A 67-year-old man presenting with ischemic cardiomyopathy and an episode of sustained VT, underwent implantation of a Biotronik Ilesto dual chamber ICD; at the end of the procedure, a testing of the upper limit of vulnerability was performed; measurement of the spike (RV pacing at 150 bpm) to peak of T wave interval: 310 ms;
Tracing 1a
The 4 channels available are: 1) the markers with the time intervals, 2) the shock channel (FF = far field) between the coil of the RV lead and the pulse generator, 3) the atrial sensing channel and 3) the RV sensing channel.
Tracing 1b
Tracing 1c
Tracing 1d
The maximal output of this device is 40 Joules. We decided to start the first test with an amplitude of 30 J (10 J less than the maximal capacity). We did not induce ventricular arrhythmia; we then repeated a test with the same amplitude but with 2 different coupling intervals (290 and 330 ms) without induction of an arrhythmia. We could have stopped the procedure at the time after proving the existence of a safety margin. The major advantage would have been to prevent the patient from the complications associated with VF without preventing him from the complications of the shocks and of general anesthesia. The limitation would have been the lack of information regarding the quality of the ventricular sensing. We decided to measure the upper limit of vulnerability and decreased progressively the amplitude (3 tests for each amplitude with different coupling intervals) until induction of an arrhythmia. In this patient, the upper limit of vulnerability was 10 J. We could confirm the existence of reliable sensing during VF. This test did not prevent the patient from complications associated with VF or shocks (high number of required shocks for precise measurement of the upper limit of vulnerability).
