From the Guidelines
Heart rate variability (HRV) is a valuable marker of cardiac health, as it reflects the heart's ability to respond to physiological and environmental stimuli, with higher HRV generally indicating better cardiovascular health and autonomic nervous system function. HRV measures the variation in time between consecutive heartbeats and has been extensively studied as a predictor of cardiac events and mortality. According to the study by Huikuri et al 1, HRV was found to be a better predictor of total mortality than of sudden cardiac death (SCD) mortality. The study also found that nonlinear methods, such as the power-law relationship, can be used to examine HRV and provide additional prognostic information.
The physiological basis for HRV's importance lies in the balance between sympathetic ("fight or flight") and parasympathetic ("rest and digest") nervous system activity. A healthy heart demonstrates flexibility in responding to these competing signals, resulting in greater beat-to-beat variability. Reduced HRV often indicates autonomic dysfunction and increased sympathetic dominance, which places greater stress on the cardiovascular system. The ATRAMI study 1 found that depressed HRV and baroreflex sensitivity (BRS) were significant predictors of cardiac mortality, and that the combination of low HRV and depressed BRS further increased the risk.
In terms of improving HRV, regular aerobic exercise, stress management techniques like meditation, adequate sleep, and maintaining a healthy weight can all be beneficial. The European Society of Cardiology's task force on sudden cardiac death 1 noted that heart rate turbulence, which represents another measure of vagal activity, has been applied to the data from MPIP and EMIAT and represented a strong independent predictor of total mortality. However, more research is needed to fully understand the prognostic value of heart rate turbulence in the general MI population.
Key points to consider when using HRV as a marker of cardiac health include:
- HRV decreases naturally with age
- Lower HRV is associated with increased risk of cardiac events and mortality
- HRV can be improved through lifestyle modifications such as regular exercise and stress management
- HRV should be considered alongside other clinical measures rather than in isolation
- Nonlinear methods, such as the power-law relationship, can provide additional prognostic information.
From the Research
Heart Rate Variability as a Marker of Cardiac Health
- Heart rate variability (HRV) is a non-invasive technique used to identify the functioning of the autonomic nervous system, which plays a key role in regulating cardiac health 2, 3.
- HRV is the variation in the time between two heartbeats and is influenced by various factors, including pathological, physiological, psychological, environmental, lifestyle, and genetic factors 2.
- A high HRV is associated with a healthy condition, while a low HRV is associated with pathological conditions, such as cardiovascular diseases, arrhythmias, and cardiac death 2, 3, 4, 5.
Clinical Applications of Heart Rate Variability
- HRV has been recognized as a predictor of risk of arrhythmic events or sudden cardiac death after acute myocardial infarction, and as a clinical marker of evolving diabetic neuropathy 5.
- HRV also has a role in the evaluation and management of heart failure, and its measurement can provide information on the risk of subsequent morbid events in subjects without obvious heart disease 4, 5.
- However, the methodology of HRV has remained poorly standardized, and further investigation is required to determine the exact sensitivity, specificity, and predictive value of HRV, as well as the normal values of standard measures in the general population 5.
Relationship between Heart Rate and Heart Rate Variability
- HRV is significantly associated with average heart rate, and the removal of the heart rate impact on HRV can make HRV more predictive for non-cardiac death, while the enhancement of this impact can cause HRV to be a better predictor of cardiovascular mortality 6.
- The interaction between heart rate and HRV is both a physiological phenomenon and a mathematical one, and the association between HRV and heart rate is determined by the autonomic nervous system activity and the nonlinear relationship between RR interval and heart rate 6.