First Experience of Measuring Index of Microcirculatory Resistance at Auckland City Hospital

Abstract

Patients with angina and non-obstructive coronary artery disease (NOCAD) present an important diagnostic and management challenge. Measurement of the index of microcirculatory resistance (IMR) with a coronary pressure wire at the time of invasive coronary angiography can help distinguish between microvascular angina and non-cardiac chest pain. A retrospective audit was undertaken of consecutive patients with NOCAD and measurement of microvascular indices from the Northern region between March 2020 and January 2023 at Auckland City Hospital (ACH). Coronary flow reserve, IMR, and fractional flow reserve were measured, as shown in the Table. Sixty-two patients had IMR measured and seven were excluded as they were out of area; 75% were male and the mean age was 65 (SD 8.6) years. An elevated IMR was found in 24 (43%); 47% had history of smoking, 24% previous myocardial infarction, 7% previous stroke, and 51% diabetes; 52% presented with stable angina, 24% with unstable angina, and 22% with non-ST elevation myocardial infarction; and 70% were on aspirin, 44% on beta blockers, 18% on calcium channel blockers, 31% nitrates, 38% statins, and 2% nicorandil.TableMedianInterquartile rangeHeart rate (per minute)75.9(64.6, 87.2)Coronary flow reserve (CFR)3.51(2.18, 4.79)Index of microcirculatory resistance (IMR)22.8(14.8, 39.8)Fractional flow reserve (FFR)0.85(0.81, 0.90)Gensini score7.5(2.6, 18.6) Open table in a new tab This study describes initial experience in measuring IMR amongst patients with NOCAD at ACH. This cohort had a low burden of coronary disease. IMR provides useful diagnostic information that informs management.