T-wave oversensing and sensing polarity

N° 22
Manufacturer Medtronic Device ICD Field Oversensing

Patient implanted with a single-chamber ICD for Brugada syndrome; episodes of T-wave oversensing.

Graph and trace
  1. when the device is programmed in the traditional bipolar mode, the amplitude of the R waves is low (1.4 mV), explaining the increased risk of T-wave oversensing;
  2. after modifying the sensitivity programming (integrated bipolar), a substantial and prolonged increase in the amplitude of the R wave with amplitude values measured at between 6 and 8 mV.

We have seen on the previous tracing the value of a specific algorithm for preventing the occurrence of inappropriate therapies due to T-wave oversensing. This type of oversensing often reveals an inadequate quality of ventricular sensing (low amplitude R-wave) thus increasing the risk of undersensing of a true VF episode. There is a specific programming feature in MedtronicTM devices that may allow, in some patients, to resolve a difficult situation and avoid repositioning the lead. It is indeed possible to program ventricular sensing in "true" bipolar mode (detection between the 2 distal electrodes) or in integrated bipolar mode (detection between distal electrode and right ventricular coil). Upon averaging over a large number of patients, the amplitude of the R-wave measured in the two configurations is not significantly different. There is therefore no guarantee that the amplitude will be systematically higher in integrated bipolar mode. However, in some patients with a low amplitude R-wave in true bipolar mode, reprogramming of the sensing in integrated bipolar mode allows to substantially increase the size of the R-wave and thus solve the issue of T-wave oversensing (improved R-wave amplitude/T-wave amplitude ratio). This is an important competitive advantage in that it is the only manufacturer enabling this feature. Changing the sensing polarity should therefore be considered when faced with any issue of under- or oversensing, albeit without guarantee of success but with spectacular results in some patients.