Comparative Significance of Invasive Measures of Microvascular Injury in Acute Myocardial Infarction

Area of Science:

• Cardiovascular Medicine
• Interventional Cardiology
• Microvascular Function Assessment

Background:

• Microvascular dysfunction is a key factor in ST-segment-elevation myocardial infarction (STEMI) outcomes.
• Assessing microvascular function post-primary percutaneous coronary intervention (PCI) is crucial for risk stratification.
• Resistive reserve ratio (RRR) measures microvascular vasodilatory capacity, while index of microcirculatory resistance (IMR) quantifies resistance.

Purpose of the Study:

• To compare the predictive value of RRR, IMR, and coronary flow reserve (CFR) for microvascular obstruction (MVO), myocardial hemorrhage, infarct size, and clinical outcomes following STEMI.
• To evaluate the independent prognostic significance of these microvascular indices in STEMI patients undergoing primary PCI.

Main Methods:

• Prospective enrollment of 440 STEMI patients in the T-TIME trial; microvascular indices (IMR, CFR, RRR) measured post-primary PCI in a subset of 144 patients.
• Cardiovascular magnetic resonance imaging (CMR) used to quantify MVO extent and infarct size at 2–7 days and 3 months, respectively.
• One-year clinical outcomes, including major adverse cardiac events (MACE) and heart failure hospitalizations, were assessed.

Main Results:

• IMR > 40 was significantly associated with increased MVO, myocardial hemorrhage, larger infarct size, and adverse clinical outcomes (MACE, heart failure hospitalization, death).
• RRR was independently associated with reduced MVO extent, lower likelihood of myocardial hemorrhage, smaller infarct size, and fewer heart failure hospitalizations.
• CFR showed no significant association with infarct characteristics or clinical outcomes in this cohort.

Conclusions:

• IMR and RRR are valuable predictors of MVO, infarct characteristics, and clinical outcomes in acute STEMI patients post-primary PCI.
• CFR is not a reliable predictor of these adverse events in this setting.
• These findings highlight the importance of assessing microvascular function using IMR and RRR for risk stratification and management of STEMI.