A Decade of Nuclear Pacing

In April, 1973, a decade-long study was begun on nuclear-powered pacemakers. The first 15 of these were designed by the Numec Corporation under a contract from the United States Atomic Energy Commission. Altogether 151 units powered by the isotope plutonium 238 were implanted in 131 patients; the pacemakers of 4 different manufacturers were used. The last nuclear pacemaker was implanted in January, 1983. The actuarial survival at 10 years was 92%, meeting the original performance goal of the Commission of 90%. Ninety pulse generators are still in service today; 25 patients have died and 36 pulse generators have been replaced with non-nuclear units. The most common indication for replacement was an inappropriate pacing mode. This high reliability and superior performance suggest that continued use of a radioisotopic power source is justified, particularly if combined with the electronic circuits of today's dual-chambered, multiprogrammable, and multifunctional pacemakers.     

Study of interactions between permanent pacemakers and electronic antitheft surveillance systems

Interference of electronic antitheft systems (EASs) with pacemakers has been an object of controversy. This study was performed in 204 patients followed by our pacemaker surveillance center. The data from a total of 408-patient exposures to the EAS were analyzed. The device tested consisted of 129 DDD, 71 VVI, and 4 VDD pacemakers from seven manufacturers. The EAS studied consisted of an "acoustomagnetic" system that emits an intermittent 58-kHz signal, and a magnetic audio frequency system that emits a continuous 73-Hz signal. Complete interrogation of the pacemakers was performed before and after the consecutive exposure of the patients to both EASs. Electrocardiograms were recorded while the patients were exposed to the magnetic fields of each EAS for up to 30 seconds. One or more EAS interferences occurred in 17% of patients. EAS was observed in 26 (20%) of 129 patients with DDD, 7 (10%) of 71 patients with VVI, and 2 (50%) of 4 patients with VDD pacemakers. Over twice as many instances of EAS interference were observed with the "acoustomagnetic" system as were with the magnetic audio frequency system. Among pacemakers programmed in the DDD mode, a considerably greater prevalence of interference was observed at the atrial versus ventricular level, despite the same programmed sensing polarity in both chambers in all but one case. Sensing anomalies were the most common EAS induced disturbance, and typically lasted for the duration of exposure. In a few instances of pacing inhibition, the phenomenon was limited to 1 cycle at the onset of EAS exposure. No changes occurred in the programming of the pacemakers, and a single patient experienced palpitation during EAS induced rapid pacing. During exposure to EAS mimicking the normal use of the systems, interference with a variety of pacemakers was relatively common. However, the anomalies observed were transient and the cause of no symptom or device reprogramming. Patients should be advised to not stand unnecessarily in the close proximity of EASs.     

No gender differences in pacemaker selection in patients undergoing their first implantation

Recent studies have indicated that women were less likely to receive sophisticated pacemaker devices than men. These differences could not be fully explained by demographic and clinical variables. The purpose of the present study was to assess whether a gender related difference might exist in pacemaker mode selection in patients undergoing their first implantation in The Netherlands. Records of first implants (n = 39,217) collected from 1988 through 1997 covering 95% of all implantations in The Netherlands. From this population 33,564 (85.6%) patients were included for final analysis. We observed no significant sex differences in pacemaker selection in patients with atrioventricular conduction disorders and bundle branch block. In patients with sick sinus syndrome, only very old women (> or = 85 years) had more atrial systems implanted than men of similar age (6.5% vs 3.5%), whereas men received more double chamber pacemakers (12.3% vs 10.3%) (P = 0.002). However, the relative distribution of physiological versus nonphysiological pacemakers in this subgroup was similar for men and women. In patients with chronic atrial fibrillation/flutter associated with bradycardia, sex differences were only apparent in the age group of 75-85 years; women received more dual chamber pacemakers (8.8% vs 5.3%) whereas men received more single chamber ventricular pacemakers (94.2% vs 89.8%) (P = 0.0011). With increasing age, sex differences in pacemaker selection were absent, but there was a considerable drop in implantation rate of dual chamber systems. Our study showed no major sex differences in the selection of pacemaker devices. Physicians select pacemaker devices by age rather than gender, which might be a rational choice.     

Spontaneous Heart Activity in Pacemaker Treated Patients with High-grade Atrioventricular Block A Holter Monitor Study

A Holter monitor study. A Holter monitor study was performed to assess the occurrence of spontaneous heart activity in 70 pacemaker treated patients (mean age 72.1 years) with high-grade atrioventricular (AV) block, who had been treated with permanent pacemakers for a mean of 60 months (range 5-161). Nineteen patients had asynchronous (VOO), and 51 QRS-inhibited (VVI) pacemakers. The patients were monitored for a mean of 23 hours (range 15.5-26). Twenty-five patients were re-studied for day-by-day variations in spontaneous heart activity. At clinical observation, thirty-eight patients had pacemaker rhythm only. During monitoring, all patients studied had some kind of spontaneous cardiac activity, mostly ventricular ectopic beats. Three patients had short episodes of sinus rhythm of more than 70 beats/min. Patients in functional class III-IV (NYHA) or with an enlarged heart had the most spontaneous heart activity; those with asynchronous pacemakers had the least spontaneous cardiac activity. No tachyarrhythmias precipitated by interference between intrinsic heart beats and asynchronous pacemakers were seen. Twenty patients studied twice had a relatively stable occurrence of spontaneous heart activity, while five (20%) varied considerably. On the basis of these long-term observations it is difficult to predict when interference rhythm will occur, and asynchronous pacemakers therefore cannot be recommended for the first implantation. (PACE, Vol. 4, November-December, 1981)     

Valsalva-Induced Variations in the Intracardiac Signal

Variations in the intracardiac signal may substantially affect the sensing function of cardiac pacemakers. As the Valsalva maneuver causes a change in heart volume, its effect on the intracardiac signal was studied in seven patients with an adequate escape rhythm who had permanent ventricular pacemakers. During generator replacement, they were asked to perform a standardized Valsalva maneuver. An increase from the baseline amplitude ranging from 5% to 70% was noted during forced expiration against the closed glottis. There was a decrease from the baseline ranging from 15% to 50% after termination of this maneuver. Similar changes were noted for the rate of voltage change (slew rate). The magnitude of these alterations was most pronounced in patients with comparatively low intracardiac amplitudes. Because marked changes in the intracardiac signal can result from the Valsalva maneuver, it might be an important source of undersensing among patients with permanent pacemakers.     

Characteristics and Clinical Effects of Myopotential Signals in a Unipolar DDD Pacemaker Population

Myopotential signals were recorded from atrial and ventricular leads during isometric exercise in 25 patients who had chronically implanted dual chamber pacemakers using the electrogram telemetry capability of the pacemakers. Average electrogram amplitude on the atrial channel was 0.92 mV (range 0.3 to 1.9) and on the ventricular channel was 0.98 mV (range 0.3 to 2.2); the difference was not significant. There was a strong correlation (R = 0.82) between the amplitude of myopotentials on the atrial and ventricular leads for individual patients. Myopotential sensing caused ventricular output inhibition in two patients (8%) and ventricular tracking in sixteen patients (64%). Pacemaker reprogramming abolished ventricular myopotential inhibition in all patients and stopped ventricular myopotential tracking in seven patients. We conclude that myopotentials can be analyzed and their effects ameliorated by a multiprogrammable pacemaker with electrogram telemetry capability.     

Aspergillus Infection of a Permanent Ventricular Pacing Lead

Fungal infections of intracardiac pacemakers are extremely rare. We describe what appears to be the first reported case of Aspergillus infection of a permanent pacing lead and review the three reported cases of other fungal infections of pacemaker leads which we could find in the literature. These infections may be encountered more frequently as the number of permanent pacemakers implanted in elderly patients with underlying medical illnesses continues to increase.     

The nature and frequency of postimplant surgical interventions: a realistic appraisal

The purpose of this retrospective study was to investigate the nature and frequency of surgical reinterventions after primary pacemaker implantation in patients who survived at least 20-30 years. Eighty-five such patients were identified, 32 of whom had radioisotopic (nuclear) implants, and 53 lithium battery powered lithium units. Excluding reoperations within the first 3 months, patients with nuclear implants experienced about two reoperations in 25 years, while those with lithium experienced one every 8 years. The most frequent reasons for surgery were pulse generator replacements, lead revisions, and mode changes, particularly in the nuclear group. There were no premature device failures. This study allows us to make reasonable predictions to patients about the experience a pacemaker implantation, and reassures us about the reliability of the devices that were implanted in the past.     

The Value of DDD Pacing in Patients with an Implantable Cardioverter Defibrillator

Although the beneficial effects of DDD pacing are well known, currently available ICDs provide only fixed rate ventricular antibradycardia pacing. In a consecutive series of 139 patients with ICDs, we have analyzed the need for antibradycardia pacing and the indications for DDD pacing. We also report our initial experience with the Defender 9001 (ELA Medical, France) DDD-ICD. Out of 139 patients, 25 (18%) were in need of antibradycardia pacing. Ten patients already had a pacemaker at the time of ICD implantation and ten other patients had a conventional pacemaker indication at that time. Five patients became pacemaker dependent during a follow-up of 20 ± 8 months. The disorders necessitating pacemaker therapy were high degree AV conduction disturbances in 72%, sick sinus syndrome in 12%, and AF with a slow ventricular response in 16% of patients. Based upon current indications, DDD pacing was indicated in 20 (80%) of 25 patients. The Defender 9001 DDD-ICD (ELA Medical) was used in two patients with ischemic cardiomyopathy and pacemaker syndrome with VVI pacing. Cardiac output during DDD pacing increased by 36% in one patient with an increase in VO₂ max during exercise of 29%. The other patient showed an increase in cardiac output of 50% with DDD pacing, and, while unable to exercise with VVI pacing, had a VO_2max of 24 mL/kg per minute during DDD pacing. Up to 18% of our ICD patients are in need of antibradycardia pacing. Of these pacemaker dependent patients, 80% have an indication for DDD pacing. Our first clinical experience with a DDD-ICD confirms the hemodynamic benefit of AV synchronous pacing in ICD patients with pacemaker syndrome.     

Myopotential Inhibition of Unipolar QRS-inhibited (VVI) Pacemakers, Assessed by Ambulatory Holter Monitoring of the Electrocardiogram

Seventy-four patients with unipolar QRS-inhibited pacemakers (VVI) were Holter monitored to assess the occurrence of pacemaker inhibition caused by skeletal muscle potentials during daily activities. Fifty patients had high-grade atrioventricular block and 24 had sinoatrial disease. Chest wall stimulation prior to monitoring revealed asystole of > 4 seconds duration in 22 patients, and ventricular rates between 25 and 56 beats per minute in 52 patients. Fifty-one patients (69%) had one or more episodes of pacemaker inhibition from myopotentials. Inhibition occurred in all types of pacemakers studies, but was most frequent and of longest duration in patients with Siemens-Elema 207/70 (13/14 patients), Cordis Omni-Stanicor (6/7 patients), CPI Microlith (5/6 patients), and Medtronic 5945 (8/10 patients). This was not unexpected considering the filter characteristics of the pacemakers. Nine patients (12%) presented symptoms which might be ascribed to pacemaker inhibition. The longest asystole observed was 3.2 s. Seven patients had pacemakers spikes falling on or near T-waves of spontaneous heart beats because their pacemakers had been rendered refractory by myopotentials. No serious arrhythmias were seen during episodes of pacemaker inhibition or interference. More emphasis should be put on the improvement of filter characteristics of unipolar VVI-pacemakers. Pacemaker patients with symptoms of myopotential inhibition should be equipped with either a bipolar or ventricular triggered (VVT) pacemaker or with a sensitivity and/or pacing mode programmable pacemaker.     

Electromagnetic interference in implantable pacemakers.

The inhibited pacemaker (VVI or AAI) has become the most popular in recent years because of its ability to combine a physiological advantage with economical current consumption in cases with spontaneous activity. One of its disadvantages is its sensitivity to external electromagnetic interference. Though today's pacemakers possess effective protection against most interference signals there may be instances in which patients are subjected to uncomfortable or even life-threatening situations. This is the case of "amplitude modulated" or "pulsed" fields with modulation frequencies in the physiological range. Fields of that sort have been found in the vicinity of a welder, an electric steel plant, and in medical practice where therapeutic currents were applied. Even touch-actuated switches may influence a demand pacemaker. However, these situations may be overcome by a device within the pacemaker for simple time analysis which can be carried out with few components. If electromagnetic fields of diathermy equipment are applied, today's pacemakers may react with intolerably high or low rates. They should, therefore, be avoided.     

The Use and Interaction of Permanent Pacemakers and the Automatic Implantable Cardioverter Defibrillator

The adverse interactions of permanent pacemakers and automatic implantable cardioverter defibrillators (AICD) were studied in nine patients in whom both devices were implanted. Both unipolar and bipolar pacemakers were evaluated. The permanent pacemakers were also used to do noninvasive electrophysiological studies and to induce ventricular fibrillation. Undersensing of ventricular fibrillation by the permanent pacemakers caused inappropriate pacemaker stimuli, which caused undersensing of ventricular fibrillation by the AICD in three of four patients with unipolar pacemakers. After an AICD discharge, pacemaker noncapture was seen in eight of 22 episodes for an average 4.9 seconds and inability to sense was seen in 11 of 20 episodes for an average 9.0 seconds. Counting of pacemaker stimuli and QRS by the AICD caused inappropriate discharges. Noninvasive electrophysiological testing by the pacemakers correlated with invasive testing. Furthermore, induction of ventricular fibrillation was successful in four of five patients attempted, though requiring long bursts at high outputs at the shortest cycle lengths obtainable by these pacemakers. Operation of the AICD and permanent pacemakers must be clearly understood to avoid adverse interactions of these devices.     

Transtelephonic Monitoring of 25,919 Implanted Pacemakers

In order to evaluate the behavior of lithium-powered cardiac pacemakers, a database of 25,919 lithium-powered pacing systems including 23,517 single and 2,402 dual chambered pacemaker generators were followed in 21,750 patients. Of this group, 11,319 were currently active in addition to 7,560 who died, as well as 2,871 patients who terminated their follow-up service prior to the end-of-life of the pacemaker system. A total of 23,517 single chambered pacemakers were followed for 719,173 months of pacing. The mean time to explant for generator malfunctions was 42 months and for all pacing system malfunctions it was 38 months compared to 31.9 months and 28.6 months, respectively, for the 2,402 dual chambered units that were observed for 38,718 months. In the single chambered units, the most frequent reason for explant was battery exhaustion (37% of explants) followed by lead problems (26%) compared to 49% and 12%, respectively, for the dual chambered units. The incidence rates, defined as a transtelephonic test result, required physician decision for action or clarification of the pacing mode or program parameters and showed a high incidence rate immediately post-implant; thereafter, there was a relatively trouble-free period until the 36th month when capture, sensing, and battery problems began to occur at a steady rate reaching 4% at the end of 48 months. Similarly, for dual chambered units, an 8% incidence rate was seen within the first 3 months, followed by a quiescent period until the 28th month when the incidence rate jumped to 16%.(ABSTRACT TRUNCATED AT 250 WORDS)     

Optimum AV Interval in Dual Chamber Pacemakers

Approximately 50-70% of permanent implanted pacemakers are dual chamber pacemakers. However, little is known concerning adjustment of the atrioventricular (AV) interval to maximize cardiac output. Ten consecutive patients with complete heart block and dual chamber pacemakers were paced at heart rates of 80, 100, and 118 beats/minute and at five AV intervals with simultaneous measurements of cardiac output using pulsed Doppler. Maximum cardiac output occurred at AV intervals of 150 and 200 ms at rates of 80 and 100 beats/minute, and at 150 ms at a rate of 118 beats/minute (p less than .05). An increase in the AV interval to 250 ms resulted in a decrease in cardiac output at all heart rates (p less than .01). We recommend the noninvasive measurement of cardiac output, if available, for determining the optimum AV interval in an individual patient; otherwise, an AV interval of 150 or 200 ms will provide the highest cardiac output in most patients.     

Myopotential Inhibition of Unipolar AV Sequential (DVI) Pacemaker

Whereas myopotential inhibition of QRS-inhibited (VVI) pacemakers is well known, its occurrence in patients with AV sequential (DVI) pacemakers has not been reported. The present communication deals with spontaneous and induced myopotential inhibition of a multiprogrammable Intermedics unipolar AV sequential (DVI) pacemaker. The bedside maneuvers that were performed in the patient exposed the problem, therefore serving to establish the diagnosis. Although external adjustment of the sensitivity was the simple, non-invasive solution in this case, more studies are required to determine the success rate of this approach as well as the incidence and clinical significance of myopotential inhibition of unipolar DVI pacemakers.     

Long-Term Management of Ventricular Tachycardia by Implantable Automatic Burst Tachycardia-Terminating Pacemakers

This report describes the Jong-term follow-up of two patients who received implantable automatic burst tachycardia-terminating ventricular pacemakers for the treatment of drug-refractory sustained ventricular tachycardia. After implantation, both pulse generators continued to terminate ventricular tachycardia without any major complications. In one patient, after three years, many episodes of ventricular tachycardia were slower than the tachycardia-detection criterion rate of 137 per minute; ventricular tachycardia was then terminated by chest wall stimulation that activated the burst function of the pacemaker. In this particular patient, the pulse generator was removed after four and one-half years and replaced with a DDD system because of the pacemaker syndrome and attacks of ventricular tachycardia, often at a rate of about 100/minute. In the second patient, the pacemaker continued to terminate ventricular tachycardia for over five and one-half years as determined by the repeated activation of the flag (memory) function of the pacemaker indicating detection of tachycardia by the pulse generator and resultant delivery of burst pacing.     

Programmable External Automatic Antitachycardia Pacing as a Bridge to Definitive Therapy in Patients with Recurrent Sustained Ventricular Tachycardia

The efficacy and safety of external programmable automatic antitachycardia pacemakers (ATPs) used in the critical care setting for recurrent sustained monomorphic ventricular tachycardia (VT) was evaluated. Ten patients who had failed a mean of 4.0 +/- 1.4 antiarrhythmic medications (range 2-7) and who had previously required electrical cardioversion for VT were enrolled. Prior to ATP use, successful overdrive pacing termination of VT was demonstrated in all patients. Intertach (Intermedics, Inc.; n = 9) and Orthocor II (Cordis, Inc.; n = 1) ATPs were attached to temporary bipolar transvenous or epicardial pacing leads. Mean patient age was 66.4 +/- 11.5 years, and mean left ventricular ejection fraction was 22 +/- 7.5%. At the time of initial ATP use, mean VT cycle length was 347 +/- 88 msec (range 280-550 msec). A burst scanning antitachycardia pacing algorithm was used in each patient; one patient was also treated with a fixed rate burst adapted to VT cycle length. The duration of ATP use ranged from 2-25 days (median 5), successfully terminating greater than 3,369 VT episodes (median 3, range 0 to greater than 3,103 episodes per-patient). Two episodes of ATP induced rate acceleration occurred, each successfully terminated by the ATP. Only two patients required external cardioversion during ATP use, one for primary ventricular fibrillation and one for rapid polymorphic VT associated with antiarrhythmic drug withdrawal. ATPs also provided antibradycardia pacing and allowed for serial programmed ventricular stimulation. No complications were associated with transvenous catheter or ATP use.(ABSTRACT TRUNCATED AT 250 WORDS)     

The acute effect of cardiac pacing mode on endothelial vasodilation: prospective, double-blind, cross-over, comparative clinical study

Background: Compared to atrioventricular sequential pacing, ventricular demand pacing is known to have somewhat more deleterious hemodynamic effects, which probably arise from increased sympathetic tonus and inappropriate baroreceptor activation. Endothelial function is affected by various local and systemic factors including baroreceptor activity. The aim of this study was to explore whether cardiac pacing would have any effect on endothelial functions.
Methods: Twelve patients (six male, mean age: 75 ± 9 years) with previously implanted DDD or VDD cardiac pacemakers were included. All patients had stable atrial rhythms during the study. Patients were randomized to either atrial-based pacing mode (VDD or DDD) or ventricular demand pacing mode (VVI) first, and then cross-over was performed with the other pacing mode. Endothelial function was assessed by brachial artery ultrasonography. Basal diameter of the brachial artery, and both flow-mediated dilation (FMD) and endothelium-independent vasodilation with nitroglycerin were measured 1 hour after each pacing mode.
Results: Compared to atrial-based pacing mode, ventricular demand pacing was associated with a significantly worse FMD both as absolute and percentage values (0.17 ± 0.09 mm vs 0.28 ± 0.11 mm, P = 0.015 and 4.84 ± 2.37 % vs 7.00 ± 2.88 %, P = 0.028, respectively). However, there was no significant difference in nitroglycerin-mediated vasodilation values between the two pacing sessions.
Conclusions: Acute ventricular demand pacing (VVI pacing) is clearly associated with attenuation of FMD in patients with atrial-based pacing systems. The attenuation of endothelial vasodilation might have a role in hemodynamic and clinical deterioration in patients with VVI pacemakers.     

The Use of Exercise Testing in Children to Evaluate Abnormalities of Pacemaker Function not Apparent at Rest

The purpose of this study was to evaluate the use of exercise testing in identifying abnormalities of pacemaker function and in confirming set parameters not apparent at rest in children with implanted atrial synchronous physiologic pacemakers. Maximal exercise tests were performed on 24 children (15 boys, 9 girls) from 4.5 to 18 years of age (median = 15) with physiologic pacemakers. The lower rate limit was observed before or following testing in 19 of 24 cases. In each case this correlated with the set lower rate limit. The upper rate limit was reached in 10 of 24 cases and was found to be lower than that programmed in one case in which a long atrial refractory period had limited the upper rate limit. Six children reached the maximum upper rate limit to which their pacemaker could be programmed. No abnormalities of atrial capture or ventricular capture occurred during exercise testing. Ventricular sensing was normal in each case. Atrial sensing was observed to be normal in 15 of the 24 cases. Two patients had decreased atrial sensing with exercise. Reversion to the "noise rate" due to myopotential inhibition was found in seven other cases. Subsequent tests on two of these children showed normal sensing.(ABSTRACT TRUNCATED AT 250 WORDS)     

Acute and Chronic Pulse-Width Thresholds in Solid Versus Porous Tip Electrodes

Sixty-one patients given programmable pacemakers at initial implantation have been followed for a mean of 18 months (3-42) with non-invasive measurements of myocardial pulse-width threshold. Fifty of the patients had CPI 0505/0522 (Microlith-P/Microthin-PI) pacemakers with either Cordis 322-462 8 mm2 ball tip (n=12), Cordis 322-620 17.5 mm2 (n=23), or CPI 4116 porous tip electrodes (stimulation area 7.5 mm2 and sensing area 50 mm2) (n=15). Eleven patients had Medtronic 5985 (Spectrax-SX) pacemakers with either Medtronic 6907-R 8 mm2 ring tip (n=7), 6907 11 mm2 (n=3) or 6917 myocardial electrodes (area 12 mm2) (n=1). At acute implant, the ball tip and porous tip electrodes had the lowest stimulation thresholds, but the differences were only statistically significant in comparison with the 17.5 mm2 electrode (p less than 0.01). Chronically there were no significant differences between the various electrodes (p greater than 0.1), but the ball tip electrode tended to give best long-term results, and the porous tip electrode the poorest. Thirty-eight of the 61 patients (62.3%) had chronic pulse-width thresholds of 0.1 ms or less at approximately equal to 5 V output, indicating that pulse-width programming is a useful way to conserve battery energy. However, at some stage of the study, six of the patients (9.8%) had a pulse-width threshold of 0.5 ms or more. Pulse width should therefore not be set too narrow in standard nonprogrammable pacemakers.