Biventricular vs Right Ventricular 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.

Synopsis: In patients with LV dysfunction who need permanent ventricular pacing support, BV stimulation is superior to conventional RV pacing with regard to LV function, quality of life, and maximal, as well as submaximal exercise capacity.

Source: Kindermann M, et al. Biventricular Versus Conventional Right Ventricular Stimulation for Patients With Standard Pacing Indication and Left Ventricular Dysfunction: The Homburg Biventricular Pacing Evaluation (HOBIPACE). J Am Coll Cardiol. 2006;47:1927-1937.

In this paper, Kindermann and colleagues describe a randomized cross-over study comparing right ventricular and biventricular pacing in patients with symptomatic bradycardia and impaired AV conduction. Thirty-three patients who required permanent ventricular pacing were enrolled in the study. All patients had a left ventricular end diastolic diameter greater than or equal to 60 mm and a left ventricular ejection fraction less than or equal to 40%. Of 33 patients initially enrolled, 3 died before completion of the study period and were therefore excluded from analysis. Atriobiventricular devices were implanted in 24 patients. Six patients, all of whom had permanent atrial fibrillation, got biventricular pacing. The initial lead position tested for right ventricular stimulation was the right ventricular septum, and this site was satisfactory in 17 patients. In 13 patients, the right ventricular lead was positioned in the right ventricular apex. Left ventricular lead position was a lateral or posterolateral position in 20 patients and an anterolateral position in 10. Patients underwent implantation and then a 3-month period with biventricular pacing to stabilize the patient and to detect and correct any device or lead related malfunctions. After this 3 month run-in, each patient underwent a quality of life assessment and a cardiopulmonary exercise test and then was randomized to receive right ventricular pacing or biventricular pacing for 3 months. After the 3 months, the patients were crossed over to the complementary pacing mode. At the end of each 3-month period, left ventricular end systolic volume, left ventricular ejection fraction, and peak oxygen consumption, as well as New York Heart Association functional class, quality of life and serum, N-terminal pro-B type natriuretic peptide were measured.

During the run-in period, reoperations were required in 3 of the 30 patients due to dislodgement of the LV lead (2 patients) or a device defect (1 patient). One patient who was initially randomized to the biventricular mode did not tolerate cross-over to the right ventricular mode and completed only one month of observation in the right ventricular pacing mode. Both right ventricular and biventricular pacing improved left ventricular volumes, left ventricular ejection fractions, New York Heart Association classes, and left ventricular function over preimplant conditions, but greater improvements were seen with biventricular stimulation. When compared with right ventricular pacing, biventricular stimulation reduced LV end systolic volume by 17% (P < 0.01), increased LV ejection fraction by 22% (P < 0.0002), and improved peak oxygen consumption by 12% (P < 0.0003).

Other improvements noted with biventricular pacing were an increase in cardiac index, a decrease in left ventricular mass index, and a decrease in LV hypertrophy index. Biventricular pacing similarly improved Doppler indices of left ventricular electromechanical activation and global left ventricular performance. Biventricular stimulation reduced N-terminal pro-brain natriuretic peptide (NT-proBNP) levels. Biventricular stimulation was associated with an improvement of New York Heart Association functional class by an average of 1.1 vs 0.6 for RV pacing. The Minnesota Heart Failure Score was 6 points slower with biventricular vs right ventricular pacing. Twenty of 30 patients preferred biventricular pacing in contrast to 2 who preferred right ventricular pacing and 8 patients who reported no preference.

In subgroup analyses, left ventricular lead position did not seem to have much effect on outcome. However, patients with septal right ventricular leads had an improved functional result compared to those with right ventricular apical leads. However, an improvement with biventricular stimulation was still seen even in the 17 patients with right ventricular septal leads.

Kindermann et al conclude that in patients with left ventricular dysfunction who require ventricular pacing support for AV conduction defects, biventricular pacing should be considered. Biventricular pacing is associated with better left ventricular function, better quality of life, and better exercise capacity.

Commentary

Cardiac resynchronization therapy has now been clearly established as an important mode of treatment for patients with systolic dysfunction and heart failure. Right ventricular apical pacing results in ventricular dyssynchrony, and may not be tolerated by patients with significant ventricular dysfunction. Biventricular pacing, however, requires placement of a left ventricular pacing lead, either by a transvenous or a direct epicardial approach, and this significantly increases the risk of malfunction or complications. As recently reported by Leon and colleagues (J Am Coll Cardiol. 2005;46:2348-2356), early and late complications after coronary sinus lead placement are seen in 10% to 20% of patients. In this report, complications were observed in 10% of patients.

Many of the studies reporting on the benefits of cardiac resynchronization have used a cross-over design such as used in this paper. Since all patients in a cross-over study receive a left ventricular lead, all patients in both groups are subject to these complications, and their effect is thereby eliminated in any analysis. The true comparison would be a standard right-sided approach versus the biventricular approach, with all events from the time of randomization counted in both groups using an intent-to-treat analysis. Such an analysis might eliminate benefits from resynchronization unless there were significant heart failure symptoms at baseline.

Until left ventricular lead placement is as simple and reliable as right ventricular lead placement, we must consider the complications associated with left ventricular lead placement before we implant a pacing system. In patients with preserved left ventricular function and/or a good New York Heart Association functional class, a net benefit from the left ventricular lead is likely to be small, at least during short-term follow-up. However, in patients with advanced heart failure or severe left ventricular dysfunction, the benefits are likely to be significant and, therefore, increasing the complexity of the biventricular system is fully justified.