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Over the course of the past two decades, numerous studies (on both animals and human beings) have shown a significant relationship between the autonomic nervous system (ANS) and cardiovascular mortality, particularly in patients with myocardial infarction and congestive heart failure. Perturbations of the ANS and its imbalance consisting of either increased sympathetic or reduced vagal activity may result in ventricular tachyarrhythmias and sudden cardiac death, which is nowadays one of the leading causes of cardiovascular mortality. 

There have emerged numerous methods available for assessing the status of the ANS, which include cardiovascular reflex tests, and biochemical and scintigraphic tests. In recent years, noninvasive techniques based on the electrocardiogram (ECG) have been used as markers of autonomic modulation of the heart. These include heart rate variability (HRV), baroreflex sensitivity (BRS), QT interval, and heart rate turbulence (HRT), a new method based on fluctuations of sinus rhythm cycle length after a single premature ventricular contraction. Among these techniques, analysis of HRV has emerged as a simple, noninvasive method to evaluate the sympatho-vagal balance at the sinoatrial level. 

Heart rate variability is the physiological phenomenon of the variation in the time interval between consecutive heartbeats in milliseconds. A normal, healthy heart 
does not beat evenly like a metronome, but instead, when looking at the milliseconds between heartbeats, there is constant variation. Heart rate variability is a noninvasive electrocardiographic marker reflecting the activity of the sympathetic and vagal components of the ANS on the sinus node of the heart. It expresses the total amount of variations of both instantaneous HR and R-R intervals (intervals between QRS complexes of normal sinus depolarisations). HRV, in other words, measures the heart’s contractile variation from beat to beat by evaluating the consistency between R waves (R-R intervals), as seen on an electrocardiogram (ECG) reading and gives information about the tonic baseline of autonomic nervous system function.


The following selected articles describe HRV as it pertains to bioregulation and the autonomic nervous system. 

Acharya, U. Rajendra, K. Paul Joseph, Natarajan Kannathal, Choo Min Lim, and Jasjit S. Suri. Heart rate variability: a review. Medical and biological engineering and computing 44, no. 12 (2006): 1031-1051.

Appelhans, Bradley M., and Linda J. Luecken. Heart rate variability as an index of regulated emotional responding. Review of general psychology 10, no. 3 (2006): 229-240.

Aubert, André E., Bert Seps, and Frank Beckers. Heart rate variability in athletes. Sports medicine 33, no. 12 (2003): 889-919.

Berntson, Gary G., J. Thomas Bigger Jr, Dwain L. Eckberg, Paul Grossman, Peter G. Kaufmann, Marek Malik, Haikady N. Nagaraja et al. Heart rate variability: origins, methods, and interpretive caveats. Psychophysiology 34, no. 6 (1997): 623-648.

Carney, Robert M., Roger D. Saunders, Kenneth E. Freedland, Phyllis Stein, Michael W. Rich, and Allan S. Jaffe. Association of depression with reduced heart rate variability in coronary artery disease. The American journal of cardiology 76, no. 8 (1995): 562-564.

Carney, Robert M., James A. Blumenthal, Phyllis K. Stein, Lana Watkins, Diane Catellier, Lisa F. Berkman, Susan M. Czajkowski, Christopher O’Connor, Peter H. Stone, and Kenneth E. Freedland. Depression, heart rate variability, and acute myocardial infarction. Circulation 104, no. 17 (2001): 2024-2028.

Casolo, Giancarlo, Enrico Balli, Tamara Taddei, John Amuhasi, and Cesare Gori. Decreased spontaneous heart rate variability in congestive heart failure. The American journal of cardiology 64, no. 18 (1989): 1162-1167.


Gold, Diane R., Augusto Litonjua, Joel Schwartz, Eric Lovett, Andrew Larson, Bruce Nearing, George Allen, Monique Verrier, Rebecca Cherry, and Richard Verrier. Ambient pollution and heart rate variability. Circulation 101, no. 11 (2000): 1267-1273.

Kleiger, Robert E., Phyllis K. Stein, and J. Thomas Bigger Jr. Heart rate variability: measurement and clinical utility. Annals of Noninvasive Electrocardiology 10, no. 1 (2005): 88-101.

Kleiger, Robert E., J. Philip Miller, J. Thomas Bigger Jr, and Arthur J. Moss. Decreased heart rate variability and its association with increased mortality after acute myocardial infarction. The American journal of cardiology 59, no. 4 (1987): 256-262.

Kurths, Jürgen, A. Voss, P. Saparin, A. Witt, H. J. Kleiner, and N. Wessel. Quantitative analysis of heart rate variability. Chaos: An Interdisciplinary Journal of Nonlinear Science 5, no. 1 (1995): 88-94.

Lake, Douglas E., Joshua S. Richman, M. Pamela Griffin, and J. Randall Moorman. Sample entropy analysis of neonatal heart rate variability. American Journal of Physiology-Regulatory, Integrative and Comparative Physiology 283, no. 3 (2002): R789-R797.


La Rovere, Maria Teresa, Gian Domenico Pinna, Roberto Maestri, Andrea Mortara, Soccorso Capomolla, Oreste Febo, Roberto Ferrari et al. Short-term heart rate variability strongly predicts sudden cardiac death in chronic heart failure patients. Circulation 107, no. 4 (2003): 565-570.


Malik, Marek, and A. John Camm. Heart rate variability. Clinical cardiology 13, no. 8 (1990): 570-576.

Malliani, Alberto, Federico Lombardi, and Massimo Pagani. Power spectrum analysis of heart rate variability: a tool to explore neural regulatory mechanisms. British heart journal 71, no. 1 (1994): 1.

Stauss, Harald M. Heart rate variability. American Journal of Physiology-Regulatory, Integrative and Comparative Physiology 285, no. 5 (2003): R927-R931.

Stein, Phyllis K., Matthew S. Bosner, Robert E. Kleiger, and Brooke M. Conger. Heart rate variability: a measure of cardiac autonomic tone. American heart journal 127, no. 5 (1994): 1376-1381.

Sztajzel, Juan. Heart rate variability: a noninvasive electrocardiographic method to measure the autonomic nervous system. Swiss medical weekly 134, no. 35-36 (2004): 514-522.

Thayer, Julian F., Fredrik Åhs, Mats Fredrikson, John J. Sollers III, and Tor D. Wager. A meta-analysis of heart rate variability and neuroimaging studies: implications for heart rate variability as a marker of stress and health. Neuroscience & Biobehavioral Reviews 36, no. 2 (2012): 747-756.

Thayer, Julian F., Shelby S. Yamamoto, and Jos F. Brosschot. The relationship of autonomic imbalance, heart rate variability and cardiovascular disease risk factors. International journal of cardiology 141, no. 2 (2010): 122-131.

Tsuji, Hisako, Ferdinand J. Venditti, Emily S. Manders, Jane C. Evans, Martin G. Larson, Charles L. Feldman, and Daniel Levy. Determinants of heart rate variability. Journal of the American College of Cardiology 28, no. 6 (1996): 1539-1546.

Umetani, Ken, Donald H. Singer, Rollin McCraty, and Mike Atkinson. Twenty-four-hour time domain heart rate variability and heart rate: relations to age and gender over nine decades. Journal of the American College of Cardiology 31, no. 3 (1998): 593-601.

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