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Microvascular Resistance Reserve After Primary PCI
Quick Takes
- Microvascular function is comprised of minimal microvascular resistance (measured by index of microcirculatory resistance [IMR]) and vasodilatory capacity (measured by novel index of microvascular resistance reserve [MRR]).
- The current study included patients from prior trials who had undergone IMR and CMR imaging testing after STEMI and in whom MRR could be calculated (n = 446). Findings identified MRR of 1.25 as being predictive of all-cause mortality or hospitalization for HF.
- Low MRR (≤1.25) was associated with a four-fold higher risk of all-cause mortality or hospitalization for HF over 3 years of follow-up (HR, 4.16; 95% CI, 2.31-7.50; p < 0.001).
Study Questions:
What is the prognostic value of microvascular resistance reserve (MRR) in patients with ST-segment elevation myocardial infarction (STEMI), and how does MRR compare with cardiac magnetic resonance (CMR) imaging parameters of microvascular resistance?
Methods:
From a pooled analysis of individual patient data from six cohorts that measured the index of microcirculatory resistance (IMR) directly after primary percutaneous coronary intervention (PCI) in patients with STEMI (n = 1,265), a subgroup analysis was performed in patients in whom both MRR [MRR = (coronary flow reserve/fractional flow reserve) x (Pa,rest/Pa,hyper)] and IMR were available. The primary endpoint was the composite of all-cause mortality or hospitalization for heart failure (HHF).
Results:
Both MRR and IMR could be calculated in 446 patients. The optimal cut-off of MRR to predict the primary endpoint in this STEMI population was 1.25. During a median follow-up of 3.1 years (interquartile range, 1.5-6.1), the composite of all-cause mortality or HHF occurred in 27.3% and 5.9% of patients (hazard ratio [HR], 4.16; 95% confidence interval [CI], 2.31-7.50; p < 0.001) in the low MRR (≤1.25) and high MRR (>1.25) group, respectively. Both IMR and MRR were independent predictors of the composite of all-cause mortality or HHF.
Conclusions:
MRR measured directly after primary PCI was an independent predictor of the composite of all-cause mortality or HHF during long-term follow-up.
Perspective:
Presence of microvascular dysfunction after primary PCI has been shown to have prognostic implications. Microvascular function is comprised of minimal microvascular resistance (measured by IMR) and vasodilatory capacity (measured by novel index of MRR). There remain challenges around reliably measuring microvascular function independent of epicardial disease.
The current study included patients from prior trials who had undergone IMR and CMR imaging testing after STEMI and in whom MRR could be calculated (n = 446). Findings identified MRR of 1.25 as being predictive of all-cause mortality or HHF. Low MRR (≤1.25) was associated with a four-fold higher risk of all-cause mortality or HHF over 3 years of follow-up (HR, 4.16; 95% CI, 2.31-7.50; p < 0.001).
Barring the limitations of the current analysis (post hoc analysis, predominantly male cohort, limitations of bolus thermodilution), the findings add to a growing body of evidence linking post-MI microvascular dysfunction with adverse clinical outcomes, and is a step in the direction of more reliably identifying microvascular dysfunction to allow for eventual therapeutic targets.
Clinical Topics: Invasive Cardiovascular Angiography and Intervention, Stable Ischemic Heart Disease, Vascular Medicine, Interventions and Vascular Medicine, Chronic Angina, Acute Coronary Syndromes
Keywords: Microcirculation, Percutaneous Coronary Intervention, ST Elevation Myocardial Infarction
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