CRT pacing interrupt

Trace category: 

57-y old woman implanted with a Biotronik CRT-D because of dilated cardiomyopathy (LVEF 28%, normal coronary arteries, meets criteria of ARVD).

This is extracted from a yellow alert: CRT pacing below limit (< 85%).

What is going on?  What more would you like to know? How can we increase biventricular pacing percentage?

A lot of interesting things going on!

1) We see a PVC with surpisingly slow VA conduction (~380 ms) and then another PVC which is undersensed on the RV channel.

2) The next retrograde atrial event, not within a PVARP, is sensed and tracked, initiating a PMT. VA conduction is very slow, resulting in a PMT rate well below the upper rate.

3) The LV lead is not paced throughout the PMT since every time it's timed too soon after the previous intrinsic LV sense (left ventricle T‐wave protection algorithm). This lack of LV pacing is what triggers the episode.

4) The PMT is not detected since VA criterium is not met. For PMT detection the VA conduction needs to be within the VA criterium which is 350s by default and in this case is aroumd 380 ms. The PMT continues for an unknow period and, together with the PVCs decreased %CRT. Even when PMT would be detected (normally after 8 cycles), it would not trigger recording of the episode, this is only the case for Abott and Boston Scientific, so 'catching' PMTs is rare in Biotronik (and Medtronic) devices.

5) By increasing the VA criterium to for example 420 ms, PMT detection and treatment is enabled, resulting in higher %CRT.

6) We also increased BB to decrease PMT-inducing PVCs!