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According to a study in the February 15 edition of the Journal of Cardiovascular Electrophysiology, abnormal heart rate turbulence is associated with an increased risk of heart disease death in otherwise older, low-risk individuals . Additional studies need to be done in order to understand whether this potential biomarker will be a clinically valuable tool.
The observational study was conducted by Drs. Phyllis K. Stein, Ph.D., from the Washington School of Medicine in St. Louis and Joshua I. Barzilay, M.D., from the Emory University School of Medicine in Atlanta. They measured heart rate turbulence in 1,272 patients aged 65 or older using a 24-hour heart monitoring device called a Holter monitor, which records a person’s electrocardiogram.
Patients were divided into three groups based on their cardiovascular health. Those in the “clinical” group had a history of cardiovascular disease such as a heart attack. Those in the “subclinical” group had some signs of heart disease such as high blood pressure but had never been treated for cardiovascular disease. Those in the “healthy” group had no evidence of clinical or subclinical disease.
Among the nearly 1,300 study participants, heart rate turbulence was an even stronger heart disease risk factor than elevated levels of C-reactive protein (CRP), a potential heart disease biomarker that has emerged in recent years.
Study participants considered at low risk of heart disease based on traditional risk factors were on average 8-9 times more likely to die of heart disease during the 14-year follow-up period if they had abnormal heart rate turbulence values. Traditional risk factors include age, gender, high blood cholesterol, high blood pressure, obesity, diabetes and smoking. Low-risk individuals with elevated CRP in their blood were about 2.5 times more likely to die than those with normal or low CRP.
In the healthy group, even after controlling for other risk factors, abnormal heart rate turbulence and CRP levels both appeared to independently correlate with an increased likelihood of dying of heart disease. Abnormal heart rate turbulence — present in about 7% of the study participants — also predicted an increased likelihood of heart disease death in the clinical and subclinical groups, though these results were not as pronounced.
Study author Phyllis K. Stein, PhD, research associate professor of medicine and director of the Heart Rate Variability Laboratory at the Washington School of Medicine in St. Louis, said :
These are people we do not expect to die of cardiac causes. They appear healthy, but they’re not. We have shown a way they’re not healthy that isn’t showing up using standard tests.
This study is part of the National Heart, Lung and Blood Institute (NHLBI) Cardiovascular Health Study, an NHLBI-funded observational study of risk factors for cardiovascular disease in adults 65 years or older that ran for 10 years, from 1989 to 1999. Study participants underwent annual extensive clinical examinations, which included measurements of traditional risk factors such as blood pressure and lipids as well as measures of subclinical disease, including echocardiography of the heart, carotid ultrasound and cranial magnetic-resonance imaging (MRI).
Dr. Stein said that the measurement reflects how well a person’s nervous system works :
A heart rate turbulence measurement is insightful because it offers a sign of how well the autonomic, or subconscious, nervous system is functioning. If someone’s heart doesn’t react well to these uncoordinated beats that might mean it’s not good at reacting to other issues like sudden stress or severe arrhythmias.
Researchers don’t yet know if abnormal heart rate turbulence can be treated or prevented. Nevertheless, this study shows great potential value for measuring heart rate turbulence in clinical practice, since it suggests that signs of heart rate turbulence may be present a year or more before clinical manifestations of heart disease.
- Stein and Barzilay. Relationship of Abnormal Heart Rate Turbulence and Elevated CRP to Cardiac Mortality in Low, Intermediate, and High-Risk Older Adults. J Cardiovasc Electrophysiol. 2011 Feb;22(2):122-7.
- ‘Healthy’ patients at high risk of cardiac death identified. Washington University in St. Louis Newsroom. 2011 Feb 14.
- NIH-funded study finds new possible risk factor of heart disease. NIH News. 2011 Feb 15.