Influence of microvascular resistance reserve on cardiac magnetic resonance evaluation of left ventricular function in patients with ST-segment elevation myocardial infarction

In patients with ST-elevation myocardial infarction (STEMI), coronary microcirculatory dysfunction (CMD) may predict the risk of heart failure and mortality, and can be assessed by the index of microcirculatory resistance (IMR) and the more novel index, microvascular resistance reserve (MRR). We investigated MRR measurements and its relationship with left ventricular function changes assessed by cardiac magnetic resonance (CMR).

In 26 patients with STEMI and single-vessel disease treated with primary percutaneous coronary intervention (PPCI), invasive flow- and pressure measurements were performed after PPCI and repeated after 3 months. CMR was performed within 72 h of PPCI and after 3 months. CMD was defined as MRR ≤ 3 and patients were divided into two groups: MRR ≤ 3 and MRR > 3, as well as into IMR ≥ 40 and IMR < 40. Six years clinical follow-up was conducted in all patients.

Median MRR after PPCI was 2.6 [Interquartile range (IQR) 1.5, 4.0] and 15 patients (58 %) had a MRR ≤ 3, while median IMR was 33 [IQR 13, 79]. Patients with MRR ≤ 3 had significantly greater infarct size (IS) at both index (IS(late gadolinium enhancement (LGE)): median 1796 [IQR 827, 4167] vs 788 [IQR 308, 1201], p = 0.024) and at 3-month follow-up (IS(LGE): median 928 [IQR 566, 2024] vs 232 [IQR 82, 807], p = 0.027) compared to patients with MRR > 3. Assessing the CMD with IMR, IS did not differ significantly, neither at baseline (IMR ≥ 40 IS(LGE) median: 1483 [IQR 827, 4167] vs IMR < 40,870 [IQR 310, 2000], p = 0.21) nor at 3-month follow-up (IS(LGE): median 824 [IQR 587, 1850] vs 566 [IQR 107, 834], p = 0.22). After six years, two patients died (one cardiac cause), and one patient was hospitalized for heart failure, all patients had MRR ≤ 3.

In this small pilot study, patients with STEMI and MRR ≤ 3 had significantly greater IS after PPCI and after 3 months compared to patients with MRR > 3, while IS did not differ in IMR groups.