Leah Bernard

Myocardial Performance and its Acute Response to Angiotensin II Infusion in Fetal Sheep Adapted to Chronic Anemia

Fetal chronic anemia causes lengthening of cardiomyocytes. In adults, severe left ventricular overload may lead to irreversible ventricular dysfunction. We hypothesized that in sheep fetuses with chronic anemia, remodeled myocardium would less successfully respond to angiotensin II (AT II) infusion than in fetuses without anemia. A total of 14 ewes with twin pregnancy underwent surgery at 113 ± 1 days of gestation. After a recovery period, anemia was induced by isovolumic hemorrhage in 1 fetus of each pair. At 126 ± 1 days of gestation, longitudinal myocardial velocities of the right (RV) and left (LV) ventricles were assessed at the level of the atrioventricular valve annuli via tissue Doppler imaging. Cardiac outputs were calculated by pulsed Doppler ultrasound. All measurements were performed at baseline and during fetal AT II infusion. Fetal serum cardiac natriuretic peptide (N-terminal peptide of proatrial natriuretic peptide [NT-proANP] and B-type natriuretic peptide [BNP]) concentrations were determined. Nine ewes successfully completed the experiment. At baseline, ventricular free wall thicknesses, cardiac outputs, and NT-proANP levels were significantly greater in the anemic fetuses than in the controls. The LV isovolumic contraction velocity (IVCV) acceleration and isovolumic relaxation velocity (IVRV) deceleration were lower (P < .05) in the anemic fetuses than in the controls. In the anemic fetuses, there was a positive correlation (R = .93, P < .01) between RV IVRV deceleration and NT-proANP concentration. Angiotensin II infusion increased (P < .05) LV IVCV acceleration in the anemic fetuses. We conclude that in anemic sheep fetuses, myocardial adaptation is associated with impaired LV early contraction and relaxation. However, the LV can improve its contractility with an inotropic stimulus, even in the presence of increased afterload.

REGIONAL MYOCARDIAL FUNCTION AND RESPONSE TO ACUTE AFTERLOAD INCREASE IN CHRONICALLY ANEMIC FETAL SHEEP: EVALUATION BY TWO-DIMENSIONAL STRAIN ECHOCARDIOGRAPHY

We hypothesized that in chronic fetal anemia, remodeling of the myocardium is related to abnormalities in regional wall motion and acutely increased afterload further disturbs myocardial strain. Chronic anemia was induced in one fetus of each of seven sheep twin pregnancies. The fetuses were studied by two-dimensional (2-D) strain echocardiography at baseline and during increased afterload via angiotensin II (AT II) infusion. At baseline, the peak systolic longitudinal, radial and circumferential strains in the left ventricular lateral wall in anemic fetuses were lower than those in the controls (all p<0.05). During AT II, the circumferential strain of right ventricular free wall decreased significantly both in the control and anemic fetuses. Left ventricular free wall systolic strains were not affected by AT II. Fetal myocardial remodeling in chronic anemia decreases left ventricular systolic free wall strains. The myocardial adaptation does not change ventricular responses to acutely increased afterload.

Fetal Ventricular Diastolic Filling Characteristics in a Primate Model: The Role of Fetal Heart Rate and Pulmonary Vascular Impedance:

Objectives: We hypothesized that fetal ventricular diastolic filling characteristics are related to fetal heart rate (FHR) and pulmonary vascular impedance. Methods: Rhesus monkeys underwent Doppler ultrasonography at near-term gestation. Tricuspid (TV) and mitral valve (MV) blood velocity waveforms were used to calculate maximum velocity (V-max) and velocity time integral (VTI) E/A ratios (early filling/ventricular filling during atrial contraction) at baseline and during maternal hyperoxygenation. Right pulmonary artery (RPA) pulsatility indices (PIs) and FHR were measured. Results: Hyperoxgenation significantly decreased FHR and RPA PI. The TV V-max and the MV VTI E/A ratios increased significantly and correlated with a decrease in FHR but not with a decrease in RPA PI. The TV and MV A-wave V-max decreased during hyperoxygenation and their decrease correlated significantly with a drop in FHR. Conclusions: Fetal ventricular diastolic filling characteristics are related to FHR but not to pulmonary vascular impedance.