Editorial: Spontaneous coronary artery dissection: Left-off clinical phenotype in acute coronary syndrome.

Spontaneous coronary artery dissection (SCAD) is an uncommon cause of acute coronary syndrome (ACS). However, SCAD is clinically important with a wide spectrum of clinical presentation. The prevalence of SCAD is 0.2%–0.7% in all angiographic series, but most SCAD patients present with ACS 1, 2. In particular, the clinical significance of SCAD should be emphasized in young women. It has been reported that 74%–98% of SCAD cases were in women 1, 2, 3, 4. Among women, prevalence of SCAD is higher in the younger generation compared to the elderly (1.2% in <70 year old, 2.1% in <60 year old, 4.0% in <50 year old, and 7.6% in <40 year old) [2]. The prevalence of SCAD increased up to 8.7% among female patients below 50 years of age with ACS, and reached 10.8% in those with ST elevation acute myocardial infarction [2]. It has been reported that SCAD occurs especially in peripartum or postpartum status; however, recent reports show that pregnancy is not closely related to SCAD. According to the report from the Mayo Clinic, only 13 of 71 women (18%) were postpartum [3]. Moreover, in the series of Saw et al. [4] only 1 of the 49 women was postpartum.

The etiology of SCAD is multifactorial. Pregnancy, postpartum, collagen disease, systemic inflammatory disease, fibromuscular dysplasia (FMD), vasospasm, and emotional stress are raised as the cause of SCAD. The changes in hormonal balance, hemodynamics, and arterial wall stress induced by increased intrathoracoabdominal pressure may well result in weakening of the media of coronary arteries. Borczuk et al. [5] observed an association between eosinophilic infiltration and peripartum SCAD in autopsies series; however, its potential role in SCAD is not well clarified. Recently, FMD has attracted considerable attention as a cause of SCAD. Saw et al. revealed that 86% of 50 nonatherosclerotic SCAD patients had FMD in noncoronary territory (58% in renal, 49% in iliac, and 47% in cerebrovascular) [4]. Tweet et al. [3] also observed iliac FMD in 50% of 16 patients with SCAD. Furthermore, Saw et al. reported four cases of SCAD with suspected coronary FMD, in whom prominent intimal-medial thickening was visualized with the use of optical coherence tomography (OCT) and intravascular ultrasound (IVUS) [6]. FMD in the peripheral arteries can progress to dissection, and thus, it seems reasonable to speculate that coronary FMD induces SCAD with the same mechanism.

SCAD consists of two phenotypes: (1) initiation of a medial dissection and hemorrhage by an intimal tear and creation of a false lumen; (2) an intramedial hemorrhage without an intimal tear causing a medial dissection, perhaps caused by rupture of the vasa vasorum 7, 8. The former case may appear with presence of coronary flow both in true lumen and pseudo-lumen separated by a radiolucent flap; however, it is not always possible to identify an intimal tear angiographically. The latter cases may present only smooth stenosis on coronary angiography as luminal compression by hematoma is not detectable only in angiography. Thus, the assessment solely with angiography tends to miss SCAD. IVUS [8] and OCT [9] are mandatory tools to diagnose SCAD especially when SCAD is angiographically inapparent. These modalities enable us to detect not only intracoronary dissection or intramural hematoma but also the entry point of the dissection and the longitudinal length of the lesion, both of which are useful information in coronary intervention.

In terms of the therapeutic strategy, there is no available guideline or recommendation to date. Treatment for SCAD should be chosen according to the clinical status and the severity of cardiac ischemia. Conservative strategy is the first line in patients without cardiac ischemia as hematoma and dissection heal spontaneously in most cases. Antiplatelet therapy, statins, and beta-blockers should be administered for the purpose of secondary prevention of the ACS. However, nitrate or calcium channel blocker rather than beta-blocker should be added if vasospasm is suspected. In cases with chest pain, ongoing cardiac ischemia or instability of cardiac status, revascularization should be considered. If extensive coronary dissections involve the left main coronary artery, left anterior descending coronary artery (LAD), and left circumflex coronary artery, emergent coronary artery bypass grafting (CABG) is likely recommended.

In this issue of the Journal, Yamanaga et al. reported three SCAD cases with ongoing ischemia who were treated with different therapeutic strategies: plain-old balloon angioplasty (POBA), stent implantation, or medical therapy [10]. As they mentioned in the report, PCI is feasible in cases with evident ischemia and diseased vessels suitable for PCI. Tips of PCI techniques in SCAD cases described in their paper are helpful for interventionists [10]. In the procedure of PCI, it is important to cross the guide wire in the true lumen and to cover the entry point of dissection completely. In the intramural hematoma cases, POBA and stent should be avoided if antegrade coronary flow is preserved, for fear of hematoma shift. When false lumen compresses the true lumen and disturbs coronary flow, POBA using long length balloon, as the authors chose, is appropriate [10]. PCI procedure for SCAD is difficult compared to the usual ACS cases due to atherosclerosis, and the success rate was only 65% according to previous literature [3]. Medical therapy should be considered in cases with lesions inadequate for PCI such as small vessel or distal lesion, because most SCAD lesions would be healed spontaneously.

Prognosis of SCAD is generally fair. According to the recent report by Ito et al. [11], 7 in 23 SCAD patients were postpartum. SCAD in postpartum involved more proximal coronary segments and LAD and was associated with higher peak troponin I levels, lower left ventricular ejection fraction, and more frequent congestive heart failure on presentation compared with nonpostpartum SCAD. However, all 23 SCAD patients were alive at 3 years follow-up [11]. Thus, postpartum SCAD tends to present poor cardiac status, but patients who survive the acute phase have a good long-term prognosis. Their survival rate in 2 years is 95% as previously reported 12, 13. Recurrence rate of SCAD is estimated as 10–30% 3, 7; therefore, careful monitoring is necessary. In cases with suspected vasospasm, it appears to be important to administer nitrate or calcium channel blocker to prevent recurrence of SCAD as Yamanaga et al. [10] described.

Incidence, pathology, optimal treatment, and prognosis of SCAD are not well clarified so far. The DISCOVERY study [14], the first prospective registry of SCAD, is ongoing in Italy which will be the milestone for further understanding of SCAD.