A Meta-Analysis and Simplified Nomenclature for Diagonal Coronary Artery and Ramus Intermedius Across Adult and...

Anatomical descriptions of left-sided oblique coronary branches remain inconsistent, hindering imaging interpretation and surgical planning. To quantify the prevalence, branching patterns and morphometry of the ramus intermedius (RI) and diagonal branches, and propose a unified nomenclature. Following PRISMA guidelines, a PubMed search up to 12 June 2025 yielded 623 records. Forty-six studies involving 25,602 hearts were included, and random-effects meta-analysis was applied to pool prevalence and continuous outcomes. Overall, an additional left-main branch (RI) was present in 25.2% (95% CI: 8.7-54.5). Trifurcation dominated (22.7%), whereas quadrifurcation and pentafurcation occurred in 3.7% and 1.3% respectively. The pooled RI/diagonal diameter averaged 2.21 mm (95% CI 2.02-2.39), and mean branch length was 49.1 mm (95% CI 37.8-60.5). Methodological heterogeneity was high but consistent patterns emerged across cadaveric and imaging modalities. An oblique "diagonal artery", whether arising from the left main (RI) or anterior interventricular artery, is present in roughly 25% of hearts, averages 2.2 mm in caliber and extends to 49 mm. Recognizing this vessel family and standardizing the term "diagonal arteries" will improve coronary imaging reporting and guide revascularization strategies.