This study leveraged the prospective Coronary Microvascular and Vasomotor Dysfunction (CMVD) registry at The Christ Hospital (TCH) in Cincinnati, Ohio, which operates under the approval of the TCH Institutional Review Board. Consecutive ANOCA patients who had ICFT performed between October 2020 and December 2023 with CFR assessment in both the proximal LAD and the proximal LCx were included in this analysis. Exclusion criteria were obstructive epicardial CAD (>50% stenosis or positive fractional flow reserve (FFR) <0.80), need for PCI at the time of procedure, or prior history of CABG. Of 289 patients screened, 17 were excluded due to obstructive CAD, 2 due to history of CABG, and 39 due to missing CFR in one or both vessels, resulting in 231 ANOCA patients in the final cohort.

All ICFT procedures at THC have been previously described in detail in a methods manuscript. All were performed as scheduled procedures and none were performed in the setting of acute coronary syndrome (ACS). After a diagnostic coronary angiogram, a Doppler-tipped guidewire (ComboWire XT ^TM or Flowire, Philips Volcano Corporation, San Diago, CA, USA) was advanced into the target vessel to assess CMD. The multivessel CFR assessment protocol was standard for all the ICFT procedures at TCH during the study years. The Doppler protocol included: 1) CMD assessment of CFR in the proximal LCx followed by the proximal LAD with intracoronary (IC) adenosine; 2) coronary endothelial dysfunction and epicardial spasm with IC acetylcholine (ACH); 3) followed by intracoronary nitroglycerin. ^,, Nitroglycerin was intentionally not given until after ACH testing to avoid impacting the assessment of epicardial spasm. In the very rare case of severe baseline epicardial spasm or severe catheter or wire induced spasm, IC nitroglycerin was administered and ACH testing was not performed.

For adenosine testing once the Doppler wire was positioned in the proximal target vessel and optimal flow signals achieved, the baseline average peak velocity (APV) was recorded. Steady-state hyperemia was achieved with intracoronary adenosine using 18 mcg and 100 mcg doses and hyperemia average peak velocity (APV) was recorded. After each adenosine administration there was adequate time for washout and return of APV to baseline prior to sequential adenosine test. CFR was calculated for each adenosine dose (18 mcg and 100 mcg) at each location (LCx and LAD). The highest CFR measured for each vessel was used as it represented true hyperemia. A CFR (≤ 2.5) in the LCx and/or LAD was diagnostic for CMD.

For ACH testing, IC infusions were delivered into the left main artery via the six French guide catheter using a micro-infusion pump and performed at different doses: safety-dose (5mcg infused at 0.75ml/min for 2.5min), mid‐dose (44mcg infused at 0.75 ml/min for 2.5 min), and high dose (108 mcg infused at 1.875 ml/min for 2.5 min) as previously described in detail. Baseline and peak APV were recorded for mid and high dose ACH in the proximal LAD. Following the procedure, coronary diameter change by quantitative coronary angiography (QCA) was performed in the proximal LAD, 5 mm from the tip of the guidewire at the same position at baseline and mid-dose ACH cine images. Coronary blood flow (CBF) was calculated based on the equation at baseline and mid-dose ACH: CBF = 0.5 x APV x (diameter ² x π)/4.

Continuous variables were summarized using means and standard deviations or median (Interquartile range (IQR)), and categorical variables as frequencies and percentages. Comparisons used t-test or Wilcoxon rank-sum test for continuous variables, and Chi-square or Fisher’s exact tests for categorical variables. McNemar’s test assessed the diagnostic performance of the multivessel (LAD and LCx) CMD assessment against the LAD assessment.

No extramural funding was used to support this work. The authors are solely responsible for the design and conduct of this study, all study analyses, the drafting and editing of the paper and its final contents.