50 hz alternating current as a cause of inhibition of monopolar ventricular pacemakers

It is not well established the importance of 50 Hz alternating current (AC) (that supplies most of house appliances) as a source of inappropriate inhibition of today cardiac pacemakers (PM). This problem has been studied in 58 consecutive patients permanently paced (VVI unipolar) for AV block with 27 different PM models from 11 manufacturers. Under ECG monitoring, 50 Hz AC was applied through a pair of electrodes set at both patient's wrists using a battery powered external source, with voltage ranging between 0 and 45 V. Inappropriate inhibition was considered if PM pauses longer than twice the programmed escape interval of the PM were observed during interference. This happened in 46 patients (79.3%), with PM from all 11 manufacturers, with voltages ranging from 3 to 28 V. In each case, inhibition was seen with a narrow voltage window between no interference detection and interference reversion of the PM. Only 3 patients (5.2%) referred perception of electrical current during the study. Three of the patients studied had complained, prior to the study, about dizziness or presyncope related to touching electrical devices and in all of them inappropriate inhibition was observed during interference. We conclude that: 1) it is possible to demonstrate inappropriate inhibition caused by 50 Hz AC galvanic interference in a high percentage of unipolar PM; 2) This inhibition occurs at current levels that in most cases are not sensed by the cutaneous nerves, and 3) although the problem seems to have little clinical significance it should be investigated in paced patients with symptoms attributable to inappropriate inhibition of their PM.     

DDD起搏器选择心室起搏部位对血流动力学的影响

目的比较右室间隔部(RVS)和右室心尖部(RVA)起搏对血流动力学的影响。方法42例置入DDD起搏器的患者,分为RVS组和RVA组;比较2组术前和术后3个月随访的左室射血分数(LVEF)、心脏指数(CI)、每搏量(SV)、左室最大压力上升速率(dp/dtmax)、左室最大压力下降速率(-dp/dtmax)、二尖瓣血流E峰和A峰最大充盈速度比值(E/A)、等容舒张时间(IVRT)差异。结果与术前相比,RVA组3个月随访的LVEF、CI、SV、dp/dtmax、-dp/dtmax、E/A、IVRT均显著降低(0.51±0.04vs0.54±0.03;2.33±0.09L/min.m-2vs2.68±0.11L/min.m-2;71.11±14.2mlvs80.17±16.12ml;1614±133mmHg/svs1702±155mmHg/s;2230±234mm-Hg/svs2404±242mmHg/s;1.38±0.47vs1.86±0.28;73.2±3.86msvs77.6±4.15ms,均P<0.05),RVS组无明显变化。3个月随访RVS组LVEF、CISV、SV、dp/dtmax均显著高于RVA组(P<0.05)。结论RVS起搏对血流动力学无不良影响。     

Hierarchy of ventricular pacemakers.

To characterize the pattern of pacemaker dominance in the ventricular specialized conduction system (VSCS), escape ventricular pacemakers were localized and quantified in vivo and in virto, in normal hearts and in hearts 24 hours after myocardial infarction. Excape pacemaker foci were localized in vivo during vagally induced atrial arrest by means of electrograms recorded from the His bundle and proximal bundle branches and standard electrocardiographic limb leads. The VSCS was isolated using a modified Elizari preparation or preparations of each bundle branch. Peacemakers were located by extra- and intracellular recordings. Escape pacemaker foci in vivo were always in the proximal conduction system, usually the left bundle branch. The rate was 43+/-11 (mean+/-SD) beats/min. After beta-adrenergic blockade, the mean rate fell to 31+/-10 beats/min, but there were no shifts in pacemaker location. In the infarcted hearts, pacemakers were located in the peripheral left bundle branch. The mean rate was 146+/-20 beats/min. In isolated normal preparations, the dominant pacemakers usually were in the His bundle, firing at a mean rate of 43+/-10 beats/min. The rates of pacemakers diminished with distal progression. In infarcted hearts, the pacemakers invariably were in the infarct zone. The mean firing rates were not influenced by beta-adrenergic blockade. The results indicate that the dominant pacemakers are normally in the very proximal VSCS, but after myocardial infarction pacemaker dominance is shifted into the infarct. Distribution of pacemaker dominance is independent of sympathetic influence.     

Myopotential inhibition of demand pacemakers

Two patients are described in whom skeletal muscle potentials originating in the shoulder girdle muscles during isometric movement suppressed the discharge of a ventricular demand unipolar pacemaker, resulting in syncope. Converting the pulse generator into a fixed-rate mode with the magnet prevented the inhibition. Improved filters or wider use of bipolar electrodes should prevent this form of interference.     

Noninvasive electrophysiologic study using standard permanent pacemakers in patients with spontaneous sustained ventricular tachycardia or ventricular fibrillation

Permanent pacemakers capable of noninvasive electrophysiologic testing were used to study and treat 26 patients with spontaneous sustained ventricular tachycardia (VT) or fibrillation (VF). One hundred nine episodes of sustained VT or VF were induced in these patients. In 8 patients spontaneous VT was reverted by noninvasive means. Drug changes based on noninvasive testing were made in 12 patients. In the 1- to 67-month follow-up period, drug therapy based on noninvasive electrophysiologic testing was predictive of outcome in patients with spontaneous arrhythmias. Thus, noninvasive electrophysiologic testing using permanent pacemakers is a useful method for studying and treating patients with recurrent sustained ventricular arrhythmias.     

Left ventricular performance at rest and during exercise in patients with dual-chamber pacemakers.

In 13 patients with an implanted dual-chamber atrioventricular (AV) demand pacemaker, left ventricular performance was elicited by pacing mode manipulation for study using gated cardiac pool scintigraphy at rest and during exercise. There was no significant difference between DDD and VVI at 70 and 90 beats/min with respect to cardiac output, peak ejection rate or peak filling rate. At 110 beats/min, the cardiac output was greater with DDD as compared to VVI. The peak filling rate was also significantly greater with DDD as compared to VVI (DDD: 3.6 vs VVI: 2.8 EDV/s, p less than 0.05). During exercise the cardiac output was greater with DDD as compared to VVI at the same rate. The peak filling rate during exercise was significantly greater with DDD as compared to VVI (DDD: 3.0 vs VVI: 2.5 EDV/s, p less than 0.01). We conclude that DDD is more beneficial than VVI in maintaining cardiac performance during exercise.     

心室起搏管理功能降低病窦综合征患者高比例的右室起搏

目的评估具有心室起搏管理(MVP)功能的双腔起搏器对高比例右室起搏的病窦综合征(SSS)患者的疗效。方法 35例SSS患者,房室传导正常或合并间歇性房室传导阻滞(AVB),至少植入了两年双腔起搏器(DDD/R),并计划更换,入组前1个月以上的心室起搏比例超过40%。均植入具有MVP功能的双腔起搏器,随机程控MVP启动(MVP on组,n=17)或者关闭(MVP off组,n=18)。术前、术后6个月行血浆脑钠肽(BNP)测定;心脏超声测定左室收缩末期内径(LVESD),左室舒张末期内径(LVEDD),左室射血分数(LVEF);并于术后6个月程控起搏器了解右室起搏比例、心房高频事件。结果术前两组血浆BNP及LVESD、LVEDD、LVEF比较无显著差异(P>0.05);术后两组有关心脏超声指标无明显变化(P>0.05)。MVP on组术后较术前血浆BNP有明显下降(P﹤0.05),与MVP off组比较,MVP on组术后右室起搏百分比、心房高频事件发生率均有显著下降(2.6%±0.6%vs 48.4%±10.5%,15.7%±2.3%vs 62.0%±7.8%;P﹤0.01)。结论具有MVP功能的DDD/R起搏器能降低高比例右室起搏的SSS的右室起搏比例及心房高频事件的发生率。     

Modulation and suppression of parasystolic ventricular pacemakers

Using a three part model of canine false tendon in which an inexcitable gap intervenes between the proximal and distal region of Purkinje fibers, Jalife and Moe recently individualized a biological model of parasystole and showed how the electrotonic depolarization can modulate, entrain or annihilate pacemaker activity. We report the ECG of 9 patients with parasystole (as assessed by the direct recording of ectopic cycle length) in which the early nonparasystolic beats delayed whereas the late shortened the parasystolic cycle length. The phase response curve is specific for a given patient. In two cases a nonparasystolic impulse falling at a critical point in the ectopic cycle length was followed by the suppression of any parasystolic activity on the surface EKG. The recently described phenomenon called pace maker annihilation is thus discussed.