Threshold tracking pacing based on beat by beat evoked response detection:Clinical benefits and potential problems

Continuous monitoring of pacemaker stimulation thresholds and automatic adj ustment of pacemaker outputs were among the longstanding goals of the pacin g community. The first clinically successful implementation of threshold tr acking pacing was the Autocapture feature which has accomplished automatic ventricular capture verification for every single stimulus by monitoring th e Evoked Response (ER) signal resulting from myocardial depolarization. The Autocapture feature not only decreases energy consumption by keeping the s timulation output slightly above the actual threshold, but also increases p atient safety by access to high-output back-up pulses if there is loss of c apture. Furthermore, it provides valuable documentation of stimulation thre sholds over time and serves as a valuable research tool. Current limitation s for its widespread use include the requirements for implantation of bipol ar low polarization leads and unipolar pacing in the ventricle. Fusion/pseu dofusion beats with resultant insufficient or even non-existent ER signal a mplitudes followed by unnecessary delivery of back-up pulses and a possible increase in pacemaker output is not an uncommon observation unique to the Autocapture feature. The recent incorporation of the Autocapture algorithm in dual chamber pacemakers has been challenging because of more frequent oc currence of fusion/pseudofusion beats in the presence of normal AV conducti on. Along with a review of the previously published studies and our clinica l experience, this article discusses the clinical advantages and potential problems of Autocapture.