A cardiac evoked response algorithm providing automatic threshold tracking for continuous capture verification: a single-center prospective study.

BACKGROUND: The AutoCapture algorithm as implemented in Regency and Microny pacemakers (Pacesetter Inc., Sylmar, CA, USA) provides beat-by-beat monitoring of capture based on proper detection of the evoked response, provides high output back-up pulse when loss of capture occurs, performs periodic threshold evaluations and acquires the capture threshold data in a time-based event counter for later retrieval. The safety and efficacy of this algorithm was prospectively evaluated at a tertiary care hospital of north India. METHODS AND RESULTS: Fifty-four patients (38 males, mean age 66+/-13 years) received a ventricular pacemaker model Regency SC+ with low polarization bipolar lead for high-grade atrioventricular block (n=42) and sick sinus syndrome (n=12). Evoked response and polarization signal were assessed initially at 24 hours postimplant, and follow-up measurements were systematically conducted at week 1 and months 1, 3 and 6. Further evaluation of eligible patients was performed at 6-monthly intervals. Lead implantation parameters were optimum in all patients. At 6 months, the algorithm was functional in 51 patients. The pacing threshold increased to 0.89+/-0.36 V (p<0.001) in the first month and stabilized thereafter. Significant saving of energy was accomplished by a constant output safety margin of 0.3 V instead of the traditional 100%. While the evoked response signal remained stable throughout the study period, the potential signal increased significantly from 0.6+/-0.7 mV to 1.0+/-0.6 mV (p<0.001) in the first month and remained steady subsequently. Back-up pacing in the event of exit block was confirmed in all 25 patients who underwent a 24-hour Holter test. Based on the suggested sense margins, ventricular undersensing was observed in 7 (28%) patients, the majority of whom had competitive cardiac rhythms. An elderly patient with pneumonic illness succumbed to pulmonary embolism at 6 months. CONCLUSIONS: This large single-center experience on AutoCapture demonstrates the success of this algorithm in low-energy ventricular pacing without compromising the patient's safety.