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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 Current eliminates high peaks • Fixed 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 Defibrillation Threshold (Volts) Performance Varies with Shape 300 250 200 150 100 ) 50 0 10M 2.5-7.53.5-6.5 5-5 6.5-3.57.5-2.5 Waveform Shape (msec) (Canine) epicardial electrodes Dixon et al. Circulation 1987;117:358-364. Lower Defibrillation Threshold Key Findings 120 80±30 100 DFT (J) 1 Monophasic DFT increased by 40% (p <0.05) 2 Biphasic DFT remained constant 80 54±19 60 38±10 41±5 40 20 M B M B 0 5 min 10 sec Fibrillation time Canine heart 3 minutes untreated followed by 2 minutes femoral compression Walcott et al. Circulation 1998; 98:2210-2215. Reduced Dysfunction - 7 min VF Biphasic defibrillation produces less dysfunction Mean arterial pressure higher (p<0.05) Ejection fraction higher (p<0.01) Studied in pigs Tang et al. Journal of American College of Cardiology, 1999;34:815-822. 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 Randomized Patients in Peer-Reviewed Journals Low-Energy Biphasic 912 Patients 1,2,3,4,5 200J High-Energy Biphasic 0 Patients > 200J 0 1 200 400 600 Brady et al. Circulation 1996;94:2507-2514. Mittal et al. Journal of American College of Cardiology, 1999; 34:1595-1601. 3 Mittal et al. Circulation 2000;101:1282-1287. 4 Schneider et al. Circulation 2000;102:1780-1787. 5 Higgens et al. Prehospital Emergency Care 2000;4:305-313. 2 800 1000 Agilent VF Trial - BTE Waveform 100% n = 316 p = ns 86% 86% 80% 60% 130J BTE Bardy et al. Circulation 1996;94:2507. 200J MDS Medtronic VF Trial - BTE Waveform 100% 90% 83% 80% 60% 130J BTE Higgins, et al. Prehospital Emergency Care. 2000;4:305-313. 200J MDS n = 115 p = ns ZOLL VF Trial - RBW 100% n = 184 p = 0.05 99% 93% 95% 90% 85% 80% 75% 120J RBW 200J MDS Mittal et al. Journal of American College of Cardiology, 1999; 34:1595-1601. RBW Superior for Difficult Patients 100% 100% 99% p = 0.02 95% 80% 63% 60% <90 ohms 120J RBW >90 ohms 200J MDS Mittal et al. Journal of American College of Cardiology, 1999; 34:1595-1601. Out-of-Hospital Experience Last Rhythm Recorded Key Findings ~6.5 (1-17) minutes fibrillation 100% Organized Asystole VF 1 All biphasic patients defibrillated 90% 70% 55% 2 Significantly more converted to an organized rhythm with biphasic waveform (P<0.0003). 60% N=210 80% 93% 50% N=129 40% 30% 26% 20% 10% 19% 7% 0% MONO 200-360J Gliner & White: Resuscitation 1999. 0% BI 3 x 150J Out-of-Hospital Experience ORCA Trial (n=115) • Comparison of 200-360J monophasic shocks • with 150J biphasic shocks for out-of-hospital cardiac arrest Collapse to first shock = 8.9 minutes Outcome Monophasic Biphasic 1st shock success 36/61 (59%) 52/54 (96%) p<0.0001 3rd shock success 42/61 (69%) 53/54 (98%) p<0.0001 Overall Success 49/58 (84%) 54/54 (100%) p=0.003 Schneider et al. Circulation. 2000; 102:1780-1787. Agilent AF Trial - BTE Waveform 100% 91% 86% 80% 60% 40% 20% 0% 200J BTE 360J MDS Page, et al. Circulation 2000; Supplement 102: II-574 (abstract). n = 209 p = ns ZOLL AF Trial - RBW Randomized MultiCenter n=165 p=0.005 p<0.0001 Cardioversion Efficacy 100% 91% 85% 79% 80% 68% 94% 68% 60% 44% 40% 21% 20% 0% 100 J 200 J 300 J 360 J Monophasic Mittal et al. Circulation 2000; 101:1282-1287. 70 J 120 J 150 J 170J Rectilinear Biphasic RBW in Clinical Practice Initial Report: • 100% efficacy for 125 AF patients • 85% converted at 50 joules • 100% efficacy in subset of patients previously converted with 720J monophasic Energy (J) Current (Amp) AF – Mono 185 32 AF – Bi 67 10 -64% -69% p < 0.01 p < 0.01 Diff p value In a continuation of the series they reported success in 713 of 714 patients (99.8%). Niebauer MJ, et al. PACE 2000; 23: 605 (abstract). Niebauer, MJ, et al. Circulation. 2000 Supplement 102:II-574 (abstract). 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 = Current Impedance 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 Low Impedance First Generation Biphasic 50 50 40 40 30 30 20 20 10 10 0 0 -10 -10 -20 -20 0 Rectilinear Biphasic High Impedance 4 8 12 50 50 40 40 30 30 20 20 10 10 0 0 -10 -10 -20 -20 0 4 8 12 0 4 8 12 0 4 8 12 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 Monophasic at 200 Joules RBW @ 120J 15 Biphasic Truncated Exponential at 150 Joules Current Rectilinear Biphasic at 120 Joules BTE @ 130J 35 Mono @ 200J 43 0 Time 10 20 Amps 30 40 50 Average Current at 150 Joules Current (amps) 20 150J BTE 150J RBW 17 14 11 8 5 75 100 125 Resistance (ohms) Source: ZOLL Medical Corporation 150 Average Current at Max Energy Current (amps) 25 360J BTE 200J RBW 20 15 10 75 100 125 Resistance (ohms) Source: ZOLL Medical Corporation 150 Next to a Common Standard Studies Used 200J MDS as the Control 100% E f f i c a c y 95% 90% 85% 80% 75% 1 200J 130J MDS BTE 200J 130J MDS BTE 200J 120J MDS RBW Medtronic1 Agilent2 ZOLL3 Higgens et al. Prehospital Emergency Care 2000;4:305-313. Bardy GH, et al. Circulation. 1996; 94: 2507-2514. 3 Mittal S., et al. Journal of the American College of Cardiology. 1999; 34: 5. 2 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: 1677-1682. Guidelines 2000 . . . • 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