Even though the electrocardiogram (ECG) is the standard diagnostic test for the evaluation of symptoms of acute myocardial ischemia or infarction, the prognostic value of various ECG features of cardiac ischemia is ill-defined. Savonitto and colleagues conducted a retrospective study of the ECG findings among patients in the Global Use of Strategies to Open Occluded Arteries in Acute Coronary Syndromes (GUSTO-IIb) trial.
A total of 12,142 patients were enrolled in the GUSTO-IIb trial. To be enrolled in the study, patients had to have ECG signs of myocardial ischemia, including transient or persistent ST-segment elevation or depression of more than 0.05 mV or persistent and definite T-wave inversion of more than 0.1 mV. All patients had to have reported symptoms of cardiac ischemia at rest within 12 hours of hospital admission. Since the GUSTO-IIb trial was a comparison of heparin and desirudin, patients were excluded if they had active bleeding, a history of stroke, an elevated serum creatinine level, a systolic blood pressure of more than 200 mm Hg or a diastolic blood pressure of more than 110 mm Hg.
This study of the prognostic value of ECG findings included 12,124 patients. They were categorized into one of four groups according to the ECG findings: (1) T-wave inversion of more than 0.1 mV, (2) ST-segment elevation of at least 0.05 mV in two contiguous leads, (3) ST-segment depression of more than 0.05 mV, either alone or with concomitant T-wave inversion and (4) ST-segment elevation and depression. ST-segment depression was present in 35 percent of the patients, ST-segment elevation in 28 percent, T-wave inversion in 22 percent and a combination of ST-segment elevation and depression in 15 percent. Patients with left bundle branch block were included in the ST-segment elevation group.
Patients were considered to have had a myocardial infarction at admission if the creatine kinase (CK) level was elevated at baseline or during the first eight hours of hospitalization. Patients were also considered to have had a myocardial infarction at the time of admission if they did not have symptoms of ischemia between admission and the 16-hour samples, but the CK level remained elevated at 16 hours. If ischemic symptoms occurred between admission and the CK level was elevated at 16 hours only, the acute coronary syndrome was classified on the basis of expert review. The end points used were death and a repeat myocardial infarction during the first 30 days of follow-up. Also examined were the end points of coronary artery bypass grafting, angioplasty, death or myocardial infarction at six-month follow-up.
Analysis of the data revealed that men and smokers were more likely to present with ST-segment elevation, either alone or with ST-segment depression. Patients presenting with T-wave inversion or ST-segment depression had a higher prevalence of hypercholesterolemia and hypertension, and were more likely to have a longer history of coronary artery disease. The data also showed that early death (within the first few days after presentation) was most likely in patients with ST-segment elevation (alone or with depression).
At the 30-day follow-up, patients with T-wave inversion were found to be the patients least likely to have died or to have had a reinfarction. The group with ST-segment depression and elevation was significantly more likely to have these events compared with the other groups. At the six-month follow-up, those with T-wave inversion were still less likely to have reinfarction or to have died. Patients with ST-segment depression with or without elevation had the highest incidence of death or reinfarction at six months.
CK was elevated in 10.9 percent of the patients with T-wave inversion, in 15.7 percent of those with ST-segment elevation, in 10.9 percent of those with ST-segment depression and in 11.5 percent of those with ST-segment depression and elevation. CK elevation at admission was associated with a higher incidence of death or reinfarction at 30 days, with an odds ratio of 2.36 for death and 1.56 for death or reinfarction. The significance of an elevated CK seemed to be restricted to patients with ST-segment elevation or depression.
The incidence of death at 30 days ranged from 1.7 percent in the group with T-wave inversion and a normal CK level to 14.4 percent in the group with ST-segment elevation plus depression and an elevated CK level. The incidence of death was 8.7 percent in patients with ST-segment elevation and CK elevation and 11.3 percent in those with ST-segment depression and CK elevation.
The authors conclude that the ECG findings and the CK level on admission allow stratification of risk in patients presenting with symptoms of myocardial ischemia. The findings suggest that patients with ST-segment elevation plus depression and an elevated CK level are at greatest risk of death or reinfarction.