The clinical effects of pacemaker battery depletion come from two aspects: 1. Automatic reprogramming of the pacemaker: It occurs in the early stage of battery depletion (ERI period), and it has adverse clinical repercussions in some patients related to loss of rate response, loss of atrioventricular synchrony and ventricular synchrony, changes in lower rate limit (Usually decreases by 10 to 11%, or becomes a fixed rate), or a combination of these factors [
3,
5]. Sinha et al. [
5] surveyed the cardiorespiratory symptoms and adverse clinical events of 266 patients with pacemaker battery depletion in the ERI status. The results showed that 83 patients (31.2%) had symptoms and 28 patients (10.5%) had clinical events, associated with clinical conditions included heart failure (32%), chest infection (21%), pacemaker syndrome (18%), pre-syncope (14%), and palpitations (11%). 2. Bradycardia: With the progress of pacemaker battery depletion, the symptoms will gradually worsen. Syncope and pre-syncope were reported to be the most frequent symptoms [
4,
6]. However, syncope in bradycardia is not always caused by asystole but may instead be caused by TdP. TdP is a fatal polymorphic ventricular tachycardia, which is caused by many conditions that prolonged QT interval, such as drug, electrolyte abnormalities, bradycardia, myocardial infarction, congestive heart failure et al. [
7]. In Case 2, no electrolyte abnormalities were found and she was not taking drugs that were known to prolong the QT interval. Cardiac biomarkers were negative and the evidence for the diagnosis of myocardial infarction was insufficient. Although complicated with heart failure and fever, it could not fully explain the QT interval prolongation. Complete atrioventricular block was the main cause of prolongation of QT interval [
8].When associated with premature ventricular contractions, it was very easy to induce TdP. However, the predictors of TdP in AV block-induced acquired long QT syndrome(LQTS) are not well defined. Previous studies suggested that female sex, the increased time from the peak to the end of the T wave, a combination of LQT2-like notched T waves, or cardiac memory resulting from a change in QRS morphology [
9‐
11]. Therefore, syncope in AV block may be caused by malignant ventricular tachycardia. When patients with pacemaker have unexplained ventricular arrhythmias, especially TdP, we should be alert to the possibility of pacemaker battery depletion, and the placement of a temporary pacer could be the key to treatment.
Timely diagnosis of pacemaker battery depletion is crucial, helping to take targeted treatment. However, many health care providers do not have ready access to pacemaker interrogation. Carison et al. [
12] presented a simple method to predict whether the pacemaker has progressed the ERI status through the ECG alone, that is, the “Rules of ten”, and the patient can be diagnosed by meeting any of the following:1. Atrial pacing not at a multiple of ten; 2. Non-synchronous ventricular pacing not at a multiple of ten. The diagnostic criteria have a sensitivity of 79% and a specificity of 92.6%. It should be noted that this method is relevant to 3 major pacemaker manufactures (Abbott, Biotronik, Medtronic) excerpt Boston Scientific and MicroPort. This is because most manufacturers decrease the lower rate limit when reprogramming occurs. When Abbot’s, Biotronik’s, and Medtronic’s pacemakers are automatically reprogrammed, the lower rate decreased by 10,11%, and to 65 bpm, respectively (Table
1). The ECG performance of case 1 complies with the second diagnostic criteria. The non-synchronous ventricular paced at a fixed rate of 65 bpm, which violates a multiple of ten, so the pacemaker battery could be diagnosed as exhausted.
Table 1
Manufacturer-Specific Pacemaker Programming at Replacement Notification
Loss of Rare Response? | Yes | Yes | Yes | Yes | Yes |
Loss of AV Synchrony? | No | No | No | Yes(VVI) | Yes(VVI) |
Change in Lower Rate Limit? | No | Yes (−10%) | Yes (−11%) | Yes (65 bpm) | Yes (70 bpm) |
Magnet rate following replacement Notification | ≤85 bpm | ≤86.3 bpm | ≤80 bpm | ≤65 bpm | ≤80 bpm |
In conclusion, these cases emphasize that serious morbidity can arise from pacemaker battery depletion, even in the early stages. We not only need to improve the understanding of how to detect clinically pacemaker battery depletion, but also should pay attention to the follow-up of pacemaker patients.