Cardiologists have used the electrocardiogram (ECG) since the turn of the 20th century to monitor heartbeats and identify cardiac disease. Until now, an important clue to predicting sudden cardiac arrest has remained hidden on the ECG.
Physicians knew the clue was there, but were unable to confirm that it meant their patients were at high risk for ventricular arrhythmia, a heartbeat abnormality that triggers sudden cardiac arrest. Unfortunately, many of these patients who undergo ECG tests eventually join the ranks of the 300,000-plus Americans who die annually from sudden cardiac arrest, the most common cause of death in the country.
That grim scenario may be about to change due to new research by David Rosenbaum, an associate professor of medicine and biomedical engineering at CWRU's School of Medicine, and a cardiologist at University Hospitals of Cleveland.
In the March 16 issue of the American Heart Association journal Circulation, Rosenbaum and colleagues provide the scientific foundation for a new clinical test that has the potential to dramatically reduce the death toll from sudden cardiac arrest.
Their work focused on T-wave alternans, a heartbeat pattern that often appears on an ECG before a sudden cardiac arrest. Rosenbaum's team set out to determine why this pattern was linked to fatal cardiac arrhythmias.
They detected oscillations in the electrical impulse generated by individual heart cells, causing beat-to-beat alternations. Shortly after the process began, neighboring heart cells oscillated out of phase with one another, beating asynchronously, leading to fibrillation and death.
Their findings explain the link between T-wave alternans on the ECG and voltage changes occurring within individual heart cells.
"What we find, if you look at the cardiac cell very carefully, is that the cell's voltage is oscillating. Such beat-to-beat oscillations are the source of the T-wave alternans pattern on the ECG," he says. "You reach a critical heart rate where the heart begins oscillating in a disorganized fashion. When that happens, the heart becomes electrically unstable. You have a loss of electrical synchronization, such that the heart can go into fibrillation. We found this pattern over and over again."
These research findings have direct implications to diagnosing potential risk of sudden cardiac arrest in patients.
"T-wave alternans is a marker of susceptibility to sudden cardiac death in patients," Rosenbaum says. "Survival studies of patients with arrhythmia reveal that 95 percent of patients whose ECGs do not show T-wave alternans are alive after 20 months, compared with 18 percent of patients whose ECGs exhibit T-wave alternans."
This pattern often appears so subtle that it goes unrecognized on ECG recordings, so a new test was developed in part at UHC and the School of Medicine that highlights this pattern for easier detection by physicians. This test, similar to a routine exercise stress test, currently is awaiting FDA approval.
"When the test becomes available," Rosenbaum says, "physicians will be able to screen patients quickly for ventricular arrhythmia and prescribe therapy to prevent sudden cardiac arrest."
Lead author of the study is Joseph Pastore, a CWRU Ph.D. candidate in biomedical engineering.
Other authors are Steven D. Girouard, Kenneth R. Laurita, and Fadi G. Akar from CWRU and UHC.
The study received funding from the National Institutes of Health, the Department of Veterans Affairs, the Whitaker Foundation, and the American Heart Association.