CAD Prevalent in Patients With Type 2 MI but Usually Non-obstructive

Recurrent cardiovascular events are common after type 2 myocardial infarction (T2MI). Still, patients are less likely than those with T1MI to be evaluated for coronary artery disease (CAD), undergo revascularization, or be discharged on secondary preventative therapies.

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In a prospective study, Massachusetts General Hospital researchers have found that coronary artery plaque is prevalent among patients with T2MI, but most lesions do not produce hemodynamically significant focal stenosis. The mediators of ischemia in these patients are probably multifactorial, they conclude.

Cian P. McCarthy, MD, cardiologist and researcher in the Corrigan Minehan Heart Center at Mass General, James L. Januzzi, Jr, MD, cardiologist and director of the Dennis and Marilyn Barry Fellowship in Cardiology Research at the Center, and colleagues detail the findings and their implications for management in the Journal of the American College of Cardiology.

Methods

The DEFINE TYPE 2 MI trial, conducted at Mass General, identified eligible patients with T2MI between April 2021 and February 2023. Amenable patients were consecutively enrolled until the target was reached of 50 adults with T2MI who had interpretable results from coronary CT angiography (CCTA) with derivation of the fraction flow reserve (FFR_CT).

Obstructive CAD was defined as ≥70% stenosis in any epicardial vessel except the left main coronary artery, where ≥50% stenosis was considered obstructive. Hemodynamically significant focal stenosis was defined as FFR_CT ≤0.80 1 to 2 cm distal to a stenosis or an occluded vessel.

Coronary Artery Stenosis

10% of patients had a prior diagnosis of CAD but none had a known history of obstructive CAD. Findings from CCTA significantly increased the diagnosis of CAD:

• 92% of patients had stenosis of ≥1 artery (P<0.0001 vs. the prior figure of 10%)
• 42% of patients had ≥1 artery with stenosis ≥50%
• 26% of patients had obstructive CAD (1 vessel, 12%; 2 vessels, 2%; 3 vessels, 12%)
• 6% of patients had severe (≥50%) stenosis of the left main artery

There were no significant differences in the prevalence of obstructive CAD according to cause of T2MI.

Coronary Artery Plaque Characteristics

The median total coronary plaque volume was 257 mm³. Most of the plaque volume (median, 82%) consisted of noncalcified plaque, which is associated with higher risk of future cardiovascular events.

Ischemia According to FFR_CT

21 patients had ≥50% stenosis of potential hemodynamic significance. However, FFR_CT excluded a lesion-specific hemodynamic stenosis (i.e., ischemic potential) in eight (38%), yielding 26% of all patients with a focal stenosis of hemodynamic significance.

This suggests the mediators of ischemia in T2MI are multifactorial. They might include diffuse plaque impeding coronary flow, microvascular ischemia, and the V/M relationship (ratio of total epicardial coronary artery lumen volume to left ventricular myocardial mass).

Insights for Patient Management

Confirmation of these findings in wider studies would support more routine use of aspirin and lipid-lowering therapy among patients with T2MI. In those being considered for revascularization, a noninvasive test such as CCTA with FFR_CT may be the preferable first-line imaging, since most patients do not have obstructive CAD.

CCTA permits the identification of nonobstructive coronary plaque and the exclusion of severe left main coronary artery stenosis. However, if the diagnosis of T1MI versus T2MI is uncertain, invasive coronary angiography is advised, because it permits intravascular imaging to assess for plaque rupture, erosion and thrombus.

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