Double counting of the R wave and T wave oversensing
Tracing
Manufacturer Abbott
Device ICD
Field Sensing
N° 20
Patient
A 57-year-old man suffering from ischemic cardiomyopathy and old anterior myocardial infarction, received a single chamber ICD. On a routine follow-up, multiple charges of the capacitors were found without shock delivery.
Graph and trace
1: Spontaneous rhythm;
2: Probable VT with sudden onset and change in the ventricular EGM morphology visible on the ventricular sensing channel (above the markers) and on the shock channel (below the markers). The R wave was double counted and the T wave was oversensed (F). The morphology of each F classified event is different from the normal reference (X and concordance index = 0). However, since the events were in the VF zone, the discriminators (e.g. morphology) were not applied;
3: Detection of VF episode and charge of the capacitors (asterisks);
4: Return of slow rhythm without oversensing and end of episode (5 ventricular cycles were outside of the VT and VF zones).
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This patient presented with multiple, very brief episodes of non-sustained monomorphic VT. Each episode caused the charge of the capacitors without shock deliveries. These repeated charges deplete the batteries prematurely. Remote monitoring is a valuable resource in these cases, as it enables an early detection and a prevention of inappropriate shocks. In this patient, a modest prolongation of the blanking period eliminated the double counting of the R wave during VT. One must not, however, compromise the detection of VF by excessively lengthening the post-ventricular ventricular blanking period. On the other hand, T wave oversensing could not be prevented by the usual means (sensitivity, adaptation level and delay). This patient underwent radiofrequency ablation of this very frequent non-sustained VT, which solved the problem, at least temporarily.