Alterations of Systolic Time Intervals During Pregnancy

Systolic time interval measurements were made sequentially throughout pregnancy and during the postpartum period. Recordings were made in the supine and lateral positions. Although the greatest deviations from predicted values were present in the third trimester, changes were evident as early as the first trimester. During the first two trimesters the pre-ejection period (PEP) was significantly shortened. The left ventricular ejection time (LVET) remained normal while the PEP/LVET decreased.The third trimester was characterized by a markedly shortened LVET, a prolonged PEP, and an increased PEP/LVET, all more apparent in the supine than in the lateral position. These findings are consistent with impaired left ventricular performance and are probably due to decreased left ventricular preload resulting from diminished venous return secondary to inferior vena caval obstruction by the gravid uterus.In the postpartum period, the PEP/LVET remained elevated in both positions; the PEP was prolonged and the LVET shortened in the lateral posture. It is concluded that alterations in systolic time interval measurements occur normally during the course of uncomplicated pregnancy and persist into the postpartum period. Possible mechanisms are discussed.