Normal physiologic changes during pregnancy can exacerbate symptoms of underlying cardiac disease even in previously asymptomatic individuals. Maternal blood volume rises progressively until the end of the sixth or seventh month. Stroke volume increases over the same time course as a result of the volume change and an increase in LVEF. The latter reflects predominantly a decline in peripheral resistance due to vasodilation and the low-resistance shunting through the placenta. The heart rate then rises in the third trimester to further increase the cardiac output as the stroke volume maximizes out. Overall, cardiac output increases by 30–50%, peaking (and remaining constant) at about the 14th week; systolic BP tends to rise slightly or remain unchanged, but diastolic pressure falls significantly. Venocaval compression of the inferior vena cava from the gravid uterus can lead to reduced venous return and a lower cardiac output in the supine position.
High cardiac output causes alterations in the cardiac examination. A third heart sound is prominent and normal (see AUDIO 10–6), and a pulmonary flow murmur is common. A mammary souffle may be heard over the breasts. ECG changes include rate-related decreases in PR and QT intervals, a leftward axis shift, inferior Q waves due to the more horizontal position of the heart, and nonspecific ST–T wave changes. Normal echocardiographic findings include slightly increased chamber sizes, functional valvular regurgitation, and occasionally small pericardial effusions.
MANAGEMENT OF PREEXISTING CONDITIONS
The physiologic changes imposed by pregnancy can cause cardiac decompensation in patients with any significant cardiac abnormality, but the most severe problems are encountered in patients with valvular stenosis (especially mitral and aortic stenosis), congenital or acquired abnormalities associated with pulmonary hypertension or right-to-left shunting, heart failure due to any cause, CHD, and hypertension. Valvular insufficiency or left-to-right shunting often diminishes because of the fall in peripheral resistance and is better tolerated than other lesions.
Coarctation of the aorta is usually well tolerated unless severe, when perfusion of the gravid uterus and upper extremity hypertension become an issue. Patients with symptoms or significant upper extremity hypertension before pregnancy should have corrective surgery before embarking on a pregnancy. Patients with severe pulmonary hypertension and cyanotic congenital heart disease and those with severe aortic stenosis are at extremely high risk and should avoid pregnancy. Balloon valvuloplasty of severe aortic stenosis is feasible and preferable to surgical intervention during pregnancy if possible (see VIDEO 10–10). Patients with most right-sided lesions do well with pregnancy, including those with ASD, pulmonic stenosis, pulmonary valve regurgitation, operated tetralogy of Fallot, and Ebstein anomaly. Those with an RV that supports the systemic circulation can usually tolerate pregnancy unless symptomatic heart failure has already occurred. Most adult patients with a systemic RV have transposition of the great vessels that has been surgically corrected or the condition is congenitally corrected (L-transposition of the great vessels). Patients with hypertrophic cardiomyopathy also do well, though the risk of pregnancy is ...