Coronary blood flow in myocardial infarction with nonobstructive coronary arteries
Authors: Magnani I , Toniolo S , Rinaldi A , Paolisso P , D'Angelo E.C , Bergamaschi L , Bartoli L , Donati F , Angeli F , Foa' A , Pizzi C , Galie' N 
Published: November 2020

Abstract

Background
Myocardial infarction (MI) is mainly caused by atherosclerotic plaque thrombosis but several registries show that in 1–13% of cases MI occurs in the absence of obstructive coronary artery disease (MINOCA) utilizing the conventional cut-off of &lt;50% stenosis. MINOCA is generally related to coronary arteries abnormalities (epicardial or microvascular dysfunction – MINOCA-co). However, non-coronary conditions may underlie MINOCA as a consequence of supply-demand mismatch (MINOCA-nco). The TIMI flow gradient (TFG) and the corrected TIMI frame count (CTFC) are established methods able to respectively provide a qualitative and semiquantitative estimation of epicardial blood flow at rest. No studies have yet evaluated these indices in patients with MINOCA.

Purpose
To evaluate the clinical characteristics of patients with MINOCA and the angiographic indices in MINOCA-co versus MINOCA-nco.

Methods
Among all consecutive patients undergoing coronary angiogram at our Centre for MI based on the 4th Definition of Myocardial Infarction, the ones showing &lt;50% coronary artery stenosis were retrospectively analyzed; patients with previous coronary stenting were excluded from the study. According to the presence or absence of pre-specified criteria of supply-demand mismatch (SAP &gt;180 mmHg, DAP &gt;110 mmHg, HR &gt;110 bpm, Hb &lt;6 gr/dl, SatO2 &lt;91% or P/F ratio &lt;300), the study cohort was divided into MINOCA-nco and MINOCA-co, respectively. We defined as slow flow phenomenon a TFG &lt; = 2 and/or a CTFC &gt;40 for the left anterior descending artery, &gt;27 for the right coronary artery and &gt;24 for the left circumflex.

Results
453 patients were retrospectively evaluated and 112 (24.7%) met the inclusion criteria. Mean age was 68±13.2 years and 41 (36.6%) were males. MINOCA-co was the more prevalent entity accounting for 73 (65.2%) patients while 39 (34.8%) were MINOCA-nco. The two subgroups presented similar baseline characteristics with regards to gender and classic cardiovascular risk factors including hypertension, hypercholesterolemia, diabetes and smoking habit. Peripheral vasculopathy was more prevalent in MINOCA-nco patients (MINOCA-nco=15.4% vs. MINOCAco= 4.2%; p=0.04). Regarding the angiographic indices, there was no statistically significant difference in TFG between subgroups; conversely, the number of patients with a slow flow phenomenon as defined by CTFC was significantly higher in the MINOCA-nco group (MINOCAnco= 25.7% vs. MINOCA-co=9.8%; p=0.039).

Conclusions
Our data suggest that among patients with MINOCA clinical characteristics were not useful in differentiating between the two disease entities (MINOCA-nco vs. MINOCA-co). However, MINOCA-nco patients had higher coronary flow impairment as evaluated by CTFC. The pathophysiological reason is still not clear; we hypothesized that, in this clinical setting, an increased heart rate, systemic arterial pressure or low oxygen supply might worsen unbalanced coronary perfusion.

Funding Acknowledgement
Type of funding source: None