Introduction:
Microvascular obstruction (MVO) after myocardial infarction is associated with adverse left ventricular remodeling and worse clinical outcomes. Restoration of epicardial vessel flow is the main goal in acute myocardial infarction and is commonly assessed by postprocedural thrombolysis in myocardial infarction (TIMI) flow grade. However, the gold standard for assessment of microvascular obstruction is cardiocascular magnetic resonance (CMR) imaging with late gadolinium enhancement. In the present study, we sought to investigate the relationship between angiographic reperfusion markers, including TIMI flow grade and myocardial blush grade (MBG) and MVO detected by CMR.
Methods:
We retrospectively investigated all patients with an acute MI and subsequent CMR during the same hospital stay between October 2008 and August 2023. Correlations between TIMI flow grade/MBG and the extent of microvascular obstruction, expressed as a percentage of total left ventricular myocardial mass, were assessed. Predictors of the presence of MVO were evaluated using univariate and multivariate logistic regression. Subgroup analyses according to TIMI flow grade were performed.
Results:
The study cohort consisted of 597 patients who underwent CMR 3 days [interquartile range 2-4 days] after myocardial infarction. TIMI flow grade showed a statistically significant but weak inverse correlation with MVO extent on CMR (rho = -0.28, p < 0.001). MBG was also significantly but weakly inversely correlated with MVO extent (rho = -0.33, p < 0.001). In multivariable analysis, TIMI flow remained independently associated with MVO (OR 0.35, 95% CI 0.19-0.63, p < 0.001). In contrast, MBG was no longer significantly associated with MVO after adjustment (OR 0.87, 95% CI 0.39-1.98, p = 0.742). Subgroup analyses among patients with angiographically optimal epicardial reperfusion (TIMI III, n = 405) revealed that MVO remained present in 79 patients (19.5%).
Conclusion:
The associations between the presence and extent of MVO and post-PCI TIMI flow grade and MBG were significant but weak. MVO was frequently observed despite angiographically successful reperfusion, occurring in nearly one-fifth of patients with TIMI III flow. CMR provides important information on myocardial injury beyond angiographic reperfusion markers.
