Absolute coronary flow and microvascular resistance before and after TAVR

Abstract Purpose This study aims to investigate microcirculatory changes, both at rest and during hyperemia, using continuous intracoronary thermodilution, before TAVR, immediately post-TAVR, and at 6-month follow-up. Methods We included consecutive patients with high-gradient AS undergoing TAVR with non-obstructive coronary artery disease in the left anterior descending artery (LAD). Absolute coronary flow (Q) and microvascular resistance (R) were measured in the LAD using continuous intracoronary thermodilution at rest (Qrest) and during hyperemia (Qhyper) before and after TAVR, as well as at 6-month follow-up. Echocardiography and cardiac computed tomography (CCT) were used to quantify total myocardial mass and LAD-specific mass. Regional myocardial perfusion (QN) was calculated by dividing absolute coronary flow by the subtended myocardial mass. Results In 51 patients, absolute flow and microvascular resistance were assessed at rest and during hyperemia before and after TAVR. The mean age was 84.1 ± 5.0 years, and 35 participants were male (68.6%). Measurements were also obtained 6 months after TAVR in 20 (39%) patients. Overall, there were no significant changes in resting and hyperemic flow and resistance before and after TAVR (Qrest 68 [55-88] mL/min vs 69 [54 – 92] mL/min, p=0.776; Qhyper 158 [129 – 200] mL/min vs 172 [132, 216] mL/min, p=0.449, before and after TAVR, respectively). Consequently, coronary flow reserve (CFR) and microvascular resistance reserve (MRR) remained unchanged. At 6 months, there were no significant changes in flow and resistance both at rest and during hyperemia compared to baseline (Qrest: 72 [63-84] vs 83 [59-108] mL/min, p=0.658; Qhyper: 181 [158-200] vs 194 [167-222] mL/min, p=0.492; pre-TAVR and at 6 months follow-up, respectively), resulting in unchanged CFR and MRR. However, at follow-up, there was a noteworthy reduction in left ventricular mass of approximately 13% (from 201.9 ± 37.9g to 175.1 ± 46.6 g, p<0.001), leading to an increase in hyperemic perfusion (QN,hyper: 0.86 [0.69-1.06] vs 1.20 [0.99-1.32] mL/min/g, p=0.008; pre-TAVR and follow-up, respectively), but not in resting perfusion (QN, rest: 0.34 [0.30-0.48] vs 0.47 [0.36-0.67] mL/min/g, p=0.06). Conclusion Immediately after TAVR, there are no changes in absolute coronary flow and coronary flow reserve. Over time, LV remodeling is associated with increased hyperemic perfusion, indicating that, in the context of the observed pathophysiological changes in coronary microcirculation in AS patients after TAVR, the reverse LV remodeling has a more significant impact than the acute LV unloading achieved by valve replacement itself.