Pregnancy imposes profound physiological adaptations on the maternal cardiovascular system to support the developing fetus. While these changes are normal and necessary, they significantly increase the workload of the heart. For women with pre-existing cardiac conditions or those who develop cardiac issues during gestation, these adaptations can precipitate clinical decompensation. Heart disease in pregnancy is a leading cause of maternal mortality and morbidity worldwide, necessitating a multidisciplinary approach involving cardiologists, obstetricians, and anesthesiologists.
Pathophysiology of Heart Disease in Pregnancy
To understand how heart disease manifests in pregnancy, one must first understand the baseline cardiovascular changes that occur in a healthy gestation. These changes begin as early as the sixth week and peak by the late second trimester, remaining elevated until delivery and the immediate postpartum period.
A. Systemic Hemodynamic Changes
The most significant change is a dramatic increase in blood volume. Total body water increases, leading to a 40% to 50% increase in plasma volume and a 20% to 30% increase in red blood cell mass. This “physiologic anemia of pregnancy” results in a decrease in systemic vascular resistance (SVR) and blood pressure (particularly diastolic pressure), while simultaneously increasing venous return.
Simultaneously, cardiac output (CO) increases by 30% to 50%. This is achieved through two mechanisms:
- Increased Stroke Volume: Due to the increased preload (volume returning to the heart).
- Increased Heart Rate: An average rise of 10 to 20 beats per minute.
In patients with compromised cardiac reserve, this volume overload can lead to pulmonary congestion and heart failure. Conversely, conditions with low cardiac output (such as Eisenmenger syndrome) may tolerate the volume load better than the drop in SVR, which can exacerbate right-to-left shunting.
B. Structural Changes and Shunts
The hormonal environment of pregnancy causes changes in the connective tissue of the heart valves and aorta. Valves may become more floppy, and the aortic root can dilate. For women with mechanical valves, the hypercoagulable state of pregnancy creates a dangerous paradox requiring anticoagulation.
C. The Postpartum Risk Period
While hemodynamic changes are significant throughout pregnancy, the highest risk period for maternal hemodynamic collapse is actually during the first 48 to 72 hours postpartum. During labor, autotransfusion occurs with each uterine contraction. Immediately after delivery, the relief of vena cava compression by the gravid uterus causes a sudden increase in venous return (preload). The mobilization of extravascular fluid (diuresis) also puts a strain on the heart. This “dynamic flux” requires careful monitoring.
Symptoms and Signs of Heart Disease in Pregnancy
Diagnosing heart disease in pregnancy is notoriously difficult because the symptoms of normal pregnancy mimic those of heart failure.
A. Overlapping Symptoms
Pregnant women often experience:
- Dyspnea: Usually due to the elevated diaphragm and increased oxygen consumption. Pathologic dyspnea (heart failure) is characterized by orthopnea (shortness of breath when lying flat) or paroxysmal nocturnal dyspnea.
- Fatigue: Extremely common in normal pregnancy.
- Edema: Lower extremity edema occurs in up to 50% of normal pregnancies due to venous stasis from the enlarging uterus.
B. Pathologic Signs (Red Flags)
Clinicians must distinguish normal changes from warning signs of cardiac decompensation:
- Resting Tachycardia: Persistent heart rate >110 bpm.
- Gallop Rhythm: An S3 or S4 heart sound suggests ventricular dysfunction.
- New Murmurs: A flow murmur is common due to volume overload, but a harsh systolic or diastolic murmur suggests valvular pathology (e.g., mitral stenosis).
- Cyanosis: Central cyanosis is never normal in pregnancy and suggests shunt reversal or severe hypoxemia.
- Hemoptysis: Coughing up blood is a classic sign of pulmonary edema associated with mitral stenosis.
- Syncope: Fainting, particularly when occurring while standing or with exertion.
Diagnosis of Heart Disease in Pregnancy
Because physical examination is limited by the physiologic changes of pregnancy, imaging and specific scoring systems are vital.
A. Electrocardiogram (ECG): ECG is safe and recommended. While mild deviations (such as slight left axis deviation or T-wave changes) can occur, significant arrhythmias or signs of ischemia (ST-segment depression) are abnormal and require investigation.
B. Echocardiography: The transthoracic echocardiogram (TTE) is the primary diagnostic tool. It uses ultrasound waves and has no known adverse effects on the fetus. It is safe to perform throughout pregnancy. Doppler imaging allows for the assessment of valve function, ejection fraction, and estimation of pulmonary artery pressures. Any woman with a known cardiac lesion or new pathological findings should undergo echocardiography.
C. Chest X-ray: If essential for diagnosis (e.g., suspected aortic dissection or severe pneumonia), a chest X-ray can be performed with shielding of the abdomen. The radiation exposure to the fetus from a standard PA chest X-ray is negligible (less than 0.01 rad).
D. Cardiac MRI: Magnetic Resonance Imaging (MRI) is the preferred modality for evaluating aortic pathology (like coarctation or dissection) and complex congenital heart disease. It uses no ionizing radiation. Gadolinium contrast is generally avoided due to fetal transplacental passage, unless the benefit clearly outweighs the risk.
E. Risk Stratification (CARPREG and ZAHARA Scores): To quantify risk, physicians use validated scoring systems:
- CARPREG Score: Assigns points for prior cardiac events, NYHA functional class >II, cyanosis, left heart obstruction, and reduced systemic ventricular systolic function.
- ZAHARA Score: Focuses on specific valve diseases and congenital lesions.
Treatment of Heart Disease in Pregnancy
Management of heart disease in pregnancy requires a delicate balance between maternal hemodynamic stability and fetal safety.
A. Pharmacologic Management
- Heart Failure: Diuretics (e.g., Furosemide) are the mainstay for volume overload. Digoxin can be used for rate control. Beta-blockers (e.g., Labetalol, Metoprolol) are used for hypertension and rate control but must be monitored for fetal growth restriction.
- Hypertension: Methyldopa, Labetalol, and Nifedipine are first-line agents. ACE inhibitors and ARBs are contraindicated due to teratogenicity (fetal renal dysplasia, oligohydramnios, and skull defects).
- Arrhythmias: Electrical cardioversion is safe during pregnancy if hemodynamically unstable. Pharmacologic management usually involves beta-blockers or digoxin.
B. Anticoagulation in Pregnancy
This is the most complex area of management, particularly for mechanical heart valves (MHV).
- Warfarin: Crosses the placenta and is teratogenic (fetal warfarin syndrome), causing nasal hypoplasia and skeletal abnormalities. It also carries a risk of fetal intracranial hemorrhage. However, it is often more effective for preventing valve thrombosis.
- Heparin (Unfractionated or Low Molecular Weight Heparin – LMWH): Does not cross the placenta. LMWH is generally preferred for prophylaxis. For high-risk mechanical valves, careful management with adjusted-dose unfractionated heparin or LMWH is required, particularly in the first trimester, followed by a switch to Warfarin in the second and third trimesters (if the patient is compliant and levels are monitored). Aspirin is often added.
C. Management of Labor and Delivery
- Mode of Delivery: Vaginal delivery is preferred for most cardiac patients, as it involves less fluid shifts than a C-section. Cesarean section is reserved for obstetric indications or patients with unstable hemodynamics who cannot tolerate the stress of labor.
- Analgesia: Epidural analgesia is highly beneficial. It blunts the sympathetic surge of labor, reducing heart rate and blood pressure spikes.
- Positioning: Laboring patients should avoid the supine position (which compresses the vena cava) and be placed in a semi-recumbent or left lateral position.
D. Postpartum Monitoring
As noted, the postpartum period is the highest risk. Women with moderate-to-high risk heart disease should remain under cardiac monitoring for at least 48 to 96 hours after delivery. Fluid management is critical to prevent pulmonary edema during the diuretic phase.
Conclusion
Heart disease in pregnancy is a high-stakes clinical scenario requiring vigilance, sophisticated diagnostic capabilities, and a collaborative care team. The pathophysiology involves navigating a 50% increase in blood volume and cardiac output against a background of existing cardiac pathology. Distinguishing normal pregnancy symptoms from cardiac decompensation is the first step in diagnosis, followed by safe imaging modalities like echocardiography and MRI. Treatment is individualized, focusing on hemodynamic support and safe anticoagulation strategies. Finally, meticulous planning for labor, delivery, and the postpartum period is essential to ensure the best outcomes for both mother and child.
References
- American College of Obstetricians and Gynecologists (ACOG). (2019). ACOG Practice Bulletin No. 212: Pregnancy and Heart Disease. Obstetrics & Gynecology, 133(5), e320-e356.
- Thilen, S. R., et al. (2018). 2018 American Society of Anesthesiologists (ASA) Practice Guidelines for Obstetric Anesthesia. Anesthesiology, 128(5), 1-28.
- Regitz-Zagrosek, V., et al. (2018). 2018 ESC Guidelines for the management of cardiovascular diseases during pregnancy. European Heart Journal, 39(46), 3165–3241.
- Siu, S. C., et al. (2001). Prospective multicenter study of pregnancy outcomes in women with heart disease. Circulation, 104(6), 670-676.
- Dempsey, N. J., & Mabie, W. C. (2020). Cardiovascular Physiology in Pregnancy. In: Cardiac Problems in Pregnancy. Wiley.
