Evaluation of a New Sensor-Based Algorithm to Protect Against Atrial Arrhythmias

The SmarTracking (ST) algorithm (Marathon 294–09, Intermedics Inc.) uses the sensor-calculated rate (SCR) to define a "variation band" for the intrinsic sinus rate. If the sinus rate exceeds the upper limit of the band, the ventricular pacing rate is limited by the ST rate (STR) and Wenckebach behavior is observed. The present study was aimed at evaluating the behavior of the ST mechanism in patients with healthy sinus node, during exercise and at rest. Methods: Twenty-one patients (15 men; mean age 67.8 ± 9.7 years) with normal sinus function were studied. Heart rate was recorded via the rate profile of the implanted pacemaker (Relay 294–03, Intermedics Inc.), and STR and SCR were obtained via a previously calibrated strap-on pacemaker. A 15-minute protocol was used during which subjects alternated periods of walking with periods of rest. Results: The relative difference between the average STR and the average sinus rate (DST) was calculated for each phase of the protocol as well as the maximum number of patients showing inappropriate Wenckebach behavior (#W). At nominal settings, DST was always positive and did not fall below 20%. #W was maximum at rest (5) and during heavy exercise (3). By increasing the STR at rest to 95 ppm and the maximum pacing rate to 150 ppm, the #W was reduced to zero for all types of activity except during very fast walk where #W was 1. Conclusion: In general, there was no competition observed between the STR and the intrinsic rhythm. In some cases, the STR at rest and the maximum pacing rate had to be reprogrammed for optimal performance.