What are the causes of myocardial infarction (MI) in pregnant women, particularly those with a history of preeclampsia?

Causes of Myocardial Infarction in Pregnancy

Spontaneous coronary artery dissection (SCAD) is the most common cause of myocardial infarction in pregnancy, followed by atherosclerotic coronary artery disease, with the risk of MI increased 3-4 fold during pregnancy compared to non-pregnant women of reproductive age. 1, 2, 3

Primary Etiologies

Spontaneous Coronary Artery Dissection (SCAD)

• SCAD is the leading cause of pregnancy-associated myocardial infarction in recent series, accounting for the majority of cases particularly in the peripartum period 2, 3, 4
• The pathophysiology involves spontaneous formation of an intramural hematoma within the coronary artery wall, with or without an intimal tear 5
• Pregnancy-related hormonal changes contribute to structural alterations in collagen of vessel walls, increasing vulnerability to dissection 5
• Up to one-third of SCAD cases occur in the third trimester or within three months postpartum 4
• Fibromuscular dysplasia is present in up to 72% of SCAD patients and represents the strongest predisposing arteriopathy 5

Atherosclerotic Coronary Artery Disease

• Atherosclerosis is the second most common cause of pregnancy-associated MI, with increasing prevalence as women defer pregnancy to older ages 1, 2
• Women with preeclampsia history have significantly higher prevalence of coronary atherosclerosis (36.3% vs. 28.3% in controls) and stenosis >50% 6
• The incidence of MI in pregnancy increased throughout the 1990s, correlating with delayed childbearing and increasing prevalence of traditional risk factors 1, 7
• Rupture of small coronary artery plaques can be triggered by pregnancy-related hypertension 7

Coronary Artery Thrombosis

• Pregnancy induces a hypercoagulable state through increased platelet adhesion, elevated fibrinogen, increased factors VII, VIII, IX, X, and XII, decreased protein S and C levels, and reduced fibrinolysis 8, 7
• Arterial thrombosis can occur with or without coronary artery spasm 7
• Thrombophilia and postpartum infections increase the risk of thrombotic MI 9

Coronary Artery Vasospasm

• Coronary vasospasm with or without arterial thrombosis represents another mechanism of pregnancy-associated MI 7
• Rapid and excessive blood pressure reduction from sublingual or intravenous calcium channel blockers has caused myocardial infarction or fetal distress 1

Risk Factors and Precipitating Conditions

Preeclampsia/Eclampsia

• Preeclampsia is a critical risk factor, with women having a history of preeclampsia showing 2.5-fold increased risk of coronary artery disease 6
• Severe preeclampsia confers greater cardiovascular risk (OR 2.74) compared to moderate preeclampsia (OR 2.24) 6
• Recurrent preeclampsia dramatically escalates MI risk, with women experiencing repeat episodes having 3-fold higher rates of MI 6
• The systemic endothelial dysfunction and angiogenic imbalance in preeclampsia creates persistent vascular vulnerability 6

Demographic and Obstetric Factors

• Advanced maternal age increases atherosclerotic risk, with older women having higher likelihood of coronary disease 1, 9
• Multigravida status and third trimester pregnancy are associated with increased MI risk 9
• Over 90% of SCAD cases occur in women, with the condition disproportionately affecting young to middle-aged women without traditional cardiovascular risk factors 5

Precipitating Stressors

• Intense emotional stress can trigger SCAD in predisposed individuals 5
• Physical stressors including intense exercise, Valsalva-type activities, or labor and delivery can precipitate SCAD 5
• Hypertension is an independent predictor of recurrent SCAD 5

Medical Comorbidities

• Blood transfusions, thrombophilia, and postpartum infections increase MI risk 9
• Congenital heart disease: 85% of neonates born with congenital heart disease now survive to adulthood, translating into higher risk for cardiac events during pregnancy 1
• Illnesses related to congenital heart disease and pulmonary hypertension are the third most common cause of maternal cardiac deaths 1

Clinical Context

Timing of Events

• The highest risk period is the third trimester and postpartum, with thrombi and dissections occurring more frequently in the peripartum period than before delivery 5
• The number of cardiac deaths during pregnancy has increased steadily since 1991, with cardiac disease being the primary cause of maternal mortality 1

Mortality Impact

• Myocardial infarction is the most common cause of maternal death from cardiac disease, followed by aortic dissection 1
• Acute myocardial infarction in pregnant women carries high morbidity and is a significant contributor to maternal morbidity and mortality 2, 9, 3