How pregnancy changes the heart
The cardiovascular system goes through enormous changes during pregnancy. By the second trimester, blood volume is up roughly 40–50%, the resting heart rate is up about 10–20 beats per minute, and the heart is pumping more blood per minute than it has ever pumped before. Estrogen and progesterone levels rise dramatically, both of which affect the heart’s electrical properties.
The result is that pregnancy makes the heart’s electrical system more active and more aware. Most pregnant patients notice their heart at some point — feeling extra beats, occasional racing, or simply being more aware that the heart is working. The vast majority of this is normal physiology, not pathology.
But some genuine rhythm problems do emerge or worsen during pregnancy. Recognizing which is which is the central task of the EP consultation.
What’s usually benign
- Palpitations from sinus tachycardia. A resting heart rate of 90 in pregnancy is normal. Feeling the heart at that rate is also normal.
- Premature beats (PACs and PVCs). Far more common during pregnancy and usually harmless.
- Awareness of normal beats, especially when lying down. Common, particularly in the third trimester.
For most pregnant patients with palpitations, the workup confirms normal rhythm, an unremarkable echocardiogram, and reassurance is the treatment.
What deserves a closer look
Supraventricular tachycardia (SVT)
Patients with a known history of SVT often find their episodes become more frequent or more difficult during pregnancy. Patients without prior SVT can have their first episode in pregnancy because the heart’s higher baseline rate and hormonal changes lower the threshold for these reentry circuits to start.
Treatment in pregnancy:
- Vagal maneuvers first — Valsalva and modified positions work the same in pregnancy
- Adenosine if needed — safe in pregnancy, the standard acute therapy
- Beta-blockers (metoprolol, propranolol) for maintenance — safe in pregnancy, the workhorse here
- Catheter ablation is usually deferred until after delivery; if symptoms are severe and refractory, ablation can be done in pregnancy (typically in the second trimester) with shielding and minimal fluoroscopy
Atrial fibrillation
Less common in pregnancy than in older patients, but it does happen — particularly in patients with underlying structural heart disease, hyperthyroidism, or rheumatic heart disease. AFib in pregnancy needs careful management of:
- Rate control — beta-blockers are preferred; some calcium channel blockers are also safe
- Rhythm control — flecainide and sotalol are commonly used; amiodarone is avoided when possible because of fetal thyroid effects
- Anticoagulation — heparin or low-molecular-weight heparin during pregnancy (warfarin is avoided in early pregnancy because of teratogenicity; DOACs are not approved in pregnancy)
Ventricular arrhythmias
Sustained ventricular tachycardia in pregnancy is uncommon but serious. It often points to an underlying condition — peripartum cardiomyopathy, structural heart disease, or an inherited arrhythmia syndrome. Workup typically includes echocardiogram, family history, ECG analysis for long QT or Brugada pattern, and sometimes cardiac MRI postpartum.
Long QT syndrome and other inherited conditions
Pregnancy and especially the postpartum period can be a high-risk window for women with long QT syndrome. Continuing beta-blocker therapy through pregnancy and the first nine months postpartum is now standard. Discontinuing beta-blockers because of “wanting to be off medication during pregnancy” is unsafe in this population — the risk of cardiac events goes up.
Medications: a quick orientation
Pregnancy medication choices in arrhythmia care fall into rough tiers:
Generally safe and commonly used:
- Metoprolol, propranolol (beta-blockers)
- Diltiazem, verapamil (calcium channel blockers — usually after first trimester)
- Adenosine (acute SVT termination)
- Digoxin
- Flecainide (with careful monitoring)
- Sotalol (with careful monitoring)
- Heparin and low-molecular-weight heparin
Avoided when possible:
- Amiodarone — causes fetal hypothyroidism and is considered a last resort
- Warfarin — teratogenic in the first trimester; sometimes used in the second/third trimester with mechanical valves
- DOACs (apixaban, rivaroxaban, dabigatran, edoxaban) — not enough data, generally avoided
- ACE inhibitors and ARBs — for blood pressure control, contraindicated in pregnancy
Every situation is individualized — there are exceptions to each of these. The conversation with your obstetrician and EP together is what determines the right plan.
Cardioversion in pregnancy
Cardioversion is safe in pregnancy when it’s needed. The shock itself does not affect the fetus appreciably; the electrical current does not cross the placenta meaningfully. Fetal monitoring during the procedure is standard. For AFib or atrial flutter that’s hemodynamically problematic or symptomatically severe, cardioversion is a reasonable option throughout pregnancy.
Ablation in pregnancy
Catheter ablation is technically possible in pregnancy but is usually deferred until after delivery for two reasons:
- Fluoroscopy exposure to the fetus, even with shielding, is not zero
- Most arrhythmias can be controlled medically through pregnancy and ablated definitively afterward
When ablation can’t wait — refractory SVT failing all medications, or hemodynamically significant arrhythmia — it can be done in the second trimester with abdominal shielding and using fluoroscopy-sparing techniques (intracardiac echo, 3D mapping).
Postpartum considerations
The first few weeks after delivery are a transitional period for the cardiovascular system. Blood volume drops, hormones shift, sleep is disrupted. Some patients have:
- A flare of AFib or SVT in the postpartum period
- Peripartum cardiomyopathy that can present with arrhythmias as the first sign
- Symptomatic palpitations from postpartum thyroiditis
- Long QT events (especially in the first nine months) — beta-blocker continuation is critical
Follow-up with cardiology in the first weeks postpartum is appropriate for any patient who had an arrhythmia during pregnancy or who has an underlying inherited condition.
What to expect at your visit
If you’re pregnant (or planning to be) and have a rhythm question, the visit usually covers:
- Your symptom story and any prior rhythm history
- Family history of arrhythmia or sudden death
- Current ECG and prior tracings
- Echocardiogram if not recently done
- Discussion of medication options compatible with pregnancy
- A plan that is shared with your obstetrician — we’ll communicate directly with your OB team about anything we decide together
Most patients with arrhythmia concerns in pregnancy go on to have healthy pregnancies, healthy deliveries, and well-controlled rhythms throughout. Knowing the plan in advance makes a big difference.