Cerebral angiography is essential for diagnosing cerebrovascular diseases and crucial to separate the internal and external carotid arteries during angiography. The femoral artery approach is more invasive than the brachial artery approach. In some cases, guiding the catheter through the right brachial artery to the left internal and external carotid arteries is feasible. This study retrospectively investigated factors influencing successful catheter guidance to the left carotid arteries. We studied 30 patients (17 men
mean age 64.9 years) in whom catheter guidance to the left internal and external carotid arteries was attempted via the right brachial artery. A 4Fr Simmons-type catheter and a 0.035-inch diameter guidewire were used. We retrospectively analyzed patient characteristics and aortic arch anatomy. Guidance was successful in 20 patients (66.7%). There were no significant differences in sex, age, height, weight, BMI, aorta type, or bifurcation type between the brachiocephalic and left common carotid arteries between the successful and unsuccessful cases. However, a significant difference was observed in the angle formed by the Simmons catheter during insertion into the left common carotid artery (45.7° vs 19.3°