Purpose. We evaluated the relationship between PCFT and both CFR and hyperemic myocardial blood flow (MBF) in patients with suspected CAD and normal myocardial perfusion imaging (MPI).
Method. From a pool of 1550 subjects referred for the evaluation of suspected or known CAD to stress-rest 82Rb PET/CT, 583 patients without overt CAD showing normal MPI were considered. To estimate the regional PCFT, the maximum fat thickness, assessed as the largest distance from the myocardium to the visceral epicardium, was measured (mm) on unenhanced CT images, in the left anterior descending (LAD), left circumflex (LCx), and right (RCA) coronary artery. The mean PCFT value of the three coronary arteries was used to calculate the global PCFT. Myocardial perfusion was considered normal when the summed stress score was <3. Absolute MBF was computed (in milliliters per minute per gram) from the dynamic rest and stress imaging series. CFR was defined as the ratio of hyperemic to baseline MBF and CFR < 2 was considered reduced.
Results. Among 583 patients with normal MPI, 103(18%) patients showed reduced CFR and 479 (82%) normal CFR. Compared to patients with normal CFR, those with impaired CFR were older (69.9±13.6 vs 58.9±12.7, P<0.001) and showed higher prevalence of hypertension and diabetes (92% vs 75 %; 44% vs 22% respectively; both P<0.005). While baseline MBF did not differ between the two groups, patients with impaired CFR demonstrated blunted response to pharmacological stressor (1.95±0.57 vs 2.89±0.70; P<0.001) and higher values of global PCFT values (11.6±1.9 vs 10.93±2.1; P<0.005), as compared to those with normal CFR. At univariate linear regression analyses, age, hypertension, diabetes, and PCFT were predictors of both decreasing CFR and hyperemic MBF (all P<0.005). The relationship of PCFT of each coronary with MBF and CFR of the underlying vessel was also evaluated. While baseline MBF of each vessel was not associated with analogous PCFT values, a significant inverse correlation of each regional PCFT with corresponding hyperemic MBF was found (r=-0.290 for LAD; -0.190 for LCx; and -0.113 for RCA, respectively, all P<0.001). Such a relationship was also seen between LAD and LCx PCFT and corresponding CFR values (both P<0.001).
Conclusions. In patients with suspected CAD and normal MPI, a significant decrease of global and regional hyperemic MBF was observed with increasing global and regional PCFT. LAD and LCx PCFT are also associated with corresponding CFR values. Our findings suggest that PCFT may have a local effect on underlying coronary function.