Bi-ventricular vs. RV Apical Pacing
Abstract & Commentary
By John P. DiMarco, MD, PhD, Professor of Medicine, Division of Cardiology, University of Virginia, Charlottesville. Dr. DiMarco is a consultant for Novartis, and does research for Medtronic and Guidant.
Source: Yu C-M, et al. Biventricular pacing in patients with bradycardia and normal ejection fraction. N Engl J Med. 2009;361:2123-2134.
Yu et al report a multi-center trial evaluating the relative benefits of right ventricular apical pacing compared to biventricular pacing in patients with a standard indication for pacing and a baseline preserved left ventricular ejection fraction. The Pacing to Avoid Cardiac Enlargement (PACE) study was a multi-center trial testing this hypothesis. Patients with a standard pacing indication of either AV conduction disease or sinus node dysfunction received atrial synchronized biventricular pacemakers at the time of their initial implant. Two days after successful implantation of the device, the patients were randomly assigned to either right ventricular apical pacing or biventricular pacing and their pacemakers reprogrammed appropriately. All devices were programmed to the DDDR mode with a lower rate limit of 60 bpm and an upper tracking rate of 140 bpm. Baseline assessments included echocardiography with core lab readings, a six-minute walk test, and a quality-of-life assessment using the SF-36. Patients were then followed at routine intervals for one year. The two primary endpoints of the study were changes in left ventricular ejection fraction and changes in left ventricular end-systolic volume at 12 months. Secondary endpoints included distance coverage during the six-minute walk test, quality-of-life measures on the SF-36, and heart failure hospitalizations. Echocardiographic assessment of left ventricular ejection fraction was done using either real time 3-D echocardiography or, if this was not available, 2-D echocardiography.
Over a three-year period, a total of 251 patients were screened for participation. One hundred and ninety-three patients were eligible for the trial, but 16 had unsuccessful implantation of a left ventricular pacing lead. The remaining 177 patients were randomly assigned to either biventricular pacing (89) or right ventricular apical pacing (88). The mean age for the group was 68 years, and 54% were male. The groups were similar with regard to heart rate, QRS duration, and cardiac diagnoses at baseline. The mean left ventricular ejection fraction for the entire group was 61.7%. Fifty-seven percent of the patients received their pacemaker because of advanced atrioventricular block and 43% because of sinus node dysfunction.
Long-term data from four patients were not included in the analysis. Two patients were lost to follow-up; one patient died, and one patient had echo images that were inadequate for analysis. Two patients had diaphragmatic stimulation during left ventricular pacing that could not be corrected with reprogramming but were analyzed with the biventricular pacing group according to the intention-to-treat principle.
Biventricular pacing resulted in a significantly better left ventricular ejection fraction than did right ventricular apical pacing at 12 months (58.9 + 9.1% vs. 62.2 + 7.0%; p < 0.01). This translated to a decreased ejection fraction over a 12-month period of 6.7% in the right ventricular pacing group vs. no significant change in the biventricular pacing group. Left ventricular end systolic volume also was better with biventricular pacing. The absolute difference between the groups was 8.1 mL at 12 months; clinical variables showed little difference. There was no difference in the distance covered during the six-minute walk, with both pacing groups having an increase over baseline of more than 30 meters at 12 months. Similarly, there was no difference in quality-of-life measures, as assessed by the SF-36. There were 11 hospitalizations for heart failure; six in the right ventricular pacing group and five in the biventricular pacing group. Only two of these patients had a left ventricular ejection fraction of less than 45% at 12 months. Seven patients in the biventricular pacing group had diaphragmatic pacing, but this could be managed with reprogramming with continuing biventricular pacing in five.
The authors conclude that right ventricular apical pacing results in better ejection fractions and left ventricular systolic volumes compared to standard right ventricular conventional pacing. However, at 12-month follow-up, these changes do not correlate with a decrease in clinical events or in quality of life changes.
Numerous studies have shown that right ventricular apical pacing induces ventricular dyssynchrony, and some studies have suggested that excessive or unnecessary right ventricular apical pacing results in clinical events. This paper is in agreement with these observations but still leaves open the question of whether the added cost and risk for procedural complications associated with current techniques for biventricular pacing would be justified in patient without systolic heart failure at baseline. In this study, there was a 7% deterioration in left ventricular ejection fraction and an 8 mL change in left ventricular end systolic volume associated with right ventricular apical pacing. However, at least over a 12-month time period, these changes did not result in an increased frequency in heart failure hospitalizations and no changes in functional capacity or quality of life measures. These hemodynamic improvements were achieved at the cost of 16 unsuccessful initial implants and seven patients who had left ventricular lead-related problems during the one year follow-up. At this time, therefore, it seems that standard biventricular pacing cannot be justified without evidence that clinical outcomes can be favorably affected. In patients with sinus node dysfunction, alternate strategies to avoid unnecessary right ventricular pacing are available and seem a better first option.