

Battery Packs ................................................................... 9-9

HeartStart Defibrillation Pads .............. ........................ 9-9

10 Features of th e ForeRunner , FR2,

and HS1 AEDs

Overview .................. ............................... .....................................10-1

Feature Comparison .............. ............... .....................................10-2

Voice Prompt Co mpa r ison ................. .... .... .... .... ... .... .... .... ...... 10 -3

Additional HS1 Voice Instructions ............................. . 10-5

AED Trainers .................................. ............................................. 10-6

Training Scenarios .................. ........................................ 10-7

Pediatric Pads ............................ ................................................10-8

11 HeartStart D ata Manag ement S oftware

Appendix

TECHNIC AL REFERENCE GU ID E

Comparison of Event Review Pro 2.3 and

Event Review 3.0 .......................................................................11-2

System Requirements ...............................................................11-3

Operating Systems ......................................................... 11-3

Data Card Readers .......... ............... ................................ 11-4

Previous Data Management Software Versions .................11-5

System An notations ..................................................................11-6

Technical Support for Data Man a gement Software ..........11-8

Online ................................................................................ 11-8

Via Telephone .................................................................. 11-8

Philips Medical Systems

Troubleshooting the HeartStart the ForeRunner and

FR2 Series AEDs ....................................................................... A-1

1 HeartStart Automated External

Defibrillators

Each year in the United States alone, approximately 250,000 people suffer sudden cardiac arrest (SCA). Fewer than 5% of them survive. SCA is most often caused by an irregu lar hear t rhyth m called ventr icula r fibrill ation (VF), for which the only eff ective t reatme nt is de fibr illati on, an electr ical shoc k . Of ten, a victim of SCA does not survive because of the time it takes to deliver the defibrillation shock; for every minute of VF, the chances of survival decrease by about 10%.

T raditi onally , on ly trained medical personne l were allow ed to use a de fibrillat or 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 defi brillated. In 19 69, par ame di c pr ograms 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 outs id e the hos pi tal, 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 adva nces , 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 a defibrillator to be used by the first people (typically lay persons) responding to an emergency. 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 r apidly than ever be fore , an d t hey have a better chance of su rviving until more highly trained medical personnel arrive who can treat the underlying causes .

Design Ph iloso phy for HeartStart AED s

The HeartStart AEDs are designed specifically to be used by the first people responding to an emergency. It is reliable, easy to use, and virtual ly maintenance free. The design allows HeartStart AEDs to be used by people with no medical training in places where defibrillators have not traditionally

Philips Medical Systems

been used. In order to accomplish this, consideration was given to the fact that an AED might not be used very often, may be subjected to harsh environments, and probably would not have personnel available to perform regular maintenance.

1-1

1-2

The HeartStart AED was not designed to replace the manual defibrillators used by more highly trained individuals. Instead, it was 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. Some models of HeartStart AEDs can be configured for advanced mode use, to allow the device to be used as a manual defibrill ator. This can be beneficia l for transitioning the p atient care from a lay rescue r to more highly t rained medical personnel.

Design Features of HeartStart AEDs

Reliability and Safety

• Fail-Safe Design - The HeartStart AED is intended to detect a shockable rhythm and deliver a shock if needed . It will not allow a shoc k if one is no t required.

•

Rugged Mechanical Design - The HeartStart AED is built with

high-impact plastics, has few openings, and incorporates a rugged defibrillation pads connector and bat tery inter f ace. Using the carry case provides additional protection as well as storage for extra sets of pads and a spare batt e r y.

Daily Automatic Self-Test - The HeartStart AED performs a daily

• self-test to help ensure it is ready to use when needed. An active status indicator demonstrates at a glance that the unit is working and ready to use.

•

Environmental Parameters - Ex tensive environmental tests were

conducted to prove the HeartStart AED’s reliability and ability to operate in conditions relevant to expected use.

•

Non-Rechargeable Lith ium Batte ry - The HeartStart AED

battery pack was design ed for us e in an emer gen cy environment and is therefore small, lightweight, and safe to use. Each battery pack contains multiple 2/3A size, standard lithium camera batteries. These same batteries can be purc has ed at lo cal drug st ores for use in other consumer products. These batteries have been proven to be reliable and safe over many years of operation. The HeartStart AED battery pack uses lithium manganese diox id e (L i/MnO

) technology and does not contain

pressurized sulfur dio xid e. T he battery pac k meets the U.S. Environme ntal Protection Agency's Toxicity Characteristic Leaching Procedure and may be disposed of with normal waste.

Philips Medical Systems

TECHNICAL REFERENCE GUIDE

1-3

Ease of Use

• Small and Light - The b ip has ic waveform technology used in the

HeartStart AEDs have allowed them to be small and light. They can easily be carried and operated by one person.

•

Self-Contained - The carr y case ha s room for ex tra defibrilla tion pa ds

and an extra battery. When stored in the carrying case, the AED has everything necessary for a person to respond to an event of SCA.

•

Voice Prompts - The HeartStart AED provides audible prompts that

guide the user through the process of using the device. The prompts reinforce the messages that appear on the AED screen (F R 2 series models) and allow the user to attend to the patient while receiving detailed instructions for each step of the rescue.

• Pads Connector Light and Flashing Shock Button - The

indicator light next to the pads connector port on the FR2 series AED draws the user's attention to where the pads connector should be plugged in. The HS1 famil y of AEDs uses a pads c art ri dge t hat is connected as soon as it is installed in the AED. The illuminated Shock button identifies the button to be pushed to deliver a shock; the Shock button only flashes w hen the unit has char g ed for a s hock and directs the user to press the orange shock button.

Clear Labeling and

•

Graphics

- The HeartStart AED is 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. The Quick Reference Card mounted inside the carrying case reinforces these instructions. The pad placement icon on the FR2 series AED indicates clearly where pads should be placed, an d t h e pads themselves are labele d to specify where each one should be placed. T he polarity of the pads does not affect the operation of the HeartStart AED, but user testing has shown that people apply the pads more quickly and accurately if a specific

Philips Medical Systems

position is shown on each pad.

LCD Screen (on the FR2+) - The text screen displays message

• prompts to remind the user what steps to follow during an incident. On some HeartStart AED models, the screen also displays the vict im’s ECG signal. The ECG helps ALS providers when they arrive on the scene, by

Introduction to the HeartStart D efibrillators

1-4

enabling them to rapidly assess the patient's heart rhythm to prioritize their initial care of the patient.

•

Proven Analysis System - The rhythm analysis system is the

decision-maker insi de the AED that analyzes the patient’s ECG rhythm and determines whether or not a shock sh ould be administered. The algorithm’s decision criteria allow the user to be confident that the AED will only advise a shock when it is appropriate treatment for the patient.

Artifact Detection System - The AED’s artifact detection system

• indicates if the ECG has been corrupted by some forms of art ifa ct fr om electrical “noise” in the surrounding environment, patient handling, or the activity of an implanted pacemaker. Because such artifact might inhibit or delay the AED from making a shock decision, the AED compensates by filtering out the noise from the ECG, prompting the user to stop patient handling, or det er mining that the level of artifact does not pose a p r obl em for the algorithm.

Pads Detection System - The HeartStart AED’s pads detection

• system helps ensure good defibrillation pad contact by providing a voice prompt to the user if the pads are not making proper contact with the patient's skin.

No Maintenance

Unlike manual defibr illators (used in a hospi tal or by ALS providers) automated external defib r illators may be used infreque ntly, possibly less than once a year. However, they must be ready to use when needed.

•

Automatic Daily/Weekly/Monthly Self-tests - There is no

need for calibration, energy verification, or manual testing with the HeartStart AED. Calibration and energy ver if ication are automatically performed once a month as part of the AED’s self-test routine.

•

Active Status Indicator - The HeartStart AED’s status indicator

shows whether or not the AED has passed its last self-test. The FR2+ is ready to use when the indi cator is a flashing bla ck hourglass. If the status indicator displ ays a flashing red X accompanied by an audible beep, this means the AED needs attention. A soli d red X means tha t the AED cannot be used. For the HS1, a flashing green lig ht ind ica tes that it is ready to use.

Non-rechargeable Lit hium Battery - Non-rechargeable

• batteries store more energy in the same size package , have a longer shelf life than recha rgea b le ba tteries, and eliminate the need to manage and maintain a recharging process. The HeartStart AED prompts the user via the Status Indicator and an audibl e alarm when the battery needs to be replaced.

Philips Medical Systems

TECHNICAL REFERENCE GUIDE

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.

Sinus Node

(primary pacemaker cells

are located here)

A-V Node

Right Bundle Branch

Ventricles

Relation of an ECG to the

Anatomy of the Cardiac Conduction System

Atria

Left Bundle Branch

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

Philips Medical Systems

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.

2-1

2-2

-1

-2

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

Millivolts

0 0.4 0.8 1.2 1.6 2.0 2.4 2.8 3.2 3.6 4.0 4.4

Seconds

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.

Philips Medical Systems

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.

TECHNICAL REFERENCE GUIDE

2-3

-1

-2

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

Millivolts

0 0.4 0.8 1.2 1.6 2.0 2. 4 2.8 3.2 3.6 4.0 4.4

Seconds

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

Philips Medical Systems

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

2-4

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.

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.

(

Electrical power is defined as the voltage (V) times the current (volts= joules/coulomb, amps = coulombs/sec):

From Ohm's law, voltage and current are related by resistance (R) (impedance):

Power is therefore related to voltage and resistance by:

Substituting this back into the equation for energy means that the energy delivered by the biphasic waveform is represented by:

* Voltage 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.

P = V x I

V = I x R or

I = V/R

P = V2/R or

E = V2/R x t or

P = I

E = I

R x t

Philips Medical Systems

TECHNICAL REFERENCE GUIDE

2-5

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.

1500

1000

500

Volts

-500

0 2 4 6 8 10 12 14 1 6 18 20 22

Milliseconds

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. The three graphs shown here 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.

Philips Medical Systems

Defibrillation and Electricity

2-6

Amperes

-10

0 2 4 6 8 10 12 14 16 18 20

50 ohm patient

Milliseconds

Amperes

-5

80 ohm patient

-10

0 2 4 6 8 10 12 14 16 18 20

Milliseconds

Amperes

-10

0 2 4 6 8 10 12 14 16 18 20

125 ohm patient

Milliseconds

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 150 J for each shock. The phase ratio, or the relative amount of time the waveform spends in the

Philips Medical Systems

TECHNICAL REFERENCE GUIDE

2-7

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.

Philips Medical Systems

Defibrillation and Electricity

Notes

TECHNICAL REFERENCE GUIDE

Philips Medical Systems

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) defibrillation was first used in the 1950s.

2000

Volts

Milliseconds

Alternating Current (AC) Waveform

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 cardioverterdefibrillator (AICD) was implanted in a human.

Philips Medical Systems

3-1

3-2

During the last 30 years, 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.

The MDS waveform requires

3200

high energy levels, up to 360 J, to defibrillate effectively. MDS waveforms are not designed to

Volts

compensate for differences in impedance -- the resistance of the body to the flow of current

-- encountered in different

Milliseconds

Biphasic Damped Sine (MDS) Waveform

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

1200

up to 360 J. Because it uses a lower voltage than the MDS waveform, the MTE waveform

Volts

requires a longer duration to deliver the full energy to patients with higher impedances. This form of impedance compensation

Monophasic Truncated Exponential (MTE) Waveform

20-40

Milliseconds

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.

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

Philips Medical Systems

TECHNICAL REFERENCE GUIDE

3-3

external defibrillation waveform technology. Extensive studies for implantable defibrillators had shown biphasic waveforms to be superior to monophasic

2,3,4

waveforms.

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.

Heartstream pursued the use of the biphasic waveform in

1750

AEDs for similar reasons; use of the biphasic waveform allows for smaller and lighter AEDs. The SMART Biphasic

Volts

waveform has been proven effective at an energy level of 150 joules and has been used in HeartStart AEDs since they

5-20

Milliseconds

were introduced in 1996.

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

Monophasic WaveformBiphasic Waveform

waveform, the current flows in one direction and then

Defibrillation Current Flow

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.

Philips Medical Systems

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

SMART Biphasic Waveform

3-4

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.

The characteristics for the monophasic damped sine and monophasic truncated exponential waveforms are specified in the AAMI standard DF2-1989; 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. HeartStart was the first company to develop a biphasic waveform for use in AEDs.

Safety Check impedance measurement

2000

1500

1000

500

Voltage (v)

-500

-1 0 1

SMART Biphasic Waveform

Waveform adjustment to impedance measurement

398

Phase I

675

Phase II

Time (msec)

+ Polarity

- Polarity

Philips Medical Systems

TECHNICAL REFERENCE GUIDE

3-5

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.

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)

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.

Isolated Rabbit Heart

Fixed-energy dose

100%

80%

60%

40%

20%

Probability of Defibrillation

Philips Medical Systems

Based on data from Snyder et al., Resuscitation 2002; 55:93 [abstract]

NO NEED TO ESCALATE

SMART Biphasic

ESCALATION REQUIRED

Edmark MDS

Current (amperes)

Patient-to-patient

variation

SMART Biphasic Waveform

3-6

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

fact, combined with the lower energy requirements of BTE waveforms, 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 HeartStart 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. waveform has several clinical advantages. It has equivalent efficacy to higher energy monophasic waveforms but shows no significant ST segment change from the baseline. when the biphasic waveform is used. biphasic waveform has improved performance when anti-arrhythmic drugs are

12,13

present,

and with long duration VF. demonstrated improved neurological outcomes for survivors defibrillated with SMART Biphasic when compared to patients defibrillated with monophasic waveforms.

Other studies have demonstrated that the biphasic

There is also evidence of less post shock dysfunction

9,10,11,29

14,20

There is evidence that the

A more recent study has also

Philips Medical Systems

TECHNICAL REFERENCE GUIDE

3-7

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 five years, 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 18 peer-reviewed manuscripts to prove the efficacy and safety of the SMART Biphasic waveform. Ten 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.

Using criteria established by the AHA in its 1997 Scientific Statement,

data from the ORCA study

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.

the

Philips Medical Systems

SMART Biphasic Waveform

3-8

Key Studies

waveforms studied results

1992

1994

1995 171 patients (electrophysiology laboratory). First-shock efficacy of biphasic

1995

1996

1997

low-energy vs. high-energy damped sine monophasic

biphasic vs. damped sine monophasic

low-energy truncated biphasic vs. high-energy damped sine monophasic

115 J and 139 J truncated biphasic vs. 200 J and 360 J damped sine monophasic

249 patients (emergency resuscitation). Low-energy and high-energy damped

sine monophasic are equally effective. Higher energy is associated with increased incidence of A-V block with repeated shocks.

19 swine. Biphasic shocks defibrillate at lower energies, and with less post-shock arrhythmia, than monophasic shocks.

damped sine is superior to high-energy monophasic damped sine.

30 patients (electrophysiology laboratory). Low-energy truncated biphasic and high-energy damped sine monophasic equally effectiveness.

294 patients (electrophysiology laboratory). Low-energy truncated biphasic and high-energy damped sine monophasic are equally effective. High-energy monophasic is associated with significantly more post-shock ST-segment changes on ECG.

18 patients (10 VF, emergency resuscitation). SMART Biphasic terminated VF at higher rates than reported damped sine or truncated exponential monophasic.

1998 30 patients (electrophysiology laboratory). High-energy monophasic showed

significantly greater post-shock ECG ST-segment changes than SMART

SMART Biphasic vs.

1999 286 patients (100 VF, emergency resuscitation). First-shock efficacy of SMART

standard high-energy monophasic

Biphasic.

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.

1999

low-energy (150 J) vs. high-energy (200 J) biphasic

low-capacitance biphasic vs. high-capacitance biphasic

1999

SMART Biphasic vs. escalating high-energy

2000

TECHNICAL REFERENCE GUIDE

monophasic

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.

20 swine. Low-energy biphasic shocks increased likelihood of successful defibrillation and minimized post-shock myocardial dysfunction after prolonged

arrest.

10 swine. Five of five low-capacitance shock animals were resuscitated, compared to two of five high-capacitance at 200 J. More cumulative energy and longer CPR were required for high-capacitance shock animals that survived.

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.

338 patients (115 VF, emergency resuscitation). Demonstrated superior defibrillation performance in comparison with escalating, high-energy monophasic shocks in out-of hospital cardiac arrest. SMART Biphasic defibrillated at higher rates than MTE and MDS, 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).

Philips Medical Systems

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. Consequently, 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 low-energy 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 J designed for high-energy defibrillation may not defibrillate effectively at lower energies. (The Tang 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. that the 200 µF capacitance biphasic waveform performed better at 200

J than at 130 J.

)

). Conversely, a biphasic waveform

Higgins manuscript from 2000 showed

3-9

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.”

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 just to satisfy the current AHA recommendation.

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

The way the energy is delivered makes a significant difference in the

Philips Medical Systems

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

SMART Biphasic Waveform

3-10

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 V

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

Low Impedance (50 ohms)

70 60 50 40 30 20 10

Current (amps)

360 J

Monophasic

150 J SMART

Biphasic

MPC 200 J

Biphasic

MPC 300 J

Biphasic

MPC 360 J

Biphasic

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.

Philips Medical Systems

TECHNICAL REFERENCE GUIDE

-15

Patient Current (amps)

-30

0 0.005 0.01 0.015

-15

Patient Current (amps)

-30

0 0.005 0.01 0.015

SMART Biphasic (C =100 µF)

Time (seconds)

Other biphasic (C=200 µF)

Time (seconds)

3-11

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.

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. Biphasic waveform would not be more effective at higher energies

Animal studies have indicated that the SMART

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

Is escalating energy required?

Not with SMART Biphasic technology. In the “Guidelines 2000,”5 the AHA states, “Energy levels vary with the type of device and type of waveform used.” (I-90) The SMART Biphasic waveform has been optimized for ventricular defibrillation efficacy at 150 J. Referring to studies involving the SMART Biphasic waveform, it states, “This research indicates that repetitive lower-energy biphasic waveform shocks (repeated shocks at < 200 J) have equivalent or higher success for eventual termination of VF than defibrillators that increase the current (200, 300, 360 J) with successive shocks (escalating).” (I-90)

Philips Medical Systems

All HeartStart AEDs use the 150 J SMART Biphasic waveform. Two products, the HeartStart XL and XLT, provide an AED mode as well as manual defibrillation, synchronized cardioversion, electrocardiogram monitoring,

SMART Biphasic Waveform

3-12

SpO2 monitoring, and non-invasive pacing. Selectable energy settings (from 5 to 200 J for the XLT or 2 to 200 J for the XL) are available in the XL and XLT 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

25,26

rhythm.

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.

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 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.

The bottom line is that the SMART Biphasic waveform does not

require more than 150 J for high-impedance patients.

Philips Medical Systems

TECHNICAL REFERENCE GUIDE

+ 84 hidden pages