SPONTANEOUS CORONARY ARTERY DISSECTION

Background Spontaneous coronary artery dissection (SCAD) is a rare cause of acute coronary syndrome (ACS), mainly affecting fairly young otherwise healthy and predominantly but not exclusively female patients1,2. The underlying pathophysiology is unknown and although anecdotal associations have been reported, until recently there has been little systematic data on the presentation, management and outcomes of patients with this condition. A recent international collaboration between UK/EU researchers (http://scad.lcbru.le.ac.uk/) and US partners at the Mayo Clinic (http://www.mayoclinic.org/spontaneous-coronary-artery-dissection/) has been developed to study a sizeable cohort of patients with a view to a better understanding of all aspects of this condition. This research programme is actively seeking to recruit incident and prevalent cases of SCAD (via the web-portals above).

Pathogenesis
The pathogenesis of SCAD is unknown. The condition is characterised by the development of an intramural haematoma that usually runs in the outer media or between the media and adventitia of the coronary artery, resulting in haemodynamic compromise due to the resulting external compression on the lumen3.
Although coronary dissection can occur in patients with atherosclerotic coronary disease, there is a distinct population where dissection occurs in the absence of co-existent atherosclerosis and therefore is truly ‘spontaneous’4. A dissection flap is frequently not present even on intracoronary imaging suggesting in some cases at least, the pathological mechanism may be spontaneous intramural haematoma formation rather than true dissection. A number of potential risk factors have been anecdotally reported. In addition to female sex hormones, these include increased shear stress (such as after exercise), connective tissue disorders disorders (including Marfan and Ehlers-Danlos syndromes) and cocaine use5.

Epidemiology
SCAD is a rare condition reported in 0.2% - 1.1% of patients undergoing coronary angiography. However interpretation of these figures is complicated by the variable inclusion of atherosclerotic plaque associated dissection which is not ’true’ SCAD.  The condition affects predominantly young adult patients with mean age of 30-45 years at presentation.   At least 70% of SCAD cases are women and 26 - 38% of cases occur in late pregnancy, peripartum or postpartum.  The reported incidence of involvement for the left anterior descending coronary artery (LAD) is 57-75%; the right coronary artery (RCA), 20-32%; the left circumflex (LCx) 4-21% and the left main (LM), <1-21%6, 7. Multi-vessel SCAD is rare but have been reported.

Clinical Presentation
The clinical presentation of SCAD depends on the site and extent of the coronary dissection and the degree of restriction of coronary blood flow.  It is possible some dissections may be asymptomatic. Most clinically evident SCAD events present with acute chest pain syndromes ranging from unstable angina (7%), non ST-elevation myocardial infarction (NSTEMI – 44%) to ST-elevation myocardial infarction (49%)6.  In some patients myocardial ischaemia leads to ventricular arrhythmias and sudden cardiac death.  In autopsy series the prevalence of SCAD in deaths in pregnancy complicated with myocardial infarction has been reported as 27%8.

Diagnosis
Diagnosis is invariably made at coronary angiography. Although patients may present with clear angiographic evidence of a dissection flap and extending spiral false lumen, these features are frequently absent. Angiographic misdiagnosis may be common and a low index of suspicion is recommended, particularly in patients presenting acutely at low risk of atherosclerotic coronary disease. Diagnosis can frequently be confirmed by intracoronary imaging (e.g. with intravascular ultrasound or optical coherence tomography)9. CT coronary angiography has also been described in cases of SCAD.

Figure: Angiographic appearance of spontaneous coronary artery dissection of the left anterior descending coronary artery causing luminal restriction (arrows) (A). Optical Coherence Tomography (OCT- catheter C) of dissection with true lumen (TL) and false lumen (FL) (B and C).

Prognosis
In-hospital mortality of SCAD is relatively low, with a mean rate of around 3% (0-4%)6. Patients who survive the acute phase were initially thought to have good long- term prognosis, with a very low recurrence rate of SCAD or acute coronary syndrome and a 95% 2 year survival rate. However a recent series has suggested the longer term outlook may not be benign with recurrent SCAD in 17% (median follow-up 47 months) and an estimated 10-year MACE of 47%6. It is currently unknown in SCAD patients are at risk of other non-coronary events although an increased prevalence of femoral fibromuscular dysplasia has been reported, suggesting the arteriopathy in SCAD may not be localised5,6.

Conclusions
Spontaneous coronary artery dissection (SCAD) is a rare cause of acute coronary syndromes and as such, although many cases are described, there remains little reliable information on the epidemiology, optimal clinical and interventional management and outcomes of this condition. There has been little systematic research to date into SCAD, although a current international collaboration seeks to systematically address some of the key questions about this condition.

References