BackgroundMicrovascular angina (MVA) is increasingly recognized as an endotype of ischaemia with no obstructive coronary artery disease (INOCA), but assessment remains difficult while validated diagnostic investigation is invasive. This pilot study assessed the correlation between left ventricular contractile reserve (CR), measured via speckle-tracking imaging on low dose dobutamine stress echocardiography (DSE) and the invasive coronary microvascular function in patients with INOCA.MethodsForty-two patients with INOCA and abnormal coronary vasomotor dysfunction were prospectively screened at a single tertiary centre covering the Northern metropolitan area of South Australia, from February 2018 to December 2020 (ACTRN12618000149268). Forty patients were invited into to the DSE study after coronary angiography demonstrated NOCAD and abnormal coronary epicardial and microvascular function (n = 40).Results: Of the 40 participants undergoing DSE study, 30 were suitable to be included in the final analysis. Average age of 54.8 ± 10.8 years old and more female (76.2%) than male recruited. 92.1% of patients were of Caucasian ethnicity. 65.8% were considered obese. The study cohort demonstrating a degree of angina burden, with 73.7% experiencing > once angina in a week. Weak positive association between CR with hyperaemic microvascular resistance (HMR); at 5mcg/kg/min, CR(absolute) (r=0.427, p-value=0.019); between 5 and 10 mcg/kg/min, CR(absolute) (r = 0.481, p-value = 0.007). The relationship between CR and HMR showed a trend of increase in CR at a DSE of 5mcg/kg/min, but a blunted response at the higher doses of 10 and 20mcg/kg/min (p=0.400). Weak positive association between CR with coronary flow reserve (CFR); at 5mcg/kg/min, CR(absolute) (r = 0.442, p-value = 0.015). The relationship between CR and CFR showed a trend of increase in CR at a DSE of 5mcg/kg/min, but a blunted response at the higher doses of 10 and 20mcg/kg/min (p=0.393).Conclusion:This pilot study has provided the possible utility of speckle tracking technique in assessment of INOCA with a MVA endotype.
