Heart attacks are a leading cause of death in the United States. This is especially true among people who have a history of heart disease and previous heart attacks. Heart rate variability is a predictor for the risk of death from heart arrhythmia, in some cases. However, heart rate variability is a complex issue and thus far has narrow limits for use as a diagnostic tool. Potential exists for expanding its use, but more research is necessary first, according to the American Heart Association.
Terminology
Heart rate variability is the variation in the beat-to-beat intervals of your heartbeats. The term "heart rate variability" describes both variations of instantaneous heart rate, which tells you how long each of your heartbeats takes, and measures of heart period intervals, or the time frame in between individual beats of your heart. You'll see this referred to as "IBI." Such intervals decrease, for example, when you take shallow and rapid breaths. Your heart rate variability is measured with an electrocardiograph, or ECG.
Risk
A reduction in your heart rate variability, which indicates less power output, is used as a predictor that your risk of death is higher after an acute heart attack. It's also used as an early warning sign that you have diabetic neuropathy. These are the only two conditions in which heart rate variability is clinically recognized as a diagnostic tool, notes Marek Malik in the American Heart Association journal Circulation. Diabetic neuropathy causes degeneration of small nerve fibers in the nervous system.
Potential
Lower heart rate variability is also linked to heart dysfunction, which can lead to an initial heart attack and is found among people who have cervical spinal cord lesions. However, clinical consensus has not been reached for using it as a predictor of mortality in these conditions, though some studies look promising. Malik notes that heart rate variability may someday be used as a predictor for death in more conditions related to the cardiovascular and nervous systems. Your heart rate and heart rhythm are largely controlled by your autonomic nervous system, which is why heart rate variability may be used as a tool to assess how well this system is functioning.
Types
Researchers quantify two main types of heart period intervals: low-frequency, or LF, and high-frequency, or HF, which also is sometimes called respiratory sinus arrhythmia, or RSA. HF and LF may increase under different conditions. For example, you'll see an increased LF when standing, exercising moderately and with mental stress. You'll see an increase in HF when you control your breathing, but activity of the vagus nerve is the main contributor to the HF component. More HF heart period intervals indicate better health and a better immediate ability to adapt to any stresses put on your body, according to P. J. Gianaros, author of the "Heart Rate Variability Tutorial" for the Pittsburgh Mind Body Center.
Standards
Your doctor may someday measure your heart rate variability when you go in for a visit, just like he does your pulse, temperature, weight and blood pressure. That's because it has the potential to be more closely tied to specific clinical outcomes than other variables such as heart rate or blood pressure, according to Gianaros. However, the meaning of different measures for heart rate variability, how exactly such measures should be taken, and the significance of each of these measures is still being researched by a task force set up in 1996 by the European Society of Cardiology and the North American Society of Pacing and Electrophysiology. Standardizing such information is important to eliminate the potential for jumping to incorrect conclusions, says Malik.
References
- Circulation; Reduced heart rate variability and mortality risk in an elderly cohort. The Framingham Heart Study; H. Tsuji et al.; 1994
- Pittsburgh Mind Body Center: "Heart Rate Variability Tutorial"; P. J. Gianaros; October 2003
- Circulation: Prospective Study of Heart Rate Variability and Mortality in Chronic Heart Failure; James Nolan et al.; 1998
- "Computer Analysis of Cardiovascular Signals"; M. Di Rienzo; 1995
- "Physiological Assessment of Human Fitness"; Peter J. Maud and Carl Foster; 2006
- European Society of Cardiology: Heart rate variability as a predictor of mortality in patients with AA and AL amyloidosis; A. K. L. Reyners et al.; 2002
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