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1144 Prediction of Defibrillation Success From a Single Defibrillation Threshold Measurement With Sequential Pulses and Two Current Pathways in Humans Douglas L. Jones, PhD, George J. Klein, MD, FRCP(C), FACC, Gerard M. Guiraudon, MD, FRCS(C), FACC, Arun D. Sharma, MD, FRCPC, FACC, Raymond Yee, MD, FRCP(C), and Michael J. Kallok, PhD, PE Downloaded from http://circ.ahajournals.org/ by guest on June 11, 2017 The ultimate aim of defibrillation testing is to predict consistent defibrillation. This study tested the hypothesis that defibrillation success could be predicted from a single measurement of defibrillation threshold. We measured defibrillation threshold by using three patch electrodes and a standard protocol intraoperatively in 49 patients undergoing arrhythmia surgery. Each patient was then assigned to one of five energy subgroups (0.5, 1.0, 1.5, 2.0, or 2.5 times defibrillation threshold) for a single shock (followed by a rescue shock if necessary) for a subsequent ventricular fibrillation episode. A curve relating percent success to energy was then constructed for the group. Defibrillation threshold averaged 4.7 2.98 J for the group (mean + SD). There was a curvilinear relation between the energy of the defibrillation threshold ratio test shock and percent success: 33.3%, 58.3%, 81.8%, 91.7%, and 100% at mean defibrillation threshold ratios of 0.56 0.14, 1.02 0.07, 1.53 0.14, 1.88 0.09, and 2.60 0.14, respectively. We conclude that consistent defibrillation is predictable from a single measurement of defibrillation threshold. Furthermore, for an individual patient, a safety margin of 2.6 times defibrillation threshold should approximate 100% successful defibrillation for a single test shock. (Circulation 1988;78:1144-1149) I mplantation of an automatic defibrillation device necessitates an estimate of the energy requirements for defibrillation to ensure that the device will defibrillate consistently at its maximum output. In experimental animals, many defibrillation attempts may be performed, and the relation may be plotted between percentage of successful defibrillation and defibrillation energy delivery. 1-3 In patients, the number of defibrillation episodes is limited, and defibrillation threshold is a more readily attainable measure.4-6 The purpose of this From the Departments of Medicine and Physiology, The University of Westem Ontario, and Department of Medicine, University Hospital, Department of Cardiovascular and Thoracic Surgery, University Hospital, London, Ontario, Canada; and Medtronic Incorporated (M.J.K.), Minneapolis, Minnesota. Supported in part by The Medical Research Council of Canada, The Heart and Stroke Foundation of Ontario, and Medtronic Incorporated. D.L.J., A.D.S., and R.Y. are Ministry of Health Career Scientists. G.J.K. is a Research Associate of the Heart and Stroke Foundation of Ontario. Address for correspondence: Dr. D.L. Jones, Department of Medicine and Physiology, The University of Western Ontario, London, Ontario, Canada N6A 5C1. Received January 21, 1988; revision accepted May 26. 1988. study was to evaluate how a single defibrillation threshold could be used to estimate a margin of safety for successful defibrillation and to provide '"acceptable and unacceptable" criteria for a specific lead system and device. Patients and Methods Patient Population Fifty-one successive volunteer patients undergoing arrhythmia surgery (33 men and 18 women) provided written and verbal, informed consent in accordance with the regulations of the Health Sciences Standing Committee on Human Research of The University of Western Ontario, London, Ontario, Canada. The mean age was 31.7+9.4 years (range, 19-54 years) with mean weight 73.4 + 13.5 kg (range, 51.1-109.6 kg). Patients were randomized to one of five test-energy subgroups (0.5, 1.0, 1.5, 2.0, or 2.5 times defibrillation threshold). Surgical Procedure Patients were prepared for surgery, and the heart was exposed by a median sternotomy. The heart Jones et al Prediction of Percent Defibrillation Downloaded from http://circ.ahajournals.org/ by guest on June 11, 2017 FIGURE 1. Diagram of electrode locations on an anterior view of the heart. First pulse was passed between electrode a (anode) on the anterior right ventricle and electrode b (common cathode) on the left lateral ventricle. Electrode on the posterior right ventricle was the anode for the second pulse of the sequential pulse shock. c was prepared for cardiopulmonary bypass in patients as needed.4 Epicardial mapping verified the site of origin of the arrhythmia before the initiation of the experimental defibrillation protocol. Three electrode patches were sutured on the heart (three TX7 mesh, or two 6889 and one 6890 coil electrodes, Medtronic, Minneapolis, Minnesota), on the ventricular epicardium of the left lateral free wall, posterior right free wall, and anterior right free wall (Figure 1). Current for the first pulse of the sequential shock was delivered between the electrode on the anterior right ventricle (anode) and the left lateral electrode (common cathode). The anode for the second pulse of the sequential shock was the right posterior electrode. Leads from the electrodes were interfaced to two custom-designed defibrillators. The output from the defibrillators delivered trapezoidal pulses at preset energy increments. Each pulse of the sequential shock was approximately 2.5 msec in duration separated by 0.2 msec.7-10 Fibrillation and Defibrillation Ventricular fibrillation was induced by passing a low-energy alternating current directly to the heart by the fibrillator available in the operating room. 1145 After a minimum ventricular fibrillation of 10 seconds, defibrillation was attempted. The defibrillation threshold was determined as follows. The initial defibrillation setting was at a stored voltage of 300 V, which corresponded to an estimated energy delivery of approximately 3 J. Subsequent shocks in the fibrillation episode were at increments of approximately 1 J for shocks up to 10 J, then at increments of 2.5 J for shocks up to 15 J until defibrillation was successful. If the first shock of a fibrillation episode was successful, an additional episode was allowed that started at a stored voltage of 170 V, which corresponded to a calculated energy delivery of approximately 1 J. Increments of 1 J were used until defibrillation was successful. Defibrillation threshold was defined as the minimum energy required to cause defibrillation.4 Once defibrillation threshold had been determined, estimated stored voltage for a test shock was calculated, which would correspond to that necessary to deliver the randomly selected ratio of defibrillation threshold energy for that patient. The initial stored voltage was set at the test shock voltage level. Ventricular fibrillation was reinduced after 5 minutes, and the defibrillation test shock was delivered and was followed immediately by rescue shock if necessary. A maximum of three ventricular fibrillation episodes, each separated by 5 minutes, were allowed. The total potential duration of circulatory arrest for all fibrillation episodes in a single patient averaged 44.8+12.4 seconds (range, 29-71.5 seconds). Energy Delivery Determination Scaled output waveforms from the defibrillators were delivered to an analog-to-digital converter mounted in a portable personal computer. The computer program allowed on-line display of waveforms immediately after the delivery of a shock, and after successful defibrillation, it permitted determination of the peak voltage, peak current, impedance, duration of each pulse, energy delivery from each pulse, and total delivered energy for every shock. Energy was calculated by the integrated area under the curve and the correction for the logarithmic decay of the capacitive discharge.4 Statistical Analysis Analysis of the difference in the total energy, leading edge peak voltages, and currents for each energy ratio was made by analysis of variance." Data are presented as the mean + SD. A probability of 0.05 or less was considered significant. Results Two patients were not included in the analysis because of technical problems. The remaining 49 patients had defibrillation thresholds determined and were administered one of the five energy ratio test shocks. Defibrillation threshold for the 49 patients averaged 4.7 + 2.9 J. Circulation Vol 78, No 5, November 1988 1146 3-0 s 4 LUC -1 2-5 0 0 0 2-0 Ir 1 u U. r I1.5 <0.75 1.0 1.5 2.0 >2.25 DFT RATIO LL. 1-0 FIGURE 3. Bar graphs of mean values of test shock- 9i -I'--- :1 delivered, leading-edge peak voltage for the first (Panel A) and second (Panel B) pulses. End bars represent ± SD. Numbers of patients in each group from left to right are 6, 12, 11, 12, and 8, respectively. 0-5 1 U - -r SUCCESSFUL - 1.5 2.0 >2.25 DFT RATIO (0.75 1.0 1- UNSUCCESSFUL Downloaded from http://circ.ahajournals.org/ by guest on June 11, 2017 FIGURE 2. Plot of energy ratio of all shocks delivered to all patients. Note that shocks below defibrillation threshold (<DFT ratio= 1.0) were mostly unsuccessful. In contrast, shocks equal to or greater than defibrillaton threshold (-DFT ratio-1.0) were mostly successful. By definition, there are 51 successful shocks at 1.0 times defibrillation threshold because this was the criterion for defibrillation threshold. Although the value for the mean defibrillation threshold of the group receiving test shocks greater than 2.25 times defibrillation threshold was the lowest, there was no statistical difference between the groups (F= 2.01 at 4 and 44 df, p>0.05) of the 51 patients, 50 of whom were undergoing surgical ablation of the accessory pathway for Wolff-ParkinsonWhite syndrome. The additional patient was having an internal defibrillator implanted. His defibrillation threshold was 1.41 J, and he was successfully defibrillated with the test shock of 3.56 J. Figure 2 represents the delivered energy ratio of all shocks delivered to the patient population. The predominance of unsuccessful shocks fell below the defibrillation threshold, whereas most successful shocks were with ratios equal to or greater than the defibrillation threshold. Mean peak voltages for the first and second pulse of the test shock ranged from approximately 200 to 450 V (Figure 3). There was a slight diminution in the peak voltage of those patients receiving more than a 2.25 times defibrillation threshold. This was due to the inaccuracy of calculation of the defibrillation threshold ratio and to not attempting to correct stored voltage of the test shock for different impedances. These inaccuracies were greatest in those patients in whom defibrillation threshold was approximately 1-2 J. This resulted in more patients with low defibrillation threshold in the highest group. The corresponding mean peak current of these test shocks was from 2.5 A to a maximum of approximately 6.5 A. There was a slight diminution in the mean peak current for the patients receiving greater than 2.25 times defibrillation threshold ratio (Figure 4). CL 0 0 0 E FIGURE 4. Bar graphs of mean values of test shockdelivered, leading-edge peak current for the first (Panel A) and second (Panel B) pulses. End bars represent ±SD. Numbers of patients in each group from left to right are 6, 12, 11, 12, and 8, respectively. Iz Iz W cc W cc LL CL UJ <0.75 1.0 1.5 2.0 >2.25 DFT RATIO DFT RATIO Jones et al Prediction of Percent Defibrillation 1147 A~ W 6I.- ° o 0~~~~~~~~~~~~ 6 0~~~~~~ z~~~~~~~ 0<0.75 1.0 1.5 2.0 >2.25 DFT RATIO 0<0.75 1.0 1.5 2.0 >2.25 DFT RATIO 0 1.5 2.0 >2.25 DFT RATIO <0.75 1.0 FIGURE 5. Bar graphs of mean values for test shock-delivered energy for thefirst (Panel A) and second (Panel B) pulses and total shock (Panel C). End bars represent ±SD. Numbers of patients in each group from left to right are 6, 12, i1, 12, and 8, respectively. Downloaded from http://circ.ahajournals.org/ by guest on June 11, 2017 The resultant calculated mean delivered energy of the test shocks ranged from approximately 2 J for the lowest ratio to a maximum of approximately 9.5 J for the maximum total energy delivered (Figure 5). Of note, this total energy was delivered to two different pathways. Thus, the delivered energy through each pathway was one half of the total (Figure 5). Defibrillation threshold for the 49 patients averaged 4.7 + 2.9 J. There was a difference noted depending on the particular electrode configuration. The average defibrillation threshold for the coil electrode configuration was slightly, but significantly, lower than that of the mesh electrode configuration (Figure 6). A curve relating the percentage of successful defibrillation to test shock-delivered energy was constructed for the group (Figure 7A). When plotted as a log of the defibrillation threshold ratio, the plot was linear and ranged from approximately 35% at 0.5 times defibrillation threshold to 100% at approximately 2.6 times defibrillation threshold. After having determined that defibrillation threshold with the coil configuration was slightly lower than that of the mesh electrode configuration, we replotted data with only test-shock data from patients with the coil electrodes (Figure 7B). By this method, the plot had a plateau with 100% successful defibrillation between 2.0 and 2.5 times defibrillation threshold. Again, the plot was linear between the minimum of approximately 35% at the 0.5 times defibrillation threshold and 100% at 2.0 times defibrillation threshold. Of note, these curves are constructed from the first shock only of the test sequence and therefore are the percent success of the first shock of the new fibrillation episode. Discussion This study demonstrates that defibrillation in humans can be consistently achieved with threshold energy averaging 4.7 J with coil and mesh electrode systems. These results are consistent with our previous studies in animals and humans in which we found low thresholds with patch electrodes and sequential pulse technique for defibrillation. 12-14 For patients receiving an implanted automatic defibrillator, it is essential to estimate the energy necessary for consistent defibrillation and to predict the safety margin available for a specific lead system and device. Several methods have been suggested for such determinations.2-4,15-18 However, with patient studies, it is not reasonable to have a large number of defibrillation episodes. On the other hand, a single defibrillation threshold determination is rapid, easy to obtain, and, thus, more 0 0 ~1 Z 4 mI- COIL MESH FIGURE 6. Bar graph of means of total delivered energy at defibrillation thresholdfor all patients that had current delivered through coil (n=35) or mesh (n=14) electrodes. End bars represent +SD. Differences between the two means, although small, are statistically significant (t=-2.43, p<O.05). Circulation Vol 78, No 5, November 1988 1148 100.gA .0- n=8 1001 n-6 n=5 P ----D B ,i'n - 12 n=11 80 CO, (n ,,' ,,' cn U) ,1' 60 ,S'01 40 0.5 80 I. m 60] -n 12= 401 o n-6 1.0 1.5 2.0 2.5 DFT RATIO FIGURE 7. Plots relating the test shock defibrillation threshold (DFT) energy ratio to percentage of successful defibrillation. Note that the relation to the log dose ratio is linear to 100% success at 2.6 times defibrillation threshold with the combined data (Panel A) and has a plateau at 100% between 2.0 and 2.6 times defibrillation threshold with the coil electrode data only (Panel B). Straight line was drawn to connect the maximum and minimum points. U) L) n-12 n-6 801 n= 6 0.5 1.0 1.5 2.0 2.5 DFT RATIO Downloaded from http://circ.ahajournals.org/ by guest on June 11, 2017 feasible considering the restrictions of the operating room environment. This study suggests that a single measurement of defibrillation threshold can be used to predict successful defibrillation from the first shock of subsequent ventricular fibrillation episodes under similar circumstances in the same patient. In this study, 2.6 times defibrillation threshold achieved 100% successful defibrillation with the first shock. Of note, the shape of the curve between percent success and the defibrillation threshold ratio depended on the particular electrodes used. This suggests that in addition to surface area of electrodes, the efficiency of a particular electrode system may also be important in determining the shape of a curve of percent success and defibrillation threshold ratio. Direct cardiac shocks with single-pulse current delivery with either intravascular catheters4,5 '5 17 or an epicardial system'3. 5.16 have been successful in humans when energies range from 15-35 J and when there is a relatively shallow slope for the dose-response curve. In the present study, the slope was relatively steep, and the maximum threshold with the coil electrode configuration was approximately 14 J. The electrode configuration of this patient was found to have a very low impedance, suggesting a partial short in the current delivery to the heart. The remaining 34 patients in this group had defibrillation threshold energies below 7.5 J. In addition, 100% success with the first test shock could be achieved with energies of only 2.0 times defibrillation threshold with the coil electrodes. Additional factors may influence defibrillation success. Most patients (50 of 51) in this study had no myopathology. Patients who are candidates for an implanted device often have extensive myocardial pathology and ischemia, which may or may not alter defibrillation threshold.6'19-25 Also, these studies were short term. The effects of long-term lead placement and antiarrhythmic drug therapy on de- fibrillation remains controversial3 25-29 and requires further investigation. Since Mirowski and colleagues30 and Denniston and colleagues3' first described the concept of an implantable defibrillator, there has been a great interest in searching for the optimum electrode configuration and the best method for predicting defibrillation success. From these studies, we conclude that the sequential pulse shock with moderatesized electrodes provides acceptably low-energy requirements for defibrillation. In addition, a single measurement of defibrillation threshold can be used to predict subsequent defibrillation for an individual patient. The value of approximately 2.6 times defibrillation threshold should approximate 100% successful defibrillation with the first shock for the electrode system. Finally, the determination of population curves of success and defibrillation threshold ratio may be valuable in estimating safety margin for any particular electrode system. Acknowledgments We thank the staff of OR #5 for their patients and assistance. We also thank K. Clarke for typing the manuscript. References 1. Rattes MF, Jones DL, Sharma AD, Klein GJ: Defibrillation threshold: A simple and quantitative estimate of the ability to defibrillate. PACE 1987;10:70-77 2. Davy JM, Fain E, Dorian P, Winkle RA: The relationship between successful defibrillation and delivered energy in open chest dogs: Reappraisal of the "defibrillation threshold" concept. Am Heart J 1987;113:77-84 3. Fain ES, Billingham M, Winkle RA: Internal cardiac defibrillation: Histopathology and temporal stability of defibril- lation energy requirements. JAm Coll Cardiol 1987;9:631-638 4. Jones DL, Klein GJ, Guiraudon GM, Sharma AD, Kallok MJ, Bourland JD, Tacker WA: Internal cardiac defibrillation in man: Pronounced improvement with sequential pulse delivery to two different lead orientations. Circulation 1986; 73:484-491 5. Klein GJ, Jones DL, Sharma AD. Kallok MJ, Guiraudon GM, Sharma AD, Kallok MJ, Tacker WA, Bourland JD: Internal cardiac defibrillation in man: Influence of cardiopulmonary bypass. Am J Cardiol 1986;57:1194-1195 Jones Downloaded from http://circ.ahajournals.org/ by guest on June 11, 2017 6. Jones DL, Klein GJ, Guiraudon GM: Sequential pulse defibrillation in man: Comparison of thresholds in normals and those with cardiac disease. Med Instrum 1987;21:166-169 7. Bourland JD, Tacker WA, Wessale JL, Kallok MJ, Graf JE, Geddes LA: Sequential pulse defibrillation for implantable defibrillators. Med Instrum 1986;20:138-142 8. Jones DL, Klein GJ, Kallok MJ: Improved internal defibrillation with twin pulse energy delivery. Am J Cardiol 1985; 55:821-825 9. Jones DL, Sohla A, Bourland JD, Tacker WA, Kallok MJ, Klein GJ: Internal ventricular defibrillation with sequential pulse counter-shock in pigs: Comparison with single pulses and effects of pulse separation. PACE 1987;10:497-502 10. Rattes MF, Jones DL, Sohla A, Sharma AD, Jarvis E, Klein GJ: Defibrillation with the sequential pulse technique: Reproducibility with repeated countershocks. Am Heart J 1986; 111:874-878 11. Sokal RR, Rohlf FJ: Biometry. San Francisco, Calif, WH Freeman, 1981, p 859 12. Jones DL, Rattes MF, Sohla A, Sharma AD, Klein GJ: Internal cardiac defibrillation: Single and sequential pulses and a variety of lead orientations. PACE 1988;11:583-591 13. Jones DL, Klein GJ, Guiraudon GM, Sharma AD: Sequential pulse defibrillation in man: Orthogonal sequential pulses with 4 mesh electrodes versus single pulse with 2 mesh electrodes. J Am Coil Cdrdiol 1988;1 1:590-596 14. Kallok MJ, Bourland JD, Tacker WA, Jones DL, Klein GJ, Wessale JL: Optimization of epicardial electrode size and implant site for reduced sequential pulse defibrillation thresholds. Med Instrum 1985;20:36-39 15. Mirowski M: Treatment of malignant ventricular tachyarrhythmias with the automatic implantable defibrillator. Int J Cardiol 1983;2:409-413 16. Winkle RA, Stinson EB, Bach SM, Echt DS, Oyer P, Armstrong K: Measurement of cardioversion/defibrillation thresholds in man by a truncated exponential waveform and an apical patch-superior vena caval spring electrode configuration. Circulation 1984;69:766-771 17. Zipes DP, Heger JJ, Miles WM, Mohamed Y, Brown JW, Spielman SR, Prystowsky EN: Early experience with an implantable cardioverter. N Engl J Med 1984;311:485-490 18. Reid PR, Mirowski M, Mower MM, Platia EV, Griffith LSC, Watkins L Jr: Clinical evaluation of the internal automatic cardioverter-defibrillator in survivors of sudden cardiac death. Am J Cardiol 1983;51:1608-1613 19. Mirowski M, Mower MM, Gott IL, Brawley RK, Denniston RH: Transvenous automatic defibrillator-preliminary clinical 20. 21. 22. 23. 24. 25. 26. 27. 28. 29. 30. 31. 32. 33. et al Prediction of Percent Defibrillation 1149 tests of its defibrillating subsystem. Trans Am Soc Artif Int Organs 1972;18:520-525 Mower MM, Mirowski M, Denniston RH: Intraventricular defibrillation in dogs with impaired coronary circulation (abstract). Clin Res 1972;20:388 Tacker WA Jr, Geddes LA, Cabler PS, Moore AG: Electronic threshold for defibrillation of canine ventricles following myocardial infarction. Am Heart J 1974;88:476-481 Ruffy R, Schwartz DJ, Heib BR: Influence of acute coronary artery occlusion on direct ventricular defibrillation in dogs. Med Instrum 1980;14:23-26 Babbs CF, Paris RL, Tacker WA Jr, Bourland JD: Effects of myocardial infarction on catheter defibrillation threshold. Med Instrum 1983;17:18-20 Kerber RE, Pandian NG, Hoyt R, et al: Effects of ischemia, hypertrophy, hypoxia, acidosis and alkalosis on canine defibrillation. Am J Physiol 1983;244:H825-H831 Chang M-S, Inoue H, Kallok MJ, Zipes DP: Double and triple sequential shocks reduce ventricular defibrillation threshold in dogs with and without myocardial infarction. J Am Coil Cardiol 1986;8:1393-1405 Jones DL, Sohla A, Klein GJ: Internal cardiac defibrillation threshold: Effect of acute ischemia. PACE 1986,9:322-331 Pearson JW, Redding JS: Epinephrine in cardiac resuscitation. Am Heart J 1963;66:210-214 Deeb MG, Hardesty RL, Griffith BP, Thompson ME, Heilman MS, Myerowitz RL: The effects of cardiovascular drugs on the defibrillation threshold and the pathological effects on the heart using an automatic implantable defibrillator. Ann Thorac Surg 1983;35:361-366 Ruffy R, Schechtman K, Monje E: P-Adrenergic modulation of direct defibrillation energy in anaesthetized dog heart. Am J Physiol 1985;248:H674-H677 Mirowski M, Mower MM, Staewen WS, Tabatznik B, Mendeloff AI: Standby automatic defibrillator. Arch Int Med 1970;126: 158-161 Denniston RH, Mower MM, Mirowski M: Automatic standby defibrillator (abstract). J Assoc Adv Med Instrum 1971;5:110 Rattes MF, Sharma AD, Klein GJ, Szabo T, Jones DL: Adrenergic effects on internal cardiac defibrillation threshold. Am J Physiol 1987;253:H500-H506 Szabo TS, Jones DL, McQuinn RL, Klein GJ: Flecainide acetate does not alter the energy requirements for direct ventricular defibrillation using sequential pulse defibrillation in pigs. J Cardiovasc Pharmacol 1988 (in press) KEY WORDS * implantable automatic defibrillator * sequential pulse defibrillation * defibrillation threshold * defibrillation prediction Prediction of defibrillation success from a single defibrillation threshold measurement with sequential pulses and two current pathways in humans. D L Jones, G J Klein, G M Guiraudon, A D Sharma, R Yee and M J Kallok Downloaded from http://circ.ahajournals.org/ by guest on June 11, 2017 Circulation. 1988;78:1144-1149 doi: 10.1161/01.CIR.78.5.1144 Circulation is published by the American Heart Association, 7272 Greenville Avenue, Dallas, TX 75231 Copyright © 1988 American Heart Association, Inc. All rights reserved. Print ISSN: 0009-7322. Online ISSN: 1524-4539 The online version of this article, along with updated information and services, is located on the World Wide Web at: http://circ.ahajournals.org/content/78/5/1144 Permissions: Requests for permissions to reproduce figures, tables, or portions of articles originally published in Circulation can be obtained via RightsLink, a service of the Copyright Clearance Center, not the Editorial Office. Once the online version of the published article for which permission is being requested is located, click Request Permissions in the middle column of the Web page under Services. 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