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Different Waveforms, Different Results

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)

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Different Waveforms, Different Results

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  1. Different Waveforms, Different Results Understanding the Differences Between Biphasic Technologies

  2. 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)

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

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

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

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

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

  8. 300 250 ) 200 150 Defibrillation Threshold (Volts) 100 50 0 10M Waveform Shape (msec) 2.5-7.5 3.5-6.5 5-5 6.5-3.5 7.5-2.5 (Canine) epicardial electrodes Dixon et al. Circulation 1987;117:358-364. Performance Varies with Shape

  9. Lower Defibrillation Threshold Key Findings • Monophasic DFT increased by 40% (p <0.05) • Biphasic DFT remained constant 120 80±30 100 80 54±19 60 DFT (J) 38±10 41±5 40 20 B M B M 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.

  10. 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.

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

  12. 912 Patients 1,2,3,4,5 0 Patients Published Data is on Low Energy Randomized Patients in Peer-Reviewed Journals  200J > 200J 1 Brady et al. Circulation 1996;94:2507-2514. 2 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.

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

  14. Medtronic VF Trial - BTE Waveform n = 115 p = ns First-Shock Efficacy Higgins, et al. Prehospital Emergency Care. 2000;4:305-313.

  15. ZOLL VF Trial - RBW n = 184 p = 0.05 99% 93% First-Shock Efficacy Mittal et al. Journal of American College of Cardiology, 1999; 34:1595-1601.

  16. RBW Superior for Difficult Patients 100% 99% 100% p = 0.02 95% Defibrillation Efficacy 80% 63% 60% <90 ohms >90 ohms 120J RBW 200J MDS Mittal et al. Journal of American College of Cardiology, 1999; 34:1595-1601.

  17. 100% 90% Organized 80% Asystole VF 70% 60% 50% 40% 30% 20% 10% 0% Out-of-Hospital Experience Last Rhythm Recorded Key Findings • All biphasic patients defibrillated • Significantly more converted to an organized rhythm with biphasic waveform (P<0.0003). ~6.5 (1-17) minutes fibrillation 55% N=210 93% N=129 26% 19% 0% 7% MONO 200-360J BI 3 x 150J Gliner & White: Resuscitation 1999.

  18. Outcome Monophasic Biphasic 49/58 (84%) 42/61 (69%) 54/54 (100%) 53/54 (98%) 3rd shock success Overall Success p=0.003 p<0.0001 1st shock success 36/61 (59%) 52/54 (96%) p<0.0001 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 Schneider et al. Circulation. 2000; 102:1780-1787.

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

  20. ZOLL AF Trial - RBW p=0.005 p<0.0001 100% 94% 91% 85% 79% 80% 68% 68% 60% Cardioversion Efficacy 44% 40% 21% 20% 0% 100 J 200 J 300 J 360 J 70 J 120 J 150 J 170J Monophasic Rectilinear Biphasic Randomized MultiCenter n=165 Mittal et al. Circulation 2000; 101:1282-1287.

  21. 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 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).

  22. 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.

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

  24. “. . . 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.

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

  26. 50 50 40 40 30 30 20 20 10 10 0 0 -10 -10 -20 -20 0 4 8 12 0 4 8 12 50 50 40 40 30 30 20 20 10 10 0 0 -10 -10 -20 -20 12 12 8 8 0 0 4 4 Effect of Patient Impedance on Biphasic Waveforms Low Impedance High Impedance First Generation Biphasic Rectilinear Biphasic

  27. “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.” The Current Paradox American Heart Association. Circulation. 2000:1029(suppl I):I-90-I-94.

  28. 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

  29. RBW @ 120J 15 BTE @ 130J 35 Mono @ 200J 43 50 0 10 20 30 40 Amps Peak Current by Waveform Monophasic at 200 Joules Biphasic Truncated Exponential at 150 Joules Rectilinear Biphasic at 120 Joules Current Time

  30. Average Current at 150 Joules Source: ZOLL Medical Corporation

  31. Average Current at Max Energy Source: ZOLL Medical Corporation

  32. Next to a Common Standard Studies Used 200J MDS as the Control 100% E 95% f f 90% i c 85% a c 80% y 75% 200J MDS 120J RBW 200J MDS 130J BTE 200J MDS 130J BTE ZOLL3 Agilent2 Medtronic1 1Higgens et al. Prehospital Emergency Care 2000;4:305-313. 2 Bardy GH, et al. Circulation. 1996; 94: 2507-2514. 3 Mittal S., et al. Journal of the American College of Cardiology. 1999; 34: 5.

  33. 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.

  34. 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

  35. 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

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