The Value of Dye Dilution Curves in the Diagnosis of Intracardiac Shunts

Abstract

In an earlier paper (Resnekov, 1962), the effects of valvular incompetence on the nomal dye dilution curve were described. This paper deals with the effects of intracardiac shunts on the normal dye curve. Broadbent et al. (1951) have shown that with a left-to-righit shunt, the peak concentration is lower than would be expected for the amount of dye injected (Fig. 1), the disappearance slope is prolonged, and systemic recirculation of blood and dye causes an absence of the normal secondary peak of dye concentration. The appearance and build-up times are normal. The prolongation of the disappearance slope is only partly related to the cardiac output and cannot be used alone in the diagnosis of a left-to-right shunt. Broadbent and Wood (1954) have suggested that if the ratio of the disappearance to build-up time is calculated, the variation of the disappearance time with the cardiac output is no longer important and, further, the ratio will correlate with the volume of a leftto-right shunt as long as this is at least 35 per cent of the total pulmonary artery flow. With a right-to-left shunt as shown by Swan, Zapata-Diaz, and Wood (1953), there is a shortened appearance time (Fig. 2), a hump on the build-up slope, and the peak concentration is less than would be expected for the amount of dye injected. The build-up slope is thus divided into two separate fractions, for blood and dye arrives at the sampling point via two routes-the right-toleft element completely by-passing the lungs to arrive first, and the remainder following closely in the normal way.