From the Guidelines
Heart rate variability (HRV) is a significant predictor of total mortality, particularly in patients with underlying cardiac disease.
Significance of HRV
The significance of HRV can be understood by its ability to predict arrhythmic, cardiac, or total mortality in various populations, including patients with angina, heart failure, or those who have experienced a myocardial infarction (MI) 1.
- Time- and frequency-domain measures: These measures of HRV have been extensively studied and have shown a high degree of correlation, with a relative risk of 2 to 3 for mortality in patients with low HRV 1.
- Nonlinear methods: Nonlinear methods, such as the power-law relationship, have also been used to examine HRV and have shown promising results, with a relative risk of 7.9 for all-cause mortality in one study 1.
- Autonomic markers: HRV is an autonomic marker that provides information about autonomic balance, and reduced vagal activity to the heart is associated with increased risk 1.
- Clinical applications: HRV has significant prognostic value independent of established clinical predictors, such as ejection fraction (EF) and ventricular arrhythmias, and can be used to identify patients at high risk for sudden and non-sudden cardiac death (SCD) 1.
Limitations and Future Directions
While HRV is a significant predictor of total mortality, its role in risk stratification for SCD is still unclear and requires further study 1. Additionally, the prognostic value of HRV may be influenced by factors such as age, with the predictive power of baroreflex sensitivity (BRS) declining more markedly than HRV over age 65 1.
From the Research
Significance of Heart Rate Variability (HRV)
The significance of heart rate variability (HRV) can be understood from the following points:
- HRV is significantly associated with average heart rate (HR) and provides information on both HR and its variability 2
- The association between HRV and HR is both a physiological phenomenon and a mathematical one, determined by the autonomic nervous system activity and the nonlinear relationship between RR interval and HR 2
- HRV has been observed to be depressed in many clinical scenarios, including autonomic neuropathy, heart transplantation, congestive heart failure, myocardial infarction (MI), and other cardiac and noncardiac diseases 3
- HRV is a predictor of risk of arrhythmic events or sudden cardiac death after acute MI, and a clinical marker of evolving diabetic neuropathy 3
- HRV is influenced by various factors, including pathological, physiological, psychological, environmental factors, lifestyle factors, and genetic factors 4, 5
- Low HRV is associated with increased mortality and is a marker of poor cardiovascular health 4, 5, 6
- HRV can be used to guide the training of athletes and as a part of fitness programmes, and can be measured using mobile health technologies (mHealth) and commercial wearable fitness devices 6
Clinical Applications of HRV
The clinical applications of HRV include:
- Prediction of risk of arrhythmic events or sudden cardiac death after acute MI 3
- Clinical marker of evolving diabetic neuropathy 3
- Evaluation and management of heart failure 3
- Assessment of autonomic nervous system function 4
- Identification of risk of cardiac diseases and state of autonomic nervous system 4
- Guidance of training for athletes and fitness programmes 6
Factors Influencing HRV
The factors influencing HRV can be grouped into four categories:
- Non-influenceable physiological factors (e.g. age, gender, ethnicity) 5
- Diseases (e.g. psychiatric diseases, myocardial infarction, heart failure) 5
- Influenceable lifestyle factors (e.g. alcohol abuse, overweight, physical activity) 5
- External factors (e.g. heat, noise, shift work, harmful- and hazardous substances) 5