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.