Problems and pitfalls in evaluating studies for pacing in heart failure

Pacing therapy has been recently proposed as a new non-pharmacological approach to patients suffering from congestive heart failure refractory to medical therapy (refractory CHF), but the extention and the real benefit of this method remains to be defined. Although pacing therapy for refractory CHF has been restricted to patients in sinus rhythm presenting atrial, atrioventricular or interventricular conduction disturbances, considerable conflicting results have been published. The contradictory data is most likely due to large heterogeneity of the investigated study population (ie etiology of CHF, NYHA class, duration of follow-up, end-points of the study, etc.), to difference in study methology as well as in the site and modality of acute and chronic pacing. Although several empirical data indicates, at least in some individuals, major improvement in CHF symptoms by properly coordinating the atria and the ventricles thus reducing pre-systolic mitral and/or tricuspidal regurgitation or finally, prolonging the diastolic filling time, a lack of understanding of the mechanisms responsible for acute and chronic benefit persists. In evaluating pacemaker therapy as a new supportive treatment for CHF, the clinical investigator must consider that each study protocol embodies assumptions and methodological limitations and thus provides an incomplete analysis of potential benefit. Relying solely on noninvasive measures is risky due to problems of sensitivity and repeatability.