Mild aortic stenosis may not pose significant problems during pregnancy. However, moderate or severe aortic stenosis is associated with significant maternal (17%) and fetal (32%) mortality. Maternal mortality may be as high as 50% after therapeutic abortion.
The transvalvular gradient increases during pregnancy as vascular volume increases and systemic vascular resistance decreases. However, the greatest risk occurs at the time of labor and delivery, when significant decreases in preload can lead to diminished cardiac output and myocardial ischemia, cerebral ischemia, and death. Invasive cardiac monitoring may be required to monitor preload.
What are the risks of mitral stenosis during pregnancy?
Mitral stenosis accounts for nearly 90% of rheumatic heart disease during pregnancy. Approximately 25% of women with mitral stenosis have their first symptoms during pregnancy.
As blood volume, heart rate, and cardiac output increase during pregnancy, the increased relative obstruction to flow across the stenosed mitral valve causes increased pulmonary venous congestion which, in turn, may lead to frank pulmonary edema. During delivery, the maternal circulation receives an additional 500 ml autotransfusion‚ from the placenta, which can cause acute pulmonary edema. Medical management includes bed rest, digoxin if the patient is in atrial fibrillation, and diuresis. Cardioversion may be safely used when necessary. Closed valvulotomy is relatively safe during pregnancy. If this fails, mitral valve replacement has been performed with low fetal mortaltiy.
As indicated, atrial fibrillation may complicate mitral stenosis as atrial circumference increases. This leads to congestive heart failure as well as thromboembolic disease. In addition to treatment of the arrhythmia, patients should be chronically anticoagulated, usually with heparin.
During labor, patients with mitral stenosis may require invasive hemodynamic monitoring (remembering that pulmonary capillary wedge pressures do not reflect left ventricular filling pressures, so cardiac output must be monitored). Valsalva maneuver may acutely decrease preload, causing cardiac output to fall precipitously. Tachycardia can also cause diminished cardiac output, so regional anesthesia is generally used to minimize pain.