Continuous Versus Bolus Thermodilution‐Derived Coronary Flow Reserve and Microvascular Resistance Reserve and Their Association With Angina and Quality of Life in Patients With Angina and Nonobstructive Coronaries: A Head‐to‐Head Comparison

BACKGROUND: Coronary flow reserve (CFR) and microvascular resistance reserve (MRR) are physiological parameters to assess coronary microvascular dysfunction. CFR and MRR can be assessed using bolus or continuous thermodilution, and the correlation between these methods has not been clarified. Furthermore, their association with angina and quality of life is unknown. METHODS AND RESULTS: In total, 246 consecutive patients with angina and nonobstructive coronary arteries from the multicenter Netherlands Registry of Invasive Coronary Vasomotor Function Testing (NL‐CFT) were investigated. The 36‐item Short Form Health Survey Quality of Life and Seattle Angina questionnaires were completed by 153 patients before the invasive measurements. CFR and MRR were measured consecutively with bolus and continuous thermodilution. Mean continuous thermodilution‐derived coronary flow reserve (CFR(abs)) was significantly lower than mean bolus thermodilution‐derived coronary flow reserve (CFR(bolus)) (2.6±1.0 versus 3.5±1.8; P<0.001), with a modest correlation (ρ=0.305; P<0.001). Mean continuous thermodilution‐derived microvascular resistance reserve (MRR(abs)) was also significantly lower than mean bolus thermodilution‐derived MRR (MRR(bolus)) (3.1±1.1 versus 4.2±2.5; P<0.001), with a weak correlation (ρ=0.280; P<0.001). CFR(bolus) and MRR(bolus) showed no correlation with any of the angina and quality of life domains, whereas CFR(abs) and MRR(abs) showed a significant correlation with physical limitation (P=0.005, P=0.009, respectively) and health (P=0.026, P=0.012). In a subanalysis in patients in whom spasm was excluded, the correlation further improved (MRR(abs) versus physical limitation: ρ=0.363; P=0.041, MRR(abs) versus physical health: ρ=0.482; P=0.004). No association with angina frequency and stability was found. CONCLUSIONS: Absolute flow measurements using continuous thermodilution to calculate CFR(abs) and MRR(abs) weakly correlate with, and are lower than, the surrogates CFR(bolus) and MRR(bolus). Absolute flow parameters showed a relationship with physical complaints. No relationship with angina frequency and stability was found.