Activation and repression in the nervous system

Corrosion castings of 60 human hearts were used to demonstrate that the point of origin of the posterior interventricular artery (PIA), in relation to the crux cordis, is responsible for its subsequent course with respect to the posterior interventricular vein (PIV). In seven cases (12%), the PIA appeared as the continuation of the left circumflex, descending rightwards and on a deeper level of the PIV. In 53 cases (88%), the PIA arose from the right coronary artery (RCA) and 50 of these were selected to be classified into three groups, according to the PIAs origin and course. In group A (29 cases, 58%) and B (seven cases, 14%), the PIA emerged before the crux cordis and descended to the right or left of the PIV, respectively. In group C (14 cases, 28%), it originated at, or beyond, the crux cordis and descended along the left side of the PIV. Among the 50 cases, the PIA was found to be long in 34 (68%), large in 32 (64%), and long and large in 29 cases (58%). In 18 of the latter 29 cases (62%) or 36% of the 50 cases in total, the PIA arose as a continuation of the RCA (group A) and therefore these cases were easily accessible to interventional cardiologists and also to surgeons, since the PIA lay on the same or on a superficial level in relation to the PIV. This work describes and explains the variations of the PIA and concludes that at least 36% of these may be helpful in coronary artery angioplasty and bypass surgery.