May 2018

Oversensing shortly after an ICD implant

Jason Collinson – Chief Cardiac Physiologist
Essex Cardiothoracic Centre, Basildon and Thurrock University Hospital
Twitter: @cardiacjase


A 77 year old male with a history of coronary heart disease, ischemic cardiomyopathy and aborted sudden death from a ventricular arrhythmia underwent implantation of a dual chamber implantable cardiac defibrillator (ICD).  An active bipolar atrial lead and an active dual coil DF4 right ventricular integrated bipolar defibrillator lead were implanted to the right atrial appendage and right ventricular apex respectively. There were normal intracardiac electrograms and satisfactory parameters during lead tests and immediately post connection to the generator.  Three therapy zones were programmed with rate cut offs of 220/180/150 bpm. Brady settings are displayed below.  Approximately 40 minutes post procedure the device was interrogated for a routine post implant check. The presenting rhythm strip is displayed below. Of note all lead measurements were within a normal range.

Mode: AAIR with VVI back up
LR/UR: 55/130 bpm
Paced/Sensed AV delay: 180/150 ms
A sensitivity threshold: 0.25 mV
V sensitivity threshold: 0.6 mV

Figure 1
Presenting rhythm strip. Top to bottom. ECG lead II (10mm/mV), Atrial EGM (5 mm/mV), Ventricular EGM (1 mm/mV), Shock EGM (1mm/mV), Marker channel.


What is the most likely explanation for the discrete low frequency potentials seen on the RV EGM?

  • P waves sensed on the RV channel

  • T wave oversensing

  • T wave oversensing

  • Loose set screw

  • Air escaping from the sealing plugs