Congestive heart failure treatment: the pacing approach.
Early reports of physiologic pacing for congestive heart failure (CHF) yielded conflicting results, and little enthusiasm was generated for pacing as a mode of therapy for CHF. Small, uncontrolled studies, which had little or no follow-up demonstrated that pacing from the left ventricle could synchronize contraction of the ventricles and improve overall ventricular performance. These encouraging reports led to a number of larger, multicenter trials, which have been recently reported. These trials have consistently shown improvements in such objective measurements as peak exercise oxygen consumption, ejection fraction, heart rate variability, 6-minute walk test distance and anaerobic threshold, as well as subjective improvements such as quality of life assessment. A number of large, multicenter double-blinded trials are ongoing which will seek to further assess the benefits of biventricular or multisite pacing. Among the important issues, which will be addressed by ongoing trials, are the possibility of pacing induced arrhythmias, the benefit of adding defibrillator capability to these pacing systems, and the development of novel delivery systems, which will make implantation of these systems more accessible to clinicians. Studies to date have largely excluded patients with traditional indications for pacing, and have been confined chiefly to patients with PR interval prolongation, and left bundle branch block with a QRS duration greater than 120 milliseconds, with New York Heart Association class II or III CHF. Whether this therapy will offer benefit to other patients who do not meet these criteria is also unknown at present. Another novel mode of pacing therapy, which may be clinically appropriate for a broader range of CHF patients, is contractility modulation, which involves subthreshold pacing to increase intracellular calcium and enhance inotropy. Early data suggests that the benefits of these two forms of pacing therapy may be additive.