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Today's pacing techniques and technologies have gone a long way toward the ideal and in the 1980s will make further strides toward a possible universally responsive, sophisticated, single instrument. These advances include the use of programmability of at least mode, rate, output, sensitivity, and refractory period; dual-chamber as well as single-chamber pacing; CMOS and LSI circuits; lithium batteries and possibly a limited revival of plutonium batteries; new lighter, longer-lasting, positive attachment leads; and new methods of triggering pacing. However, the increase in complexity and expense of the new devices has led to a question of their need, to a disputed question as to the possibility of overuse of pacing in general, and a need to reconcile government-mandated cost containment with medical as well as socioeconomic reality.

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A 3-year study by three medical centers has revealed a 1-year electrode malfunction rate of 7.4%; most malfunctions occurred within the first 30 days. The incidence of unavoidable early malfunction (3.2%) fell within the 5% standards suggested by the committee report of the Inter-Society Committee on Heart Diseases. Incidences of obscure cause (3.2%) may be difficult to identify prospectively and may be, to a certain extent, unavoidable. The majority of the malfunctions (4.2%) showed specific clues that indicated that they were preventable. Successful repositioning was achieved on the first attempt in 80.6% of the cases with malfunction, and only 0.7% required ultimate myocardial electrode implantation. The principal clues to potentially unsatisfactory positioning included the presence of a large right ventricle with or without tricuspid insufficiency, current thresholds greater than 0.5 mA and ST-segment deviations on the intracardiac electrogram of less than 2 mV. Electrode malfunction may be more common with bipolar than with unipolar electrodes; but significant differences in the incidence of malfunction among different unipolar electrodes were observed. These data indicate that further developments in transvenous electrode design are warranted.

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The place of pacemakers in the treatment of tachyarrhythmias has expanded far beyond the initial role in the brady-tachy syndrome, of providing a "minimum guaranteed rate" while medications suppress the tachycardia. Techniques have been developed for prevention, termination, and duplication of a patient's spontaneous tachycardia under safe catheterization laboratory conditions. Combined with accumulating information about the normal responses to electrophysiologic stresses, these techniques have led to a new dimension in arrhythmia control. Most tachycardias previously felt to be refractory can be controlled after serial electrophysiologic-pharmacologic testing, during which sequential pharmacologic and pacer regimens are tested until a combination is found which prevents induction of tachycardias, and/or a pace mode is found which reliably terminates the tachycardia. Use of such an approach reduces hospital admissions and referral for surgery, and eliminates prolonged hospitalization for assessment of therapy in patients with infrequent but potentially lethal spontaneous tachycardias.

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Pulse generator failure caused by continuous leakage of direct current through an output capacitor has not previously been appreciated. Routine post-explant electronic evaluation has identified the defect in six implanted and one external pulse generator. The constant direct current in the implantable units, 0.14 to 0.26 milliamperes, is in the range that produces ventricular arrhythmias in dogs although this did not occur in our patients. Evidence of local myocardial damage existed in four cases and of electrode deterioration in three. The implant failures occurred without warning and in four cases within 2 weeks of demonstrated normal function, blunting the predictive benefits of pacemaker monitoring programs. Capacitor discharge circuits used in many pacers are inherently capable of developing direct current leakage in the event of output capacitor short circuit. In one model of pacemakers such continuous direct current leakage caused 8.3 percent (3 of 36) of pulse generator failures, widely scattered in time at 23, 27 and 46 months after implant. Capacitor short circuit causing constant direct current leakage can masquerade as primary battery failure and should be suspected when cessation of pacer function is associated with increased threshold or poor myocardial electrogram without evidence of wire break or displacement.

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Six hundred nineteen patients have been followed by remote monitoring of pacemaker function using ECG and rate or rate alone; 278 of 280 have had battery exhaustion or electronic failure demonstrated. Ten percent of exhausted pacemakers failed prior to the average longevity of the particular model, and 32% (89 of 280) exceeded 36 months' longevity; of these, 13% (37 of 280) lasted more than 40 months and 4.6% (13 of 280) exceeded 50 months. The error rate is 0.7% (2 of 280). With pulse generator longevity increasing, monitoring is done less frequently during the first 2 years, then calls are made weekly after 24 months.

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