66-year-old man implanted with a triple-chamber defibrillator Viva XT CRT-D for idiopathic dilated cardiomyopathy with complete AV block; pacemaker interrogation 3 days post implant.
The first line corresponds to an electrocardiographic lead with superimposed markers (MA), the second line to the bipolar right ventricular EGM (EGM3) and the third line to the bipolar atrial recording (EGM1);
In patients with preserved atrioventricular conduction, which represents the majority of CRT patients, the prolongation of the AV delay leads to a progressive fusion with spontaneous activation. The AV delay setting changes the delay interval between atrial systole and ventricular systole, interferes with the quality of filling but also with the degree of capture and fusion with intrinsic activation; this setting must therefore be performed under electrocardiographic control.
As with the previous patient, the shortest AV delay was associated with an amputated A wave but was also with the longest AV delay enabling complete biventricular capture. While prolonging the AV delay improved the quality of filling, it was also associated with a fused pattern gradually approaching the spontaneous pattern. The overall difficulty in setting the AV delay is to determine the optimum degree of fusion for the patient. One of the few elements of certainty is that the CRT device was implanted to modify the patient’s activation sequence deemed to be deleterious to his cardiac function. While it is difficult to determine which is the optimal activation sequence, it appears essential that it be completely different from that observed before implantation. A too high degree of fusion does not seem to be desirable. A setting of the AV delay paced at 130 ms was selected in this patient without the certainty that this programming truly corresponds to the optimal AV delay.
