Effect of chronic tocolytic therapy on maternal ventricular function in pregnant rabbits

Our purpose was to determine whether peripartum cardiomyopathy may be associated with chronic beta-mimetic tocolytic therapy.

On gestational day 20 (term 31 days), two 200 microliter Alzet miniosmotic pumps were implanted in the subcutaneous tissue of pregnant New Zealand White rabbits. Each pump was filled with terbutaline (20 micrograms/microliter, n = 7) or saline solution (0.9%, n = 7) and infused continuously for 7 days. The rabbits were killed on the twenty-eighth gestational day. Maternal hearts were placed on a Langendorff (nonejecting) perfusion apparatus for assessment of cardiac function. At a constant perfusion pressure and heart rate left ventricular diastolic pressure was varied while left ventricular developed pressure and left ventricular +/- rate of pressure rise, index values of left ventricular contractility and relaxation, were continuously recorded. Comparisons between groups at each preload were made by analysis of variance.

Hearts taken from terbutaline-treated rabbits exhibited periodic arrhythmias and mechanical alternans in five of seven hearts versus one of seven in the saline solution group. At a preload of 0 mm Hg both left ventricular developed pressure (88.0 vs 48.4 mm Hg, p < 0.001) and left ventricular rate of pressure rise (1406 vs 653 mm Hg/sec, p < 0.001) were 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 rate of pressure rise (1424 vs 694 mm Hg/sec, p < 0.001) were also significantly less in terbutaline-treated rabbits. Left ventricular relaxation was also impaired at all preloads.

In this model chronic administration of terbutaline during late pregnancy significantly depresses global maternal cardiac function.