Acute myocardial infarction in the young--the role of smoking. The Investigators of the International Tissue Plasminogen Activator/Streptokinase Mortality Trial.

Patients who received thrombolytic therapy for acute myocardial infarction in a large international trial were divided into two groups on the basis of age; those < or = 40 years (n = 269) and those > 40 years (n = 7787). The younger group included more men (89.9% vs 75.9%, P = 0.009) and fewer patients had a history of coronary artery disease, hypertension, and diabetes mellitus. A family history of cardiovascular disease was significantly more prevalent among the young patients (53.4% vs 41.9%, P = 0.0002). Significantly more younger patients than older patients were smokers at the time of infarction (76.2% vs 42.9%, P < 0.0001) and the average number of cigarettes smoked per day was also significantly higher in young patients (27.8 +/- 14.3 vs 19.9 +/- 12.9, P < 0.01). Younger patients had a better outcome, with lower rates of cardiogenic shock (1.1% vs 7.0%, P = 0.0002), stroke (0.0% vs 1.9%, P = 0.02) and haemorrhage (1.9% vs 5.9%, P = 0.006), as well as a better Killip class at discharge (Killip > 1 in 4.5% vs 8.0%, P < 0.001), and lower hospital and 6-month mortality (0.7% and 3.1% vs 8.3% and 12%, P < 0.001, respectively). The better outcome of younger patients with acute myocardial infarction is related to their better baseline characteristics. Young patients with acute myocardial infarction have a strong family history of cardiovascular disease and a high prevalence of smoking. Smoking is the most important modifiable risk factor in these patients.