DISCUSSION
The increasing growth in the elderly population and expanding
indications for pacemaker use have led to a progressive rise in the
number of pacemaker implants since the invention of the first
implantable pacemaker in the 1950s. As is well known, the typical
lifespan of a pacemaker is generally 6 to 10 years, depending on factors
such as the percentage of pacing and sensing, output settings, frequency
parameters, and impedance. Each pacemaker has indicators that suggest
the recommended replacement time, including the elective replacement
indicator, pacing mode, and changes in magnetic frequency. Ignoring
these indicators or failing to follow up regularly can lead to serious
consequences for patients, such as output malfunction, capture failure,
extended RR intervals, or even cardiac arrest. As the number of
pacemaker implants continues to grow, the demand for pacemaker
replacements also increases. Therefore, regular follow-up and timely
detection of pacemaker issues are particularly important.
Our study observed three spike signals during the AV delay (Figure 1),
which is more commonly seen in cases of CRT, His bundle
pacing1, and left bundle branch pacing. In these
cases, dislocation or an increase in threshold can lead to pacing
failure of left ventricular lead, His bundle pacing lead, or left bundle
branch pacing. As a result, the spare right ventricular pacing electrode
may capture the myocardium. However, transient three-spike signals can
also occur with advanced pacemaker functions, such as atrial or
ventricular threshold examinations. Considering the medical history,
chest X-ray examinations, and repeated ECGs of the patient, it was
determined that the patient, who had two pacemakers implanted,
experienced constant three spike signals during the AV delay purely by
coincidence.
The pacing spikes generated by a pacemaker with battery depletion
exhibit alternation between long and short intervals, resulting in a 3:2
spike output pattern. Most of these spikes result in loss of capture,
which can be attributed to spikes occurring during the refractory period
of the ventricular myocardium or during the diastolic period. In the
former case, the spikes occur on the QRS complex, ST segment, or T wave,
while in the latter case, the spikes represent a subthreshold stimulus.
Our findings indicate that pacing capture is not influenced by whether
the spike signals are even or odd, thereby excluding transient power
contributions from an exhausted battery. Additionally, our report
highlights a supernormal period at the end of myocardium repolarization,
which is considered a subthreshold stimulus that can excite myocardial
tissue.
A recent study suggests that syncope caused by pacemaker malfunction is
a rare cause of hospitalization2. From our study, we
learn that operators must exercise caution when dealing with patients
requiring replacement due to pacemaker power depletion. Rushed decisions
can lead to adverse effects. For instance, although the patient in our
study avoided severe consequences, he faced economic burdens and mental
distress.