Heart beat to predict cardiac death risk
A new study from Washington University School of Medicine in St. Louis has found that the manner in which the heart responds to an early beat is predictive of cardiac death, even in seemingly healthy people.
Doctors are in a constant search for better ways to identify patients at risk of cardiac death because conventional risk factors, such as high cholesterol, smoking, diabetes and high blood pressure aren`t always the best indicators.
"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," said Phyllis K. Stein, research associate professor of medicine and director of the Heart Rate Variability Laboratory at the School of Medicine.
The new study indicates that abnormal response to an early beat in the left ventricle can identify high-risk patients even when they have no other evidence of cardiovascular disease.
When the ventricle beats early, the heart has not finished filling and it pumps less blood to the body than it should. To compensate, the heart rate speeds up to increase blood flow.
But an early beat also empties the heart early, leaving extra filling time afterward. So on the second beat after the VPB, the heart is extra full and pumps more blood to the body than it should. To compensate properly, the heart rate slows down.
A healthy heart will alternately speed up and slow down to compensate for the over- and under-filling that follows a VPB until the amount of blood filling the heart returns to normal.
Abnormal heart rate turbulence occurs when the heart can`t compensate in this way.
The patients were divided into three groups based on an assessment of their cardiovascular health – clinical, subclinical and healthy.
The patients were divided into three groups based on an assessment of their cardiovascular health but the association was especially strong in the healthy group.
Of the 357 patients classified as healthy, 21 had abnormal heart rate turbulence. These 21 people were almost eight times more likely to die of cardiac causes than the rest of the healthy group.
"They`re actually not healthy," Stein said. "Something is wrong. But the conventional risk factors don`t pick it up."
Stein and her colleagues also looked at levels of C-reactive protein, a measure of inflammation associated with cardiovascular disease. While C-reactive protein predicted cardiac death in the healthy group, it had no impact in the subclinical and clinical groups.
Stein speculates that this work and other studies showing the value of measuring heart rate turbulence may make the Holter software more widely available.
The work appears Feb. 15 in the Journal of Cardiovascular Electrophysiology.