EFFECT OF CHRONIC TOCOLYTIC THERAPY ON MATERNAL VENTRICULAR-FUNCTION IN PREGNANT RABBITS

OBJECTIVE: Our purpose was to determine whether peripartum cardiomyopa thy may be associated with chronic beta-mimetic tocolytic therapy. STU DY DESIGN: On gestational day 20 (term 31 days), two 200 mu l Alzet mi niosmotic pumps were implanted in the subcutaneous tissue of pregnant New Zealand White rabbits. Each pump was filled with terbutaline (20 m u g/mu l, n = 7) or saline solution (0.9%, n = 7) and infused continuo usly for 7 days. The rabbits were killed on the twenty-eighth gestatio nal day. Maternal hearts were placed on a Langendorff (nonejecting) pe rfusion apparatus for assessment of cardiac function. At a constant pe rfusion pressure and heart rate left ventricular diastolic pressure wa s varied while left ventricular developed pressure and left ventricula r +/- rate of pressure rise, index values of left ventricular contract ility and relaxation, were continuously recorded. Comparisons between groups at each preload were made by analysis of variance. RESULTS: Hea rts taken from terbutaline-treated rabbits exhibited periodic arrhythm ias and mechanical alternans in five of seven hearts versus one of sev en in the saline solution group. At a preload of 0 mm Hg both left ven tricular developed pressure (88.0 vs 48.4 mm Hg, p < 0.001) and left v entricular rate of pressure rise (1406 vs 653 mm Hg/sec, p < 0.001) we re less in terbutaline-treated rabbits. At a preload of 10 mm Hg left ventricular developed pressure (104.4 vs 56.7 mm Hg, p < 0.01) and rat e of pressure rise (1424 vs 694 mm Hg/sec, p < 0.001) were also signif icantly less in terbutaline-treated rabbits. Left ventricular relaxati on was also impaired at all preloads. CONCLUSIONS: In this model chron ic administration of terbutaline during late pregnancy significantly d epresses global maternal cardiac function.