Aims: Coronary microvascular function has important diagnostic and prognostic implications but routine assessment is difficult. The index of microcirculatory resistance (IMR) is a reliable but invasive measure. We evaluated whether left ventricular contractile reserve (CR), measured with strain imaging on dobutamine echocardiography (DSE), is a reliable non-invasive measure of coronary microvascular function.
Methods and results: Forty-five patients underwent low-dose DSE and invasive coronary angiography with IMR measurement in the left anterior descending artery. Global mean peak systolic longitudinal strain was measured in three apical views at rest, and with low-dose DSE. CR was the difference between the resting and low-dose values. Mean IMR was 19.8 (range 6-104): mean peak global systolic strain at rest was –17.90% and at low-dose was –21.46%, giving a mean CR of +3.6% (20% relative increase). IMR and CR were significantly correlated, IMR–1=(0.0014×CR+0.05), r=0.64, p<0.001. CR of ≥10% relative increase identified IMR <25 (100% sensitivity and specificity) and <16 (93% sensitivity, 50% specificity [AUC=0.84]). CR ≥20% identified IMR of <16 (78% sensitivity, 82% specificity) with CR ≥ 41% having 100% specificity.
Conclusions: LV CR with low-dose DSE may be used to estimate IMR non-invasively. An impaired CR indicates coronary microvascular dysfunction.