By Michael H. Crawford, MD
Professor of Medicine, Lucy Stern Chair in Cardiology, University of California, San Francisco
SYNOPSIS: In an observational, single-center study of patients with type 2 myocardial infarction who underwent coronary computed tomography (CT) angiography, researchers reported fewer than half had a significant anatomic stenosis (50% or greater), but only 26% had a hemodynamically significant lesion by CT fractional flow reserve.
SOURCE: McCarthy CP, Bao SM, Murphy SP, et al. Coronary computed tomographic angiography with fractional flow reserve in patients with type 2 myocardial infarction. J Am Coll Cardiol 2023; Sep 18: S0735-1097(23)06469-0. doi: 10.1016/j.jacc.2023.08.020. [Online ahead of print].
Although known to be associated with a high rate of subsequent cardiovascular events (CVE), little is known about the frequency and extent of coronary artery disease (CAD) in type 2 myocardial infarction (T2MI) patients. Investigators conducted a single-center, observational study: Defining the Prevalence and Characteristics of Coronary Artery Disease Among Patients with Type 2 Myocardial Infarction using CT-FFR (DEFINE TYPE2 MI).
McCarthy et al defined T2MI as a rise in troponin to higher than the 99th percentile, precipitated by a medical condition or following a procedure associated with an imbalance between myocardial supply and demand, and with either myocardial ischemia symptoms or signs, such as electrocardiogram (ECG) changes, new regional wall motion abnormalities on cardiac imaging, or new fixed myocardial perfusion defects on perfusion imaging. The authors excluded unstable patients, those with contraindications to computed tomography angiography (CTA), and patients who had undergone coronary bypass surgery or recent percutaneous coronary procedures.
The CT data collected included coronary artery calcium score (CAC) and fractional flow reserve (FFR). Researchers defined obstructive CAD as 70% or more in any distal coronary artery and 50% or more in the left main coronary artery. Investigators defined a hemodynamically significant stenosis as an FFR 0.80 or less. Between 2021 and 2023, among the 305 patients with T2MI who met the inclusion criteria, 56 enrolled in the study, 50 of whom were with adequate CTA for analysis. The mean age was 68 years, 50% were women, and 84% were white. CAD risk factors were common, but only 10% had known CAD, which was nonobstructive. The precipitating event for T2MI in these patients was arrhythmias in 36%, hypoxic respiratory failure in 22%, hypertension urgency in 12%, and a procedure in 12%. Ischemic ECG changes were noted in 90%, and 10% demonstrated new regional wall motion abnormalities.
A CAC score higher than 0 was found in 90%, with a median score of 168 Agatston units. On CTA, at least one lesion of 50% or more severity was found in 42% of patients, 70% or more in 26% of patients, and a left main lesion 50% or more in 6% of patients. Of the 21 patients with 50% or more lesions, FFR demonstrated a hemodynamically significant lesion in 13 patients (26% of the total population). Among all participants, only 14% underwent invasive angiography, and 8% underwent a subsequent revascularization. The authors concluded CAD was prevalent in T2MI patients. However, in the majority, it was nonobstructive.
COMMENTARY
Because of the reported high prevalence of subsequent CVE in patients who experience T2MI in the hospital, it has been recommended that most of these patients should undergo testing for CAD after they have recovered from their illness or procedure that occasioned hospitalization, usually as an outpatient. The authors of retrospective studies have documented a wide variation in the prevalence of obstructive CAD in T2MI patients, but many of these studies employed invasive angiography and may have suffered from selection biases.1,2 Thus, the DEFINE TYPE2 MI study is of interest.
McCarthy et al have shown almost all T2MI patients have CAD by CTA, despite the lack of CAD history. However, only about one-quarter of T2MI patients exhibited obstructive lesions by CTA or FFR. This suggests the reason for troponin elevations in T2MI patients likely is multifactorial. Deciding on appropriate management is complex. Obvious contributing factors, such as hypotension, tachycardia, blood loss, and sepsis, must be corrected, but beyond the obvious what should the clinician do? Since there is a high likelihood of CAD in these patients, starting aspirin and statins seems reasonable. That was the course of action for many patients in this study. Also, it would be reasonable to perform a subsequent noninvasive test for CAD in most and an invasive assessment in a selected few.
Although DEFINE TYPE2 MI was prospective, which will reduce bias compared to retrospective studies, bias was not eliminated. Also, of the 305 patients meeting enrollment criteria, only 56 were enrolled for a variety of reasons. There were uninterpretable CTAs for six patients, resulting in a final cohort of one out of six eligible patients. This may have influenced the results, but it is not certain in what way. In addition, the decision to prescribe drugs or more tests may have happened for reasons other than the CTA results. Finally, the study emphasized the value of CTA, especially with FFR in T2MI patients, but other noninvasive tests may be more suitable in specific patients. The timing of any further testing after T2MI is unclear and not specifically addressed in the DEFINE TYPE2 MI study, but presumably will be as soon as clinically feasible and safe. In DEFINE TYPE2 MI, the only observed adverse event from CTA was mild acute kidney injury in two patients.
REFERENCES
- Sandoval Y, Thygesen K. Myocardial infarction type 2 and myocardial injury. Clin Chem 2017;63:101-107.
- Gaggin HK, Liu Y, Lyass A, et al. Incident type 2 myocardial infarction in a cohort of patients undergoing coronary or peripheral arterial angiography. Circulation 2017;135:116-127.
