A 54-year old man suffering from ischemic cardiomyopathy with a LVEF of 56% presented after 2 syncopal episodes. After undergoing negative electrophysiologic studies and programmed ventricular stimulation, the patient underwent implantation of a Reveal DX Holter.
This episode displays characteristics often observed in presence of T wave oversensing:
1) it occurred during exercise, which is often associated with a decrease in the R wave amplitude while the T wave remains stable or increases;
2) T wave oversensing is promoted by a decrease in the R wave amplitude. This tracing shows distinctly that oversensing does not occur when the R wave is of high amplitude. Indeed, the sensing threshold detection adapts according to the previous R wave. Thus, for a T wave of the same amplitude, the likelihood of oversensing increases as the previous R wave amplitude decreases;
3) the railroad appearance on the graph is a characteristic finding due to the sensing of a supernumerary cardiac signal (double counting of the R wave, oversensing of P or T wave) with alternating incidence and morphology of the 2 signals. The programmable settings that can prevent this oversensing are a) the refractory period and b) the duration of threshold stability before its decrease, which, in these patients, must be increased.
In absence of recurrent syncope, the ILR recorded 2 FVT and 1 VT episodes.
