Electrical impulse conduction in pulmonary veins.

It has been documented that the cardiac musculature of many mammalia, including man, extends from the heart along the pulmonary veins to the lungs, and, at least in some rodentia, as far as the small venules, and that smooth muscle is not present (1-3). However, these reports are of structural studies only, and in the one publication where a speculation is made concerning the spread of the contractile impulse, it is based on the assumption that the contraction has to assist the flow of blood, that is, pass from the lung to the heart (2). A study of the ontogenetic development of this musculature by two of the present authors (Challice and Chohan) prompted some preliminary experiments to ascertain whether or not the passage of a wave of excitation along this musculature might be detectable, and if so, in which direction it traveled. It is well accepted that in embryonic development of the mammalian heart the governing pacemaker migrates from ventricle to atrium and finally to the sinoatrial node (4). No evidence suggesting that this pacemaker might arise from a site on the pulmonary veins in the lungs has been produced, and it is difficult to envisage how this might happen. It therefore appears that there is an anomaly. If the primary pacemaker is indeed located in the sinoatrial node, it is difficult to see how this extension of the cardiac musculature along the pulmonary vein can carry an electrical impulse other than in a direction opposite to that of normal blood flow. If this occurred, it would presumably produce a retrograde peristaltic contraction along the pulmonary veins. Should this prove to be the case, it could have interesting implications concerning the blood flow through the pulmonary veins and into the heart, and possibly, within the pulmonary capillaries. It was with this in mind that some preliminary experiments on the conduction of the electrical impulse in the pulmonary veins were undertaken. Electrophysiological recordings were made from the pulmonary veins in situ on mice