Automated left ventricular capture management.

BACKGROUND: The stimulation thresholds of left ventricular (LV) leads tend to be less reliable than conventional leads. Cardiac resynchronization therapy (CRT) requires continuous capture of both ventricles. OBJECTIVE: The purpose of this study is to evaluate a novel algorithm for the automatic measurement of the stimulation threshold of LV leads in cardiac resynchronization systems. METHODS: We enrolled 134 patients from 18 centers who had existing CRT-D systems. Software capable of automatically executing LV threshold measurements was downloaded into the random access memory (RAM) of the device. The threshold was measured by pacing in the left ventricle and analyzing the interventricular conduction sensed in the right ventricle. Automatic LV threshold measurements were collected and compared with manual LV threshold tests at each follow-up visit and using a Holter monitor system that recorded both the surface electrocardiograph (ECG) and continuous telemetry from the device. RESULTS: The proportion of Left Ventricular Capture Management (LVCM) in-office threshold tests within one programming step of the manual threshold test was 99.7% (306/307) with a two-sided 95% confidence interval of (98.2%, 100.0%). The algorithm measured the threshold successfully in 96% and 97% of patients after 1 and 3 months respectively. Holter monitor analysis in a subset of patients revealed accurate performance of the algorithm. CONCLUSION: This study demonstrated that the LVCM algorithm is safe, accurate, and highly reliable. LVCM worked with different types of leads and different lead locations. LVCM was demonstrated to be clinically equivalent to the manual LV threshold test. LVCM offers automatic measurement, output adaptation, and trends of the LV threshold and should result in improved ability to maintain LV capture without sacrificing device longevity.

Reduction of RV pacing by continuous optimization of the AV interval.

BACKGROUND: In patients requiring permanent pacing, preservation of intrinsic ventricular activation is preferred whenever possible. The Search AV+ (SAV+) algorithm in Medtronic EnPulsetrade mark dual-chamber pacemakers can increase atrioventricular (AV) intervals to 320 ms in patients with intact or intermittent AV conduction. This prospective, multicenter study compared the percentage of ventricular pacing with and without AV interval extension. METHODS: Among 197 patients enrolled in the study, the percentage of ventricular-paced beats was evaluated via device diagnostics at the 1-month follow-up. Patient cohorts were defined by clinician assessment of conduction via a 1:1 AV conduction test at the 2-week follow-up. The observed percentage of ventricular pacing with SAV + ON and the predicted percentage of ventricular pacing with SAV + OFF were determined from the SAV + histogram data for the period between the 2-week and 1-month follow-up visits. RESULTS: Of 197 patients, 110 (55.8%) had intact 1:1 AV conduction, of which 109 had 1-month data. SAV + remained ON in 99/109 patients; 10 patients had intrinsic A-V conduction intervals beyond SAV + nominal and therefore SAV + disabled. The mean percentage of ventricular pacing in the 109 patients was SAV+ ON = 23.1% (median 3.7%) versus SAV + OFF = 97.2% (median 99.7%). In 87 patients without 1:1 AV conduction, SAV + was programmed OFF in 6, automatically disabled in 52, and remained ON in 29. In 8 of these patients, 80-100% reduction in ventricular pacing was observed with SAV + ON. CONCLUSION: The Search AV+ algorithm in the EnPulse pacemaker effectively promotes intrinsic ventricular activation and substantially reduces unnecessary ventricular pacing.

Automatic measurement of atrial pacing thresholds in dual-chamber pacemakers: clinical experience with atrial capture management.

BACKGROUND: The Medtronic EnPulse pacemaker incorporates the new atrial capture management (ACM) algorithm to automatically measure atrial capture thresholds and subsequently manage atrial pacing outputs. OBJECTIVES: The purpose of this study was to evaluate the clinical performance of ACM. METHODS: Two hundred patients with an indication for a dual-chamber pacemaker underwent implantation. ACM thresholds and manually measured atrial pacing thresholds were assessed at follow-up visits. Clinical equivalence was defined as the ACM-measured threshold being within -0.25 V to +0.5 V of the manually measured threshold. The clinician analyzed all ACM measurements performed in-office for evidence of proarrhythmia. RESULTS: All 200 implanted patients had a 1-month visit, and validated manual and in-office ACM threshold data were available for 123 patients. The ACM threshold was 0.595 +/- 0.252 V, and the manual threshold was 0.584 +/- 0.233 V. The mean difference was 0.010 V with a 95% confidence interval of (-0.001, 0.021). The mean difference over all visits was 0.011 V. For all patients, the individual threshold differences were within the range of clinical equivalence at all visits. No atrial arrhythmias were observed during 892 ACM tests in 193 patients. CONCLUSION: This study demonstrated that the ACM algorithm is safe, accurate, and reliable over time. ACM was demonstrated to be clinically equivalent to the manual atrial threshold test in all patients at 1 month and over the entire follow-up period of up to 6 months. ACM ensures atrial capture, may save time during follow-up, and can be used to manage atrial pacing outputs.