The rhythm seen on the electrocardiogram (ECG) is a slow ventricular tachycardia (VT) with a cycle length of 640 ms originating from the left ventricular (LV) lateral wall.
Due to advanced heart failure with severe biventricular dilation and the underlying LMNA gene mutation, there is significant intraventricular conduction delay. This causes a remarkable latency in right ventricular (RV) sensing after the onset of ventricular depolarisation in the left lateral wall during this VT.
With the lower rate set at 80 beats/min (750 ms cycle length), a paced atrioventricular (AV) interval of 200 ms and atrial based timing, an atrial pace spike occurs 550 ms after a ventricular sensed event. Therefore atrial pacing occurs during ventricular depolarisation of the LV wall and an atrial pacing spike is seen in the QRS complex on the surface ECG. Shortly after the atrial pacing spike the ventricular depolarisation reaches the RV lead and is sensed. Due to ventricular sensing within the AV interval, ventricular safety pacing (VSP) is delivered with a short AV delay of 100 ms, as seen in Fig. 1. VSP is a safety mechanism that is activated in case of possible cross-talk by delivering ventricular pacing shortly after atrial pacing if a ventricular sensed event occurs after the ventricular blanking period within the programmed AV interval. Thereby it prevents ventricular asystole. Furthermore, the short AV delay prevents pacing in the vulnerable period of ventricular depolarisation (‘R on T’ phenomenon) in case the sensed event was a premature ventricular beat.
After electrical cardioversion, normal AV pacing was re-established (Fig. 2).
Conflict of interest
L. Baris and E.J. van den Bos declare that they have no competing interests.
Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/.