Management of Spontaneous Coronary Artery Dissection in the Primary Percutaneous Coronary Intervention Era
- Volume 22 - Issue 11 - November, 2010
- Posted on: 10/29/10
- 0 Comments
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ABSTRACT: Spontaneous coronary artery dissection (SCAD) is a rare cause of acute coronary syndromes. The increasing use of early angiography in the primary percutaneous coronary intervention (PPCI) era has led to earlier identification of patients with SCAD and may encourage an increased use of percutaneous revascularization strategies in this population. However, the pathophysiology of SCAD is distinct from the usually stenotic atherosclerotic plaque-rupture events responsible for most ST-elevation and non-ST-elevation myocardial infarctions, but our approach to managing these patients utilizes largely the same medical and revascularization therapies used in conventional acute coronary syndromes. This review examines the literature on SCAD and contemporary management issues.
Spontaneous coronary artery dissection (SCAD) is a rare cause of acute coronary syndromes. The increasing use of early angiography in the primary percutaneous coronary intervention (PPCI) era has led to earlier identification of patients with SCAD and may encourage an increased use of percutaneous revascularization strategies in this population. However, the pathophysiology of SCAD is distinct from the usually stenotic atherosclerotic plaque-rupture events responsible for most ST-elevation and non-ST- elevation myocardial infarctions, but our approach to managing these patients utilizes largely the same medical and revascularization therapies used in conventional acute coronary syndromes. This review examines the literature on SCAD and contemporary management issues.
Epidemiology and Pathophysiology
SCAD is characterized by the presence of blood or thrombus in a false lumen usually occurring in the outer third of the vessel media.1 This false lumen extends for a variable distance down the coronary artery and may be circumferential or take a spiral passage as it extends down and around the coronary lumen within the vessel wall. Compression of the coronary lumen by the false lumen or by a dissection flap may obstruct or restrict flow within the true lumen, causing myocardial ischemia or infarction (Figure 1). SCAD is reported to occur most commonly in the left anterior descending coronary artery.2–6 The population incidence is difficult to quantify, but is reported from angiographic series to be between 0.1 and 1.1%.2,5–7 Some cases are not diagnosed until post mortem, and angiographic appearances may be atypical and unrecognized unless there is a high index of clinical suspicion or use of intracoronary imaging (with intravascular ultrasound [IVUS] or optical coherence tomography [OCT]).
The initial pathophysiological events in SCAD are debated.8 Although the most obvious potential source is a bleed into the vessel wall from the lumen itself, it seems increasingly likely that the process is initiated in the media and adventitia. Hematoma within the wall of the vessel alters the tolerance of the endothelium to shear stress, resulting in an intimal tear. This process is akin to the process of intramural hematoma, which can precede aortic dissection. Patients can present with coronary hematoma alone with no evidence of an intimal flap. In these cases, the hematoma causes luminal compression, which may then limit antegrade flow.
SCAD affects a younger and predominantly female population,4–6,9,10 particularly in the peri- and postpartum periods9,11,12 (although the most common cause of acute coronary syndromes in pregnancy remains conventional atherosclerotic disease). There may be an association with situations of increased sheer stress such as after exercise13–15 or sneezing, in association with cocaine abuse16,17 or in high output states such as pregnancy, although there is no clear association with hypertension. SCAD has been described in association with heritable connective tissue disorders such as Marfan’s syndrome18 and Ehlers-Danlos syndrome.19 Inflammatory conditions including autoimmune connective tissue disorders and vasculitides20–22 may be associated and the presence of an eosinophilic infiltrate has been described in some idiopathic and peripartum cases23,24 although this is not a universal finding).25 Cystic medial necrosis has been reported in some postmortem cases of SCAD.1,26,27 It may be that either an inflammatory, a pregnancy related or a hereditary molecular abnormality contributes to a weakening of the integrity of the vessel wall and/or vasa vasorum increasing the risk of SCAD.
Management of Spontaneous Coronary Artery Dissection
Medical management. The optimal medical strategy in patients with SCAD is not clinically proven, leaving only anecdotal data and pragmatic advice. Most patients presenting with acute coronary syndromes are diagnosed angiographically and there is considerable anecdotal evidence that patients without ongoing ischemia, with thrombolysis in myocardial infarction (TIMI) 3 flow, and especially those with more distal vessel dissections can be stabilized and managed in the long term on medical therapy alone.28
Beta blockade reduces sheer stress and is clinically useful in treating aortic dissection and theoretically might be beneficial in SCAD. However, some beta blockers can promote coronary vasospasm with potential disadvantages, although this is probably not a class effect.29 The coronary hemodynamic effects of different beta blockers may also vary.30 There is no clear indication for thrombolysis, anticoagulation with heparin or glycoprotein IIb/IIIa inhibitors, with some reports of beneficial responses31–37 and some evidence of detrimental effects.38,39 The role of oral antiplatelet agents in the short- and long-term in patients not receiving stents is also unclear, with only anecdotal evidence of benefit.15,40
Interval angiography may show a complete resolution of the false lumen and angiographically normal coronary arteries.37,41 While recurrent dissection has been described, this is rare from the available published data,6 but a minority of patients managed conservatively may suffer an acute progression, usually within a few days of the index event.49
Percutaneous intervention. SCAD presents a number of particular challenges for percutaneous intervention and careful consideration on a case by case basis is necessary. Initially even further selective angiography can lead to deterioration as contrast injection can increase pressure in the false lumen. During intervention, the guidewire can easily enter the false lumen with the associated risk of extension or extravasation. Unlike atherosclerotic plaque, where the volume of any luminal lipid pool is usually small, in SCAD the luminal compression is due to extensive hematoma within the vessel wall. When extensive hematoma is present with no luminal flap and antegrade flow is preserved, stenting should probably be avoided, as stenting the angiographically evident area of stenosis may simply displace the compressive hematoma blood either proximally or distally to the stent (Figure 2). Long segments of stent may therefore be required to completely exclude the false lumen and restore the true lumen to its normal dimensions with TIMI 3 flow. An alternative strategy of stenting just the proximal end of the dissection, or targeting the presumed entry point of the hematoma identified by OCT or IVUS for stenting has been suggested. The aim would be to “seal the flap” and allow spontaneous healing of the remaining false lumen while limiting the overall stent length. However, there are no outcome data to support either the partial or “conventional” complete stenting strategies.
Coronary luminal imaging using IVUS42–44 or OCT45 may help guide PCI procedures for SCAD (Figure 3). This can resolve diagnostic uncertainty, for example, where there is no contrast penetration of the false lumen, and to identify clearly the extent of the false lumen with respect to anatomical landmarks. IVUS or OCT may help to ensure accurate guidewire placement in the true lumen (Figure 3B) and appropriate stent diameter, length and optimal deployment (Figure 3C). The necessity for ballooning or stenting can be reconsidered after imaging, as extensive stenting risks side-branch compromise, in-stent restenosis46 and stent fracture.47
The prevalence of in-stent restenosis in patients with SCAD is unknown, but the frequent need for long stented segments in SCAD has been used to justify the preferential use of drug-eluting stents (DES). However, the impact of DES on healing of a non-atheromatous vessel has not been assessed, nor has the impact of the longer duration of antiplatelet therapy required for DES. Thus, routine selection of DES in this young, predominantly female population is still controversial.
Surgical revascularization. Emergency coronary artery bypass grafting has been described in patients presenting with SCAD causing acute ischemia or cardiogenic shock. A surgical strategy is unlikely to be optimal unless there proximal dissection of multiple vessels with good distal target vessels or the percutaneous option has been abandoned (e.g., a total occlusion where the true lumen cannot be re-entered with a coronary guidewire).
Suggested management. There are no current guidelines for managing SCAD. Figure 4 describes our proposed algorithm for treatment of SCAD (Figure 4). In patients presenting with dissections in small-caliber distal vessels or side branches with TIMI 3 flow, conservative management is appropriate. Where SCAD involves large-caliber or major epicardial coronary vessels and flow is impaired with accompanying ischemia and electrocardiographic changes, revascularization is indicated. Where flow is not impaired, conservative management is optimal, and angiographic assessment should be limited to reduce the risk of iatrogenic deterioration.
Once a decision has been taken to attempt revascularization, the choice of revascularization strategy depends largely on anatomical and technical issues. If the left main stem is not involved and the dissection is limited to a single vessel, PCI would be favored if technically possible. PCI should ideally be performed with intracoronary imaging guidance (IVUS or OCT) and DES used if a long length of stent is anticipated. If PCI proves technically impossible (e.g., if the true lumen cannot be wired), the alternatives are surgical revascularization versus conservative management depending on the balance of risks of surgery and the size of myocardial territory under threat. If the left main stem is dissected or there is multivessel involvement but PCI is technically possible, this remains an option. PCI would particularly be favored in pregnancy, in cases where limited stent lengths would suffice or in an acute PPCI context where delays to surgical revascularization would be prohibitive. However, surgical revascularization is clearly an alternative that should be actively considered in these more complex cases.