Spontaneous Coronary Artery Dissection: Time for a Concerted Effort to Better Understand This Rare Condition

Spontaneous coronary artery dissection (SCAD) is a challenge for the interventional cardiologist. Not least because it occurs so rarely that even someone with a large clinical practice will only see a small number of cases, and in addition, the presentation and angiographic findings may be extremely heterogeneous. One of the important issues is that the natural history of coronary dissection is poorly understood. Dependent on the extent and distribution of the dissection, some patients present acutely unwell with chest pain, changes on the electrocardiogram and hemodynamic compromise, or the diagnosis is only made at post-mortem examination. Other patients may present in relatively stable condition with a comparatively localized dissection of one coronary vessel, and have an uncomplicated course. There is, however, a risk of sudden acute deterioration due to either extension of the dissection and/or the development of dissection elsewhere in the coronary tree which may occur entirely unpredictably with no data available to identify factors predictive of such decline. Some patients who present with an ST-elevation acute myocardial infarction may (at least initially) respond well to thrombolysis,^1,2 and a high index of suspicion is needed, particularly in those at most risk of SCAD, to ensure coronary angiography is performed promptly and the diagnosis made. An accurate knowledge of the true prevalence of SCAD and its relationship to factors such as ethnicity is unknown; however, it is estimated to account for between 0.1 and 0.28% of all patients with acute coronary syndrome or sudden cardiac death.3 There are, however, a number of well-described associated risk factors, in particular, female gender, during pregnancy or the early post-partum period, oral contraceptive use, heavy exertion, chest trauma, collagen disorders, and drug use, particularly cocaine and methamphetamine. ^3–6 In this issue of the Journal, Shamloo et al⁷ have reviewed the published data on SCAD with the aim of trying to consolidate all the available information. In particular, they have evaluated the potential difference in outcomes dependent on whether patients have been treated with revascularization or medical therapy alone. They found that of those patients who reached the hospital, approximately half included in published reports were managed aggressively with revascularization, a figure that is consistent with the preliminary results of the DISCOVERY study (DISsection of COronary Arteries: Veneto and Emilia RegistrY), where 46% of the 42 consecutive patients with SCAD were treated with revascularization. ⁸ This ongoing multicenter registry will include 50 consecutive patients with SCAD and, for the first time, provide detailed prospective data. ³ The report by Shamloo et al also identified that early intervention following diagnosis had a better outcome and less need for further intervention as compared with a conservative watchful-waiting approach to management. ⁷ However, it is important to understand that these two groups of patients are unlikely to be comparable, as the choice of treatment strategy will be clearly influenced by both the patient characteristics and presentation, and the angiographic findings and extent of dissection. What the report does indicate is that if a conservative strategy is chosen, the patient should be closely monitored for any deterioration in status, particularly in the first few days after presentation, with a low threshold for performing repeat angiography with a view to undertaking revascularization. The need for revascularization in patients initially managed conservatively was relatively high at 21%. As these patients often deteriorate acutely, this makes a strong argument for the transfer of these patients to a specialized cardiac center if the diagnosis was made on angiography performed at a unit without on-site angioplasty (PCI) and coronary artery bypass graft surgery (CABG) facilities. Detailed information on the etiology and pathogenesis of SCAD remains somewhat limited, though autopsy studies have demonstrated eosinophilic infiltration and cystic medial necrosis in one-third. ⁷ The high incidence of SCAD occurring in the peripartum period raises the possibility of the role of hormonal changes that may weaken the arterial wall, thereby predisposing it to dissection. Other possible influences include increased hemodynamic stress such as may occur in the last trimester of pregnancy or during heavy exertion. Further research is needed to gain an increased understanding of the processes involved in SCAD, as this may help facilitate improved risk stratification. This, in turn, may enable identification of those most likely to remain stable and therefore be managed safely with medical therapy alone. In accordance with other rare conditions, the problem faced in understanding this condition is that the majority of existing data are based on sporadic case reports. Such a reliance on anecdotal reports has clear limitations due to the inherent bias of the available information. Indeed, the details of perhaps the majority of patients with SCAD are not in the public domain — each of us will have an anecdotal story or two of a patient with SCAD, but most of us will not write up the case report. In particular, if a patient is managed medically and has an uncomplicated course of treatment, then perhaps this is deemed not to be of interest for publication. On the contrary, information on such “benign” cases is extremely important to provide a comprehensive understanding of SCAD. To avoid such bias, what is needed is a comprehensive large, multicenter, prospective study of a consecutive group of SCAD patients along the lines of the DISCOVERY study. ³ The angiographic features seen in SCAD may be extremely heterogeneous and so caution must be exercised before making a recommendation for undertaking a revascularization strategy from the outset in all cases. Indeed, there have clearly been cases that have been managed successfully with medical therapy alone. ^4,8,10 No data exist as to what optimal medical therapy should entail. In the acute setting, thrombolysis may improve the clinical state of the patient, as it is thought to restore blood flow to the distal vessel by lysing the associated blood clot compressing the true lumen. ^1,2 However, in other studies, lysis has been thought to be detrimental, as it may be associated with proliferation of the dissection. ¹¹ The majority of patients do not have any evidence of associated atherosclerosis. Theoretically, however, beta-blockers should play a role in reducing the risk of extension of the dissection by lowering the heart rate and reducing the shear stress on the vasculature. In addition, the use of antiplatelet agents such as aspirin and clopidogrel will reduce the risk of thrombus formation/propagation. Such medication has been used successfully in several patients with SCAD, with follow-up angiography demonstrating complete angiographic resolution. ^10,11 Revascularization is not without its difficulties. With PCI, the true lumen of the vessel may be difficult to wire, particularly when the dissection involves the ostium of the left main stem or right coronary artery. To achieve a good angiographic result, the interventionist may be drawn into performing stent implantation to cover the entire length of the dissection. Theoretically, this is not necessarily mandatory, but there is very little clinical experience of undertaking a “spot stenting”-type approach to tack down the split and prevent further propagation of the dissection. Deployment of a “full metal jacket” of stents may be complicated by a relatively high risk of restenosis and need for target lesion revascularization (TLR), even in the era of drug-eluting stents. A recent paper by Sharp et al of 617 consecutive patients treated for 658 long (≥ 60 mm) lesions demonstrated a TLR rate of 23% at a median follow up of 39 months. ¹² As described in one case report of a SCAD patient, such a long stented length may also be associated with stent fracture, ¹³ which has the potential for major adverse clinical events. In addition, if the entire length of the vessel is stented, this may lead to the loss of blood flow into major side branches, resulting in periprocedural myocardial infarction, and will also inevitably limit the possibility of performing CABG, as there is no longer a sizeable distal vessel suitable for graft insertion. A strategy of PCI is therefore perhaps best limited to those patients with a relatively localized dissection, with consideration of CABG in those with more extensive or multi-vessel involvement. Even CABG surgery may itself be challenging, as the patient may be extremely unstable, and it is not always easy to identify the true lumen of the vessel. Surgery is less likely to be effective if the dissection involves the very distal vessel. Bearing in mind the complications associated with revascularization in these patients, there are potential benefits of recommending a treatment strategy of medical therapy alone, even if this is only suitable in a minority. This is, however, a difficult dilemma, as all too often, these patients present out-of-hours where there is less possibility for discussion with other colleagues. Particularly for those of us trained in the era of stent implantation, if we identify coronary dissection on angiography, it seems almost a reflex reaction to ask for the guiding catheter and reach for the stent(s) to improve the angiographic appearance. However, for those patients who are stable, a strategy of watchful waiting and close observation may not necessarily be an unreasonable one. In summary, therefore, the paper by Shamloo et al is a useful summary of all the available data in this difficult population. Definitive information as to the best strategy for managing these patients is not possible due to the heterogeneity of the population and it is not appropriate to perform a randomized study to compare medical therapy with revascularization. Though the literature is predominantly in the form of case reports, our future practice can be guided by the experiences of others. Each new case should be evaluated on an individual basis and the decision regarding therapy based on the stability of the patient and the extent of dissection/suitability for revascularization. Importantly, there is a real need for additional information to gain a better understanding of the pathogenesis of SCAD, and detailed clinical information from a large-scale registry may shed additional light on the optimal management of this group of patients.

References

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______________________________________________________________________ From the Cardiology Department, Castle Hill Hospital, Kingston-upon-Hull, United Kingdom. The author reports no conflicts of interest related to the content herein. Address for correspondence: Angela Hoye, MB ChB, PhD, Consultant Cardiologist, Cardiology Department, Castle Hill Hospital, Kingston-upon-Hull, HU16 5JQ United Kingdom. E-mail: drhoye@yahoo.co.uk