Continuing Education Activity

Spontaneous coronary artery dissection (SCAD) is a tear in the wall of the epicardial coronary artery not caused by trauma, coronary intervention, or atherosclerotic plaque rupture. It is characterized by intimal tear, intramural hematoma, and false lumen formation, which can obstruct coronary blood flow and cause myocardial ischemia. SCAD is an emerging cause of acute coronary syndrome (ACS) in young females without any known cardiovascular risk factors. The etiopathogenesis of this entity is unclear, and studies are underway. The hypotheses proposed in the literature are about its association with fibromuscular dysplasia (FMD), exposure to female sex hormones like estrogen and progesterone, and extreme physical or emotional stress. The most common presentation is ACS. ECG may show ST-segment changes, and lab work may show an elevation in cardiac troponins. An echocardiogram may reveal regional wall motion abnormalities. Diagnosis is confirmed primarily by cardiac catheterization and coronary angiogram; intravascular imaging can be done if a coronary angiogram is inconclusive. Coronary computed tomography angiography (CCTA) and magnetic resonance angiography can be done in follow-up. General and interventional cardiologists, advanced cardiovascular imaging specialists, and cardiac surgeons should be on board for the management.

Objectives:

• Describe the possible etiopathogenesis and types of spontaneous coronary artery dissection.
• Recognize spontaneous coronary artery dissection as the possible cause of ACS in a young female without any cardiovascular risk factors.
• Discuss the importance of cardiac catheterization, coronary angiogram, and intravascular imaging in diagnosing spontaneous coronary artery dissection.
• Review the acute management strategy and outline the differences in long medical management post-hospital discharge between ACS due to spontaneous coronary artery dissection and plaque rupture.

Introduction

Spontaneous coronary artery dissection (SCAD) is a tear in one of the epicardial coronary arteries. The spectrum ranges from the intimal rupture to intramural hematoma and false lumen formation without preceding events like atherosclerotic plaque rupture, trauma, or coronary artery interventions. It is the leading cause of ACS in young women, including peripartum women, without any cardiovascular risk factors.[1] 

The clinical presentation varies from ST-elevation myocardial infarction (STEMI) to non-ST-elevation ACS, ventricular tachyarrhythmias, congestive heart failure, and sudden cardiac death. The most common cause of ACS in the general population is rupture of atherosclerotic coronary plaque leading to superimposed thrombosis, obstruction to the distal coronary flow, and coronary ischemia. SCAD leads to the formation of an intramural hematoma, compression of the true lumen, and obstruction to the distal coronary flow, resulting in ACS.[2]

Human coronary circulation is comprised of three epicardial coronary arteries. The left coronary artery (LCA) divides into the left anterior descending (LAD) and the left circumflex arteries (LCx). LAD branches into diagonal and septal branches and supplies the anterior wall, anterior and apical septum, and apical cap. LCx divides into obtuse marginal branches and supplies left ventricular anterolateral and posterolateral walls. Sometimes a separate branch arises from the left main between LAD and LCx and is called ramus intermedius.

The right coronary artery (RCA), which is dominant in 80% of patients, arises from the right sinus of Valsalva and supplies the right atrium, the sinoatrial node, right ventricle, and posterior two-thirds of the interventricular septum (in the right dominant circulation), and inferior wall and posterior left ventricular segments.[3]

The branches of the right coronary artery are the conus artery, the sinoatrial branch, the right ventricular branch, the acute marginal, the right posterior descending, and the right posterolateral branches.

The cross-section of the coronary arteries comprises three concentric histologic layers, tunica intima, media, and adventitia. Tunica intima is the primary site for atherosclerosis and consists of endothelial cells, smooth muscle cells, and connective tissue. Tunica intima is separated from tunica media by internal elastic lamina.

The tunica media consists of smooth muscle cells separated from tunica adventitia by the external elastic lamina. Tunica adventitia is made up of collagen and elastic fibers and consists of vasa vasorum, which supplies oxygen to the vessels, lymphatics, and nerve fibers.[4]

Coronary dissection occurs when there is an accumulation of blood in the tunica media leading to the formation of an intramural hematoma. The source of blood in intramural hematoma is either injury to the vasa vasorum or an intimal tear. Intramural hematoma separates tunica intima from the outer layer creating the false lumen that compresses the true lumen obstructing blood flow and causing ACS.[5]

The left anterior descending artery is the most affected by spontaneous coronary dissection. The involvement of the coronary arteries and their branches in order of decreasing frequency are the LAD with its branches (about 50%); circumflex, ramus, and obtuse marginals (about 30%); RCA and its branches (25%), multivessel (about 15%) and LCA (about 4%). Distal vessels are more commonly affected than the proximal vessels.[6]

There are three angiographic types of spontaneous coronary artery dissection.[7]

• Type 1:  Multiple radiolucent lumens or contrast staining of the wall
• Type 2:  Diffuse stenosis with the abrupt change in vessels caliber
• Type 3:  Focal or tubular stenosis (usually less than 20 mm) mimics atherosclerosis; intramural hematoma should be investigated by intracoronary imaging.

Etiology

The etiology of spontaneous coronary artery dissection is unclear and hypothesized to be multifactorial. Since SCAD occurs predominantly in young females, including peripartum, it is hypothesized that female sex hormones, environmental stressors, or underlying arteriopathies like fibromuscular dysplasia (FMD) contribute to its occurrence. FMD is a non-atherosclerotic and non-inflammatory vascular disease, common in younger women and can present with an aneurysm, stenosis, and dissection and affect the coronary circulation. A study showed that 10.5% of patients with FMD had an arterial dissection, and 2.5% had SCAD.[8] 

The case reports have demonstrated similar histologic and angiographic features of SCAD and FMD, suggesting SCAD could be a coronary manifestation of FMD.[9] Further large-scale research in a representative population is required to verify this association.

Spontaneous coronary artery dissection is the most common cause of ACS in young women without any conventional cardiovascular risk factors. The disproportionately high incidences of SCAD in young women, including those who are pregnant, postpartum, or on oral contraceptive pills, suggests a possible role of female sex hormones. Estrogen and progesterone may cause structural changes in the vessel wall, as in other connective tissues, and make it prone to rupture or dissection.[10]

Women with pregnancy-related spontaneous coronary artery dissection have a poor prognosis. Studies have shown they have larger infarcts, more tendency to have left main and multivessel disease, reduced left ventricular ejection fraction, cardiogenic shock, STEMI, and ventricular arrhythmias.[11]

Studies have also shown a possible association between extreme physical or emotional stress and SCAD. One study found antecedent extreme physical stressors in 40% and emotional stressors in 24% of SCAD patients.[12] Stress-induced catecholamine surge responsible for stress-induced cardiomyopathy could also contribute to SCAD by causing shear stress in the coronary arteries.[13]

Epidemiology

Spontaneous coronary artery dissection can affect both sexes, but the incidence is overwhelmingly higher in women in their fifth and sixth decades of life (about 90%) than in men.[14] The risk factors for atherosclerotic coronary artery disease risk are lower in these patients than those who have ACS due to plaque rupture. SCAD is a rare cause of acute coronary syndrome overall and constitutes only <1% of all myocardial infarctions. As the condition is rare in men, data is limited for men.[15] 

The known risk factors are pregnancy, postpartum state, concomitant FMD, arteriolopathies, and physical and emotional stressors. The majority of patients affected are white women. Mortality is low, about 1-2%, and the incidence of recurrent ACS is about 18%.[12]

Pathophysiology

Spontaneous coronary artery dissection is characterized by the separation of the tunica intima from the adventitia of the coronary arteries. The overall theory suggests that there has to be an injury or spontaneous bleeding that disrupts the vessel wall, which allows a hematoma to form. Unlike typical dissection, the inciting event in SCAD is not trauma, atherosclerosis, or intracoronary intervention.

It is hypothesized that the intimal tear from an unknown etiology is an initial event that leads to the creation of intramural hematoma and false lumen. Propagation of the hematoma leads to expansion of the false channel along the longitudinal axis and towards the center of the vessel. One study found that the primary event in SCAD is a rupture of vasa vasorum or medial dissection leading to the formation of secondary intramural hematoma and false lumen by hematoma propagation.[16] 

Irrespective of the mechanism of intramural hematoma formation, the final common pathway for myocardial infarction is an obstruction to the coronary blood flow by dissection flap or expanding hematoma. About 90% of patients with spontaneous coronary artery dissection present with myocardial infarction, approximately half present with STEMI, and about half with non-ST-elevation ACS.[17] 

Ventricular arrhythmias and cardiogenic shock have been reported as well. Since the pathogenesis does not involve plaque rupture and superimposed thrombosis like atherosclerotic coronary artery disease, revascularization with PCI or CABG  is not the first-line treatment in a stable patient. PCI is associated with an increased risk of complications.[18] 

The guidewire may enter the false lumen, and balloon dilatation and stent placement may lead to iatrogenic injury, propagation of hematoma, or false lumen leading to further vessel occlusion requiring emergent coronary artery bypass surgery. Healing of the intramural hematoma may subsequently lead to malposition of the stent.[19] Data showed that SCAD lesions heal spontaneously in most patients weeks after the conservative management.[20]

History and Physical

The primary presentation of spontaneous coronary artery dissection is anginal chest pain in >90%, followed by an angina equivalent. Peripartum patients tend to present with serious complications like ventricular arrhythmias, cardiogenic shock, or even sudden cardiac death. Elevation in jugular venous pressure with positive hepatojugular reflux, bilateral pitting pedal edema, and crepitations in the lung is present due to cardiogenic pulmonary edema and pleural effusion.

Delayed mentation and delayed capillary refill are common in congestive heart failure or cardiogenic shock from pump failure. The cardiovascular system examination may reveal sinus tachycardia and S3 gallop rhythm with anterior wall MI and congestive heart failure, sinus bradycardia, and complete heart block when the right coronary artery is involved.

A pansystolic murmur from an acute mitral regurgitation may be present when anterior wall MI is complicated by papillary muscle rupture, predominantly posteromedial papillary muscle, which is supplied by RCA only; and ventricular septal defect from acute septal wall rupture.

Distant heart sounds, raised jugular venous pressure, hypotension, and pulsus paradoxus suggest pericardial tamponade from free wall rupture. While the patient is in the hospital, daily cardiovascular system examinations are important to diagnose post-MI complications in a timely manner.

Comprehensive vascular physical examination may give clues about FMD and potential extra coronary vascular abnormalities associated with SCAD. A bounding pulse may suggest an aneurysm, while a diminished and asymmetrical pulse with a bruit may indicate a stenotic or dissected artery. The presence of an epigastric and flank bruit may suggest renal FMD, while a carotid bruit may suggest extracranial carotid artery involvement.

Evaluation

Anginal chest pain, characteristic ECG changes, and rising and/or falling pattern of cardiac troponins suggest ACS. ECG may reveal ST-elevation in transmural ischemia or infarction and T-wave inversion or ST-depression in subendocardial ischemia. An echocardiogram may reveal regional wall motion abnormalities in the involved coronary territory. The patient should be taken to the cardiac catheterization lab upon the diagnosis of ACS.

Coronary Angiography

A coronary angiogram is always the initial diagnostic procedure when a patient presents with ACS. The characteristic angiographic appearance of spontaneous coronary artery dissection is the beaded appearance of the coronary artery due to multiple radiolucent lumens with extraluminal contrast staining or near occlusion of the vessel caused by intramural hematoma or dissection flap.

The most common pattern is the stringlike appearance of the segment due to diffuse stenosis (present in about 70% of patients), and the left ventriculogram may show wall motion abnormalities.[Video 1] [Video 2]Coronary angiogram was found to be associated with iatrogenic catheter-induced dissection in about 3% of patients with SCAD.[21]

Intracoronary Imaging

Intracoronary imaging modalities like intravascular ultrasound (IVUS) or optical coherence tomography (OCT) demonstrate dissection flaps, intramural hematoma, intimal tear, and true and false lumens. Although intracoronary imaging has a higher spatial resolution than angiogram, its use is only reserved for non-diagnostic angiography.

Limited availability of intravascular imaging systems in the cardiac catheterization labs, risk of worsening dissection, and overall preference for conservative management make catheter-based angiography the first-line diagnostic modality for spontaneous coronary artery dissection.

Coronary Computed Tomography Angiography (CCTA)

CCTA is not performed in the acute setting, and invasive coronary angiography is always the initially performed procedure in ACS.[22] Noncalcified plaque can mimic intramural hematoma in CCTA. CCTA has a poor spatial resolution for small vessels commonly affected by spontaneous coronary artery dissection, which can lead to false-negative results.[23] CCTA is useful for non-invasive follow-up of patients with SCAD involving the proximal or large-diameter coronary arteries.

Treatment / Management

Conservative Management

Conservative management is usually the initially preferred modality of treatment for stable patients. Studies have demonstrated angiographic healing in more than 90% of the patients with spontaneous coronary artery dissection, usually within a month.[20] However, recurrent MI due to propagation of the dissection is not uncommon. A large-scale retrospective cohort study has shown that the recurrence rate is about 18%, and about half of the returning patients presented within the first week.

These patients should be hospitalized and monitored for 3 to 5 days and followed closely after discharge. Follow-up invasive coronary angiogram is reserved only for high-risk patients with recurrent symptoms, abnormal stress tests, or high-risk anatomies like the involvement of the left main, proximal LAD, or multivessel disease in the initial coronary angiography. Otherwise, stable patients can be followed with CCTA.

Percutaneous Coronary Intervention (PCI)

Studies have shown that PCI for spontaneous coronary artery dissection can lead to suboptimal outcomes and increased risk of complications.[18] The guidewire may enter the false lumen, and balloon dilatation or stent placement can cause a new dissection or cause upstream or downstream propagation of the existing dissection. Additionally, the distal location of most SCAD lesions makes them less amenable to PCI. PCI is only reserved for patients with ongoing ischemia or hemodynamic instability.

Coronary Artery Bypass Grafting (CABG)

CABG is reserved for spontaneous coronary artery dissection patients after attempted PCI has failed, with left main or proximal dissections, or refractory ischemia, despite conservative management. Follow-up studies have shown a high rate of graft failure from graft occlusion resulting from the competitive flow in the healed native vessels.[20]

Medical Management

Medical management of ACS due to SCAD is different from atherosclerotic ACS.

Anticoagulant and Antiplatelets

Patients are started on anticoagulation and dual antiplatelets as per the guidelines for ACS management. However, expert consensus recommends stopping anticoagulation after SCAD has been diagnosed on angiography as it may worsen intramural hematoma. Thrombolytic therapy in acute SCAD is not recommended as it can lead to coronary artery rupture and cardiac tamponade.[24] 

Research to date does not support using dual-antiplatelets in patients receiving medical management for spontaneous coronary artery dissection. The expert consensus recommends long-term aspirin use, but there is no data to support the benefit of long-term antiplatelets in SCAD. Patients undergoing PCI should receive dual antiplatelets for at least a year as per current guidelines.

Beta-Blockers and Antianginals

Beta-blocker therapy has been shown to lower the incidence of recurrent spontaneous coronary artery dissection and should always be prescribed.[12] The use of ACEI/ARB is reserved only for MI complicated with LV systolic dysfunction, and there is no role for statins as the mechanism of ACS is not plaque rupture. Chest pain is common after SCAD and may lead to frequent hospitalizations. It may be mediated by coronary vasospasm, microvascular diseases, or non-cardiac in origin and should be treated with nitrates, calcium channel blockers, or ranolazine.

Prevention of Recurrence

Recurrence of SCAD is defined as a new dissection event, usually at a different location. Beta-blockers have been shown to prevent a recurrence after an index event. These patients should be cautioned to avoid isometric exercise, high-intensity exercise, and prolonged Valsalva maneuvers.

Differential Diagnosis

The differential diagnosis of spontaneous coronary artery dissection includes other conditions causing coronary artery dissection or mimicking it on a coronary angiogram.

Iatrogenic Catheter-induced Coronary Artery Dissection

The coronary guidewires used during PCI or intravascular imaging may inadvertently cause intimal injury leading to intramural hematoma formation and the creation of a false lumen. The angiographic picture resembles spontaneous coronary artery dissection, but there is a history of antecedent coronary intervention.

Atherosclerotic Coronary Artery Disease

Type 3 SCAD presents as focal or tubular stenosis that resembles atherosclerotic coronary artery disease. This appears as a filling defect distal to the stenosis in coronary angiogram and should be confirmed with intravascular imaging like IVUS or OCT.

Coronary Artery Thrombosis

Coronary thrombosis due to plaque rupture, smoking, thrombophilia, or cardiac source of embolism may mimic type 3 SCAD. Thrombus appears hazy in coronary angiogram with filling defects and smooth meniscus at the occlusion site. Intravascular imaging is instrumental in diagnosis.

Coronary Calcification

Coronary atherosclerosis appears as areas of discrete calcifications in CCTA. Noncalcified plaques in CCTA may mimic an intramural hematoma. Diagnosis is by intracoronary imaging.

Prognosis

Most patients on conservative management have spontaneous healing within a month. MI in pregnancy due to spontaneous coronary artery dissection may lead to complications and poor outcomes. Recurrence is not uncommon, and these patients should be closely followed after discharge. Follow-up studies can be done with CCTA. A repeat invasive coronary angiogram is reserved for patients with high-risk anatomy and positive functional study.

Complications

Ventricular tachyarrhythmias, ventricular free wall or septal rupture, congestive heart failure, and cardiogenic shock are the immediate complications. About one in five patients presents with recurrence.

Post spontaneous coronary artery dissection chest pain is very common in the outpatient setting. It may be due to a sequela of dissection or noncardiac in origin, as these patients are prone to psychological stress, anxiety, or depression. Mental illnesses like post-traumatic stress disorder, depression, anxiety, and reduced quality of life are common in these patients, and they should be screened for these disorders before discharge.[25]

Postoperative and Rehabilitation Care

All patients with MI caused by spontaneous coronary artery dissection should be enrolled in cardiac rehabilitation programs. Cardiac rehabilitation has shown evidence-based improvement in physical and psychosocial wellbeing among the survivors.[26]

Deterrence and Patient Education

Women who have spontaneous coronary artery dissection and who would like to become pregnant should receive preconception counseling as SCAD tends to recur and can present with severe complications during pregnancy. Isometric exercise, high-intensity endurance activities, and exercise involving a prolonged Valsalva maneuver should be avoided after SCAD.[24]

Due to its potential association with female sex hormones, exposure to exogenous progesterone, estrogen, or their derivatives in the form of contraceptives or hormone replacement therapy should be avoided.[18]

Enhancing Healthcare Team Outcomes

Managing patients with acute spontaneous coronary artery dissection requires an interprofessional team of clinicians (MDs, DOs, NPs, and PAs), specialists, nursing staff, and ancillary staff, working collaboratively and communicating case details between various disciplines.

The patients with acute SCAD usually present with ACS in the emergency department to emergency physicians or hospitalists. An interventional cardiologist should be consulted for urgent cardiac catheterization. The cardiothoracic surgeon should be available if CABG is needed. Once admitted and stabilized, a general cardiologist follows the patient in a coronary care unit and after discharge. Psychiatrists are involved in the management of post-SCAD mental illnesses.

Pregnant patients who have a history of spontaneous coronary artery dissection should be followed by a specialized interprofessional team comprised of a cardiologist, maternal-fetal medicine specialist, and obstetric anesthesiologist.

Nurses are essential healthcare team members as they medicate and monitor patients while in the telemetry unit and during cardiac rehabilitation sessions after discharge reporting concerns to the team. Pharmacists make sure patients receive the correct medications and assist the team by evaluating the patients for adverse side effects.

An urgent initial consult with an interventional cardiologist followed by coordinated care among different services and subspecialties is vital to improving patient outcomes.