Microvascular Resistance Reserve vs Coronary Flow Reserve to Assess Age-Related Trends in Coronary Microvascular Dysfunction.

BACKGROUND

Advancing age is associated with epicardial atherosclerosis and coronary microvascular dysfunction (CMD), complicating reliable assessment of CMD using coronary flow reserve (CFR). Whether prevalence of functional and structural CMD varies with age remains unclear.

OBJECTIVES

The authors sought to evaluate the prevalence of CMD endotypes by age strata and compare CFR with microvascular resistance reserve (MRR) for diagnosis and stratification.

METHODS

Data from 1,704 patients (2,283 lesions) with stable angina in the ILIAS Registry (Inclusive Invasive Physiological Assessment in Angina Syndromes Registry) were analyzed, including obstructive (fractional flow reserve ≤0.80) and nonobstructive (fractional flow reserve >0.80) lesions. CMD was classified as no CMD (MRR ≥3.0), functional CMD (MRR <3.0, normal resistance), or structural CMD (MRR <3.0, abnormal resistance). CMD classification was repeated using CFR (<2.5 abnormal). Patients were stratified per age decade: <50, 50-59, 60-69, 70-79, and ≥80 years.

RESULTS

CMD prevalence by MRR was 48.2%, and increased across age strata (37.2% to 78.0%; P < 0.001), driven by structural CMD (10.9% to 40.0%; P < 0.001), while functional CMD prevalence remained unchanged (26.3% to 38.0%; P = 0.220). Age independently predicted functional (OR/y: 1.02; P < 0.001) and structural CMD (OR/y: 1.05; P < 0.001). In obstructive lesions, age predicted structural CMD (OR/y: 1.03; P = 0.0055); in nonobstructive lesions, age predicted functional (OR/y: 1.02; P = 0.0032) and structural CMD (OR/y: 1.06; P < 0.001). Overall CMD prevalence by CFR exceeded MRR across groups (53.3% vs 48.2%; P < 0.001), irrespective of epicardial disease.

CONCLUSIONS

Structural CMD increases with age regardless of obstructive CAD, while functional CMD prevalence increases only in nonobstructive CAD. CFR may overestimate CMD in epicardial disease, whereas MRR provides a more consistent assessment regardless of obstructive CAD, underscoring the need for prospective studies on their clinical relevance.