Increased heteroscedasticity of heart rate in fatal heart failure

¹  Educational Physiology Laboratory, Graduate School of Education, The University of Tokyo - 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
²  College of Engineering, Nihon University - 1 Naka-gawara, Tokusada, Tamura-machi, Koriyama City, Fukushima, 963-8642, Japan
³  Medical Education, Nagoya City University Graduate School of Medical Sciences - 1 Kawasumi Mizuho-cho Mizuho-ku, Nagoya 467-8601, Japan
⁴  Division of Cardiology, Department of Internal Medicine, Fujita Health University School of Medicine 1-98 Dengakugakubo, Kutsukake-cho, Toyoake, Aichi-Ken, 470-1192, Japan

Received: 23 October 2007
Accepted: 21 February 2008

Abstract

Healthy human heart rate is known to fluctuate in a highly complex manner, displaying complexity characteristics such as those shared by physical systems at a critical state. It is, however, widely believed that chronic heart failure reduces this complexity and that heart rate data from chronic-heart-failure patients can be used for the validation of complexity measures and paradigms applicable both to heart rate and more generally to assess any system's complexity. Here, we counter the above belief, showing an increase in fluctuations and in complexity of heart rate in chronic-heart-failure patients, in particular those at risk of death. This is supported by evidence of increased non-Gaussianity and heteroscedasticity resulting from the emergence of a characteristic correlation scale in the magnitude correlation landscape.