A cardiac evoked response algorithm providing threshold tracking: A North American multicenter study

The purpose of this study was to evaluate a pacing system using the recogni tion of cardiac evoked response for the automatic adjustment of pacing outp ut. Patients were prospectively followed after primary implantation of VVIR pacemakers using AutoCapture (St. Jude Medical CRMD). Sensing and pacing t hresholds, polarization signal, evoked response, and AutoCapture performanc e were evaluated with serial visits and 24-hour Holter monitoring. Three hu ndred ninety-eight patients (mean age 71 +/- 15 years) were followed for an average duration of 1 year (3 days-1.75 years) with the algorithm function al in > 90% of patients. Backup pacing in the event of exit block was confi rmed in all patients. Pacing thresholds remained stable at 0.89 +/- 0.34 V with a pulse width of 0.31 ms (with chronic output autoset at 0.3 V above t he actual threshold). Evoked response exhibited a small but statistically s ignificant increase with time (8.92 V at implant, 9.60 mV at 12 months), ho wever, this finding did not result in any change in AutoCapture function du ring our follow-up period. The polarization signal remained stable with min imal variation (1.12 mV at implant, 1.18 at 12 months). No clinical adverse events were observed using the AutoCapture algorithm. In this initial expe rience with the AutoCapture algorithm the evoked response and polarization measurements remained adequate, allowing the system to function in the majo rity of patients with safe, low output pacing. High energy backup pacing pr ovided an added safety feature over fixed output devices in cases of unexpe cted threshold rises. Longer follow-up is required for continued long-term validation of the algorithm.