Haemodynamic effects of disopyramide using a new model of intravenous administration

Intravenous treatment with disopyramide is usually performed by administration of a bolus injection of 150 mg given over 5 min. followed by a continuous infusion of 18-24 mg hour-1. A decrease in cardiac output is associated with this rapid bolus injection. Seven patients with ischaemic heart disease entered an open randomised cross-over trial to elucidate if an extension of the bolus injection time to 20 min. resulted in a smaller decrease in cardiac output. Cardiac index decreased significantly (P less than 0.001) in both situations, with maximum decrease observed at time 5 and 20 min., respectively (equivalent to the ending of the administration of 150 mg disopyramide). The decrease in Cardiac index (mean +/- S.E.M.) was identical in the two situations (2.56 +/- 0.23 to 1.78 +/- 0.21 l/min. X m2 (30%) and 2.66 +/- 0.17 to 1.94 +/- 0.19 l/min. X m2 (27%], respectively. Blood pressure was unchanged, while heart-rate (P less than 0.025) and preejection period index (P less than 0.005) increased significantly and to the same extent in the two situations. Significant correlations between the log free and log total serum concentration of disopyramide and the relative change in preejection period index of r = 0.840 (P less than 0.01) and 0.919 (P less than 0.01), respectively, were observed giving disopyramide over 5 min. A significant anticlockwise hysteresis was observed extending the time of administration to 20 min. As no haemodynamic advantages are achieved by the slower way of administration we would still recommend the bolus injection to be given over 5 min.