Added Diagnostic Value of Stress CT Perfusion to Coronary CT Angiography Across Increasing Coronary Calcium Burden

Coronary CT angiography (CCTA) may show reduced specificity in patients with extensive coronary artery calcification (CAC). We evaluated the diagnostic performance of CCTA alone versus integrated CCTA–stress myocardial CT perfusion (CTP) across different CAC burdens. In this retrospective single-center study, 102 symptomatic patients with suspected coronary artery disease underwent CCTA with stress-only dynamic CTP and were stratified into CAC 0–400 (n = 38), 401–1000 (n = 43), and >1000 (n = 21). Stress-induced hypoperfusion was defined using a prespecified relative myocardial blood flow ratio ≤ 0.85. The primary diagnostic-accuracy analysis included 68 patients with an invasive reference standard (ICA/QCA ± FFR); FFR ≤ 0.80 was used when available, whereas QCA stenosis ≥ 50% defined reference-positive disease otherwise. The remaining 34 patients had complete event-free 12-month clinical follow-up and were included exclusively in a supportive exploratory analysis. In the primary cohort, CCTA alone showed a sensitivity of 89.8%, specificity of 36.8%, and accuracy of 75.0%, compared with 87.8%, 84.2%, and 86.8%, respectively, for integrated CCTA–CTP. The integrated strategy increased specificity by 47.4 percentage points (95% CI, 24.9–69.8) and accuracy by 11.8 percentage points (95% CI, 3.1–20.4), with a significant paired difference (McNemar p = 0.021) and an NRI of 0.45 (95% CI, 0.22–0.68). In the supportive exploratory full-cohort analysis, integrated CCTA–CTP showed numerically higher accuracy across all CAC strata; however, CAC-stratified comparisons were not individually significant and these findings should be considered descriptive. Mean total radiation dose was 7.0 ± 1.4 mSv. Integrated stress CTP was associated with higher specificity and diagnostic accuracy than CCTA alone, primarily by reducing false-positive anatomical classifications.