- Estrogen activates the renin-angiotensin-aldosterone systems, increasing plasma volume (up to 40% of the prepregnancy value) and promoting sodium and water retention. The disproportionate increase in volume leads to hemodilution and results in the physiological anemia of pregnancy. To accommodate the increase in volume, vasodilatation and vascular remodeling occur with a reduction in both the systemic and pulmonary vascular resistance. By the second trimester, the systemic vascular resistance falls by 30% to 50% from pre-pregnancy values, followed by a slight increase at the end of the third trimester. Relaxin, prostacyclin, and possibly nitric oxide also contribute to a fall in blood pressure, beginning as early as 6 to 8 weeks. Cardiac output initially increases as a result of an increase in stroke volume. Later in gestation, HR increases 10 to 20 beats/min, reaching a maximum in the third trimester. The net effect of these physiological changes is increased cardiac output 30% to 50% above the pre-pregnancy level in a singleton gestation and as much as an ∼15% further increase for twin pregnancies. 1
- Normal ECG changes that may be seen in pregnancy 🤰
- Increased HR
- Ectopic beats
- Left-shift of QRS axis
- Q waves in lead III
- T wave flattening
Red Flags 🚩
Figure source: 2
- See 2
- Shortness of breath at rest.
- Severe orthopnea ≥4 pillows.
- Resting HR ≥110 bpm.
- Resting SBP ≥160 mm Hg.
- Resting RR ≥30.
- Oxygen saturations ≤94% (with or without personal history of CVD)
Footnotes
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Halpern DG, Weinberg CR, Pinnelas R, Mehta-Lee S, Economy KE, Valente AM. Use of Medication for Cardiovascular Disease During Pregnancy: JACC State-of-the-Art Review. J Am Coll Cardiol. 2019 Feb 5;73(4):457-476. doi: 10.1016/j.jacc.2018.10.075. PMID: 30704579. ↩
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Hameed AB, Tarsa M, Graves CR, Grodzinsky A, Thiel De Bocanegra H, Wolfe DS. Universal Cardiovascular Disease Risk Assessment in Pregnancy: Call to Action JACC: Advances Expert Panel. JACC Adv. 2024 Jun 23;3(8):101055. doi: 10.1016/j.jacadv.2024.101055. PMID: 39372368; PMCID: PMC11450966. ↩ ↩2