Prevention & Screening
Predicting and Preventing Sudden Death
A noninvasive test of T-wave alternans is now available for predicting ventricular arrhythmias.
It detects risk for sudden death signaled by subtle abnormalities in T-wave repolarization that predict life-threatening ventricular tachycardia, and fibrillation.
The ability to identify the risk of sudden death before it occurs has improved dramatically by an innovation that is both noninvasive and relatively inexpensive.
The new test, T-wave alternans, is FDA-approved and has the potential to play a significant role in reducing one of the most common types of cardiovascular mortality.
This test is effective in identifying those with a propensity for life-threatening ventricular arrhythmias not previously detectable by other noninvasive tests.
After inception of the test of T-wave alternans at MIT, researchers there collaborated with Cambridge Heart and NewYork-Presbyterian Hospital researchers to study it, create the rules for its interpretation, and establish the protocol for its use.
Kaplan-Meier analysis of event-free survival for patients with congestive heart failure, stratified by positive or negative T-wave alternans test results.
Adapted with permission from The Lancet, T. Klingenheben et al, August 19, 2000, Vol 356, pp 651-652.
T-wave alternans testing offers sensitivity and specificity far superior to other noninvasive tests proposed in the past, such as signal-averaged electrocardiography (ECG) or QT dispersion analyses.
In a published prospective multicenter trial of 313 patients in sinus rhythm, T-wave alternans performed as well as cardiac electrophysiological (EPS) testing, an invasive and far more expensive test not routinely administered to patients with an intermediate risk of having ventricular arrhythmias (the group of patients from which the majority of sudden death events emerge).
"About half of cardiovascular mortality is the result of sudden death. The majority of sudden death is attributed to ventricular arrhythmias. These are huge numbers," observed Hasan Garan, MD, an expert on heart rhythm disturbances.
"Although we have had devices that can save lives in patients who experience the arrhythmias that cause sudden death, until now we had no reliable way of determining who was going to need them."
T-wave alternans testing is based on the observation that very subtle microscopic fluctuations in the morphology of the T-wave on the ECG reveal abnormalities in repolarization.
These abnormalities develop in advance of ventricular arrhythmias.
With sophisticated signal-processing of the ECG, they can be detected when the heart rate is accelerated with exercise.
The exciting development is that T-wave alternans, although easily administered without invasive methodology, may even be superior to EPS for a number of patient populations at risk.
T-wave alternans testing is now FDA-approved, guidelines for its use are published, and coding for reimbursement has been established.
As it gains use, the applications of T-wave alternans may evolve both as a result of experience with the test and through additional refinements in the software that underlies its accuracy.
According to Daniel Bloomfield, MD, who made key contributions to its development, the ultimate utility of the tool may not be in clarifying the degree of risk in individuals already singled out by known ventricular arrhythmias, but in the far larger group of individuals with heart disease who are otherwise doing well but may be at increased risk for sudden cardiac death.
The task heretofore has been like looking for a needle in a haystack.
"The opportunity to save lives by detecting risk of sudden death is much greater in primary prevention than in secondary prevention, and this is where T-wave alternans may take us," Dr. Bloomfield suggested.
"A noninvasive, highly sensitive screening tool for the intermediate risk population would be expected to go a long way in addressing a major public health problem."