Discussion
While previously thought to represent a rare condition, more recent studies have reported a SCAD incidence of up to 4% among patients presenting with ACS. The initial clinical presentation can vary from atypical angina to acute STEMI with cardiogenic shock and sudden cardiac death. Classic angiographic features of SCAD with clearly defined intimal tear or spiraling dissection may not be evident, especially if the coronary dissection is contained and limited to intramural hematoma. When SCAD is suspected, invasive imaging modalities such as IVUS and OCT is advocated, if they can be performed safely. There should be a high suspicion for SCAD in young patients without classic cardiovascular risk factors who present with ACS; however, SCAD may also present in middle-aged patients with cardiovascular risk factors.
No guidelines exist for the management of SCAD. It has been suggested that patients without ongoing ischemia, preserved coronary flow (TIMI-3), single vessel involvement, or distal vessel involvement may benefit from conservative medical management. However, these patients are at risk of progression of the dissection, retrograde extension, simultaneous involvement of other major epicardial vessels, and recurrent acute myocardial infarction. Age, anatomic features, extent of SCAD, and clinical presentation contribute to large variability in clinical outcomes, and mandate individualization of clinical decisions regarding optimal management in each patient. PCI in the setting of SCAD is associated with particular challenges. Identification of the true lumen during guidewire insertion may be difficult and can lead to extension and worsening of the dissection. Similarly, repeated injections of contrast dye through guide catheters can further propagate SCAD located in proximal sections of coronary arteries. Stent deployment in SCAD cases commonly leads to compression and propagation of the intramural hematoma, which can be associated with unpredictable antegrade and retrograde extensions of the coronary dissection. This often leads to placement of multiple overlapping long stents to preserve patency of the coronary lumen. Therefore, in patients who have preserved coronary flow beyond the site of dissection and extensive hematoma within the vessel wall, stenting should likely be avoided. It has been suggested to stent only the proximal portion of the dissection, or to target the presumed entry point of the hematoma as identified by OCT or IVUS, with the aim of sealing the flap/entry point and allowing the hematoma to heal. Late stent malapposition after healing of the SCAD is likely a common feature associated with PCI in the setting of SCAD and significantly increases the risk of late stent thrombosis.
CABG has been performed successfully in patients with SCAD, but carries its own specific technical challenges. Often, the lack of structural integrity of target vessels increases the difficulty in obtaining optimal anastomotic results. Similarly, decreased coronary run-off increases the risk of graft occlusion. CABG may be a suitable revascularization strategy when a flow-limiting dissection is localized in the proximal segment of a major epicardial vessel with intact distal target vessels for bypass.
The results of our study are consistent with findings from larger case series. Demographics and clinical features of our patient population were similar to those in larger studies by Saw et al and Tweet et al. The observed mean age of 42 years in our case series was close to the mean age reported in those larger study populations. All patients in our case series were female, compared with ~80% female gender prevalence in other studies. The most common condition associated with SCAD is peripartum state, which was reflected in our study as well. STEMI was the predominant clinical presentation, with the LAD being the most common culprit vessel, which is consistent with findings from previous studies.
Previous studies have indicated that patients managed conservatively may exhibit spontaneous healing of the dissection and favorable clinical outcomes. Of note in our study, one-half of the patients who were managed conservatively had recurrence of symptoms and worsening of the dissection within the same hospitalization. One of the 6 patients who was treated conservatively demonstrated extension of the LAD artery SCAD, resulting in retrograde involvement of left main and compromise of the LCX, resulting in fatal cardiogenic shock a few days after initial presentation. Another patient with multivessel SCAD, including an extensive dissection of the LAD, was managed medically and demonstrated resolution of the initial LAD dissection on repeat angiogram 2 days later. A third patient with recurrence of ischemia after 2 days underwent PCI with multiple overlapping stents in the LAD, which were found to be significantly malapposed and undersized on repeat angiography. The remaining 3 patients had only distal vessel involvement and the length of the dissection was also relatively short, which may be a predictor of favorable outcomes with conservative management.
Beta-blockers have been shown to be beneficial in reducing sheer stress in patients with aortic dissection and thus might be useful in the treatment of patients with SCAD. There is inconclusive evidence regarding the potential risk-benefit of anticoagulation with heparin or use of glycoprotein IIb/IIIa inhibitors. Anticoagulation may prevent the thrombosis related to exposure of subendothelial matrix and acute vessel closure, but also prevent thrombosis of the false lumen and theoretically promote bleeding from vasa vasorum with possible expansion of intramural hematoma. The role of antiplatelet therapy in the short term and long term in patients not being treated with PCI is also controversial.
We did not observe a correlation between SCAD and fibromuscular dysplasia, as described in recent studies. However, none of our patients underwent specific imaging tests to screen for fibromuscular dysplasia.
In our case series, survivors of the initial event demonstrated a favorable outcome. Previous studies have reported similar findings. In-hospital mortality has been reported to be 3% in larger series, but this may possibly be an underestimation. Patients who survive the acute phase have a low recurrence of SCAD and good prognosis, with a reported 2-year survival rate of around 95%. While SCAD is relatively common among young women in the peripartum period, it may also occur in middle-aged patients presenting with ACS. Early identification and appropriate rapid intervention with advanced hemodynamic support, such as left ventricular assist devices or extracorporeal membrane oxygenation, is advised in patients presenting with cardiogenic shock secondary to extensive SCAD.