Spontaneous coronary artery dissection (SCAD) is an uncommon but potentially lethal condition in which one of the coronary arteries that supply the heart, spontaneously develops a blood collection, or hematoma, within the artery wall due to a tear in the wall. SCAD is one of the arterial dissections that can occur. SCAD is a major cause of heart attacks in young, otherwise healthy women who usually lack typical cardiovascular risk factors. While the exact cause is not yet known, SCAD is likely related to changes that occur during and after pregnancy, or possibly genetics, hormonal influences, inflammatory issues or changes due to disease. These changes lead to the dissection of the wall which restricts blood flow to the heart and causes symptoms. SCAD is often diagnosed in the cath lab with angiography, though more advanced confirmatory tests exist. While the risk of death due to SCAD is low, it has a relatively high rate of recurrence leading to further heart attack-like symptoms in the future.
Signs and symptoms SCAD often presents like a heart attack in young to middle-aged, healthy women. This pattern usually includes chest pain, rapid heartbeat, shortness of breath, sweating, extreme tiredness, nausea, and dizziness. A minority of people with SCAD may also present in cardiogenic shock (2–5%), ventricular arrhythmias (3–11%), or after sudden cardiac death. Pregnancy- and postpartum-associated SCAD generally have worse outcomes compared to other cases.
Causes Risk factors include pregnancy and the postpartum period. Evidence suggests that estrogen- and progesterone-related vascular changes affect the coronary arteries during this period, contributing to SCAD. Some case reports and case series suggest associations with autoimmune inflammatory diseases, but there have not been larger studies to explore this relationship. Underlying heritable conditions such as fibromuscular dysplasia and connective-tissue disorders (e.g., Marfan syndrome, Ehlers–Danlos syndrome, and Loeys–Dietz syndrome) are associated with SCAD, SCAD triggers may include severe physical or emotional stress, but many cases have no obvious cause.
Pathophysiology SCAD symptoms are the result of a restriction in the size of the lumen of the affected coronary artery. A bleed within the wall of the artery (tunica intima) originating from the microvessels that perfuse this muscular layer (vasa vasorum) leads to a collection of blood, or hematoma, between the layers of the artery wall. The hematoma pushes close the lumen, preventing blood from flowing to the heart muscle (myocardium). In some cases (~30%) this hematoma (also referred to as an intramural hematoma) is also accompanied by a tear in the inner most layer of the artery - a monolayer of endothelial cells called the tunica intima. It is not clear if this precedes or follows a bleed within the wall of the artery. The tracking of blood within the artery wall (both in the presence or absence of an intimal tear) is referred to as a "false lumen". The restriction of blood flow in the 'true' lumen limits the availability of oxygen and nutrients to the heart muscle, or myocardium. As a result, the myocardium continues to demand oxygen but is not adequately supplied by the coronary artery. This imbalance leads to ischemia, damage, and in some cases can lead to death of the myocardium tissue, causing a heart attack (myocardial infarction).
Involvement of the Vasa Vasorum While the molecular mechanisms that underpin SCAD are still poorly understood, studies have implicated dysfunction of the vasa vasorum, the microvessels that perfuse the muscular layer of the coronary artery, lead to the bleed. There is an inverse correlation between the amount of vasa vasorum present in regions of the coronary artery and the likelihood of an area being affected by a SCAD. It has been hypothesized that alterations in vessel wall strength, owing to dysfunction in the TGF-β pathway, the extracellular matrix, and vascular smooth muscle cell contractility alter the capacity of the vasa vasorum to perfuse the vessel wall, leading to either (1) a potential microthrombi and bleed, or (2) an area of hypoxia, which would likely induce new microvessel formation angiogenesis of new immature (and thus leaky) vessels.
Genetics It is likely that both genetics and environment play a role in SCAD onset. A number of genetic variants have been linked to an increased the risk of SCAD. As with dissection (medical) generally, the genes identified implicate dysfunction in four main cellular molecular pathways: the TGF-β pathway, extracellular matrix pathway, vascular smooth muscle cell contractility, and cellular metabolism. Variants in genes including ALDH18A1, COL3A1, COL4A1, FBN1 and ACVR1 were implicated in a study of 91 unrelated SCAD cases.
Diagnosis
Given the demographics of SCAD, it is important to maintain a high index of suspicion for the condition in otherwise low-risk women presenting with symptoms of acute coronary syndrome. Initial evaluation may show ECG changes of ST elevation, like heart attacks due to other causes. SCAD comprises 2-4% of all cases of acute coronary syndrome. With typically elevated cardiac biomarkers and ECG changes, people will often undergo coronary angiography evaluation. It is important to recognize SCAD through angiography as other confirmatory measures carry increased risks.
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