An Uncommon Cause of Pacemaker‐Mediated Ventricular Tachycardia

Abstract

pacemaker, pacemaker-mediated tachycardia, R on T, V-blanking after A-pace, ventricular tachycardia CaseDuring a hospitalization for gastrointestinal bleeding, an 87-year-old woman with a history of coronary artery disease suffered a non-ST-elevation myocardial infarction. A dualchamber pacemaker (Altrua 60, Boston Scientific, Natick, MA, USA) had been implanted for "symptomatic bradycardia" some years prior.The pacemaker settings were as follows: Telemetry revealed sinus rhythm with demand atrial pacing. As shown in Figure 1, there were frequent ventricular premature contractions and many episodes of nonsustained polymorphic ventricular tachycardia (PMVT). The device's stored intracardiac electrograms (Fig. 2) corroborated these events. Serum levels of potassium and magnesium were normal. The 12-lead ECG during sinus rhythm showed a QTc of 462 ms.What was the cause of these episodes? CommentaryThere are several possible etiologies for PMVT. In this patient with a recent myocardial infarction, ongoing ischemia was of concern. However, she was asymptomatic and the ECG was not otherwise concerning for acute ischemia. Repolarization abnormalities could be a contributor. Her QTc interval was mildly prolonged, but not so long as to raise concern for high arrhythmic risk.Review of the patient's many episodes of PMVT revealed a consistent pattern of inappropriate pacing immediately preceding the arrhythmia. Ventricular pacing occurred soon after a QRS complex (*, Fig. 1A,B), raising the question of ventricular undersensing. In addition, a pacing artifact was evident within the prior surface QRS. However, in general the ventricular amplitude was within normal limits, and the intracardiac electrogram demonstrated high enough ventricular amplitude for adequate sensing of the ventricular beat just prior to the PMVT (*, Fig. 2). This patient's PMVT was indeed the result of inappropriate ventricular pacing that occurred as follows. The ventricular activations seen just prior to the pace that initiated PMVT were a short run of idioventricular rhythm. Most of these premature ventricular contractions (PVCs) were detected by the device. However, PVCs that were concurrent with an atrial paced event (*, Fig. 2) fell into the "V-blanking after A-pace" interval (here, 40 ms) and were not sensed. This resulted in a ventricular pacing impulse at the end of the dynamically extended AV interval of 320 ms. This inappropriate V-pace occurred during repolarization from the blanked VPC, resulting in an "R on T" pattern and leading to PMVT. 1Methods of preventing this phenomenon were entertained. We considered entirely disabling V-blanking so as to ensure sensing. However, this device does not allow complete elimination of the V-blanking after A-pace period (minimum duration: 30 ms). We considered increasing the pacing rate and decreasing the AV delay, but this would not completely eliminate the problem of blanking the ill-timed PVCs, and could result in a large burden of RV-only pacing. We considered the AAI pacing mode, which was an attrac...

Two Cases of Ventricular Proarrhythmia from Automatic Threshold Measurement Features in a CRTD and an ICD

“…It is well described that unsensed events during the atrial pacing-induced cross-chamber ventricular blanking period can carry the risk of Vp during the vulnerable phase. 2,3 However, in the present case this would probably not have initiated VT, if the autocapture feature had not been programmed active. It is the autocapture related high output backup stimulus that is most probably responsible for the proarrhythmic effect in the present case by overcoming the higher threshold during the relative refractory period of the unsensed event.…”

Pacemaker‐mediated arrhythmias

“…There are reports of the induction of ventricular tachycardia with an abnormal circuit close to the right ventricular apex or by the fusion of pacemaker impulses with multiple ventricular premature beats. 37,38 Although it is very rare, PMT protection algorithms may cause ventricular arrhythmia in patient with structural heart disease. 39…”

“…The occurrence of these arrhythmias is rare, especially with a normal functioning pacemaker with no secondary causes such as acute myocardial ischemia or metabolic disturbance. There are reports of the induction of ventricular tachycardia with an abnormal circuit close to the right ventricular apex or by the fusion of pacemaker impulses with multiple ventricular premature beats …”