Key Points:
- The Microvascular Resistance Reserve (MRR), a novel measurement, assess the vasodilator reserve capacity of the coronary microvasculature while eliminating resistance of epicardial stenoses
- This novel index has both diagnostic and prognostic implications in chronic coronary syndrome, but it is unknown whether the MRR can guide symptomatic benefit from revascularization.
- The study investigators found that MRR with associated with freedom from angina and lower MRR was associated with more freedom from angina post-revascularization, as well as associations with health status and coronary perfusion
- These results suggest that the MRR may have a diagnostic and prognostic role in patients with acute chest pain on chronic coronary syndrome with coronary lesions of unclear significance to help guide revascularization decisions
Revascularization in non-high risk chronic coronary syndrome (CCS) should improve myocardial perfusion and reduce anginal symptoms. A relatively new measurement, the microvascular resistance reserve (MRR), assesses the vasodilator reserve capacity of the coronary microcirculation while eliminating resistance of epicardial stenoses. This novel index has both diagnostic and prognostic implications in CCS, but whether MRR guides symptomatic benefit from revascularization is unknown. As such, this study aimed to investigate whether MRR is associated with health outcomes after revascularization in patients with moderate coronary artery stenoses as well as whether improvement in health outcomes in associated with improvement in myocardial perfusion.
The study authors looked at patients with new-onset chest pain and moderate coronary artery stenoses (30-90%) on angiography from the DANICA 2 and DANICA 3 trials. They first obtained a baseline Seattle Angina Questionnaire (SAQ) score and PET scan, followed by invasive angiography with FFR and CFR, with 3-month follow-up SAQ score and 12-month follow-up PET. Primary outcome was freedom from angina defined by SAQ frequency score of 100. Secondary outcomes included clinically relevant health-status changes: change in SAQ frequency score > 10, change in SAQ physical limitation score > 5, and change in SAQ summary score > 5, as well as change in hyperemic blood flow on PET scan.
In the study, 222 patients were enrolled with 68% male, average age 63, 65% smoking history, 53% HTN history, 35% dyslipidemia history, and 12% diabetes history. Regarding invasive angiography, 77% of patients had 1 vessel disease, with the majority in the LAD, with mean stenosis of 45% and mean FFR of 0.82 with 1 in 4 patients undergoing revascularization.
Using regression analysis for association with freedom from angina at follow-up, the study investigators found that MRR was independently associated with freedom from angina (OR 0.86 [95% CI: 0.74-0.99]), whereas neither FFR nor CFR demonstrated this association. Also of note, the study authors found that patients with lower MRR demonstrated more freedom from angina with revascularization. Regarding secondary outcomes, the investigators also found that MRR was associated with change in angina frequency: those with low MRR who underwent revascularization showed an improvement in SAQ frequency score (+13.5%, p=0.01) whereas those with normal MRR who were revascularized did not show similar improvement (+7.4%, p=0.12), and those with normal MRR who did not undergo revascularization showed improvement in SAQ frequency score (+8.5%, p=0.002) whereas those with low MRR who did not undergo revascularization did not show the same benefit (+1.1%, p=0.78). Similar results were seen for secondary outcomes of change in general health status: those with low MRR who underwent revascularization showed an improvement in SAQ summary score (+10.8%, p=0.01) whereas those with normal MRR who were revascularized did not show similar improvement (+3.6%, p=0.32), and those with normal MRR who did not undergo revascularization showed improvement in SAQ summary score (+9.3%, p<0.001) whereas those with low MRR who did not undergo revascularization did not show the same benefit (+4.3%, p=0.10). Finally, those with low MRR who underwent revascularization demonstrated improved myocardial perfusion on PET scan (0.61, p=0.01).
Ultimately, the study authors found that in patients with stable new-onset chest pain and moderate coronary artery stenoses with unclear functional significance, low MRR is associated with freedom from angina, even beyond FFR and CFR. Furthermore, they note that patients with low MRR undergoing revascularization showed association with improved health outcomes, specifically freedom from angina, and those with normal MRR undergoing revascularization did not experience improvement in angina. Lastly, they argue that there is some correlation with these health outcomes with changes in myocardial perfusion. This study suggests that MRR may be a relevant diagnostic and prognostic measurement for acute chest pain on chronic coronary syndrome with coronary lesions of unclear significance to help guide revascularization decisions.