Some hemodynamic problems in transposition of the great vessels.

SINCE the incidence of transposition of the great vessels is approximately one in 20,000 live births, and since many of the infants affected have short lives, the prevalence of the condition is not such that the practitioner will see many cases. Still, the interest of the physician in these patients should transcend the pragmatic aspects of the minor public-health problem presented by care of the individual patient thus afflicted. The reason for this statement is that locked within the mechanism of survival may be possible clues leading to solution of control of the pulmonary and systemic circulations. Attention of the reader is drawn to two communications pertaining to transposition of the great vessels in this issue of Circulation: one, by Ferencz, describes the anatomic changes in the pulmonary vas-culature; the other, by Rahimtoola and associates , presents a method of obtaining pressure and oxygen saturation of the blood in the pulmonary artery. The extent of the vascular obstructive change reported by Ferencz is remarkable indeed , particularly among members of the very young age group. The change is such that it might well engender concern on the part of the surgeon and physician from the points of view of the optimal time for operation and the degree to which hopes for a low operative mortality rate and successful rehabilitation, can be regarded as realistic. In many instances of transposition of these vessels a transvenous catheter cannot be manipulated into the pulmonary artery. At such a time adaptation of Radner's procedure for pulmonary arterial puncture, as described by Rahimtoola and associates, should prove most helpful in measurement of pulmonary arterial pressure and flow which are crucial data in appraisal of the extent of any pulmonary vascular obstruction. The hemodynamic aberration when the Circulation, Volume XXXIII, February 1966 great vessels are transposed and two functioning ventricles are present, particularly when the ventricular septum is intact, has not been freed from wild conjecture. The diagrams that are made for the purpose of demonstrating the pattern of the fetal and neonatal circulations must be regarded as gross approximations of the true situation. When the two circulations are nearly separate , with the ventricular septum intact (parallel circulations replacing a serial circulation), one hypothesis states that the volume flows are independent. It would be presumed that the "drive" for an increased cardiac output is triggered by the oxygen requirement of tissues; with near-separation of the …