Current biventricular pacing studies : Dr. Saxon pointed out that biventricular pacing was first considered as a potential therapy because CHF patients have marked dyssynchrony in ventricular contraction, due to tissue damage from a previous infarct or simply from muscle deterioration. This damage or scarring promotes delays in left ventricular (LV) activation and reduces contractility. "The theory behind biventricular pacing is to resynchronize ventricular function by activating both ventricles at the same time. This, in turn, might improve cardiac contraction and eliminate patient symptoms."
She added that researchers have evaluated this type of pacing primarily in small groups of end-stage patients who were not transplant candidates. Bakker et al. conducted a study of 12 such patients and reported improvements in both hemodynamics and functional capacity. The investigators found that mean LV ejection fraction (LVEF) increased by 8 ± 2%, mean New York Heart Association Class improved from 4 to 2.5 (p = 0.03) and mean peak VO2 increased by 4.4 ml/min/kg (95% CI: 2.2-6.6).5, 6 Dr. Saxon has also published data on several patients whose cardiac function improved with biventricular pacing.
"Consequently the VIGOR® CHF study was developed, using a pacemaker still under investigation that paces both ventricles simultaneously," she explained. The VIGOR CHF trial is expected to enroll over 100 patients at 25 centers worldwide. All patients must have advanced CHF and, despite maximal medical therapy, must remain symptomatic.
"Patients must also have left or right bundle branch block [BBB], since in concept it seems that patients with this type of conduction system delay might benefit the most from restored synchrony."
Dr. Saxon went on to explain that patients in the VIGOR CHF study receive a dual-chamber pacemaker by standard implant techniques, with a right atrial lead to promote AV synchrony and a ventricular lead implanted in the right ventricle. Patients will be paced in the VDD mode.
"When designing this study, the investigators looked at ways to protect these very sick patients, who are susceptible to adverse effects from invasive studies. We are using co-investigators – an electrophysiologist, a heart failure specialist, an experienced cardiovascular surgeon and an echocardiographer. It takes a lot of effort to coordinate these teams at each center, but this unique approach seemed necessary to help ensure patient safety."
The endpoints of the VIGOR CHF study will assess changes in LVEF, peak exercise ability and quality of life issues, as well as medical cost. "We hope not only to resynchronize ventricular contractions, but also to reduce paradoxical septal wall motion," she said. The study is expected to take approximately three years. (guidant.com)