What causes myocardial infarction (heart attack) in young individuals?

Causes of Myocardial Infarction in Young Individuals

Young patients with myocardial infarction have a distinct risk profile dominated by smoking, dyslipidemia, and family history of premature coronary disease, but critically, you must also evaluate for nonatherosclerotic causes including spontaneous coronary artery dissection (especially in young women), coronary anomalies, recreational drug use, and inflammatory conditions that are frequently missed in this population. 1, 2

Traditional Atherosclerotic Risk Factors

Most Prevalent Risk Factors in Young MI Patients

• Cigarette smoking is the single most prevalent modifiable risk factor, present in 46-85% of young MI patients, and smoking cessation is the most effective secondary prevention measure 2, 3, 4
• Dyslipidemia occurs in 62-72% of young MI patients, with familial hypercholesterolemia having substantial prevalence in this population 1, 2, 4
• Family history of premature coronary disease is present in 31-32% of young MI patients and represents a critical risk enhancer 2, 4, 5
• Male sex accounts for 91% of young MI cases, though the proportion of young women with MI has increased from 21% to 31% between 1995-2014 1, 4

Less Common Traditional Risk Factors

• Diabetes mellitus is present in 28% of young MI patients but is less prevalent than in older populations 2, 4, 5
• Hypertension occurs in 11-22% of young MI patients, significantly lower than older cohorts 2, 4, 5
• Obesity is present in 17-27% of cases 4, 5

Nontraditional and Nonatherosclerotic Causes

Critical Nonatherosclerotic Etiologies to Evaluate

You must actively screen for these conditions as they require completely different management strategies than atherosclerotic disease: 1

• Spontaneous coronary artery dissection (SCAD) is a frequent mechanism of MI in young women, particularly in the peripartum period, and requires high clinical suspicion 1, 2
• Coronary artery anomalies, including anomalous origin from the opposite sinus of Valsalva with interarterial course, cause exercise-induced ischemia and sudden death 1
• Myocardial bridging presents with exercise-induced ischemia and requires beta-blocker therapy rather than revascularization 1
• Kawasaki disease sequelae include coronary aneurysms, stenosis, and thrombosis requiring lifelong surveillance 1

Inflammatory and Autoimmune Conditions

• Chronic inflammatory disease states including HIV, viral hepatitis, and systemic autoimmune diseases are associated with poor cardiovascular outcomes in young patients 1, 6
• Psoriasis is an independent risk factor for MI, with greatest risk in young patients with severe disease 1
• Rheumatoid arthritis doubles the risk of MI compared to the general population 1
• Systemic lupus erythematosus causes coronary microvascular dysfunction and increased CHD risk not fully explained by traditional factors 1, 6

Recreational Drug Use

• Cocaine and other recreational drugs represent important nontraditional risk factors that must be assessed in young MI patients 1

Genetic Factors

• Ch9p21 locus polymorphisms and elevated lipoprotein(a) are genetic risk enhancers requiring family screening when identified 1

Angiographic Patterns and Diagnostic Considerations

Obstructive Coronary Disease Patterns

• Young MI patients typically demonstrate single-vessel disease with less extensive atherosclerosis than older patients, though multivessel disease portends worse long-term prognosis 2, 3
• Left main involvement is rare in young patients 2

Myocardial Infarction with Nonobstructive Coronary Arteries (MINOCA)

• MINOCA occurs in 10-20% of young MI patients, requiring intravascular imaging and cardiac MRI for diagnosis 2
• Mechanisms include plaque erosion, coronary microvascular dysfunction, coronary vasospasm, and SCAD 7, 2

Sex-Specific Considerations

Young Women with MI

• Young women have 6-fold increased 30-day mortality compared to young men (adjusted OR 6.0,95% CI 2.1-17.5) 1
• Women are more likely to have hypertension (71% vs 64%) and diabetes (39% vs 26%) compared to young men 1
• Women present less frequently with STEMI (16% vs 26% in men) 1
• Diabetes is a stronger risk factor for MI in women than men 7

Clinical Pitfalls to Avoid

• Never assume normal epicardial coronary arteries exclude significant disease—coronary microvascular disease and SCAD can cause MI with normal-appearing vessels on standard angiography 6, 2
• Do not dismiss chest pain in young patients, especially young women, as noncardiac without thorough evaluation—94% of young MI patients have 3 or more risk factors 4
• Always suspect CAD in young male smokers or young female diabetics presenting with chest pain 4
• Evaluate for nonatherosclerotic causes systematically, as these require different management than standard atherosclerotic disease 1

Risk Factor Clustering

• 94% of young MI patients have 3 or more risk factors present simultaneously 4
• Only 2% of young MI patients have none of the major risk factors (cholesterol >6.5 mmol/L, triglycerides >1.7 mmol/L, smoking history, hypertension, or BP >160/95 mmHg) 5