Unexpected findings before hospital discharge in a patient implanted with a dual‐chamber pacemaker

A case of a patient implanted with a dual‐chamber pacemaker in which routine ECG before discharge shown unexpected findings.


| C A S E PRE S ENTATI ON
A 70-year-old man was admitted to the hospital because of syncope caused by transient complete atrioventricular (AV) block. Any potential reversible cause was ruled out and the patient was schedule for permanent pacemaker implantation. An echocardiogram revealed the presence of preserved left ventricular systolic function.
The baseline ECG is shown in Figure 1A. The patient underwent a dual-chamber pacemaker implantation (Accolade MRI L331, Boston Scientific). Two leads were transvenously positioned at the right atrial appendage and the right ventricular (RV) apex without any complication and excellent sensing and pacing parameters. Twelvelead ECG was performed ( Figure 1B) the next day before discharge, showed unexpected findings: The ECG showed transient presence of two different QRS morphologies.
Question: Is the pacemaker working properly?

| D ISCUSS I ON
Due to the very small pacemaker pulse amplitudes generated by bipolar pacemakers it is not always possible to detect pacing spikes in the ECG. Baseline ECG ( Figure 1A) shows sinus rhythm at a rate of 76 bpm, PR interval of 400 ms, and RBBB with normal axis. The ECG in Figure 1B shows sinus rhythm with no visible pacing spikes.  I G U R E 1 A, Baseline 12-lead electrocardiogram and lead II rhythm strip. B, Twelve-lead electrocardiogram and lead II rhythm strip performed the next day after pacemaker implantation. C and D, Postero-anterior and lateral chest X-ray projection before hospital discharge. E, Programmed pacemaker settings QRS-complexes from V4 trough V6. For the last three beats, the shorter PR intervals with wider QRS-complexes resumed. Therefore, the first two beats and the last three beats in Figure 1B Figure 1A) where RBBB also exists, in these eight beats with narrower QRS complex the QRS axis is superior with predominantly negative QRS complex in lead V6, which rules out that they F I G U R E 2 Schematic representation (A) of a fusion beat during an episode of AV delay lengthening determined by the AV Search + algorithm with its corresponding intracardiac electrograms during device interrogation (B). In (C) interrogation of the device during an episode of AV delay lengthening to check for intrinsic conduction by the AV Search + algorithm. In panel A, the sinus beat is conducted to the ventricle through the left bundle-branch, reaching it at 250 ms; then, the activation wavefront spreads through the right ventricle where the ventricular lead is placed, although the programmed search AV delay (300 ms) of the AV Search + algorithm allows ventricular pacing to occur just before the ventricular activation wavefront is detected by the ventricular lead, producing a fusion beat. In panel B, a 50msec delay is observed between the onset of the surface QRS complex and sensing of the local electrical wavefront as it reaches the right ventricular lead. This delay is due to the basal right bundle branch block and allows pacing with fusion beats. The basal native atrioventricular conduction was 250 ms and the programmed AV delay during AV Search + was 300 ms In panel C, electrocardiographic lead III, atrial electrogram, and ventricular electrogram are shown. When AV Search + is turned on, the AV delay is lengthened periodically for up to 8 consecutive paced or sensed cardiac events. It remains active as long as the intrinsic PR intervals are shorter than the programmed search AV delay value (300 ms in that case). The pacemaker switches back to the programmed AV delay when the 8-cycle search finishes without sensing intrinsic ventricular activity, resulting in fully paced QRS beats for the last three QRS complexes of the tracing. The AV delay is lengthened periodically to a programmed maximum limit (300 ms in our patient) for up to eight consecutive paced or sensed cardiac cycles. If intrinsic conduction is identified, the AV delay is automatically reprogrammed to allow for intrinsic AV conduction, otherwise the algorithm switches back to DDD if intact AV conduction is not detected, as in the preset case.
Hence, the pacemaker was working properly in the present case.
The case highlights the importance of clinicians knowing basic concepts of modern algorithms in cardiac implantable electronic devices 3 and pacing electrocardiography to avoid misinterpretations that can determine unnecessary or wrong actions.

CO N FLI C T O F I NTE R E S T
The authors declare no conflict of interests for this article.