Different Waveforms, Different Results Understanding the Differences Between Biphasic Technologies

Defibrillation Waveforms Waveforms describe the electrical pulse  Current Delivery  Time  Direction of Current Flow Three in use today  Monophasic Damped Sine Wave (MDS)  Biphasic Truncated Exponential (BTE)  Rectilinear Biphasic (RBW)

Damped Sine Wave Unchanged for 30 Years Requires high energy and current. Not highly effective for patients with high transthoracic impedance.

Biphasic Truncated Exponential The First Generation: Adapted from low impedance ICD applications. Impedance causes waveform to change shape.

Rectilinear Biphasic Waveform Designed Specifically for External Use: Constant CurrentConstant Current eliminates high peaks Fixed DurationFixed Duration stabilizes waveform in face of varying impedance levels.

The Road Map for Today Scientific Data  Experimental Studies  Human Trials A Functional Comparison  Current Delivery  Impedance Handling The AHA Position

The Biphasic Advantage Experimental Studies Have Shown: Performance varies with shape Lower defibrillation thresholds Less post-shock dysfunction

Performance Varies with Shape ) Dixon et al. Circulation 1987;117: Defibrillation Threshold (Volts) 10M (Canine) epicardial electrodes Waveform Shape (msec)

Lower Defibrillation Threshold Canine heart 3 minutes untreated followed by 2 minutes femoral compression sec 5 min Fibrillation time DFT (J) MB 54±19 38±1041±5 80±30 M B Walcott et al. Circulation 1998; 98: Key Findings 1Monophasic DFT increased by 40% (p <0.05) 2Biphasic DFT remained constant

Reduced Dysfunction - 7 min VF Mean arterial pressure higher (p<0.05) Biphasic defibrillation produces less dysfunction Ejection fraction higher (p<0.01) Tang et al. Journal of American College of Cardiology, 1999;34: Studied in pigs

Humans Data Is Plentiful Clinical Trials Show: Efficacious for both VF & AF Biphasic advantage “grows” with extended-duration VF Less energy required

Published Data is on Low Energy 912 Patients 1,2,3,4,5 0 Patients Randomized Patients in Peer-Reviewed Journals 1 Brady et al. Circulation 1996;94: Mittal et al. Journal of American College of Cardiology, 1999; 34: Mittal et al. Circulation 2000;101: Schneider et al. Circulation 2000;102: Higgens et al. Prehospital Emergency Care 2000;4:  200J > 200J

Agilent VF Trial - BTE Waveform Bardy et al. Circulation 1996;94:2507. n = 316 p = ns First-Shock Efficacy

Medtronic VF Trial - BTE Waveform n = 115 p = ns Higgins, et al. Prehospital Emergency Care. 2000;4: First-Shock Efficacy

93% n = 184 p = 0.05 Mittal et al. Journal of American College of Cardiology, 1999; 34: ZOLL VF Trial - RBW First-Shock Efficacy 99%

RBW Superior for Difficult Patients 99% 95% 100% 63% 60% 80% 100% <90 ohms>90 ohms 120J RBW200J MDS p = 0.02 Defibrillation Efficacy Mittal et al. Journal of American College of Cardiology, 1999; 34:

Out-of-Hospital Experience Gliner & White: Resuscitation % 26% 55% 93% 0% 7% 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% MONO J BI 3 x 150J N=210 N=129 Key Findings 1All biphasic patients defibrillated 2Significantly more converted to an organized rhythm with biphasic waveform (P<0.0003). Organized Asystole VF Last Rhythm Recorded ~6.5 (1-17) minutes fibrillation

Out-of-Hospital Experience ORCA Trial (n=115) Comparison of J monophasic shocks with 150J biphasic shocks for out-of-hospital cardiac arrest Collapse to first shock = 8.9 minutes Schneider et al. Circulation. 2000; 102: OutcomeMonophasicBiphasic 1st shock success36/61 (59%)52/54 (96%)p< rd shock success 42/61 (69%)53/54 (98%) p< Overall Success 49/58 (84%)54/54 (100%) p=0.003

Page, et al. Circulation 2000; Supplement 102: II-574 (abstract). n = 209 p = ns Agilent AF Trial - BTE Waveform

Cardioversion Efficacy 0% 20% 40% 60% 80% 100% Monophasic Rectilinear Biphasic 200 J100 J300 J360 J120 J70 J150 J170J 68% 85% 91% 94% 21% 44% 68% 79% p=0.005 p< Mittal et al. Circulation 2000; 101: Randomized MultiCenter n=165 ZOLL AF Trial - RBW

RBW in Clinical Practice Niebauer MJ, et al. PACE 2000; 23: 605 (abstract). Niebauer, MJ, et al. Circulation Supplement 102:II-574 (abstract). Initial Report: 100% efficacy for 125 AF patients 85% converted at  50 joules 100% efficacy in subset of patients previously converted with 720J monophasic In a continuation of the series they reported success in 713 of 714 patients (99.8%).

Overall Findings Biphasic waveforms are effective for both VF and AF. Low-energy BTE waveforms produce clinical results equivalent to monophasic technology. Low-energy RBW waveforms produce clinical results superior to monophasic technology.

A Functional Comparison Response to Impedance Current Delivery Characteristics Clinical Performance AHA View

“... the essential requirement for electrical ventricular defibrillation is the attainment of a sufficient current density...” 1 1 WA Tacker. Electrical Defibrillation. Boca Raton, Florida, CRC Press, Inc.; 1980 p14.

The Important Relationship Voltage Impedance Current= Ohm’s Law Tells Us... As the impedance increases, voltage must increase to deliver the same amount of current.

Effect of Patient Impedance on Biphasic Waveforms Rectilinear Biphasic High Impedance First Generation Biphasic Low Impedance

The Current Paradox “Defibrillation depends on the successful selection of energy to generate sufficient current flow through the heart (transmyocardial current) to achieve defibrillation while at the same time causing minimal injury to the heart.” American Heart Association. Circulation. 2000:1029(suppl I):I-90-I-94.

Two Components of Current Peak Current Highest current delivered over the course of shock delivery Associated with myocardial dysfunction Average Current Average delivered over the course of the shock Determinant of successful defibrillation

Peak Current by Waveform J Amps 130J 200J 50 Current Time Monophasic at 200 Joules Biphasic Truncated Exponential at 150 Joules Rectilinear Biphasic at 120 Joules

Average Current at 150 Joules Source: ZOLL Medical Corporation

Average Current at Max Energy Source: ZOLL Medical Corporation

1 Higgens et al. Prehospital Emergency Care 2000;4: Bardy GH, et al. Circulation. 1996; 94: Mittal S., et al. Journal of the American College of Cardiology. 1999; 34: 5. Next to a Common Standard Studies Used 200J MDS as the Control E f f i c a c y 75% 80% 85% 90% 95% 100% Medtronic 1 130J BTE 200J MDS Agilent 2 130J BTE 200J MDS ZOLL 3 120J RBW 200J MDS

Versus the AHA Thresholds The 1997 AHA Statement on Biphasic Waveforms defined thresholds for waveform equivalency and superiority. Only the clinical performance of the Rectilinear Biphasic waveform exceeds the threshold for superiority. American Heart Association. Automatic external defibrillators for public access defibrillation: recommendations for specifying and reporting arrhythmia analysis algorithm performance, incorporating new waveforms, and enhancing safety. Circulation. 1997; 95:

Guidelines Define biphasic energy levels as  200 joules Fail to address biphasic shocks in excess of >200 joules Protocols are waveform specific Given Class IIa recommendation to biphasic shocks  200 joules

Summary Biphasic waveforms differ  Shape  Response to Impedance  Current Delivery  Documented Clinical Performance Biphasic waveforms are effective for external defibrillation  Equivalent performance with less energy  Rectilinear biphasics promise superior performance