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Spontaneous coronary artery dissection (SCAD) is an increasingly recognized cause of myocardial infarction (MI), particularly affecting young women. It is defined as a non-traumatic, non-iatrogenic, and non-atherosclerotic separation of the coronary arterial wall by intramural hematoma, resulting in a false lumen with or without intimal tear. Intramural hematoma can accumulate between any arterial layer (intima, media, or adventitia) and cause compression of the arterial lumen. In turn, this can compromise antegrade coronary perfusion and result in myocardial ischemia or infarction.¹

SCAD was first reported in 1931.² Since then, there have been <1300 reported SCAD cases; most were published in the past 5 years. The Canadian SCAD Study (CanSCAD) was conducted to improve our understanding of the natural history of this relatively infrequent condition.³ This is a multicenter, prospective, observational study that enrolled 750 SCAD patients from 22 North American centers from 2014 to 2018. All coronary angiograms were adjudicated in a core laboratory. We aimed to incorporate insights learned from this study for this review.

EPIDEMIOLOGY

SCAD was previously thought to be rare and frequently associated with pregnancy. However, under-diagnosis of SCAD and under-recognition of its angiographic variants made the prevalence difficult to estimate. SCAD primarily affects young to middle-aged women. In recent studies, women accounted for >90% of patients with SCAD.^4-8 SCAD was the underlying cause in 22-43% of MI in women <50 years.^9,10 In CanSCAD, the mean age of SCAD patients was 51.8 ± 10.2; 88.5% were women (55% post-menopausal), and 87.7% were Caucasian. About a third of patients had hypertension, and a third had no cardiac risk factors. Other relevant clinical history includes migraines (33%), anxiety (20%), and depression (20%).³

HOSPITAL PRESENTATION

The majority of patients with SCAD presents with MI. In CanSCAD, 69.9% had non-ST-segment elevation MI, and 29.7% had ST-segment elevation MI; the most common presenting symptom was chest discomfort (91.5%). A small proportion (8.1%) presented with more dramatic and life-threatening ventricular tachycardia or fibrillation.³ Less frequently, patients may present with cardiogenic shock (<3%) or sudden cardiac death (<1% based on pathology series).^5,11,12 Left ventricular function is usually preserved on presentation,^5,11,13 but >80% had wall motion abnormalities that can be very helpful to aid angiographic recognition of SCAD.³

PRECIPITATING AND PREDISPOSING FACTORS

Conditions that increase intracoronary shear stress, such as increase in thoracoabdominal pressure or catecholamines, may precipitate SCAD. The most common precipitating factor in the CanSCAD cohort was emotional stress, reported in 50.3% of patients (rated as high to severe stress). Another important stressor is intense physical stress, reported in 29%, with isometric activities lifting >50 lb in 10%.³ These have management implications because changes in lifestyle or psychological well-being may impact SCAD recurrence.

In terms of predisposing arteriopathy, fibromuscular dysplasia (FMD) is most commonly observed in patients with SCAD (co-prevalence reported from 52 to 86%). Non-coronary FMD can be diagnosed on catheter-based angiography of renal and iliac arteries during coronary angiographies or with computed tomography angiography.^4,5,14 In CanSCAD, only 31% of patients had concomitant non-coronary FMD; however, this was underestimated because 45% of patients did not yet undergo any FMD screening or had incomplete screening. Non-coronary FMD can affect the renal, iliac, and cerebrovascular arteries. Other causes of SCAD were much less frequent, including peripartum SCAD in <5% of cases, connective tissue disorders in <5%, and systemic inflammatory diseases in <5%.³

DIAGNOSIS

Coronary angiography continues to be the cornerstone for diagnosing SCAD. Although dedicated intracoronary imaging with optical coherence tomography or intravascular ultrasound improves the diagnostic yield of SCAD, there can be additional risks, including propagation of dissection and iatrogenic guide-catheter dissection. In CanSCAD, optical coherence tomography or intravascular ultrasound was performed in only a small proportion (7.6%) of SCAD patients. This highlights the importance of being familiar with angiographic variants of SCAD to aid diagnosis.³

^{Figure 1: Angiographic Subtypes of SCAD}

^{Reproduced with permission from Saw et al.1}

A new SCAD angiographic classification was devised to facilitate SCAD diagnosis and stratified the angiographic appearance into 3 types (Figure 1).¹⁵ Type 1 describes the pathognomonic presence of contrast within arterial wall delineating multiple radiolucent lumens. Type 2 describes diffuse and smooth stenosis of usually >20 mm length with varying severity. Type 3 describes focal or tubular stenosis, which mimics atherosclerosis and requires intracoronary imaging to confirm the presence of intramural hematoma. In CanSCAD, the most common angiographic appearance was Type 2 (60.2%), followed by Type 1 (29%) and Type 3 (10.8%).³

SCAD CORONARY INVOLVEMENT

SCAD can affect any coronary artery, and the most commonly affected is the left anterior descending artery (LAD) (52.1%) in the CanSCAD study. The proximal segments including the left main or the proximal segment of LAD, circumflex, and right coronary artery, occurred in only 7.6% of cases. In the majority of cases, SCAD occurred in 1 coronary segment only (74.8%). In 13.1% of cases, multiple non-contiguous arteries were affected. The mean length of dissection was 33.2 mm, and the median stenosis severity was 79.0%. The majority of cases (63.8%) had Thrombolysis in Myocardial Infarction grade 3 flow.³

MANAGEMENT OF SCAD

There is no randomized trial comparing management strategies for SCAD. Therefore, much of the management recommendations were derived from observational studies and expert opinions. A suggested management algorithm is depicted in Figure 2. Conservative therapy is the preferred treatment strategy unless patients have high-risk features (e.g., left main dissection, ongoing ischemia, and hemodynamic/electrical instability). In the CanSCAD study, the majority of SCAD patients was managed conservatively (86.4%). Only 11.9% underwent percutaneous coronary intervention (PCI), 1.5% received fibrinolysis, and 0.3% underwent coronary artery bypass surgery.³ Of those treated conservatively, only 2.0% subsequently required PCI, and 0.3% subsequently required coronary artery bypass surgery. Patients treated conservatively should be monitored in-hospital for 3-5 days depending on symptoms and location of SCAD.¹⁶

For those who underwent revascularization as initial therapy, the main reasons for revascularization were ongoing ischemic symptoms (39.1%), ongoing ischemic changes on electrocardiogram (34.5%), and severe luminal stenosis (31.8%). The technical success rates with PCI remained relatively poor (30.1% unsuccessful; 40.8% partially successful). Given the underlying frailty and disrupted integrity of arterial wall, PCI can result in iatrogenic dissection and/or extension of dissection. In fact, 32% of patients who underwent PCI had propagation of SCAD during PCI. PCI improved Thrombolysis in Myocardial Infarction flow in 57.6% of patients but made no difference in 38.8% of patients.³

^{Figure 2: Suggested Management Algorithm for SCAD}