Methods. We selected 94 patients with intermediate pre-test probability of CAD. All patients underwent coronary CT angiography (CCTA) and stress-rest MPI using GE Discovery NM/CT 570?. Coronary plaques were considered significant (=70%), intermediate (40% to 69%) and non-significant (<40%). The Segment Involvement Score (SIS) was calculated as the total number of coronary artery segments with atherosclerotic plaques. The Segment Stenosis Score (SStS) was computed by grading each coronary segment with a 5-point scoring system (0 = no plaque; 1 = 1-24% stenosis; 2 = 25-49% stenosis; 3 = 50-69% stenosis; and 4 = =70% stenosis). The summed rest score (SRS), stress score (SSS), and difference score (SDS) were derived from MPI images.
Results. The median SIS and SStS were 4.0 (IQR 2.0- 5.0) and 7.5 (IQR 3.0; 13.0), respectively. Normal MPI images were observed in 40(43%) patients, abnormal in 56(54%). There were 378 segments with atherosclerotic plaques: 24(6%) in the LM, 178(47%) in the LAD, 78(21%) in the LCx, and 98(26%) in the RCA. The frequencies of normal and abnormal MPI in patients with <40% (normal MPI 53%; abnormal MPI 47%) and 40% to 69% (normal MPI 44%; abnormal MPI 56%) coronary artery stenosis did not significantly differ (p=0.40 and p=0.22, respectively). In patients with =70% coronary artery stenosis, abnormal MPI was observed significantly more often (normal MPI 29%; abnormal MPI 71%) than normal MPI (p=0.001). In the overall population, both Segment Involvement Score and Segment Stenosis Score had weak correlations with SSS (r=0.3 and r=0.34, respectively; P<0.01 for both), SRS (r=0.27 and r=0.35, respectively; P<0.01 for both), and SDS (r=0.3 and r=0.36, respectively; P<0.01 for both). In patients with <40% stenosis neither CT scores correlated with MPI parameters, while SDS correlated moderately with Segment Involvement Score (r=0.45; p=0.03) and Segment Stenosis Score (r=0.53; p=0.01) in those with 40% to 69% stenosis. In patients with =70% stenosis, the Segment Stenosis Score had moderate correlations with SSS (r=0.50; p=0.005) and SDS (r=0.43; p=0.02).
Conclusion. Myocardial ischemia may frequently develop even in the absence of critical coronary artery lesions, presenting in a consistent proportion of patients with either intermediate or even non-significant coronary stenosis. In those patients, the extent of regional myocardial perfusion defects correlates more with measures of global CAD burden than with focal stenosis severity, as a sign of the significant inter-relation between diffuse coronary atherosclerosis and myocardial ischemia.