Clinical variables such as the patient's age, blood pressure, heart rate, Killip class and location of infarction have generally been used to estimate the risk of death in patients with acute myocardial infarction and ST-segment elevation. Cardiac troponin T has been shown to be a predictor of 30-day mortality in patients with acute coronary syndromes. An elevated troponin T level is associated with a mortality rate that is three to four times higher than the rate in patients with normal levels. Ohman and associates, in a prospective sub-study of the Global Use of Strategies To Open Occluded Coronary Arteries (GUSTO-III) trial, investigated the utility of cardiac troponin T levels in risk stratification of patients undergoing thrombolytic therapy for myocardial infarction.
Data on cardiac troponin T levels were available for 12,666 patients in the study. These patients were evaluated for acute myocardial infarction within 30 minutes to six hours after the onset of symptoms and had ST-segment elevation or bundle branch block. They were randomized to receive reteplase or alteplase unless thrombolytic therapy was specifically contraindicated. The primary end point was 30-day mortality from any cause.
Cardiac troponin T results were positive at enrollment in 1,127 (8.9 percent) of the 12,666 patients. Compared with patients with normal troponin T levels, those with elevated levels were significantly older and more often had an anterior infarction, lower systolic blood pressure and a higher heart rate. In addition, patients with positive test results were more likely to have clinical signs of heart failure at enrollment. Patients with positive troponin results at the time of enrollment in the study had chest pain significantly longer than the patients with negative results.
The 30-day mortality rate was significantly higher in patients with troponin T elevation (15.7 versus 6.2 percent in patients with normal levels). Patients with elevated levels also had significantly more cardiogenic shock, congestive heart failure, asystole, electromechanical dissociation, moderate or severe bleeding and blood transfusion. Cardiogenic shock occurred in 9.0 percent of those with positive troponin T levels compared with 3.7 percent of those with negative results. Congestive heart failure was present in 23.4 percent of the patients with elevated troponin T levels. In contrast, it was present in 16.4 percent of those with normal levels. Asystole occurred in 8.0 percent of patients with positive results compared with 3.6 percent of those with negative results. Electromechanical dissociation occurred in 5.4 percent of patients with elevated troponin T levels compared with 1.8 percent of those with negative levels. Moderate or severe bleeding occurred in 10.0 percent of patients with positive troponin T levels compared with 7.2 percent of those with negative results. Blood transfusion was required in 7.4 percent of patients with elevated troponin T levels and in 5.5 percent of those with normal levels.
The authors conclude that an elevated cardiac troponin T level on admission is an independent marker of higher 30-day mortality in patients with acute myocardial infarction and ST-segment elevation. Women with an elevated troponin T level had a mortality rate that was nearly twice as high as that of men (23.7 versus 12.5 percent). The mortality rate among patients more than 75 years of age with elevated troponin T levels was high (35 percent).
editor's note: Troponin T, as opposed to creatine kinase or troponin I, is elevated in patients with multivessel disease or transient myocardial ischemia. Studies have confirmed that the troponin T level is useful for the detection of minor myocardial damage. The troponin T level has been found to reflect the gradual transition between minor myocardial damage and small acute myocardial infarction. Troponin has a higher sensitivity as a marker for irreversible myocardial injury than does the MB fraction of creatine kinase (CK-MB) because it is not elevated in patients with skeletal muscle disease or injury. Troponin is present in myocardial tissue at higher levels than CK-MB. The second-generation troponin T assays are highly sensitive and serve as a specific marker for minor myocardial damage. The troponin T level can also be elevated in patients with severe congestive heart failure.—r.s.