Abstract Body (Do not enter title and authors here): Background: Coronary microvascular disease (CMD) may be endothelium-independent (coronary flow reserve, CFR<2.5) or endothelium-dependent (<50% increase in coronary blood flow in response to acetylcholine). Endothelium-independent CMD has been subclassified into structural and functional groups based on hyperemic microvascular resistance (hMR, mmHg/cm/s). We hypothesized that endothelium-dependent CMD also has these subtypes.

Methods: Patients with non-obstructive coronary artery disease who underwent coronary catheterization of the left anterior descending artery were included (n=112). Pressure and flow were recorded at rest, with adenosine, and with acetylcholine. Patients were classified by endothelial type and functional CMD (hMR<2.5) or structural CMD (hMR>2.5). Wave intensity analysis was performed and cumulative separated wave intensity (Joules/m²) was calculated by standard formulae. Three dominant waves were analyzed (forward compression wave, FCW; backward compression wave, BCW; backward expansion wave, BEW).

Results: Seventy-four of 109 patients had CMD, of which 59 had endothelium-independent and 38 had endothelium-dependent CMD (23 had both). Functional and structural subgroups were identified (Figure 1). All CMD subtypes had significantly different wave intensities at rest, adenosine, and acetylcholine (p<0.05). Comparing subtypes, there was no difference in wave intensities at rest. However, wave intensities significantly differed between all CMD subtypes with adenosine and acetylcholine, with higher energy waves in the endothelium-independent and functional groups (p<0.05, Figure 2).

Conclusions: CMD is a heterogenous condition with distinct subtypes. Functional and structural groups exist in both endothelium-dependent and endothelium-independent CMD. These subgroups have distinct hemodynamic profiles as measured by wave intensity. A patient-specific approach to first line medical therapy may be improved by subgroup classification.