Changes in hemodynamics, ventricular remodeling, and ventricular contractility during normal pregnancy: a longitudinal study.

OBJECTIVE

To investigate the hemodynamic changes occurring in normal pregnancy and to see if these changes were associated with an increase in myocardial contractility.

METHODS

In a longitudinal study, primigravidas were studied with echocardiography in early (15 +/- 1.8 weeks), mid (26 +/- 1.2 weeks), and late (36 +/- 1.0 weeks) gestation, as well as at 6 weeks postpartum. Cardiac dimensions were measured with two-dimensional and M-mode echocardiography and hemodynamic indices were calculated. All measurements were made with subjects in the left lateral decubitus position. Statistical analysis was performed with repeated measures analysis of variance.

RESULTS

Seventy-six women with normal pregnancy outcomes completed all four studies. From the baseline study to late gestation, an increase in cardiac output of 27% (from [mean +/- standard error] 4.2 +/- 0.1 to 5.8 +/- 0.2 L/min, P = .001), and a decrease in total peripheral resistance of 33% (from 1356 +/- 69 to 941 +/- 37 dynes/second cm-5, P = .001) occurred. Over this same time period, left ventricular function, while demonstrating a small and non-significant increase in velocity of circumferential fiber shortening (from 1.25 +/- 0.02 to 1.27 +/- 0.02 cm/second), revealed a 12% decrease in wall stress (from 36.3 +/- 1.0 to 31.9 +/- 1.0 g/cm2, P = .001) and a 13% decrease in the load-independent wall stress to velocity of circumferential fiber shortening ratio (from 30.0 +/- 1.2 to 26.1 +/- 1.0, P = .01), implying enhanced intrinsic myocardial contractility.

CONCLUSION

Normal pregnancy is characterized by enhanced myocardial performance.