An x-ray microscopic study of the arterial supply to the conducting system of the human heart.

The numerous descriptive and embryological studies carried out on the sinu-atrial and atrioventricular conducting system of the heart in man and animals have been concerned principally with its structure, distribution, innervation, and development. Amongst these, the investigations of Blair and. Davies (1935), Walls (1947), Baird and Robb (1950), Field (1951), Glomset and Cross (1952), Truex, Bishof, and Hoffman (1958), and Titus, Daugherty, and Edwards (1963) may be mentioned. More recently Carbonell (1956) isolated the conducting system of the heart by demonstrating the activity of esterases with histochemical techniques, and Lev, Benjamin, and White (1958) reported a histopathological study on the conducting system in a heart with complete block of 42 years' duration. Titus, Neufeld, and Edwards (1964) reported on three cases in which the pulmonary trunk and ascending aorta originated from the right ventricle and showed that the conducting system had been displaced dorsally. Little reference, however, could be found in the reports to the pattern and distribution of arterioles and capillaries in the conducting system of the human heart. Schlesinger (1938) and Fulton (1963) demonstrated the distribution of the coronary arteries in man after the injection of radioopaque media, but the resolution of the x-ray technique did not allow the visualization of capillaries, and no mention is made of any special distribution of vessels to the conducting system. The pattern of blood supply to the sinu-atrial node in the dog has been described as coming from the right coronary artery (Meek, Keenan, and Theisen, 1929; Moore, 1930; Pianetto, 1939; Kazzaz and Shanklin, 1950), and Halpern (1954) described additional branches being distributed to the node from the left coronary artery and right internal mammary artery. In man, Last (1963) states, without further amplification, that the sinu-atrial node is supplied by a branch of the right coronary artery in 60 per cent of cases, and that the atrio-ventricular node and bundle of His are supplied by a branch of the left coronary artery in 90 per cent. This work presents an account of the pre-capillary arteriole and capillary pattern of distribution in the sinu-atrial node and atrio-ventricular conducting system of the human heart, using the Coslett Nixon X-Ray Projection Microscope. This gives an opportunity for investigating unfixed, fullthickness preparations without histological intervention, in contrast to the routine staining, injection, and clearing techniques for examining capillary beds by previous investigators (Pickworth, 1934; Williams, 1948; Scharrer, 1950; Woerner, 1959).