Biventricular pacing for heart failure

Left bundle branch block in structurally normal hearts results in loss of synchrony of ventricular contraction and impairs both regional and global left ventricular systolic function.¹ In hearts with good overall left ventricular systolic function this has very little clinical effect. But in patients with ischaemic or idiopathic dilated cardiomyopathy it further impairs already poor systolic function and may have a major clinical impact. The prevalence of conduction delay in patients with heart failure is as high as 30%,² and this has led to the development of biventricular pacing in an attempt to restore synchronous ventricular contraction and so improve left ventricular function. Biventricular pacing involves the transvenous placement of a third pacing lead via the right atrium and coronary sinus into a left ventricular cardiac vein; this is in addition to the standard pacing leads in the right atrium and right ventricle³ and permits simultaneous stimulation of the right and left ventricles.

What is the evidence that this works? Several studies have indicated that biventricular pacing improves symptoms in patients with heart failure and left bundle branch block.⁴ A recent multicentre randomised trial of resynchronisation has substantially enhanced the evidence supporting this treatment.² This was a double blind study of cardiac resynchronisation in 453 patients with chronic moderate to severe symptoms of heart failure (New York Heart Association class III-IV) due to ischaemic and non-ischaemic cardiomyopathy and dyssynchronous ventricular contraction evidenced by a QRS duration of 130 milliseconds or more in left bundle branch block. Patients were randomised to either control (n=225) or atrial synchronised biventricular pacing (n=228), with follow up for six months. In keeping with previous studies,⁴ notable improvements in the primary end points of New York Heart Association functional class, six minute walking distance, and quality of life were observed in the resynchronisation group over those in the control group. These benefits became apparent one month after randomisation and were maintained at six months.

In addition, cardiac resynchronisation seemed to reduce the risk of clinical deterioration during follow up, with the combined risk of a major clinical event (death or admission for worsening heart failure) being reduced by 40%. The number of patients requiring admission for heart failure (34 v 18 for control and resynchronisation groups, respectively) was reflected in a notably reduced number of total hospital days for management of heart failure (363 v 83). This finding has potentially major implications for cost effective use of healthcare resources.

One important limitation of this study is the relatively short period of follow up, and whether the longer term effects are as impressive remains to be seen. In addition, the prognostic implications of biventricular pacing are unknown, although they are being addressed by continuing mortality studies.⁵,⁶

The clinical response to biventricular pacing has been shown to be heterogeneous, and an important question surrounds the issue of how patients are selected. Electrocardiography, conventionally used to detect left bundle branch block and therefore presumed ventricular dyssynchrony, has been shown to be a poor predictor of patients' response.⁷ Up to 30% of patients who receive an implant do not respond.⁸ Electrocardiography will probably be surpassed by more sensitive echocardiographic techniques, such as tissue Doppler imaging,⁹ which permit accurate quantification of regional ventricular contraction. Biventricular pacing has a small but important risk in this sick population, and better selection of patients and identification of individuals who will benefit is essential to achieve maximal therapeutic advantage safely. Further, placement of the left ventricular lead in the coronary venous system is technically challenging and has an important failure rate using available technology.³

In considering devices for heart failure, the growing weight of evidence for biventricular pacing needs to be considered alongside the expanding indications for implantable cardioverter defibrillators.¹⁰ Implantable cardioverter defibrillators with biventricular pacing capabilities exist, and their use in some patients with existing (or even predicted) asynchrony may improve symptoms and prevent possible exacerbations of heart failure. Early evidence indicates that biventricular pacing reduces the number of implantable cardioverter defibrillation treatments required.¹¹ A growing overlap between groups of patients for whom implantable cardioverter defibrillation and biventricular pacing are indicated will probably result in the implantation of devices with combined capability in a subset of patients in the future.

With each new study that adds to the evidence base for device therapy for left ventricular dysfunction, the financial implications seem ever greater, but the issue of cost effectiveness remains contentious and warrants further examination when longer term outcome data are available. Whatever the eventual outcome of such studies, the key to effective device therapy in heart failure must lie in careful selection of patients. Although device therapy for heart failure is likely to remain an appropriate adjunct to optimal medical treatment and revascularisation, cost will probably be the limiting factor in determining how widespread the use of such devices will become.