Abstract 2548: The Index Of Microvascular Resistance Measured Acutely Predicts The Severity And Nature Of Myocardial Infarction In Patients With St Segment Elevation Myocardial Infarction
Background: Microvascular obstruction (MVO) revealed by contrast enhanced magnetic resonance imaging (CE-MRI) independently influences outcome in patients with ST elevation myocardial infarction (STEMI). The index of microcirculatory resistance (IMR) is a straightforward novel invasive measure of microvascular function. We investigated the relationships between IMR with MVO and other measures of myocardial injury in STEMI.
Methods: Fifty two STEMI patients were included. During PCI, a coronary pressure/temperature sensitive guidewire was advanced into the culprit artery and baseline means transit times (Tmn) were obtained following bolus intra-coronary injection of 3 ml of saline. Tmn and distal coronary pressure (Pd) were obtained under conditions of peak hyperaemia achieved by intravenous adenosine infusion (140 mcg/kg/min). IMR was calculated as PdxTmn. Patients underwent gadolinium contrast enhanced CMR 24 – 48h later. LV dimensions were assessed using retrogated (trueFISP) cinematographic breath-hold sequences and MVO was defined as a dark core of hypoenhancement within the area of hyperenhanced infarcted tissue using breath hold turboFLASH sequences following an intravenous bolus of gadolinium (0.1mmol/kg).
Results: Physiological measurements were achieved in all consenting patients and 50 patients had complete ceCMR scans 24 – 48h post PCI . The median IMR (IQR) was 34.5 (22.8 –51.1) and the range was 9.9 –114. Twenty three patients (46%) had MVO. IMR (median[IMQ]) was higher in patients with MVO (38.8 [30.2–56.2]) compared to in patients without MVO (26.8 [18.7–36.6]); p=0.002). CFIp was similar in patients with (0.29 [0.2– 0.35[) or without (0.27 [0.19 – 0.34]) or without MVO (p=0.47). An IMR above the median value predicted LV ejection fraction (r2 =30% p=<0.001) inversely and positively predicted LVESV (r2=19% p=0.001). In addition IMR correlated significantly with peak troponin I (r2 =12.5% p=0.01).
Conclusions: IMR measured acutely was higher in patients with MVO revealed by subsequent ceMRI. IMR correlated with LV dimensions, ejection fraction, and peak troponin I concentration. Potentially, this relatively simple wire based technique could be used at the time of PCI as an early marker of MVO and myocardial damage.