BACKGROUND: Non-Q wave Myocardial Infarction (non-Q AMI) is related pathophysiologically to Q wave AMI, as each represents different stages of plaque rupture and thrombosis. Post-hospital re-infarction and recurrent angina are more frequent in non-Q AMI than in Q wave AMI, offsetting the higher early risk with Q wave AMI, with one-year survival rates similar in the two types of MI. OBJECTIVES: 1--Evaluation of early (< or = 28 days) and one-year total mortality from first non-Q AMI in comparison to QMI. 2--Analysis of recurrent acute ischaemic events (non-fatal reinfarction and unstable angina) in both types of MI in the same periods of time. POPULATION AND METHODS: A retrospective study of 1146 patients, mean age 65 +/- 13 years, 65% male, admitted at CCU with a first MI, from January 1988 to December 1997 (minimum follow-up period of one year, mean follow-up 42 +/- 37 months). We compared the baseline demographics and clinical characteristics (coronary risk factors, previous angina, MI evolution, recurrent cardiac events, 28 day mortality and one year mortality) of patients with non-Q AMI (NQ group = 239) and Q wave AMI (Q group = 907). RESULTS: The NQ group patients were significantly older (mean age: 67 +/- 12.6 vs 65 +/- 12.5 years; p < 0.05), included fewer smokers (29% vs 43%; p < 0.001) and were more symptomatic before the index infarction (stable angina: 40% vs 30%; p < 0.05; unstable angina: 16% vs 6%; p < 0.001), when compared to the Q group patients. There were no significant differences in MI evolution, in Killip-Kimbal class > or = 2, recurrent angina and in-hospital mortality (Q-12% vs NQ-9%; ns), although there was a higher combined risk of arrhythmias and AV conduction disturbances in patients with QMI (Q-34% vs NQ-26%; p < 0.05). The combined risk of unstable angina and reinfarction at one year was significantly higher in group NQ (NQ-13% vs Q-8.1%; p < 0.05). The NQ group showed no significant difference in 28 day total mortality (NQ-14% vs Q-17%; ns) or at one year follow-up (NQ-24% vs Q-26%; ns) when compared to the Q group. CONCLUSION: 1--Despite a lower severity of non-Q AMI in the acute phase, 28 day and one year total mortality were similar in the two groups. 2--Patients with non-Q AMI showed a higher incidence of recurrent ischemic events at one year follow-up.