Some heart failure patients have an electrical abnormality that prevents the heart from recovering normally after each beat, Johns Hopkins physicians have discovered.
In an article published in the Sept. 2 issue of the journal Circulation, the researchers showed that although patients with heart failure maintained a steady heart rate, the ability of their hearts to recover after each beat was erratic and unstable.
"This is an important finding that requires further study clinically, to see if this is a predictor for dangerous rhythm disturbances, and mechanistically, to examine on a cellular level why this happens," says Ronald D. Berger, M.D., Ph.D., an assistant professor of medicine at Hopkins and lead author of the paper.
In the study, researchers looked at 83 patients with dilated cardiomyopathy (DCM), or heart failure, a potentially fatal form of heart disease in which the lower left chamber of the heart becomes stretched and weakened. They were compared with 60 control subjects who had no history or evidence of heart disease.
Researchers took electrocardiogram readings of each person to study the electrical activity of their heartbeats. Each heartbeat consists of three parts: the contraction of the atria (upper chambers), the contraction of the ventricles (lower chambers) and the recovery of the ventricles to their normal state.
A computer-based algorithm was then created to examine the QT interval, or time it takes for the cells of the ventricle to recover electrically from being contracted during a beat.
Results showed that in patients with DCM, the QT interval from beat to beat varied widely despite the fact that these patients had relatively stable heart rates. By contrast, in healthy patients, the QT interval from beat to beat was relatively stable, while the heart rate was more varied.
Also in healthy patients, heart rate is directly related to the QT interval. For example, if the heart rate goes up, the recovery rate is quicker. In the patients with heart disease, the coupling between heart rate and QT interval was lost.
Approximately two million Americans have heart failure. Roughly 300,000 die from it each year, half from arrhythmias.
The research was supported by two grants from the National Heart, Lung and Blood Institute and from Johns Hopkins.
The study's other authors were Edward K. Kasper, M.D.; Kenneth L. Baughman, M.D.; Eduardo Marban, M.D., Ph.D.; Hugh Calkins, M.D.; and Gordon F. Tomaselli, M.D.
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