Suppression of an external demand pacemaker by diaphragmatic myopotentials: a sign of electrode perforation?

Inappropriate arrhythmia detection in implantable defibrillator therapy due to oversensing of diaphragmatic myopotentials

Nonadequate arrhythmia detection and delivery of electrical therapy is still a main problem in current implantable cardioverter defibrillator therapy. Besides supraventricular arrhythmias extra-cardiac biosignals also can cause inadequate shock delivery. The present study focuses on nonadequate arrhythmia detection due to oversensing of diaphragmatic myopotentials. Their clinical characteristics, incidence and management are presented. Three-hundred-eighty-four recipients of a transvenous cardioverter-defibrillator who were implanted and followed-up at our institution between October 1991 and June 1999 were enrolled. During a mean follow-up of 32+/-25 months a total number of 139 nonadequate episodes of arrhythmia detection due to oversensing of diaphragmatic myopotentials were observed in 33 patients (8.6%). In 11 patients a total of 32 high energy shock deliveries occurred. Oversensing of diaphragmatic myopotentials was primarily observed in patients implanted with defibrillator leads providing "integrated bipolar" sensing. The vast majority of nonadequate arrhythmia detection were observed during intrinsic bradycardia heart rate and/or antibradycardia pacing. Electrical lead failure was ruled out in every patient. In 90% of the patients with a cardioverter-defibrillator providing programmable maximal sensitivity (n=16), the reduction of maximum sensitivity was effective in preventing further episodes of nonadequate arrhythmia detection. In 48% of the patients with devices without programmable maximal sensitivity (n=17), surgery revision was necessary to solve the problem.

Pacemaker automaticity

The automated measurement of the main electrical parameters of pacemakers, such as battery voltage, current drain, pacing impedance, sensing levels, and pacing thresholds enables a continuous monitoring of the adequate functioning of the implanted device. New technologies in device interrogation, data transfer, and patient alert functions will enhance therapy safety significantly by the immediate detection of all, including transient, device malfunctions. The introduction of this technology will result in major changes in follow-up of patients with pacemakers. Technically we are very close to the goal of a fully automated pacemaker, although clinical acceptance lags behind. Clinical studies are necessary to demonstrate the beneficial effects of automated device functions, with regard to the main rationales for pacemaker automatization: increased patient safety, improved quality of life, and an improvement in the cost-benefit ratio in pacemaker therapy.

Future of bradyarrhythmia therapy systems: automaticity

Since the first fixed-rate ventricular pacemaker was introduced in the late 1950s, pacing systems have evolved rapidly. Current developments focus on making devices more sophisticated and less complex--a challenging combination. Automaticity features such as beat-by-beat capture verification, sensitivity threshold adaptation, and algorithms to govern dynamically the maximum sensor rate have either recently been introduced or are likely to be introduced in the near future. Technologic advances are likely to allow meaningful improvements in current drain, battery performance, memory capacity, signal processing, telemetry, and programmer interface. Bradyarrhythmia therapy devices of the future promise to go beyond the pacemaker. Ultimately, pacing systems will become part of integrated cardiac rhythm management systems.

Long-term assessment of unipolar and bipolar stimulation and sensing thresholds using a lead configuration programmable pacemaker

Acute and long-term pacing thresholds were measured prospectively in 74 patients with a unipolar/bipolar multiprogrammable pacemaker. At implantation, mean current threshold was 0.48 +/- 0.16 mA with unipolar mode and 0.55 +/- 0.16 mA bipolar mode (p less than 0.01). R wave amplitude at implantation was 7.78 +/- 2.4 mV with unipolar and 7.67 +/- 2.1 mV in bipolar mode (p = NS). During long-term follow-up (mean 9.3 months; range 3 to 24), no clinically significant differences in pacing or sensing thresholds were observed between bipolar and unipolar configurations. Lead configuration was changed 23 times in 11 patients. Symptomatic myopotential inhibition was corrected in two patients by reprogramming to the bipolar pacing mode. High thresholds and loss of capture were corrected in two patients by reprogramming to the unipolar pacing mode. The remaining configurational changes were made for improved sensing or pacing thresholds. This study documents, in a large group of patients, the equivalence of long-term unipolar and bipolar pacing and sensing thresholds and, in addition, demonstrates that lead configuration programmability offered some advantage in a subgroup of patients and may have prevented reoperation in five patients.

False inhibition of an atrial demand pacemaker caused by an insulation defect in a polyurethane lead

A patient who had an atrial demand pacemaker (AAI) presented with irregular pacing at a routine examination 5 months after implantation. When a magnet was applied over the pulse generator regular fixed rate pacing was obtained, thus proving oversensing in the system. Reprogramming the input sensitivity level to 2.5 and 5.0 mV did not solve the problem. Programming the pulse generator to the triggered mode (AAT) showed acceleration of the stimulation rate but also inhibition of the system. An S-S interval of 1260 ms was measured at a programmed interval of 857 ms (70 bpm). The pulse generator was disconnected and the intra-atrial electrogram was recorded. This showed different spurious signals varying in morphology and amplitude. Fortunately we were able to remove the lead (Medtronic 6991-U) from the atrial appendage. Subsequently a Helifix 12 mm AT lead was successfully implanted in the right atrial appendage and the same pulse generator was connected to the newly implanted lead. When the removed lead was examined by the manufacturer, a small tear in the insulation of the wire was detected. The dimensions of the tear were 0.1 X 0.7 mm. The tear was caused by stress corrosion cracking in the polyurethane tubing of the lead.

Long-term comparison of unipolar and bipolar pacing and sensing, using a new multiprogrammable pacemaker system

Over a six-month period a comparison was made between uni- and bipolar myocardial stimulation thresholds and R-wave sensitivity in 15 consecutive pacemaker patients. The patients received a new multiprogrammable Cordis 336 A pulse generator, that could be programmed with either uni- or bipolar circuitry. In addition, rate, output, sensitivity and pacing mode could be noninvasively programmed. The occurrence of myopotential interference at different sensitivity levels was also studied. Cordis 325-161 bipolar endocardial leads were used in all patients. In one patient, the current output sometimes had to be programmed higher bipolarly than unipolarly to capture the ventricles, otherwise no differences in threshold were found. Acutely. R-wave sensitivity was superior in 9 patients (60%) in the bipolar mode. Unipolar and bipolar electrograms were equal in 4 (26.7%), whereas unipolar R-wave sensitivity was best in only 2 (13.3%) of the patients. At a six-month follow-up, the same tendency was found. In 5 patients, bipolar sensing was superior to unipolar, while anti- and bipolar sensitivity was equal in the remaining patients. Myopotential inhibition was never seen in the bipolar mode at highest sensitivity (0.8 mV) even during provocative tests (n = 15) or 24-hour Holter monitoring (n = 12). In the unipolar mode, 14/15 patients (93.3%) showed inhibition during provocative tests and 12/12 patients (100%) during monitoring at a programmed sensitivity of 0.8 mV. No patients had myopotential interference at a sensitivity level of 3.5 mV. All patients have their pacemakers programmed in the bipolar mode after six months. This study confirms earlier acute data that the bipolar pacing mode is superior to the unipolar mode for permanent pacemaker therapy.

Myopotential inhibition of unipolar lithium pacemakers

The effect of isometric upper extremity exercise on pacemaker function was evaluated in 27 patients who remained pacemaker-dependent during testing. Inhibition was demonstrated in eight (31 percent) of which five were symptomatic. Based on design of the sensing amplifier and return to an all-metal housing in the unipolar lithium pulse generators, myopotential inhibition is being recognized as one cause of symptomatic pacemaker inhibition that is more common than generally appreciated. A method of evaluation and management options for symptomatic patients are discussed. Routine testing of all patients should be performed at the time of a regular office evaluation. If one model pulse generator appears to be particularly prone to myopotential inhibition, this knowledge should be considered in the choice of future pacing systems.

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.

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.