心脏三腔起搏除颤器的临床应用

目的　评价具有心脏再同步化治疗 (CRT)和置入式心脏复律除颤器 (ICD)功能起搏器(CRT D)置入的安全性和有效性。方法　共 11例患者纳入研究。年龄 4 8～ 84 (71 6± 9 5 )岁 ,男 7例 ,女 4例。患者有心脏猝死或室性心动过速或电生理检查出现室性心动过速或心室颤动 ;左室射血分数≤ 35 % ,QRS≥ 12 0ms。所有患者置入的CRT D是美敦力INSYNCⅡMARQUIS 72 89,左心室电极置于冠状静脉窦左心室侧后壁分支或左后壁分支。右心房电极和右心室电极都使用主动螺旋电极 ,后者置于室间隔上部。手术在全麻下进行。术后次日在心脏超声指导下进行AV优化。结果　所有患者顺利度过手术 ,无并发症。放射时间为 19～ 73(44 7± 19 9)min。心房电极的振幅、阻抗和阈值分别为 (2 4 7± 0 77)mV、(5 90± 12 6 )Ω、(1 37± 0 71)V。右心室电极的振幅、阻抗和阈值分别为 (11 0 0± 3 4 8)mV、(5 86± 116 )Ω、(0 6 9± 0 2 1)V。左心室电极的振幅、阻抗和阈值分别为(15 37± 5 .15 )mV、(6 0 2± 12 5 )Ω、(1 6 2± 1 5 9)V。除颤阈 2 0J和 6J的各 3例 ,15J、12J和 3J各 1例。 1例患者因为原有除颤电极失效而更换为皮下电极 ,但仍除颤失败。另 1例患者因为出现心电图ST T变化而暂时未测定除颤阈值。所有患者除颤能量     

几种食管心房调搏方式的比较研究

降低有效起搏阈值、减轻刺激疼痛是顺利完成经食管心房调搏（ＴＥＰ）检查的必要条件。将１５０例患者等分成三组，分别采用常规法（常规电极、常规极间距）、互换法（两个电极可交替作为刺激电极）、宽距法（常规电极、宽极间距）和粗极法（电极直径６ｍｍ）行ＴＥＰ检查，观察指标有起搏成功率、起搏阈值、插入成功率等。当刺激电压＜２５Ｖ时，互换法与粗极法起搏成功率（分别为９０％与８４％）均高于常规法（６４％）和宽距法（７０％）；粗极法１００％成功时的起搏阈值（１７．０±５．０Ｖ）低于其他三种方法（２５．２±１０．０，１９．０±８．０和２１．０±１３．０Ｖ，Ｐ均＜０．０５），其电极插入成功率最低（８４％）、鼻衄率最高（２６％）。认为互换法具有起搏阈值较低，在一定电压范围内成功率高、并发症低等优点。     

经静脉埋藏式三腔起搏心脏转复除颤器的临床应用

探讨经静脉埋藏式三腔起搏心脏转复除颤器 (BVP ICD)的临床应用。病例入选标准 :①缺血性心脏病、扩张性心肌病合并充血性心力衰竭。②左室射血分数 <0 .35。③QRS波时限 >130ms。④ 2 4h动态心电图、临床心电监护、腔内电生理检查中 ,任一项记录到明确室性心动过速 (VT)或心室颤动 (VF)。采用经锁骨下静脉和头静脉 ,分别置入右室电极导管到右室 ,右房电极导管到右心耳 ,左室电极经冠状静脉窦到冠状静脉后侧支 ,其中 1例为经静脉埋藏三腔双室起搏器 (BVP)升级为BVP ICD。结果 :双室起搏阈值 1.7± 0 .7V ,R波幅度 10 .3± 4mV ,双室电极阻抗 896 .2± 82Ω。4例先后 2次采用电击T波诱发出VT或VF ,并除颤成功。 3例因心功能差仅诱发 1次并除颤成功。最低有效除颤能量 2例 11J ,5例 2 0～ 2 1J ,手术时间 12 9.2 8± 4 7.3min。 7例随访 3～ 12个月 ,心功能改善 1～ 2级。 2例分别各有 1例除颤事件记录 ,7例全部存活。结论 :BVP ICD临床疗效较好 ,但设定首次电击能量时不宜太小 ,力争尽快转复心律 ,以策安全。慎用快速心室起搏 (Ramp)终止VT。     

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?     

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。     

食管定向弯曲电极导管起搏、除颤及监护功能的实验研究

为确定食管定向弯曲电极导管（自制导管）在食管内行心脏起搏、心室除颤及监护的效果和安全性，用自制导管定向弯位（甲）与定向直位（乙）及国产１０Ｆ双极导管（丙）对１３只犬进行心房起搏效果对照观察。结果表明：起搏阈值甲、乙、丙分别为１２．６±０．３，１７．４±０．６．３０．２±１．６Ｖ，Ｐ＜０．０１；起搏夺获率甲、乙、丙分别为１００％、５３．５８％、１８．１８％，Ｐ＜０．０１．对食管进行组织学检查，起搏安全值脉宽为５ｍｓ、电压≤７０Ｖ、频率２００～２２０ｐｐｍ、连续起搏时间≤１８０ｍｉｎ；极限值的脉宽、频率同上，电压＝８０Ｖ，连续起搏时间＝９０ｍｉｎ。除颤安全值电能≤２００Ｊ，总电能≤６００Ｊ；电烧伤值电能达３００Ｊ，总电能达１４００～１５００Ｊ。本研究为心脏有效的复苏提供一种实验依据。     

新型食管心脏调搏电极导管的研制与应用

研制一种新型食管心脏调搏电极导管，以进一步降低食管心脏调搏术的起搏阈值，减轻受检者痛苦，便于开展食管心室调搏术。第一阶段：设制出各型食管电极导管12种，每种导管随机测试病人20例，共240例，以揭示起搏阈值与电极宽度、电极长度和电极间距三者关系。第二阶段：据此，研制2种新型食管心脏调谐电极导管，每种导管随机测试病人40例，共80例。结果发现食管心脏调搏电极导管的最适电极宽度为5～6mm、电极长度为10mm和电极间距为35mm，按此规格研制的JD－2－9－35－10－5型和JD－2－9－35－10－6型新型食管心脏调搏电极导管，心房调掉时起搏阈值分别为12．1±3．2（5．0～17．5）V和10．3±2．6（5．0～15．0）V，心室调搏时起搏阈值分别为24．0±5．5（15．0～35．0）V和20．3±4．9（12．5～30．0）V，心室调搏的成功率分别为85％（34／40）和95％（38／40）。结论：与目前国内常用的食管电极导管比较，该导管具有起搏阈值低、病人痛苦少、适应性广、性能可靠和操作方便等优点。     

应用两种电极导管紧急床旁心脏起搏的临床观察

目的比较在体表心电图指导下两种电极导管紧急床旁心脏起搏治疗心动过缓的效果,探讨床旁心脏临时起搏的方法学和可行性。方法75例严重心动过缓的患者中,50例使用带球囊漂浮电极经左锁骨下静脉穿刺,25例使用普通电极经左锁骨下静脉穿刺进行床边临时起搏,对两者的操作时间和效果分别加以回顾性分析,在一周内,38例在植入永久性起搏器时进行了导管位置的X线观察,其他存活患者也进行了导管位置的X线观察,比较两种起搏方式的成功率和安全性。结果球囊漂浮电极组,即刻起搏成功率为94%,起搏成功时间为(8.5±2.7)min,并发症发生率为2%,术后导管脱位率为6.3%;普通电极组,即刻起搏成功率为96%,起搏成功时间为(6.3±2.1)min,并发症发生率为8%,术后无导管脱位现象。结论体表心电图指导下应用两种电极导管进行心脏临时起搏是一项安全有效、可行的起搏方法,值得临床推广。     

改良下位法与吴氏下位法选择性消融慢径的比较

我们将吴氏下位法加以改良，设计了一种消融方法，称改良下位法，并与吴氏下位法进行了比较。改良下位法消融４１例，吴氏下位法消融１０例。改良下位法不插冠状窦电极，在后前位透视下，大头导管从希氏束下方１ｃｍ处逐渐移向冠状窦口反复消融。射频发放时间与能量采用渐增法。结果：改良下位法与吴氏下位法复发率分别为３％和２０％（Ｐ＜０．０５）；Ｘ线暴露时间分别为２４±１８ｍｉｎ和，３８±２Ｏｍｉｎ（Ｐ＜０．０５），操作时间分别为１１５±３８ｍｉｎ和１６４±４０ｍｉｎ（Ｐ＜０．０５），成功率分别为９５％和９０％（Ｐ＞０．０５）。     

应用自制复合电极同步记录兔左心室游离壁三层心肌的单相动作电位

应用自制复合电极同步记录家兔在体三层心肌的单相动作电位 (MAP) ,并与经典的心内膜电极、心外膜吸附电极和三层独立电极记录结果进行比较。结果显示 :①应用自制复合电极同步记录家兔在体的三层心肌MAP形态及时程与经典的记录结果相近 ;②在心动周期 (CL)为 30 0ms时 ,三层心肌的MAP复极达 90 %的时程 (MAPD90 )无显著差异 ,当CL为 80 0ms时 ,家兔心外膜心肌 (Epi)、中层心肌 (M)和心内膜心肌 (Endo)的MAPD90 分别为 2 15± 18,2 6 2± 16 ,2 16± 12ms,M与Epi及Endo相比 ,差异有显著性 (P <0 .0 5 ,n =8) ,跨室壁复极离散度为 34± 3ms。结论 :应用复合电极同步记录在体心肌跨室壁三层MAP是可行的 ,家兔心脏跨室壁心肌电生理在正常心率时无明显差异 ,而当心率减慢时则异质性增加。     

Effect of Electrode Length on Atrial Defibrillation Thresholds

Electrode Length for Atrial Defibrillation. Introduction: Catheter-based electrodes have been used previously to terminate episodes of atrial fibrillation in animals and man. Typically, these electrodes span 6 to 7 cm, and lowest energy requirements are achieved when these electrodes are positioned in the distal coronary sinus and in the right atrium. The purpose of this study was to evaluate the use of longer electrode lengths for atrial defibrillation. Methods and Results: In 15 patients, two decapolar catheters were inserted, one into the distal coronary sinus and one in the right atrium. To provide longer electrodes lengths, a third catheter was inserted and alternated positioned in the right atrium or coronary sinus. A 6-cm electrode span was obtained by using the distal 8 rings on the coronary sinus catheter or 8 consecutive electrodes on the right atrial catheter and increased from 6 to 11 cm by connecting consecutive, nonoverlapping rings of the third catheter with the 10 rings of the initial right atrial or coronary sinus catheter. Atrial defibrillation thresholds were determined twice, in a randomized order, in each patient for each of the three combinations of electrode lengths. All 15 patients could he successfully converted to sinus rhythm without complications; however, one patient could be converted reproducibly with only 2 of the 3 electrode combinations. Mean thresholds were 306 ± 102 V, 5.9 ± 4.0 J for the 6 cm/6 cm electrode length combination with an impedance of 72 ± 18 ω. For the electrode combination using the 11-cm electrode in the right atrium, the defibrillation threshold was 296 ± 107 V, 5.8 ± 3.9 J with an impedance of 61 ± 17 ω and was 294 ± 91 V, 5.6 ± 3.6 J with an impedance of 55 ± 11 ω for the 11-cm electrode in the coronary sinus. There were no significant differences in defibrillation voltage or energy (P > 0.05) associated with the longer electrode lengths; however, the longer electrode lengths did significantly lower shock impedance (P < 0.05). Conclusion: The use of longer electrodes, when using the right atrium to coronary sinus shock vector, does not lower the defibrillation requirements for restoration of sinus rhythm.     

Ventricular defibrillation in the dog using implanted and partially implanted electrode systems

Two totally implanted and two partially implanted electrode systems were studied in 2,100 fibrillation-defibrillation episodes in large anesthetized dogs. In one of the totally implanted systems, two metal disks, 7.6 cm in diameter, were implanted between the pectoralis major muscle and the rib cage, with the right electrode high on the chest and slightly to the right of midline and the left electrode over the apex of the heart. In the other totally implanted system, a unipolar catheter electrode positioned in the right atrium and superior vena cava was used together with a 7.6 cm disk electrode over the apex of the heart. In the partially implanted systems, a unipolar catheter electrode in the right atrium and superior vena cava was used together with either a 7.6 cm disk electrode or a 6.3 by 20.3 cm rectangular sheet electrode placed on the surface of the chest over the apex of the heart. Four types of unidirectional shocks were used in evaluating the twin disk system. Nine types of shocks were used with systems involving the catheter electrode. Derived curves indicate that the 90 percent level of successful defibrillation is achieved with 38 joules on the day of implantation and 54 joules 32 weeks after implantation for the twin disk system, 12 joules on the day of implantation and 19 joules 33 weeks after implantation for the catheter-internal disk system, 15 joules for the catheter-external disk system and 24 joules for the catheter-external sheet system.     

Experimental evaluation and initial clinical application of new self-adhesive defibrillation electrodes

We evaluated the efficacy of self-adhesive electrode pads for defibrillation and cardioversion in animals and patients. In 11 anesthetized dogs, the success rate of shocks given to terminate electrically-induced ventricular fibrillation was similar for both self-adhesive electrode pads and hand-held electrode paddles; success rate approached 100% at energies of 125-150 joules. Eighty patients undergoing defibrillation or elective cardioversion received shocks from self-adhesive pads. In all but 2 patients defibrillation or cardioversion was achieved at least once using these pads. The pads were equally effective from either apex-anterior or apex-posterior positions. The transthoracic impedance using self-adhesive pads was 75 +/- 21 ohms, similar to transthoracic impedance we previously reported when using standard hand-held paddles. No complications occurred with the use of the pads. We conclude that self-adhesive electrode pads are effective for defibrillation and cardioversion.     

Improved internal defibrillation efficacy with a biphasic waveform

Clinically available automatic implantable defibrillators use a monophasic truncated exponential waveform shock; after delivery the charge remaining on the device's capacitors is "dumped" internally and wasted. The efficacy of a monophasic and biphasic truncated exponential defibrillation waveform produced by a single capacitor discharge was compared in seven closed-chest, pentobarbital-anesthetized dogs. Defibrillation leads consisted of a new deployable intrapericardial electrode system. The monophasic waveform was positive and 6 msec in duration. The biphasic waveform had a positive phase identical to that of the monophasic waveform and a negative phase of equal duration with its initial voltage equal to 50% of the final voltage of the positive phase. Defibrillation shocks of varying initial voltage were delivered to construct curves of the percentage of successful defibrillation versus initial voltage and delivered energy, and the voltage and energy required for 50% (V50 and E50, respectively) and 80% (V80 and E80, respectively) success were compared. The biphasic waveform had significantly lower initial voltage (V50: 194 +/- 48 volts vs 227 +/- 48 volts, p less than 0.001; V80: 217 +/- 55 volts vs 256 +/- 66 volts, p less than 0.02) and energy (E50: 2.7 +/- 1.3 joules vs 3.4 +/- 1.5 joules, p less than 0.01; E80: 3.4 +/- 1.6 joules vs 4.3 +/- 2.2 joules, p less than 0.05) requirements than the monophasic waveform. It is concluded that a biphasic waveform produced by a single discharge that uses the "free" energy remaining on the capacitors significantly reduces the initial voltage and energy requirements for successful defibrillation and may improve the efficacy of future automatic implantable defibrillators.     

An Experimental Study of Transvenous Defibrillation Using a Coronary Sinus Catheter

The efficacy of a transvenous defibrillating system, utilizing bipolar right ventricular and coronary sinus catheters was evaluated in 14 normal mongrel dogs. Two groups of seven animals each were studied. During all shocks, the right ventricular apex electrode served as the anode. In both groups, defibrillation was performed using the proximal pole of the right ventricular catheter (superior vena cava), as the cathode served as a control (configuration A). In group 1, a coronary sinus cathode (configuration B) was compared to control. The mean energy at which 50% or more of the shocks were successful was similar for configuration B (20.7 ± 7.9 joules) and for configuration A (18.8 ± 9.4 joules). In group 2, the superior vena cava and coronary sinus electrodes served as a common cathode (configuration C). Mean defibrillation energy at which 50% or more of the shocks was successful was 21.4 ± 9.0 joules for configuration C and 27.1 ± 9.5 joules for configuration A (P < 0.01). Leading edge voltage was similar for all three configurations, hut shock duration was longer for configuration A (11.3 ± 2.8 msec) than configuration B (6.6 ± 1.8 msec) or C (6.1 ± 1.5; P < 0.05). Nonsustained ventricular tachycardia and transient heart block were common, but no damage to the coronary sinus was noted despite the delivery of up to 38 shocks. Conclusions: (1) With the catheter system used, coronary sinus to right ventricular apex defibrillation system offered no advantages over a superior vena cava to right ventricular apex system; (2) A three-electrode system with the high right atrium and coronary sinus serving as the common cathode reduced defibrillation thresholds significantly without any severe short-term adverse consequences; and (3) Improvements in catheter design may make a coronary sinus catheter part of a feasible transvenous defibrillating system.     

Evaluation of a new defibrillation pathway--the tongue-epigastric route. I. Experimental studies in dogs

The purpose of this study was to determine the efficacy of a tongue-epigastric defibrillation route in anesthetized dogs. Ventricular fibrillation was induced by rectangular pulses passed down a transvenous catheter into the right ventricle. Three groups of dogs were studied. Group I (15 dogs) received shocks from a 12 cm2 tongue electrode, a 50 cm2 circular, gelled self-adhesive electrode pad placed on the epigastrium and standard transthoracic defibrillator paddle electrodes. Shocks were given at energy levels of 50 to 460 joules (delivered energy, 50 ohm resistance). The success of the tongue-epigastric shocks in achieving defibrillation, and the resistance and current flow were determined at each energy level and compared with the same energy shocks from the standard transthoracic electrodes. In Group II (five dogs), comparisons were made between the 12 cm2 tongue electrode used in the first group of dogs and a larger tongue electrode of 40 cm2. In Group III (five dogs), intracardiac current flow (potential gradient) with tongue-epigastric and standard transthoracic electrodes was studied. In Group I, defibrillation success with the tongue-epigastric electrodes ranged from no success at 50 to 100 joules to 83% success at 460 joules. With standard transthoracic electrodes, success rates ranged from 65% at 50 joules to 100% at 300 joules. At all energies tested, the resistance was significantly higher and current significantly lower using tongue-epigastric compared with transthoracic electrodes. The higher tongue-epigastric resistance is probably related to the longer interelectrode distance; the correlation between interelectrode distance (x, in centimeters) and resistance (y, in ohms) in these dogs was y = 2.2x + 29.6, r = 0.78.(ABSTRACT TRUNCATED AT 250 WORDS)     

Clinical Shock Tolerability and Effect of Different Right Atrial Electrode Locations on Efficacy of Low Energy Human Transvenous Atrial Defibrillation Using an Implantable Lead System

Objectives. The objectives of this study were 1) to evaluate the effect of different right atrial electrode locations on the efficacy of low energy transvenous defibrillation with an implantable lead system; and 2) to qualitate and quantify the discomfort from atrial defibrillation shocks delivered by a clinically relevant method.Background. Biatrial shocks result in the lowest thresholds for transvenous atrial defibrillation, but the optimal right atrial and coronary sinus electrode locations for defibrillation efficacy in humans have not been defined.Methods. Twenty-eight patients (17 men, 11 women) with chronic atrial fibrillation (AF) (lasting ≥1 month) were studied. Transvenous atrial defibrillation was performed by delivering R wave-synchronized biphasic shocks with incremental shock levels (from 180 to 400 V in steps of 40 V). Different electrode location combinations were used and tested randomly: the anterolateral, inferomedial right atrium or high right atrial appendage to the distal coronary sinus. Defibrillation thresholds were defined in duplicate by using the step-up protocol. Pain perception of shock delivery was assessed by using a purpose-designed questionnaire; sedation was given when the shock level was unacceptable (tolerability threshold).Results. Sinus rhythm was restored in 26 of 28 patients by using at least one of the right atrial electrode locations tested. The conversion rate with the anterolateral right atrial location (21 [81%] of 26) was higher than that with the inferomedial right atrial location (8 [50%] of 16, p < 0.05) but similar to that with the high right atrial appendage location (16 [89%] of 18, p > 0.05). The mean defibrillation thresholds for the high right atrial appendage, anterolateral right atrium and inferomedial right atrium were all significantly different with respect to energy (3.9 ± 1.8 J vs. 4.6 ± 1.8 J vs. 6.0 ± 1.7 J, respectively, p < 0.05) and voltage (317 ± 77 V vs. 348 ± 70 V vs. 396 ± 66 V, respectively, p < 0.05). Patients tolerated a mean of 3.4 ± 2 shocks with a tolerability threshold of 255 ± 60 V, 2.5 ± 1.3 J.Conclusions. Low energy transvenous defibrillation with an implantable defibrillation lead system is an effective treatment for AF. Most patients can tolerate two to three shocks, and, when the starting shock level (180 V) is close to the defibrillation threshold, they can tolerate on average a shock level of 260 V without sedation. Electrodes should be positioned in the distal coronary sinus and in the high right atrial appendage to achieve the lowest defibrillation threshold, although other locations may be suitable for certain patients.     

Superiority of biphasic shocks in the defibrillation of dogs by epicardial patches and catheter electrodes

Currently available internal cardiac defibrillators use a uniphasic, truncated exponential waveform morphology of about 6 msec in duration at an energy level of 23 to 33 joules. To determine if improved defibrillation could be achieved with a different waveform morphology, we implanted 4.5 cm2 titanium patches to the left and right ventricle of 28 dogs. After ventricular fibrillation was induced, defibrillation was attempted using 7, 12, 13, or 17 joules. A 5 msec rectangular uniphasic waveform morphology was compared with a 10 msec rectangular biphasic waveform with the lagging 5 msec pulse of half the amplitude of the leading 5 msec. In an additional seven dogs, a transvenous bipolar catheter was placed with the distal electrode in the right ventricular apex and the proximal electrode in the superior vena cava. Biphasic and uniphasic shocks were compared at 14 joules. In the patch-patch system, the biphasic waveform was superior to the uniphasic waveform at 7 joules (67% versus 35%, p less than 0.001) and at 12 joules (93% versus 78%, p less than 0.001). No statistically significant differences were achieved at 13 joules or 17 joules. In the catheter electrode system with a delivered energy of 14 joules, the biphasic waveform was more effective than the uniphasic waveform (87% versus 27%, p less than 0.001). Manufacturers of automatic implantable defibrillators should consider this information in the design of future automatic implantable defibrillators.     

An abdominal active can defibrillator may facilitate a successful generator change when a lead failure is present.

AIMS: Defibrillator generator changes are frequently performed on patients with an implantable cardioverter defibrillator in an abdominal pocket. These patients usually have epicardial patches or older endocardial lead systems. At the time of a defibrillator generator change defibrillation may be unsuccessful as a result of lead failure. We tested the hypothesis that an active can defibrillator implanted in the abdominal pocket could replace a non-functioning endocardial lead or epicardial patch. METHODS AND RESULTS: An abdominal defibrillator generator change was performed in 10 patients, (mean age = 67 +/- 13 years, nine men). Initially, a defibrillation threshold (DFT) was obtained using a passive defibrillator and the chronic endocardial or epicardial lead system. DFTs were then performed using an active can emulator and one chronic lead to simulate endocardial or epicardial lead failure. We tested 30 lead configurations (nine endocardial and 21 epicardial). Although a DFT of 7.3 +/- 4.2 joules was obtained with the intact chronic lead system, the active can emulator and one endocardial or epicardial lead still yielded an acceptable DFT of 19.9 +/- 6.1 joules. In addition, a successful implant (DFT < or = 24 joules) could have been accomplished in 28 of 30 (93%) lead configurations. CONCLUSION: An active can defibrillator in an abdominal pocket may allow for a successful generator change in patients with defibrillator lead malfunction. This would be simpler than abandoning the abdominal implant and moving to a new pectoral device and lead or tunnelling a new endocardial electrode. However, loss of defibrillation capability with a particular complex lead may be a warning of impending loss of other functions (eg. sensing and/or pacing).     

Simulated Internal Defibrillation in Humans Using an Anatomically Realistic Three-Dimensional Finite Element Model of the Thorax

Finite Element Modeling of Defibrillation. Introduction: Determination of the optima) electrode configuration during implantable cardioverter defibrillator (ICD) implantation remains largely an empirical process. This study investigated the feasibility of using a finite element model of the thorax to predict clinical defibrillation metrics for internal defibrillation in humans. Computed defibrillation metrics from simulations of three common electrode configurations with a monophasic waveform were compared to pooled metrics for similar electrode and waveform configurations reported in humans. Methods and Results: A three-dimensional finite element model was constructed from CT cross-sections of a human thorax. Myocardial current density distributions for three electrode configurations (epicardial patches, right ventricular [RV] coil/superior vena cava [SVC] coil, RV coil/SVC coil/subcutaneous patch) and a truncated monophasic pulse with a 65% tilt were simulated. Assuming an inexcitability threshold of 25 mA/cm² (10 V/cm) and a 75% critical mass criterion for successful defibrillation, defibrillation metrics (interelectrode impedance, defibrillation threshold current, voltage, and energy) were calculated for each electrode simulation. Values of these metrics were within 1 SD of sample-size weighted means for the corresponding metrics determined for similar electrode configurations and waveforms reported in human clinical studies. Simulated myocardial current density distributions suggest that variations in current distribution and uniformity partially explain differences in defibrillation energy requirements between electrode configurations. Conclusion: Anatomically realistic three-dimensional finite element modeling can closely simulate internal defibrillation in humans. This may prove useful for characterizing patient-specific factors that influence clinically relevant properties of current density distributions and defibrillation energy requirements of various ICD electrode configurations.