Sudden cardiac death: role of heart rate variability to identify patients at risk

Time for primary review: 31 days. Sudden, unexpected cardiac death stands as one of the most important and unresolved problems in clinical cardiology also in the new millennium. Despite unanticipated advancement in the understanding of the mechanisms that concur to determine such a dramatic event [1], our capability of identifying patients at risk has not reached satisfactory levels. In most instances, our attention is focused on selected small subgroups of patients at highest risk while ignoring the majority of subjects in whom sudden cardiac death is the first and last manifestation of a cardiac disease [2]. In the last 20 years, the appraisal [3] of the pro-arrhythmic role exerted by transient or persistent alterations in sympathetic and vagal control mechanisms has stimulated the development of techniques capable of providing information on autonomic modulation and of its alteration in different clinical conditions such as ischemic heart disease, hypertension and congestive heart failure [4,5]. Among these methodologies, analysis of heart rate (HR) variability and of baroreflex sensitivity are the two that have provided the most interesting results in terms of feasibility, clinical results and predictive value [6,7]. The aim of the present article is to specifically address the value of HR variability analyses, not only for identifying patients at risk but also for describing changes in autonomic control mechanisms immediately prior to onset of malignant ventricular arrhythmias. A brief description of available methodologies, limitations of the study designs and of future directions in HR variability utilisation is also included. There are numerous methods to describe regulation of HR and constant fluctuation of R—R intervals. An optimal method for clinical work would be an index that could be easily computed with a simple and widely available analysis method. Despite the efforts of the Task Force of the North American … * Corresponding author. Tel.: +358-8-315-4108; fax: 358-8-315-5599 heikki.huikuri{at}oulu.fi