Heart rate dynamics and vulnerability to ventricular tachyarrhythmias

Sudden arrhythmic death is the most common mode of death in Western countries. An increased understanding of the pathophysiology and trigger mechanisms of life-threatening ventricular tachyarrhythmias in patients with structural heart disease can provide a logical basis for improved therapeutic strategies in the prevention of sudden death. Analysis of heart rate variability (HRV) from ambulatory electrocadiographic recordings can identify the patients at increased risk for arrhythmic death after an acute myocardial infarction. Despite the epidemiological evidence of an association between low HRV and sudden arrhythmic death, the pathophysiological link of this association has not been completely understood. An important approach to understand this association is to investigate the heart rate dynamics before the spontaneous onset of life-threatening arrhythmias. Analysis of heart rate behaviour preceding the spontaneous onset of ventricular tachyarrhythmias has shown that overall HRV is impaired in patients who develop spontaneous ventricular tachycardia during the Holter recording. Recently, quantitative analysis of Poincaré plots of successive R-R intervals has shown that reduced long-term R-R interval variability, associated with episodes of beat-to-beat sinus alternans, is a specific sign of a propensity for spontaneous onset of ventricular tachycardia. These studies suggest that abnormal heart rate behaviour reflects an electrical instability favoring the onset of life-threatening arrhythmia and provide evidence that altered neurohumoral or autonomic regulation is an important trigger mechanism for the spontaneous onset of life-threatening arrhythmia. Future research in larger patient populations will reveal whether analysis of dynamic behaviour of cardiac electrical signals will give new insights into the mechanisms of life-threatening arrhythmias and help in the development of new therapeutic options for the prevention of sudden arrhythmic death.