Background
The number of pacemaker implants is growing because of newer indications. There are a few million pacemaker patients worldwide with hundreds of thousands of new implants yearly. Knowledge of different modes, timing cycles, and event markers, as well as newer algorithms, is necessary for accurate diagnosis of pacing system malfunction.
Pathophysiology
Although true pulse generator failure is very rare, pacing system malfunction occurs occasionally. Pacing system malfunction can be due to malfunction of lead, electrode-tissue interface, or pulse generator. Most of these malfunctions can be corrected by simple reprogramming of the device. The majority of malfunctions in fact are due to normal programmed pacemaker function. Thorough understanding of the cause of malfunction is extremely important for accurate diagnosis and management.
Epidemiology
Frequency
United States
Maisel reported pacemaker generator failure rate of 0.46% based on US FDA reports and 1.3 malfunctions per 1000 person-years based on device registries. [1, 2] Actual incidence of pacemaker malfunction, however, would be higher since these numbers are exclusive of lead failure. Hauser et al reported a 2% device electronic failure rate at their center. [3]
International
Actual incidence of pacemaker malfunction is unknown.
Mortality/Morbidity
Overall morbidity and mortality depend on the underlying cause of malfunction as well as the patient's dependency on the pacemaker. Most pacing system malfunctions are benign, although conditions such as cross-talk inhibition or runaway pacemaker can be life threatening. Maisel reported a 1 in 75,000 death rate among pacer implants. [2]
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Atrial undersensing. Rhythm strip showing an atrial pacing artifact after the intrinsic P wave.
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Ventricular undersensing. Rhythm strip showing ventricular pacing artifacts despite normal underlying ventricular activity.
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Atrial lead dislodgement. Chest radiograph film detail showing dislodged atrial lead with tip in the right ventricular cavity.
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Ventricular noncapture. Rhythm strip showing atrial (P wave) sensing followed by ventricular spike, which failed to capture the ventricle.
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Loss of atrial capture. Rhythm strip showing intermittent loss of atrial capture.
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Pacemaker-mediated tachycardia. Rhythm strip showing ventricular pacing at 110 beats per minute (programmed maximal track rate).
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Termination of pacemaker-mediated tachycardia. Automatic postventricular atrial refractory period (PVARP) extension terminated the PMT.
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This is an artifact due to monitor malfunction or loose limb lead connection. An abrupt loss of a portion of the QRS complex followed by a flat line can be observed. If R-R intervals are matched, 2 QRS complexes are missing during the pause. If it is due to a dislodged lead, a pacing artifact with no capture should be observed.
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This is a typical example of ventricular oversensing with inhibition of ventricular pacing. In ventricular noncapture, a ventricular pacing artifact should be present after the third P wave.
