Researchers have recently found a new reason for doctors to listen to the heart: Certain heart rhythms may provide critical information about the health of our kidneys.

Daniel Brotman, professor of medicine at Johns Hopkins University, and colleagues analyzed data from 13,241 individuals enrolled in the Atherosclerosis Risk in Communities (ARIC) Study. The researchers found that participants with a high resting heart rate and a low beat-to-beat heart rate variability were more likely to develop kidney malfunction.

"The temporal pattern is intriguing in that abnormal heart rate variability preceded the development of clinical renal failure by many years," the study authors wrote. The findings suggest that heart rate monitoring may help to identify particular patients with a high risk of future kidney disease. The results were published online July 8 in the Journal of the American Society of Nephrology.

Heart rate is largely controlled by the autonomic nervous system (ANS), which also regulates other subconscious activities such as digestion, breathing and blood pressure. Previous studies suggested that abnormal ANS activity, known as dysautonomia, was linked to chronic kidney disease but how the two were connected remained unclear.

Brotman and colleagues wanted to find out whether dysautonomia preceded the onset of kidney disease, because if it did, that would suggest a possible mechanism for how kidney disease develops and may yield clues about how to predict kidney malfunction before the onset of other symptoms. The authors used data from the ARIC study, which has regularly collected medical information from a randomly selected group of individuals (aged 45 to 64 at the study's onset) from four different U.S. communities since 1987.

The researchers monitored ANS activity using standard electrocardiograph (EKG or ECG) measurements. Specifically, they examined resting heart rate and heart rate variability, or the extent with which the heart rate varies while breathing (in most healthy individuals, heart rate increases while inhaling, and decreases while exhaling). Generally speaking, healthy people tend to have a low resting heart rate and high heart rate variability.

After adjusting for factors known to contribute to kidney disease, including diabetes, high blood pressure, smoking status and presence of heart disease, the authors estimate that study participants with the highest resting heart rates had nearly double the normal risk of developing kidney disease, and those with the lowest heart rate variability had an increased risk of approximately 1.5-fold.

While dysautonomia may be a possible cause of kidney malfunction, the authors conclude that their findings do not demonstrate a cause-and-effect relationship. "We hope our findings will encourage further research to better define the putative role of the ANS in precipitating and exacerbating renal disease in humans," the authors wrote. "This, in turn, may ultimately lead to novel therapeutic approaches once the mechanisms for our findings are better characterized."

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