A phenomenon of heart-rate turbulence, its evaluation, and prognostic value

Identification of high-risk cardiac patients is crucial for stratification strategies and prevention of cardiovascular events, including death. Single ventricular premature beat triggers some oscillations in cardiac cycle duration (the shortening followed by the lengthening of the cycle intervals) in healthy subjects and low-risk patients with ischaemic heart disease and/or heart failure. This phenomenon is called heart-rate turbulence (HRT). It was shown in retrospective and prospective studies that the absence of HRT is associated with increased risk of subsequent mortality in cardiac patients. HRT can be quantified by two variables: turbulence onset (TO), describing an early acceleration phase, and turbulence slope (TS), describing a late deceleration phase of heart rate after ventricular premature beat. Both TO and TS are independent one from another and from other conventional risk predictors. The combination of TO and TS seems to be the strongest Holter-based risk predictor and has some addictive predictive value to left ventricular ejection fraction, heart rate variability, and the averaged diurnal heart rate and baroreflex sensitivity. In addition, HRT has a predictive value in patients treated with beta-blockers and amiodarone. Moreover, it is thought that HRT is mediated by baroreflex and therefore can be used as a non-invasive measure of its sensitivity and autonomic nervous system function. Blunted HRT can be observed in diabetic patients with autonomic dysfunction and in patients with atropine-blocked vagal nerve activity. Moreover, it seems that a diurnal variation of HRT exists because it is better expressed during sleep. However, the use of HRT is limited to patients with dominant sinus rhythm and the presence of single ventricular beat. Nevertheless, the assessment of HRT is an inexpensive and simple method and can be performed with a routine ambulatory 24-hour ECG recording.