Role of Heart Rate Variability in Non-Invasive Electrophysiology: Prognostic Markers of Cardiovascular Disease

Conventional heart rate variability (HRV) indices comprise time domain and frequency domain HRV indices that not only reflect the autonomic control of the heart but also serve as prognostic markers of various cardiovascular disorders. These indices have been extensively investigated as prognostic factors for patients who develop coronary artery diseases including myocardial infarction (MI). Non-linear indices of HRV such as the long (β)- and short (α1 and β2)-term fractal component indices and approximate entropy analysis have been clinically applied. In addition, heart rate turbulence (HRT) and the deceleration capacity (DC) of heart rate have been studied as potential HRV indices for predicting untoward outcomes of cardiovascular diseases. This overview examines HRV indices and their roles in the setting of cardiovascular disorders including sudden cardiac death. We describe changes in HRV indices and clarify the relationship between prognosis and the indices in critically ill patients admitted to intensive care units.