T-Wave Alternans in Patients Acute Coronary Syndrome

IRB Application

III: Title: T-Wave Alternans for Acute Coronary Syndrome Patients Objective: Chest Pain is a common and high-risk presenting symptom in the Emergency Department. One of the central challenges Emergency Physicians face is differentiating cardiac causes of chest pain from non-cardiac causes. A rich array of mature technologies exists to aid in this process. None, however, has shown adequate sensitivity within the first 12-18 hours of symptoms to reliably exclude cardiac ischemia. As a result many patients are admitted to Coronary Care Units for a period of observation which typically involves serial blood analysis and continuous cardiac monitoring. An estimated $13 billion dollars per year are devoted to this "Rule-out MI" process. The majority, typically 80%, of these patients are ultimately found not to have cardiac disease. That is, their chest pain is ascribed to gastro-esophageal reflux, or esophageal or chest wall muscle spasm as an explanation for their symptoms.

While no test can reliably discriminate cardiac from non-cardiac symptoms in the emergency department, a test that improves our ability to identify a subset of patients who are safe to discharge would be of immense utility in reducing unnecessary hospital admissions.

Background: In the past 15 years T-Wave Alternans (TWA) testing has become accepted among cardiac electrophysiologists as a means of identifying patients at high risk for ventricular arrhythmias. TWA testing is typically performed in conjunction with a cardiac stress test and involves computerized analysis of the EKG for subtle alternate beat variations in the amplitude of the T-wave segment. The test is completely non-invasive, can return results immediately, and can be performed with compact, portable equipment. An extensive body of literature has emerged demonstrating the test's very high negative predictive value for various groups of patients with regard to ventricular tachyarrhythmias and sudden cardiac death. For example, Rosenbaum studied patients referred for electrophysiological testing due to high clinical suspicion of risk of sudden cardiac death. His landmark paper (Electrical Alternans and vulnerability to ventricular Arrhythmias, N Engl J Med 1994;330:235-41) found that a positive TWA test identified a subset of patients in this group with 81% mortality over 20 months versus 6% for those in whom the test was negative. The predictive value of TWA testing for cardiac arrhythmia in this group was equivalent to invasive electrophysiological testing. Numerous subsequent studies have corroborated these findings in specific patient populations such as Post-MI patients, Congestive Heart Failure patients, and patients with Syncope. TWA testing was approved (Nov 2001) for Medicare reimbursement at approximately $260 per test. The "HearTwave System" from Cambridge Heart Inc (Boston MA) gained FDA approval in Apr 2001 for testing "any patient at risk for ventricular arrhythmia." The test has been validated in the context of traditional cardiac stress testing but there is not much clinical literature on the utility of the test in other contexts. Specifically, there are no reports of the applicability of TWA testing to Emergency Department patients with acute chest pain.

Verrier et al. (J Amer Coll Cardiol 2001; 37:1719-25) found in an animal study that emotional stress had a profound multiplicative effect on the magnitude of TWA caused by cardiac ischemia. This research supported the idea that the emotional stress of presenting to the Emergency Department with acute chest pain or shortness of breath might be an effective substitute for the stress that provocative cardiac stress tests (treadmill or pharmacologic stress testing) induce. If true, then it would be of great interest to Emergency Physicians to measure the predictive value of TWA for cardiac ischemia in patients who are "stressed" by acute chest pain.