双心室起搏埋藏式心脏转复除颤器的安置

评价一次性置入双心室起搏埋藏式心律转复除颤器 (双腔ICD)的安全性和有效性。5例冠心病冠状动脉搭桥术后的患者 ,伴有严重的慢性充血性心力衰竭和恶性室性心律失常 ,置入双腔ICD。结果 :5例左室电极导管和双腔ICD均一次成功置入 ,左室电极放入冠状静脉的侧后枝 ,急性起搏阈值 0 .8± 0 .6V ,电阻 72 2± 12 8Ω ,R波振幅18.6± 5 .3mV ,电流 1.6± 0 .5mA ,而双心室起搏时其起搏电极参数均优于左室电极 ,除颤阈值≤ 14J。结论 :对伴严重慢性充血性心力衰竭和恶性室性心律失常的患者 ,置入双腔ICD是安全、易行的。     

6例埋藏式心脏转复除颤器频繁电击分析与处理

目的分析6例埋藏式心脏转复除颤器(ICD)患者术后频繁电击的临床特点。方法回顾2008年至今42例ICD植入患者中6例术后频繁电击的临床资料。结果 6例发生频繁电击(发生率14.3%),随访8~38个月,死亡1例。1例CRT-D患者半年内发生6次ICD电风暴,多为反复发生室性心动过速(VT)、快VT(FVT),抗心动过速起搏(ATP)无效升级为电击治疗或者ATP诱发FVT、心室颤动(VF)而行电击治疗,首次电风暴9个月后死于顽固心力衰竭;1例左上腔植入单腔ICD患者出现3次血流动力学稳定的VT事件频率进入VF诊断区直接电击治疗6次且无效;1例单腔ICD患者因T波过感知致11次误放电;1例双腔ICD患者出现3次血流动力学稳定的VT事件,ATP失败后电击治疗6次且无效,此3例均经优化程控后无电击事件。1例CRT-D患者因右室电极脱位至三尖瓣环处致P、R双计数误识别为3次VF并予电击,经再次手术复位后无类似事件。1例CRT-D患者极短期内因2次VF事件及1次VT事件,10阵ATP无效而先后3次电击治疗,优化药物及程控后无电击事件。结论ICD术后频繁电击病因及诱因治疗是预防发生和及时终止的基础,优化药物及程控治疗可降低对电击治疗的需求及误放电的发生,必要时手术调整或导管消融。     

ICD不适当识别与治疗的原因与处理

目的分析埋藏式心脏转复除颤器（ICD）不适当识别或治疗事件的原因,为避免不适当识别或治疗事件提供参考。方法回顾2008年至今42例ICD植入患者中发生不适当识别及治疗的临床资料。结果 34例随访18.5±11.7月,9例发生不适当识别或治疗事件,发生率26.5%,其中单腔ICD2台,双腔ICD 1台,CRT-D6台。4例发生不适当识别12次,7例发生不适当治疗29次,其中2例不适当识别及治疗共存。1例发生3次血流动力学稳定的室性心动过速（VT）事件,经抗心动过速起搏（ATP）失败后予电击治疗6次;3例发生快VT（FVT）事件,频率进入心室颤动（VF）区即给予电击共8次;1例右室电极脱位致P/R双计数误识别为VF11次,3次予电击,余充电后放弃;1例T波过感知误电击11次及误识别2次;1例电磁干扰误电击1次;1例干扰误识别为VF1次但充电后放弃;1例窦性心动过速误识别VT1次并予ATP治疗。结论 ICD术后不适当识别或治疗比较常见,规范程控随访,利于及时发现异常调整参数,优化程控治疗,可以减少不适当识别及电击。     

双房单室三腔起搏器治疗病窦综合征并快速房性心律失常

观察双心房、单心室三腔起搏器治疗病窦综合征合并阵发性房性快速心律失常患者的疗效。三根电极导线分别置入冠状静脉窦内、右心耳和右室心尖部行三腔起搏。冠状窦电极导线与右心房电极导线通过一个Y型转接器构成心房部分。结果 :10例患者 ,9例经左锁骨下静脉径路置入导线 ,1例因存在残存左上腔静脉 ,从右锁骨下静脉置入。 10例中 9例冠状窦电极导线置于冠状静脉窦中部、1例置于冠状静脉窦远端。冠状窦起搏阈值为 1.0 6±0 .2 0V、起搏阻抗 6 11± 115 .8Ω、P波振幅为 4.0 7± 0 .88mV ;右室电极起搏阈值为 0 .5 3± 0 .12V、起搏阻抗 6 70 .3±191.7Ω、R波振幅为 9.6 6± 1.87mV。随访 5～ 2 4个月有 9例起搏器呈DDD工作方式 ,1例呈AAT工作方式。起搏和感知功能良好。 10例中 8例快速性房性心律失常完全控制 ,2例发作次数减少 ,持续时间明显缩短。无一例出现并发症。结论 :三腔起搏器技术安全、可靠。适合于缓慢型心律失常合并阵发性房性快速性心律失常     

双室同步起搏的临床应用及置入左室电极的初步体会

观察双室同步起搏治疗充血性心力衰竭 (CHF)的疗效 ,探讨左室电极置入的方法及注意事项。 10例患者均为原发性扩张型心肌病 (DCM)并CHF ,符合双室同步起搏治疗的指征。其中 8例置入Medtronic 2 187电极 ,1例置入Medtronic 2 188电极 ,1例置入右室主动固定电极。 9例左室电极置入成功 ,1例失败改行右室双部位起搏 ,术后患者左室舒张未径、左室射血分数及 6min步行距离均有改善 (术后 3个月与术前分别比较 :70 .8± 9.5vs 79.5± 12 .5mm ,0 .4 2± 0 .13vs 0 .2 5± 0 .10 ,384 .8± 4 5 .4vs 2 78.6± 34.5m ;P <0 .0 5或 0 .0 1)。借助电生理冠状静脉窦 (CS)标测电极、CS造影 (包括直接逆行CS造影和冠状动脉造影使CS间接显像 )对指导左室电极的置入有较大的价值。结论 :双室同步起搏治疗CHF疗效肯定 ,借助CS标测电极及CS造影可提高左室电极置入的成功率     

双腔埋藏式心脏复律除颤器

双腔埋藏式心脏复律除颤器 (ICD)可提供起搏及抗室性和房性心律失常的治疗。报道 11例双腔ICD应用的临床体会。男 8例、女 3例 ,年龄 6 0 .5 5± 10 .0 7岁。缺血性心脏病 9例、Brugada综合征 1例、缺血性心脏病合并肥厚型梗阻性心脏病 1例。双腔ICD安置指征有 :室上性快速心律失常伴室性快速心律失常 6例 ,室性快速性心律失常伴房室阻滞 1例、伴左室功能不全 4例 ;临床上明确记录到室性心动过速 (简称室速 )、心室颤动 (简称室颤 )和室上性快速心律失常者分别为 8,2和 5例。 8例病人术前进行电生理检查 ,诱发出持续性室速 6例、室颤 2例 ;3例行电生理检查 ,其中 2例太虚弱、1例为反复发作持续性室速。 5例安置具有心室转复除颤伴心房、心室起搏的ICD ,5例安置具有心房、心室起搏转复及除颤的ICD ,1例安置具有双心室起搏及心室转复、除颤的ICD。所有病人在置入ICD时都进行除颤阈值的测定。总共有 2 3次室颤被诱发 ,除颤阈值为 12 .0 9± 5 .2 4J,除颤电极阻抗为 44 .0 0±11.0 5Ω ,P波和R波电压幅度分别为 3.5 3± 1.32mV ,13.42± 4.73mV ,心房、心室起搏阈值分别为 1.39± 0 .71和 0 .91± 0 .38V。随访 8.82± 5 .0 0 (2～ 19)个月 ,5例共有 12 0次持续性室速发生 ,其中 118次经抗心动过速起搏成功?     

心脏再同步化起搏及除颤器在心力衰竭治疗中的应用

目的总结在心力衰竭治疗中应用心脏再同步化起搏及除颤器(CRT-D)的初步体会和随访结果。方法病例入选标准①左室射血分数(LVEF)≤0.35;②QRS波时限≥120ms;③快速室性心律失常;④心功能分级Ⅱ～Ⅳ级。采用左锁骨下静脉穿刺,左室电极置入冠状静脉后侧分支或后分支,右室电极置入右室心尖,右房电极置入右心耳。结果3例均成功置入CRT-D,无严重并发症。左室电极1例置于心脏侧后静脉,另外2例置于心脏后静脉。除颤测试,2例为20J能量1次除颤成功。另1例20J、30J能量除颤未成功,通过调整除颤波斜率,30J成功除颤。随访期间,3例心功能分级、射血分数均有改善,心室起搏比例均超过95%。2例发生持续性室性心动过速,经抗心动过速起搏或除颤治疗成功转复。结论CRT-D能恢复心脏同步活动和识别、转复恶性室性心律失常,是充血性心力衰竭并恶性室性心律失常的有效治疗方法。     

埋藏式心脏转复除颤器安置的临床经验

总结非开胸经锁骨下静脉穿刺安置埋藏式心脏转复除颤器 (ICD)的手术方法、除颤阈值 (DFT)测定及ICD工作参数设置等临床经验。 10例患者 ,6例有反复晕厥病史。 2例晕厥时心电图证实为心室颤动 (简称室颤 ) ,体外电除颤成功 ,另 8例心内电生理均诱发出持续性室性心动过速或室颤。其中冠心病 8例 (1例合并Brugada综合征 ) ,扩张性心肌病 1例 ,原发性室颤 1例。 5例术前口服胺碘酮治疗。结果 :全部经锁骨下静脉置入ICD ,术中所有患者成功诱发室颤 ,并一次电击成功。手术时间 92± 2 7min。DFT≤ 2 0J,电击阻抗 4 1.2± 15 .3Ω ,R波高度 16 .3± 6 .6mV ,无手术并发症。结论 :经锁骨下静脉置入ICD方法简单 ,安全可靠 ;术前口服适量胺碘酮对术中诱发室颤无影响。     

左室起搏电极置入的实践经验

探讨提高左室起搏电极的置入成功率,降低相关并发症的方法学及技术细节。24例难治性心力衰竭患者,男16例、女8例,年龄59.5±7.8(47~74)岁,所有患者均有双室起搏的适应证。按一定程序及方法置入导引导管及造影球囊导管。根据造影显示的冠状静脉解剖特点,选择合适的起搏电极、起搏静脉通路。结果:左室起搏电极置入成功率91.7%(22/24)。左室电极置入时间35.4±13.0min,X线曝光时间19.4±5.2min。所有手术均顺利完成,术中未发生死亡、心包压塞等严重并发症。结论:双室起搏时按照一定的程序及方法置入左室电极,既可提高置入成功率,又可降低并发症。     

植入型心律转复除颤器治疗34例随访

目的:对我院37例安装植入型心律转复除颤器患者中34例长期随访(3例失访)。方法:将随访结果进行回顾性总结分析。结果:随访时间4～69个月,平均(24.7±18)个月。29例成功接受植入型心脏复律除颤器(ICD)治疗,占全部患者的85.3%。共发作恶性室性心律失常事件587次,其中313次为非持续性,均自行终止。接受ICD治疗的274次中室性心动过速(VT)238次,占86.9%。心室颤动(VF)36次,占13.1%。VT由抗心动过速起搏(ATP)终止212次,由低能量(2～15J)转复终止23次。有3次VT在ATP治疗时转为VF,由高能量除颤(DF)终止。VF经高能量除颤36次,全部一次成功。5例患者因房性心动过速(房速)或心房颤动(房颤)被误识别为VT而发放电击。34例中有3例死亡,1例死于急性心肌梗死,1例死于心力衰竭,1例死因不明。结论:ICD可以有效的终止VT、VF,是防治心源性猝死的有效治疗手段。     

The effects of ventricular fibrillation duration and site of initiation on the defibrillation threshold during early ventricular fibrillation

Objectives. The purpose of this study was to determine if the defibrillation threshold (DFT) is lower during the first few cycles of ventricular fibrillation (VF) than after 10 s of VF and, if so, if the effect is caused by local or global factors.Background. The DFT may be low very early during VF because: (1) for the first few cycles VF arises from a localized region close to a defibrillation electrode where the shock field is strong (local factors), or (2) during early VF the effects of ischemia and sympathetic discharge have not yet fully developed and the heart has not yet completely dilated (global factors).Methods. Protocol 1 included seven pigs in which a defibrillation electrode and a pacing catheter were both placed in the right ventricular apex. VF was induced by delivering a high current premature stimulus from the pacing catheter that should have caused reentry confined to the right ventricular apex for the first few cycles of VF. A bipolar electrogram was recorded from the tip of the defibrillation catheter. Using a three reversal up–down protocol, the DFT was determined for biphasic shocks delivered after 1, 2, 3, 4, 5, 7, 10, 15, 20 and 25 activations in this electrogram and after 10 s (control). Protocol 2 included seven pigs undergoing the same procedure as in protocol 1 except that an additional pacing catheter was placed in the left ventricle. Defibrillation thresholds were determined after 1, 2, 3, 4 and 5 VF activations following VF induction from the right ventricle (RV) or the left ventricle (LV) and after 10 s (control).Results. In protocol 1, the mean ± SD DFTs were lower during the first three cycles than after 10 s of VF (3.0 ± 4.1 J for the first VF cycle vs 15.8 ± 6.6 J after 10 s of VF, p < 0.05). In protocol 2, the DFT for the first few cycles of VF induced away from the defibrillation electrode in the LV (6.9 ± 1.4 J for the first VF cycle) was significantly lower than that after 10 s of VF (16.0 ± 2.2 J), whereas the DFT for the first few cycles induced near the defibrillation electrode in the right ventricular apex was significantly lower (2.3 ± 2.7 J for the first VF cycle) than that induced from the LV.Conclusions. This study demonstrates that the DFT is significantly lower during the first few VF cycles of VF than after 10 s of VF and that this decrease may be caused by both local factors and global factors. These results provide an impetus for exploring earlier shock delivery in implantable devices.     

Cardiac Output Is Not Affected During Intraoperative Testing of the Automatic Implantable Cardioverter Defibrillator

Cardiac Output and ICD Implantation. Introduction: Perioperative mortality of patients undergoing implantation of automatic implantable cardioverter defibrillators (ICDs) has been reduced dramatically following the availibility of trans venous-subcutaneous defibrillation leads. However, patients with severely reduced left ventricular function show a substantial rate of nonsudden cardiac mortality within the first year. Whether repeated intraoperative inductions of ventricular tachycardia/fibrillation (VT/VF) during implantation lead to hemodynamic deterioration and thus might contribute to development of end-stage heart failure in these patients is unknown. The purpose of the present study was to determine cardiac output and hemodynamic performance during transvenous-subcutaneous ICD implantation in patients with severe left ventricular dysfunction. Methods and Results: In 11 patients with a left ventricular ejection fraction (EF) ≤ 0.35, cardiac output was measured automatically with a combined continuous cardiac output/mixed venous oxygen saturation pulmonary artery catheter system. ICD implantation was performed during standardized general anesthesia. In the 11 patients (EF = 27 ± 2% [mean ± SEM]) a total of 95 episodes of VT/VF followed by defibrillation were induced (epsiodes per patient = 9 ± 1; range 6 to 11). Cardiac index was 2.2 ± 0.2 L·min^-1·min^-2 after induction of anesthesia (before start of surgery), and 1.9 ± 0.1 L·min^-1·m^-2 immediately before first induction of VT/VF. After the last episode of VT/VF, cardiac index was 2.1 ± 0.2 L·min^-1·m^-2. Cardiac index measured 1, 2, and 3 minutes after induction of VT/VF was not significantly different when compared to the preinduction value during any episode of VT/VF induction. Similarly, stroke volume index was 39 ± 5 mL·m^-2 immediately before first induction of VT/VF and 36 ± 3 mL·m^-2 after the last episode of VT/VF (NS). At the end of surgery, hemodynamic parameters did not exhibit any significant difference when compared to the data obtained before start of ICD implantation and testing. Conclusion: Extensive defibrillation tests during transvenous-subcutaneous ICD implantation in patients with severe left ventricular dysfunction are not associated with acute deterioration of cardiac performance.     

Ventricular fibrillation and transient arrhythmias after defibrillation in patients with acute myocardial infarction

Ventricular fibrillation (VF) and transient arrhythmias after defibrillation were analyzed from the recordings of 28 patients containing at least one episode of ventricular fibrillation. An R-on-T extrasystole initiated VF in 60% of the episodes. Other initiating factors were a late premature beat (24%), stable ventricular tachycardia (VT) (7%), accelerating idioventricular rhythm (5%) and cardioversion of VT (5%) with a sinusoidal waveform. After the initiating beat, in most cases, evidence was found of a transient ventricular tachycardia which then deteriorated into VF. With a stable VT this may occur after a long time; in the case of apolymorphic VT (with changing amplitude) it generally occurred within 30 s. The main transient arrhythmias generated by circulatory arrest during VF and by the defibrillation shock were: total arrest, total AV-block and/or bradycardia. The combination of a longer duration of VF and a high energy level generally resulted in an increase in the duration of these arrhythmias (P less than 0.01, N = 30). Comparison of episodes of VT and VF recorded in a single patient also shows that arrhythmias are more unfavourable and of longer duration after VF than after VT. These data emphasize fast defibrillation, initially with stored energy levels less than 250J.     

Out-of-hospital defibrillation with automated external defibrillators: postshock analysis should be delayed

STUDY OBJECTIVE: The American Heart Association protocols for use of automated external defibrillators (AEDs) recommend that a rhythm analysis be done immediately after each defibrillation attempt. However, shock is often followed by electrical silence or marginally organized electrical activity before ventricular fibrillation (VF) or ventricular tachycardia (VT) recurs. The optimal timing of postshock analysis for identification of recurrent VF/VT is unknown. This study examines the time to recurrence of VF/VT after a defibrillation attempt with AED. METHODS: Over an 18-month period, all tapes from patients with out-of-hospital cardiac arrest who received shocks at least once with an AED were screened for recurrent VF/VT. All cases come from a single emergency medical services system providing basic life support, defibrillation with AED, and intubation with an esophageal-tracheal twin-lumen airway device (Combitube) for a population of 633,511 individuals. Pediatric and traumatic cases were excluded. When VF/VT recurred within 3 minutes of the defibrillation attempt, rhythm strips were printed and included in the study. Two cardiology fellows, blinded to the study objectives, measured the time from defibrillation to recurrent VF/VT for each strip. RESULTS: Over the study period, 222 tapes from 96 patients met the inclusion criteria. Only 44 (20%) occurrences of VF/VT had recurred within 6 seconds of defibrillation, 162 (73%) at 60 seconds, and 200 (90%) at 90 seconds. CONCLUSION: Eighty percent of VF/VT recurred more than 6 seconds after defibrillation and were missed when using current American Heart Association AED protocols. Subsequent analysis should be postponed until at least 30 seconds after defibrillation. Performing 30 seconds of chest compressions after defibrillation before subsequent AED rhythm analysis would increase AED identification of VF/VT to 52%.     

Effect of sotalol on ventricular fibrillation and defibrillation in humans

Antiarrhythmic drugs are frequently administered to patients receiving implanted cardioverter defibrillators. Some of these drugs may decrease the efficacy of defibrillation shocks from the defibrillator. Sotalol, a drug with β-blocking and class III antiarrhythmic properties, lowers defibrillation energy requirements in experimental animals and may do so in humans. Oral sotalol 171 ± 58 mg was administered before and after device implantation in 25 patients receiving implanted defibrillators. During sotalol therapy, the lowest energy required for successful defibrillation was 5.9 ± 3.4 J (range 2–15 J). In a concurrent non-randomized comparison group of 23 patients, including 18 treated with amiodarone, the lowest successful energy was 16 ± 10 J (p <0.01). In 5 sotalol patients, ventricular fibrillation (VF) could not be induced at all (1 patient) or more than 2 or 3 times (4 patients) despite repeated 60 Hz stimulation. The induced VF had a pronounced tendency to terminate spontaneously, with the termination occurring at up to 23 seconds after the offset of 60 Hz stimulation. The cycle length of the VF was 236 ± 34 msec, significantly greater than in patients not given drug therapy (191 ± 21 msec, p <0.01). In 10 patients, but none of the controls, intracardiac electrograms during surface electrocardiograph VF were regular, monoform, and without low-amplitude diastolic activity. In addition, monophasic action potentials during apparent VF showed maintenance of distinct and normal morphology. The ventricular effective refractory period increased after sotalol (249.4 ± 19 to 278.4 ± 24 msec; p <0.03) and the maximum heart rate response to exercise was limited to 120 ± 28 beats/min. Sotalol may modify VF and may enhance defibrillation efficacy. In view of its efficacy in life-threatening ventricular arrhythmias, it appears to be particularly well suited as adjunctive therapy in patients with implanted defibrillators.     

Role of a catheter lead system for transvenous countershock and pacing during electrophysiologic tests: an assessment of the usefulness of catheter shocks for terminating ventricular tachyarrhythmias

The practicality and safety of using a single catheter system for transvenous countershock, programmed stimulation and ventricular pacing during electrophysiologic tests were evaluated in 13 patients with inducible sustained ventricular tachycardia (VT) or ventricular fibrillation (VF). The efficacy and patient toleration of transvenous countershock were compared with other methods of arrhythmia termination. The same lead was used for programmed stimulation at the right ventricular apex and for VT termination by pacing methods during serial testing (20 ± 15 days [mean ± standard deviation]). Synchronized countershock using energies that patients found tolerable (0.01 to 5 J) terminated 31 of 50 episodes (62%) of induced VT. Episodes of VT cardioverted with these low energies were distinguished from other episodes by a longer cycle length (352 ± 62 ms versus 297 ± 50 ms, p < 0.004). Among paired episodes of VT matched for patient, date of induction, morphologic characteristics, cycle length and drugs administered, pacing methods (single extrastimuli and bursts of rapid pacing) were just as effective as low-energy countershock for VT termination (25 of 25 versus 21 of 25, difference not significant). Transvenous countershock was uniformly effective for termination of ventricular flutter and VF when sufficient energy was used (range 5 to 30 J, mean 20.4 ± 7.7). This required interfacing leads to a defibrillation unit. VT acceleration occurred during 7 of 50 synchronized low-energy cardioversion attempts (14%). There was no evidence of myocardial injury as a result of shocks as high as 30 J, but patients required increasing sedation when energy exceeded 0.5 J.Thus, a single catheter system can be used for programmed stimulation, ventricular pacing and countershock during electrophysiologic tests. Low-energy countershock (0.01 to 5 J) is no more effective than pacing methods for VT termination and is tolerated less well. The most practical use of this catheter system, including any implantable unit, may be for slightly higher energy (5 to 30 J) countershock termination of repeated episodes of very rapid VT or VF, in which pacing techniques are ineffective. This method may be safer and less traumatic than conventional transthoracic countershock.     

自主研发体外自动除颤器的实验研究

目的 评价自主设计和研制体外自动除颤器(AED)对室性心动过速(室速)/心室颤动(室颤)识别的敏感性、特异性以及除颤效果.方法 应用交流电刺激实验动物诱发室速/室颤,记录并分析AED对窜速/室颤的识别以及除颤放电的整个过程,评价其诊断识别和除颤性能.结果 诱颤96次,除颤145次,记录心电数据167段次,共计103 740 S.室速/室颤的识别准确性为99.5%,敏感性为98.2%,特异性为99.6%.除颤成功率和除颤能量呈正相关,成功除颤的能量阈值为(78.75±35.64)J,电量阈值为(0.11±0.04)C,电压阈值为(1216.67±260.87)V.结论 自主研制的AED具有较高的识别敏感性和特异性,其识别和除颤效果达到或优于国外同类产品.     

Prospective comparison of biphasic and monophasic shocks for implantable cardioverter-defibrillators using endocardial leads.

Bidirectional shocks using 2 current pathways have been used in endocardial lead systems for implantable cardioverter-defibrillators, but the optimal shock waveform for endocardial defibrillation is unknown. The clinical efficacy and electrical characteristics of bidirectional monophasic and biphasic shocks for endocardial cardioversion-defibrillation of fast monomorphic or polymorphic ventricular tachycardia (VT), or ventricular fibrillation (VF) were evaluated. Thirty-three patients (mean age 60 +/- 12 years, and mean left ventricular ejection fraction 34 +/- 13%) were studied. Defibrillation catheter electrodes were located in the right ventricular apex and superior vena cava/right atrial junction. A triple-electrode configuration including the 2 catheter electrodes and a left thoracic patch was used to deliver bidirectional shocks from the right ventricular cathode to an atrial anode (pathway 1) and the thoracic patch (pathway 2). The shock waveforms examined were sequential and simultaneous monophasic, and simultaneous biphasic. The efficacy of 580 V (20 J) shocks for fast monomorphic VT were comparable for the 3 waveforms (73% for sequential monophasic, 73% for simultaneous monophasic, and 100% for simultaneous biphasic). However, for polymorphic VT and VF, 580 V sequential monophasic shocks had a significantly lower efficacy (25%) than did simultaneous monophasic (75%; p = 0.01) or biphasic (89%; p less than 0.001) shocks. Single-shock defibrillation thresholds with simultaneous biphasic shocks were significantly lower (9 +/- 5 J) than were those with simultaneous monophasic shocks (15 +/- 4 J; p less than 0.02).(ABSTRACT TRUNCATED AT 250 WORDS)