LEFT-VENTRICULAR PARALLEL CONDUCTANCE DURING CARDIAC CYCLE IN CHILDREN WITH CONGENITAL HEART-DISEASE

This study examines the accuracy of the conductance catheter technique and, in particular, parallel conductance [expressed as offset volume (V-c)] changes during the cardiac cycle in the human left ventricle. T wo groups of patients were assessed: group 1, with an open atrial sept al defect, and group 2, with an interventricular communication. In a s ubgroup, pre- and postoperative data were compared to assess the possi ble impact of shunting or anatomic considerations on our measurements. V, is normally obtained by a saline-dilution technique previously des cribed by Baan et al. [V-c(Baan); J. Baan, E. T. Van der Velde, H. G. Debruin, G. J. Smeenk, J. Koops, A. D. Van Dijk, D. Temmerman, P. J. S enden, and B. Buis. Circulation 70: 812-823, 1984]. This does not take into account potential changes during the cardiac cycle. Four cardiac cycles were taken from the hypertonic saline washin and were divided into six equal isochrones between the maximum and mini mum first deriv atives of left ventricular pressure (dP/dt(max) and dP/dt(min), respec tively). The apparent ventricular volume was regressed against stroke volume for the corresponding cardiac cycle. The volume at the y-interc ept corresponds to the V-c at each time interval [V-c(t)]. In group I, there was a variation in V-c(t) during systole, but the temporal chan ges were quite small, on the order of 4.28% (SD = 5.18%) of total corr ected end-diastolic volume (mean maximal variation of 2.60 ml). Furthe rmore, the value of V-c obtained at dP/dt(max) was not significantly d ifferent from that obtained at dP/dt(min). For group 2 as a whole, mea n V-c(Baan) did not change significantly with ventricular septal defec t closure (preoperative, 8.85 +/- 11.1 ml; postoperative, 9.82 +/- 11. 84 ml). Group 2 children also exhibited a systolic cyclical variation in V-c(t) similar to group 1. Finally, V-c(t) as a percentage of end-d iastolic volume was no different when group 1 and group 2 were compare d. We conclude that in the left ventricle, even in the presence of a l eft-to-right shunt, there is a small but insignificant difference in p arallel conductance during ventricular ejection. The magnitude of this cyclical change does not preclude ventricular volume measurement in c ongenital heart disease by the conductance catheter technique.