Chute CRT

Type de tracés: 
Boston Scientific



Bonjour à toutes/tous,

Voici l'alerte reçue ce jour sur un Boston Scientific Autogen X4 CRTD



Que faire?



A with Loss of capture.

1st, 3rd and 5th beats with a sensed RV beat and LV beat, but device committed to pace after AP. In fact, it might be causing fusion there since the shock channel looks thinner. Would be nice to have an ecg done on this patient! If the patient was called and an ecg was performed please post the ecg!.

I would say that LV and RV electrodes are sensing fine all along. 

Sinus rhyth at 30/min

Escape rhythm at 60/min.

So, we should increase the output in the A, and set a programmed frequency at 70/min

Thank you for this wonderful website!

Dr Palazzolo,

Thanks for your sharing your thoughts about this unusual tracing. The patient was programmed DDD/ 55bpm. As you said, there is a sinus bradycardia which favors an autonomous ventricular rhythm (dissociation isorythmique in French). I m not sure we can say that there is an atrial loss of capture. I think the problem will be solved by programming a pacing lower rate faster than the ventricular rhythm (i.e. >60/min).

It is is notheworthy that RV and LV egm are on time during the V escape rhythm, which means V synchrony, whereas the patient was known to have a LBBB. There is "only" an AV dissociation and we can expect AV association during exercise. The patient has been called and will be seen in the next few days.

Thanks again Dr Palazzolo,


Dear Dr Ploux:
Why would the patient be at 30 / min, considering it is programmed at 55 if there were no loss of atrial capture? What other explanation could be? I think that in fact that would be the cause of the sinus bradicardia and finally the cause of the autonomous ventricular rhythm.
I agree with pacing at > 60/min (I meant that by pacing at 70/min just to be sure at 65 there is still no fusion because it is a CRT). For sure will visit and bring Malbec and alfajores!


Thank for this exchange!

Atrial loss of capture may not be the root cause of the problem. Whether there is an atrial capture or not, the atrial rhythm would always be lower (30 if no capture, 55 at best with atrial capture) than the junctional rhythm (around 60/min). However we see than the As are not influenced by the Ap which makes me think that there is no spontaneous atrial rhythm and the As are retrograde from the junctional rhythm. The Ap block the retrograde conduction every 2 beats.

Ok with this scenario?


Dear Sylvian:
At the beginning, I thought that a retrograde A could be a mechanism, but I think the VA is too long. 
I think that the A pacing is still not capturing and it is timed by the 1090 msec minus the PVARP extension after the PVC. 
I think that the RV and LV are sensing ok all along and I think that the RVP that we see is because of a timing issue and commitment after AP. 
I'm dying to see what was the final conclusion in the pacemaker clinic.! Do you agree that the VA is too long?


VA is around 250ms, which is compatible with a retrograde activation.

When the ICD was checked, Atrial pacing threshold was 0.6V/0.4ms, Impedance 536Ohms and detection 11mV.

The lower pacing rate was finally raised to 65/min.

Thanks for your interest.