Cardiac Memory T-wave Inversions Noted with Ventricular Pacing: A Possible Electrocardiographic Marker of Appropriate Conduction System Pacing

Abstract

Cardiac memory is a common condition occurring after a period of abnormal depolarization, such as with right ventricular apical pacing. With restoration of normal conduction, the T-wave "remembers" the direction of the QRS vector of the previously aberrantly conducted complexes, creating diffusely inverted T-waves on the electrocardiogram. The presence of diffuse T-wave inversions with this phenomenon may be confused with myocardial ischemia and may continue to be present for several weeks after restoration of normal conduction. Here, an interesting electrocardiogram obtained after pacemaker implantation showing the opposite effect, ie, the finding of memory T-waves occurring during pacing after a period of intrinsic atrioventricular nodal conduction, is presented. In this case, the patient had an underlying left bundle branch block, which subsequently normalized as a result of conduction system pacing. The memory T-waves became evident after pacing was performed, suggesting a potential marker for restoration of the normal ventricular activation sequence with left bundle branch pacing and normalization of the baseline intraventricular conduction defect.

Keywords: Cardiac memory; conduction system pacing; left bundle branch pacing; memory T-waves.

Figure 1:

Baseline 12-lead electrocardiogram demonstrating normal sinus rhythm at 63 bpm with an underlying left bundle branch block pattern with an intrinsic QRS duration of 168 ms.

Figure 2:

Chest X-ray showing ventricular lead position in the left bundle branch area.

Figure 3:

Pacing from the left bundle branch area demonstrating a QRS width of 138 ms with an incomplete right bundle branch pattern noted in lead V1. Leads II, III, and aVF are positive, suggesting a more basal location of the ventricular lead. The left ventricular activation time is 65 ms. *Comparison with the intrinsic QRS complex is seen. The intrinsic QRS demonstrates a QRS duration of 168 ms and a left ventricular activation time of 88 ms. A possible left bundle branch potential is observable from the intracardiac electrogram recorded at this location (arrow). Noted also are inverted T-waves in II, III, aVF, V5, and V6 of the paced complexes in comparison to the intrinsic complex. The axis of these T-waves is in the same direction as the patient’s intrinsic QRS complex in these leads from her baseline electrocardiogram. Abbreviation: LVAT, left ventricular activation time.

Figure 4:

Twelve-lead electrocardiogram immediately following implantation of a left bundle branch pacemaker system. Shown is an atrioventricular sequential paced rhythm at 60 bpm. The QRS width is 138 ms with an incomplete right bundle branch pattern noted in lead V1. Leads II, III, and aVF are positive suggestive of a more basal location of the ventricular lead. Diffuse symmetrical T-wave inversions are noted in the inferior and lateral leads. The axis of these T-waves is in the same direction as the patient’s intrinsic QRS complex in these leads from her baseline electrocardiogram.

Figure 5:

Twelve-lead electrocardiogram obtained 2 weeks following pacemaker implantation. Dual-chamber atrioventricular sequential pacing is noted. Resolution of memory T-waves noted in comparison to Figure 4.