Learning objective
Not all acute myocardial infarctions are due to atherosclerotic disease. There are other mechanisms, such as those related to epicardial vasculature, like spontaneous coronary artery dissection, although they are not frequent and less likely to recur. Having reproducible and reliable imaging studies allows adequate classification of patients in order to provide appropriate prognosis and follow-up.
Introduction
Spontaneous coronary dissection (SCAD) is defined as the separation of the layers of the wall of an epicardial coronary artery due to intramural hemorrhage (IMH), not related to atherosclerosis, iatrogenic injury, or trauma, and can lead to acute coronary syndrome (ACS), arrhythmias, cardiomyopathy, and sudden cardiac death (1,2). Intramural hemorrhage causes compression of the lumen and subsequent ischemia of the distal myocardium; IMH can occur due to disruption of the intimal layer as an initial change or due to rupture of the vasa vasorum. Conventional coronary angiography (CA) is the diagnostic method of choice, but the use of intravascular imaging studies such as intravascular ultrasound (IVUS) or optical coherence tomography (OCT) and occasionally coronary computed tomography angiography (CCTA) also allows for precise diagnosis and follow-up strategy. Conservative management is typically preferred, as long as there is no ongoing ischemia or hemodynamic instability. Recurrent-SCAD (R-SCAD) is an infrequent entity, however, identifying it is important for both epidemiological and therapeutic purposes.
Case report
48-year-old Hispanic woman presented to the emergency department (ED) with 10 hours of anginal chest pain. She denied any comorbidities. On arrival, her vital signs were stable and physical examination was unremarkable. However, the 12-lead electrocardiogram showed symmetrical inverted T-waves in precordial leads, compatible with Wellens type B pattern (Figure 1 A). Initial laboratory tests showed high-sensitivity troponin of 5808 ng/mL and NT-proBNP of 304 pg/mL. After diagnosis of non-ST elevation acute myocardial infarction (NSTEMI), dual antiplatelet therapy (DAPT) consisting of aspirin and clopidogrel, high-intensity statin (atorvastatin 80 mg), and enoxaparin 1mg/kg subcutaneously two times a day was initiated. An early CA (Figure 1 B andFigure 1 C) revealed an abrupt diameter reduction in the mid-segment of the left anterior descending artery (LAD), suggestive of hematoma secondary to type 2 SCAD. However, intravascular imaging could not be performed due to significant narrowing. CCTA examination (Figure 2 A andFigure 2 B) confirmed type 2 SCAD with 48 mm length and lumen reduction of 60-70% in the mid and distal segments of LAD, in addition to a calcium score of 0 UA. Transthoracic echocardiography showed left ventricular (LV) concentric hypertrophy, LV mass of 139 g/m2 and relative wall thickness of 0.43, preserved LV ejection fraction (55%), apex dyskinesia, and anterior and septal apical akinesia, congruent with the culprit artery. Additional blood tests revealed LDL 1.6 mmol/L, total cholesterol 2.72 mmol/L, and HDL 0.58 mmol/L. The patient was treated with enalapril 10 mg two times a day and bisoprolol 5 mg once a day, and was discharged after five days.
However, one month later, the patient developed anginal chest pain once again, and her blood pressure was 160/90 mmHg upon arrival. A new 12-lead electrocardiogram showed no changes compared with the previous one. Nevertheless, a dynamic change of cardiac troponin was recorded, and the patient was once again diagnosed with NSTEMI. A new CCTA showed LAD type 2 SCAD extension from the previous 48 mm to 60 mm (Figure 2 C). Since no angina or hemodynamic instability was observed, optimal medical therapy was selected. Computed angio-tomography performed to investigate for fibromuscular dysplasia (FMD) (Figure 3) was reported as normal. The patient underwent ambulatory monitoring, with a benevolent evolution.
Discussion
SCAD is no longer considered a rare and understudied disease; it has an estimated prevalence of 0.78-0.98%, and up to 1-4% of all ACS cases are secondary to this condition (3). Up to 90% of SCAD cases occur in women <65 years of age (1,4,5). Risk factors include young age, physical and emotional stressors, and inflammatory and connective tissue disease (1). Therefore, the typical profile is that of a middle-aged woman, with a low cardiovascular risk burden presenting with ACS, classified as type 2 according to the 4th universal definition of myocardial infarction (6). While the vast majority of patients are white women, it has been shown that outcomes are similar in Hispanic and African American female patients (4). The interaction between different circumstances such as emotional stress, intense exercise and hormonal status (i.e., pregnancy) might predispose towards SCAD development (3,4). Remarkably, systemic hypertension is present in up to 45% of SCAD cases (4), as in our patient.
CA is the gold standard for SCAD, however, lesions can be difficult to spot, and a revision by an experienced interventional cardiologist is therefore recommended, if feasible. SCAD usually affects the mid to distal segments of the LAD, with a diffuse narrowing and regular borders, i.e., type 2 according to the Yip-Saw classification; as in our patient. Additionally, the presence of IMH with severe stenosis of >80% predisposes to greater clinical deterioration if treated conservatively (4). Furthermore, the use of intravascular imaging (IVUS and OCT) may be helpful for differential diagnosis and possible interventional treatment (3,4). Although not yet standardized, the use of CCTA has been found to be useful for both diagnosis and follow-up.
Treatment options are similar to ACS. However, the use of thrombolytics during the acute phase is not recommended due to reported negative effects (4). Up to a third of IMH propagate just after manipulation during percutaneous coronary intervention (PCI), and thus conservative treatment is preferred as long as there is no hemodynamic instability, total occlusion, or recurrent ischemia (3,4,7). It has been observed that up to 95% of patients treated conservatively will present angiographic healing after 30 days (3,4). Medical treatment is recommended for symptomatic management and secondary prevention. If stent placement took place, DAPT is clearly justified, however, there is still no consensus for cases with conservative management as in our patient. Some authors advocate following the same strategy as a classic ACS, advising long-term aspirin monotherapy (2,3). Ventricular arrhythmias or mechanical circulatory support have been described in 6-11% of cases (4), but fortunately our patient did not develop them, due to their association with poor outcomes.
R-SCAD rates ranges from 17% to 27% during the first 30 days and up to 27% in the following 4-5 years (1,6). Female patients may account for up to 74-100% of cases (6). Saraswat et al. (7) reported a series of SCAD cases in a university hospital in Australia, which found a 25% recurrence rate, of which 36% had type 2 R-SCAD mainly affecting the LAD territory, which resembles our patient. However, Tweet et al. (8) reported that while index SCAD usually occurs in the LAD, recurrences appeared in the marginal obtuse artery as well as posterolateral artery. Additionally, the presence of IHM, severity of the lesion, and multivessel involvement all predispose to R-SCAD (3).
Although a relationship has been observed between hormonal states such as pregnancy and the occurrence of SCAD, hormone replacement therapy has not demonstrated to be effective to prevent it (4). Beta-blocker therapy is the only pharmacological strategy proven to ameliorate recurrence risk (3,9). Statins have not yet been validated and are therefore not routinely recommended. In this case, recurrence was observed despite implementation of beta-blocker therapy, but it should be noted that the antihypertensive treatment was not as effective as demonstrated at discharge and that another preventive effective measure, cardiac rehabilitation (9), was not employed. Diagnostic workup for any arteriopathy is prudent, as it may be the first manifestation (4), especially in R-SCAD, since up to 68% are ultimately diagnosed with FMD (3) and, albeit not as frequent, also with Takayasu arteritis. Long-term follow-up is advised, with a mortality rate around 0-5% during the first 5 years (4).
Conclusion
SCAD is a non-common but relevant cause of acute myocardial infarction. In addition to the classic population group, it should be considered in any situation with coronary artery abnormalities and no evidence of atherosclerotic disease. A comprehensive clinical approach and adequate implementation of treatment and prevention are key to limiting its recurrence and also providing a successful recovery.