FIGURE 4-7 Left ventricular stroke volume across pregnancy compared with 12-week postpartum (nonpregnant) values for normal-weight women in the supine and lateral positions. (Data from Nelson, 201o5.) cardiac silhouette (Enein, 1987). These factors make it dii cult to precisely identiy moderate degrees of cardiomegaly by simple radiographic studies.
graphic changes, and the most common is slight left-axis devia tion due to the altered heart position. Q waves in leads II, III and avF and lat or inverted T-waves in leads III, V1-V3 may also occur (Sunitha, 2014).
During pregnancy, many of the normal cardiac souns are modiied. hese include: (1) an exaggerated splitting ofthe irst heart sound and increased loudness ofboth components, (2) no deinite changes in the aortic and pulmonary elements of the second sound, and (3) a loud, easily heard third sound (Cut forth, 1966). In 90 percent of gravidas, they also heard a sys expiration in others and that disappeared shortly after delivery.
A soft diastolic murmur was noted transiently in 20 percent, and continuous murmurs arising from the breast vasculature in 10 percent (Fig. 49-1, p. 950).
Structurally, the expanding plasma volume seen during nor mal pregnancy is relected by enlarging cardiac end-systolic and end-diastolic dimensions. Concurrently, however, septal thick ness or ejection fraction does not change. This is because the dimensional changes are accompanied by substantive ventricu lar remodeling, which is characterized by left-ventricular mass expansion of 30 to 35 percent near term. In the nonpregnant state, the heart is capable of remodeling in response to stimuli such as hypertension and exercise. Such cardiacplasticiy likely as that in exercise, and pathological hypertrophy-such as with hypertension (Hill, 2008).
Stewart and colleagues (2016) used cardiac MR imaging to prospectively evaluate cardiac remodeling during pregnancy.
Compared with the first trimester, left ventricular mass increased signiicantly beginning at 26 to 30 weeks' gestation, and this continued until delivery (Fig. 4-8). This remodeling is concen tric and proportional to maternal size for both normal and over weight women and resolved within 3 months ofdelivery.
Certainly for clinical purposes, ventricular unction during pregnancy is normal, as estimated by the Braunwad ventricuar unction graph (Fig. 4-9). For the given illing pressures, cardiac ..I3 .g 90 ; ..c)> .J=80
FIGURE 4-8 Let ventricular mass of normal-weight and overweight women across pregnancy compared with 12-week postpartum (nonpregnant) values. (Data from Stewart, 2016.) output is appropriate andthus cardiac unction during pregnancy is eudynamic. Of the metabolic changes that occur in the heart during pregnancy, the eiciency of cardiac work-which is the product ofcardiac output X mean arterial pressure-is estimated to rise by approximately 25 percent. The associated increase in oxygen consumption is primarily accomplished via increased coronary blood low rather than increased extraction (Liu, 2014).
When measured in the lateral recumbent position at rest, cardiac output increases signiicantly beginning in earlypregnancy. It continues to rise and remains elevated during the remainder ofpregnancy. In a supine woman, a large uterus rather consistently compresses veins and diminishes venous return from the lower body. It also may compress the aorta (Bieniarz, 1968). In response, cardiac illing may be reduced and cardiac output ..J=
FIGURE 4-9 Relationship between let ventricular stroke work index (LVSWI), cardiac output, and pulmonary capillary wedge pressure (PCWP) in 10 normal pregnant women in the third trimester. (Data from Clark, 1989.)