Diagnostic value of stored electrograms in single-lead VDD systems

Evaluation of the quality of atrial sensing is indispensable to monitor the performance of VDD single-lead systems. In addition to counters, a new VDD system offers storage of intracardiac electrograms (EGMs). The clinical co ntribution of stored EGMs in a VDD pacemaker was prospectively examined in a multicenter study, and the reliability of its counters was evaluated on t he basis of EGM information. Methods: A VDD system (Pulsar 870, Guidant Co. ) was implanted in 46 patients with atrioventricular block. EGM storage wet s activated upon detection of ventricular tachycardia (VT), recurrent prema ture ventricular complexes (PVCs), and mode switch ("atrial tachy reaction, " ATR). Stored EGMs were retrieved before discharge of the patients from th e hospital, and at 6-week, 3-month, and 6-month follow-up. Results: A total of 440 stored EGMs were retrieved and analyzed. Of 30 VT episodes detected , 2 (7%) were confirmed, and all others were attributable to ventricular ov ersensing. One postmortem interrogation documented VT as the cause of sudde n death. Of 175 EGMs stored upon detection of PVCs, 43 episodes (25%) were confirmed and 124 (70%) showed intermittent atrial undersensing with sponta neous AV conduction; in 8 episodes (5%) no abnormality was observed. Of 235 episodes stored upon ATR, 82 (35%) were confirmed and 153 were due to atri al oversensing. Conclusions: (2). Stored EGMs indicated a high percentage ( 69%) of event misdiagnoses by the pacemaker. Thus, pacemaker counter inform ation without the availability of stored EGMs should be interpreted with ca ution. (2). Misclassified events are of high clinical importance since they unmask otherwise unsuspected intermittent under- or oversensing.