AIMS - This study aimed to investigate the anatomical attributes determining myocardial territory of diagonal branches and to develop prediction models for clinically relevant branches using myocardial perfusion imaging (MPI) and coronary CT angiography (CCTA).

METHODS AND RESULTS - The amount of ischemia and subtended myocardial mass of diagonal branches were quantified using MPI by percent ischemic myocardium (%ischemia) and CCTA by percent fractional myocardial mass (%FMM), respectively. In 49 patients with isolated diagonal branch disease, the mean %ischemia by MPI was 6.8±4.0% whereas in patients with total occlusion or severe disease of all diagonal branches, it was 8.4±3.3%. %ischemia was different according to the presence of non-diseased diagonal branches and dominant left circumflex artery (LCx). In CCTA cohort (306 patients, 564 diagonal branches), mean %FMM was 5.9±4.4% and 86 branches (15.2%) had %FMM ≥10%. %FMM was different according to LCx dominance, number of branches, vessel size, and relative dominance between 2 diagonal branches. The diagnostic accuracies of prediction models for %FMM ≥10% based on logistic regression and decision tree were 0.92 (95% CI 0.85-0.96) and 0.91 (95% CI 0.84-0.96), respectively. There was no difference in the diagnostic performance of models with and without size criterion.

CONCLUSIONS - LCx dominance, number of branches, vessel size, and dominance among diagonal branches determined the myocardial territory of diagonal branches. Clinical application of prediction models based on these anatomical attributes can help determine the clinically relevant diagonal branches in the cardiac catheterization laboratory.