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Transmission

This case shows an episode of “ventricular run”. Inspection of the EGM reveals two aspects. First it is not an ventricular arrhythmia but rather supraventricular. As there is no discrimination for these type of episodes, any chain of fast ventricular events triggers the recording of a ventricular run. In this case, it is caused by a supraventricular run, with preserved AV conduction.

Another aspect of the tracing is the ventricular event which is without matching marker, ventricular undersensing. The event is of sufficient amplitude (probably around 6 mV) and of normal physiological morphology (seems to follow an atrial extrasystole). It is not sensed because it occurs within the post atrial ventricular blanking. As the atrial lead paces in Volts, and the ventricular lead senses in millivolts, it is essential to protect the ventricular channel against oversensing of the atrial pacing artifact. Therefore, a blanking of 30 milliseconds occurs on the ventricular channel after atrial pacing, which is called the post atrial ventricular blanking and is non-programmable. See the ventricular refractory periods page for more information.

Next steps

As it is a functional undersensing, not related to lead dysfonction, no further action is necessary. Even when the ventricular undersensing triggers ventricular pacing after the programmed AV delay, there is no risk of pacing within the T-wave as the AV delay is much shorter. If the ventricular events would occur a bit later, during the committed window of 95 milliseconds, ventricular pacing (safety pacing) would occur at the end of this window.