The automatic implantable cardioverter defibrillator: T wave sensing in the newest generation

The AICD uses an automatic gain control amplifier for detecting the small electrograms during ventricular fibrillation. The latest generation of the AICD appears to have a more sensitive lock on gain amplifier, as 6 of 76 patients implanted with the new AICD had double counting of the QRS-T wave complex resulting in asymptomatic discharges. Solutions to the problem of limiting these asymptomatic discharges are difficult and include slowing of the heart rate with beta blockers, changing the lead system, or replacement of the device. One of the six patients was treated with beta blockers. Three patients had their device changed, two patients requested the inactivation of their device until a rate programmable unit was available. The potential for T wave sensing in a lock on gain amplifier represents the unique dilemma between detecting small electrograms of ventricular fibrillation, and detecting diastolic events which occur shortly after the QRS complex.