Clinical Significance of Low HRV During Sleep

Introduction to Low HRV

The American Heart Association states that a low HRV value of 18-25 milliseconds indicates impaired autonomic nervous system function, which is a significant warning sign for increased cardiovascular disease risk and higher overall mortality, requiring further evaluation for potential cardiovascular diseases, sleep breathing disorders, or other systemic diseases 1, 2.

The American College of Sports Medicine indicates that a sleeping heart rate of 45-50 beats per minute is normal, as deep sleep (non-rapid eye movement sleep) is dominated by parasympathetic nerves, naturally lowering heart rate 3, 4.
A resting heart rate of 60 beats per minute is considered normal 4.
The American College of Sports Medicine recommends that a heart rate response to activity, such as walking at 120 beats per minute and running at 155 beats per minute, shows a normal heart rate reserve and a proper cardiovascular response to exercise 3.

The American Heart Association points out that an HRV value of 18-25 milliseconds is significantly lower than the normal range, reflecting severely impaired autonomic nervous system regulatory function, specifically manifesting as decreased parasympathetic nerve activity 5, 6.
The American Heart Association states that low HRV directly reflects decreased autonomic nervous system regulatory capacity 5, 6.

The American Heart Association's scientific statement clearly states that low HRV increases the risk of overall mortality by 2-3 times 1, 2.
The ATRAMI study shows that patients with low HRV after myocardial infarction have a relative death risk of 3.2 times 1, 7.
Multivariate analysis of multiple studies shows that low HRV increases the risk of all-cause mortality with a hazard ratio of 1.46 (95% CI 1.1-1.94) 1, 2.

Low HRV is more predictive of non-arrhythmic death rather than sudden death 1, 2, 8.
Low HRV suggests later-stage hemodynamic disease, and patients may eventually die from congestive heart failure rather than arrhythmia 1, 7.
The American Heart Association indicates that low HRV is a predictor of hypertension and is associated with an increased risk of cardiovascular events 6.

The American Heart Association points out that sleep apnea is a common cause of low HRV during sleep, leading to sympathetic nerve enhancement and parasympathetic nerve reduction, which can trigger arrhythmias, particularly during REM sleep 9.

The American Heart Association recommends evaluating left ventricular dysfunction, as low HRV is common in heart failure patients 10, 1.
The American Heart Association states that coronary artery disease, such as myocardial infarction, often presents with low HRV 1, 7.
The American Heart Association indicates that cardiomyopathy, such as dilated cardiomyopathy, is associated with decreased HRV 1, 2.

The American College of Sports Medicine recommends completing cardiovascular checks, including electrocardiogram, echocardiogram to evaluate left ventricular function, 24-hour dynamic electrocardiogram monitoring, and exercise load test to evaluate cardiovascular reserve 3, 1, 5.
The American Academy of Sleep Medicine suggests sleep breathing monitoring, including multiple sleep latency tests to rule out sleep apnea, and evaluating sleep quality and structure 9, 3, 4.
The American Heart Association recommends metabolic assessment, including blood pressure monitoring, blood glucose and lipid tests, and evaluating other cardiovascular risk factors 7.

The American Heart Association states that short-term HRV has moderate repeatability in normal individuals but poor repeatability in heart failure patients 5, 6.
The American Heart Association recommends standardized HRV measurement under strictly controlled conditions for 4-5 minutes, using controlled breathing (15 times/minute) to avoid over-ventilation artifacts 6.