Cardiovascular Disease in Pregnancy Part I: Normal Physiology

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Basic Heart Function

Right Heart

  • Blood flows from the SVC + IVC → R atrium → tricuspid valve (3 leaflets) → R ventricle → pulmonary valve (3 leaflets) → pulmonary artery (or pulmonary trunk), which then divides to right and left pulmonary artery → lungs.

  • What happens if the right heart fails?

    • R sided heart failure basically means that the right side of the heart is not pumping out as much blood to the lung that is coming in from the peripheral veins (blood in > blood out).

      • This leads to blood backing up into the systemic circulation → lower extremity edema, hepatomegaly, jugular venous distention.

      • One of the most common causes is left heart failure.

      • Other acute causes:: pulmonary embolism with large clot burden, adult respiratory distress syndrome, RV myocardial infarction, myocarditis.

      • Causes of chronic right heart failure: pulmonary hypertension, pulmonary arterial hypertension (which is different from PH!), COPD, OSA, congenital heart disease, cardiomyopathies, or right sided valve disease.

Left Heart 

  • Oxygenated blood from lungs → left atrium → mitral valve (2 leaflets) → left ventricle → aortic valve (3 leaflets) → aorta & systemic circulation 

  • What happens if the left heart fails?

    • Left heart failure again means that the left side of the heart is not pumping out as much blood to the body as is coming in (blood in > blood out).

      • This leads to blood backing up into the pulmonary circulation → pulmonary edema, which can lead to SOB, coughing, etc 

      • Causes of left heart failure: myocardial infarction, dilated cardiomyopathy, left sided valvular disease, hypertension, congenital heart disease 

How does the cardiovascular system change with pregnancy? 

Hemodynamic changes

  • Antepartum 

    • Throughout pregnancy, there is a continuous increase in maternal cardiac output and plasma volume.

    • There is a decrease in maternal systemic vascular resistance.

    • Blood pressure will decrease initially, but will increase in 3rd trimester.

  • Intrapartum and postpartum 

    • During labor and delivery, there is increase in cardiac output, heart rate, blood pressure, and plasma volume 

    • Immediately postpartum, there is a large fluid shift (500 cc of autotransfusion), as blood flow to the gravid uterus shifts back to maternal circulation 

    • Blood pressure may increase between days 3-6 because of fluid shifts 

    • All of these shifts will make women with cardiac disease more prone to fluid overload and pulmonary edema.

Structural changes 

  • The heart itself will increase in size with pregnancy 

  • The left and right ventricular mass increase by approximately 50 and 40% 

  • LV end diastolic volumes increase by 10% 

  • Approximately 20% of women have diastolic dysfunction at term → dyspnea on exertion 

  • Structural changes return to baseline after 1 year postpartum 

ACOG PB 212