Evaluation of the localization of coronary microvascular dysfunction in obstructive hypertrophic cardiomyopathy and the therapeutic effects of alcohol septal ablation
T Terauchi, D Hiraya, S Ayuzawa, T Yaguchi, H Watabe, T Hoshi, T IshizuAbstract
Background
Coronary microvascular dysfunction (CMD) is increasingly recognised as an important pathophysiological substrate for myocardial ischaemia and adverse outcomes in obstructive hypertrophic cardiomyopathy (oHCM). However, whether CMD is diffuse or regionally localised, and how septal reduction therapy acutely affects CMD, remains unclear.
Purpose
To evaluate the regional distribution of CMD in the left anterior descending artery (LAD) and left circumflex artery (LCx) territories in symptomatic oHCM and to assess acute changes in invasive CMD indices immediately after alcohol septal ablation (ASA).
Methods
Consecutive symptomatic patients with oHCM undergoing ASA were enrolled (n=20; median age 72 [61–76] years; 30% male; New York Heart Association class II–III). Coronary microvascular function was invasively assessed using a pressure/temperature guidewire to measure coronary flow reserve (CFR) and index of microcirculatory resistance (IMR) in both the LAD and LCx territories before and immediately after ASA (Figure A). CMD was defined as CFR <2.0 and/or IMR >25.
Results
ASA significantly reduced the left ventricular outflow tract pressure gradient from 53 [13–69] mmHg to 6 [3–8] mmHg (p<0.001). At baseline, CMD was observed in the LAD, with reduced CFR (1.8 [1.3–2.1]) and elevated IMR (26 [25–39]). Immediately after ASA, LAD microvascular function improved, with increased CFR (2.3 [2.0–2.9], p=0.004) and decreased IMR (17 [13–22], p=0.002) (Figure B). In contrast, LCx indices were preserved at baseline (CFR 2.1 [1.6–3.1], IMR 14 [11–25]) and showed no significant change after ASA (Figure B). No major procedure-related complications occurred.
Conclusions
In symptomatic oHCM, CMD predominantly localises to the LAD territory, whereas the LCx territory exhibits preserved microvascular function. ASA acutely improves LAD-associated CMD in parallel with haemodynamic relief, suggesting potential benefits beyond gradient reduction. Regional invasive CMD assessment may provide mechanistic insights into oHCM and serve as a useful tool for evaluating the immediate physiological impact of ASA.