85-year-old man implanted with a Lumax 740 HF-T triple-chamber ICD for severe ischemic cardiomyopathy with left bundle branch block; recording and transmission of an EGM corresponding to a VT1 episode.
4 channels are available: the markers with the time intervals, the atrial sensing channel (A), the right ventricular sensing channel (RV) and the left ventricular sensing channel (LV).
The double counting of the R wave can occur during a sinus rhythm, during a premature ventricular contraction or solely during a slow VT as in this patient. QRS complexes can be considerably expanded in this setting, since double counting leads to the risk of incorrect classification in VT or VF zones and to the occurrence of unnecessarily aggressive therapies.
The double counting of the R wave is an exceptional occurrence on the latest generation of ICDs. The risk of oversensing has been considerably reduced by a prolongation of the post-ventricular ventricular refractory period from 80 ms to 110 ms on the new platforms. This value can also be changed using a code known to the employees of BiotronikTM. The prolongation of the ventricular refractory period generally allows eliminating the problem of double counting and must therefore be proposed in first intention, while bearing in mind that excessive prolongation can lead to an increased risk of undersensing of a true VF. Lowering ventricular sensitivity may sometimes resolve the problem, although this option may also generate a risk of VF undersensing. Moreover, this option is often ineffective since the second ventricular signal can be of at least equal amplitude to the first. Setting a very high VF zone to avoid inappropriate therapies in this setting also does not appear suitable. In the rare instances where the refractory period cannot be sufficiently prolonged, the implantation of a new pacing/defibrillation lead can be proposed.
In patients with very broad QRS, it is essential during implantation to carefully analyze the pattern and width of the ventricular intra-cardiac electrogram and to verify the absence of any double ventricular counting. It is also probably more appropriate to implant, in this setting, a dedicated bipolar lead rather than an integrated bipolar lead which favors double counting.
In this patient, the ventricular refractory period was probably programmed too short, whereas the prolongation of this refractory period to 130 ms without any change in sensitivity allowed eliminating this double counting.
