The Dilemma of dissection: JACC review summarizes "clinical pearls" of SCAD diagnosis.

Spontaneous coronary artery dissection (SCAD) is a pathophysiologically distinct cause of acute coronary syndromes (ACS). A recent JACC  review focusses on addressing the diagnostic pitfalls of SCAD from its mimickers like atherosclerosis, Takotsubo cardiomyopathy, etc. as a valuable clinical guide to cardiologists. This article by Adlam et al discusses the benefits and limitations of intracoronary imaging in the context of SCAD. Finally, the authors discuss the investigation of ambiguous cases and present an approach to minimize misdiagnosis in difficult cases.

History is (almost) everything!!

Accurate diagnosis is critical, as management of SCAD differs compared with that for ACS of atherosclerotic etiology both in the cardiac catheterization laboratory and afterward.

Before the patient arrives in the cardiac catheterization laboratory, there are a number of characteristics that influence the pretest probability of SCAD:

1. Almost all patients present with an acute coronary syndrome (ACS). Thus, a chronic history of angina essentially rules out SCAD.

2. 90% of SCAD cases reportedly occur in women between 47 and 53 years of age. SCAD is unlikely at extremes of age.

3. SCAD has been reported as the cause of up to 35% of ACS events in women younger than 50 years and 23% to 68% of pregnancy-associated ACS.

4. SCAD is relatively rare in males.

5. In some patients, potential trigger exposures have been identified, such as emotional or physical stressors.

The golden picks on angiography:

1. SCAD occurs most commonly in the left anterior descending coronary artery (LAD) and in mid to distal coronary segments.

2. Yip-Saw classification (Figure 1) was developed to aid in diagnostic pattern recognition of SCAD and divides angiographic features into 3 types:

a. Type 1 SCAD where contrast penetrates into the false lumen(s), giving a dual-lumen appearance.

b. Type 2 SCAD : the most common appearance characterized by a long smooth stenosis.

Type 2a: there is restoration of a normal vessel distal to the dissection, often with the tightest stenosis at the distal extent of the false lumen.

Type 2b:  the narrowing continues into the most distal angiographically visible segments.

c. Type 3 SCAD is described as a lesion that mimics the appearances of focal atherosclerotic disease and cannot be definitively determined as SCAD on angiographic images.

d. A recent addition is type 4: defined as vessel occlusions that do not meet the criteria for types 1 to 3.

3. Extensive atheroma on angiography is correspondingly rare in SCAD.

4. Increased tortuosity in coronaries favour SCAD.

5. Intramural hematoma in patients with SCAD is frequently bounded at its proximal and distal extent by branch points while atherosclerotic lesions have a predisposition to branching points.

6. Luminal thrombus is an uncommon feature in SCAD.

Intracoronary Imaging: Use and Limitations:

When angiography alone leaves uncertainty, intracoronary imaging is frequently helpful. IVUS has the theoretical advantages over OCT of greater depth penetration and avoidance of the need for blood clearance by high-pressure injection for imaging.

Typical IVUS features of SCAD, in particular, the triple band (white-black-white) of the intimal-medial membrane is pathognomonic of SCAD. But lower resolution with IVUS entails difficulty in differentiating from lipid rich atheroma. In such circumstances OCT is very helpful.

Work-up beyond angiography:

SCAD has a strong association with extracoronary arteriopathies, particularly fibromuscular dysplasia (FMD), which occurs in at least one third of patients. Brain-to-pelvis cross-sectional imaging to screen for coexistent aneurysm, extracoronary dissection, or FMD is currently recommended.

A unified approach to SCAD:

Most SCAD can be confidently diagnosed angiographically, and for these patients further investigations beyond extracoronary arteriopathy screening and an assessment of left ventricular function are unnecessary.

A suggested approach to investigations for different angiographic scenarios is shown in Figure 2.

Source: JACC Cardiovascular Interventions: J Am Coll Cardiol Intv. 2021 Aug, 14 (16) 1743–1756