Antiarrhythmic Medicines in Pregnancy: Risks and Safer Choices

Pregnancy changes cardiovascular physiology in ways that can expose or intensify rhythm disorders. Blood volume rises, resting heart rate increases, and hormonal and autonomic shifts may affect the electrical stability of the myocardium. A previously quiet supraventricular tachycardia can become symptomatic, while atrial fibrillation or ventricular arrhythmia may emerge in someone with structural heart disease.

Medication decisions are consequently more complex than selecting the most effective antiarrhythmic in a non-pregnant adult. The clinician must weigh maternal haemodynamic stability, the risk of recurrent arrhythmia, placental transfer, fetal development, gestational age, and the consequences of untreated disease. A fast rhythm that compromises maternal output can also threaten fetal oxygen delivery.

The phrase antiarrhythmic drug therapy in pregnancy covers several different clinical situations. Acute termination of a paroxysm, prevention of recurrence, treatment of an inherited channelopathy, and suppression of ventricular arrhythmias each require a different risk–benefit assessment. Evidence is often derived from registries, observational studies, pharmacology, and clinical experience rather than randomised pregnancy trials.

For Australian patients, care may involve a general practitioner, cardiologist, electrophysiologist, obstetric physician, maternal–fetal medicine team and neonatal service. A patient living in regional Queensland, Western Australia or the Northern Territory may also need coordinated telehealth and planned travel to a tertiary centre. Early referral makes it easier to review medicines before conception or before symptoms become urgent.

Why Rhythm Control Requires A Maternal–Fetal Balance

The first task is to establish whether the rhythm is genuinely dangerous, highly symptomatic or likely to cause tachycardia-mediated ventricular dysfunction. An ECG during symptoms, ambulatory monitoring, echocardiography and targeted blood tests can distinguish sinus tachycardia from re-entry tachycardia, atrial arrhythmia or ventricular ectopy. Electrolytes, thyroid function, infection, anaemia and stimulant exposure should be addressed where relevant.

A stable mother with brief, self-terminating episodes may need observation, vagal manoeuvres and a clear emergency plan rather than daily medicine. By contrast, syncope, hypotension, chest pain, pulmonary oedema, sustained ventricular tachycardia or rapid atrial fibrillation demands urgent specialist care. Maternal stabilisation is the priority because fetal wellbeing depends heavily on adequate maternal circulation.

Risk also changes across pregnancy. Organ formation occurs mainly in the first trimester, when concerns about structural malformations are especially important. Later exposure may be associated with fetal growth restriction, bradycardia, hypoglycaemia, altered thyroid function or neonatal drug toxicity. The decision should therefore be revisited at each trimester, rather than treated as permanent once a prescription is issued.

Medicines Commonly Considered For Supraventricular Arrhythmias

For acute regular narrow-complex supraventricular tachycardia, vagal techniques are generally attempted first when the patient is stable. Intravenous adenosine has a very short half-life and is widely used when conversion is required. Available experience has not shown a clear pattern of congenital harm, although administration should occur with maternal monitoring and appropriate fetal assessment when clinically indicated.

Beta blockers may be used for recurrent episodes or rate control, with metoprolol often preferred because of accumulated clinical experience. Propranolol and other agents may also be considered in selected circumstances. Potential effects include fetal growth restriction, neonatal bradycardia and neonatal hypoglycaemia, particularly with ongoing treatment close to delivery. Growth surveillance and a neonatal observation plan can reduce avoidable surprises.

Flecainide and sotalol are sometimes selected for prevention or for specific maternal or fetal indications, including certain fetal tachyarrhythmias. Both require attention to QRS duration, QT interval, renal function and drug interactions. Digoxin can have a role in rate control, especially in selected atrial arrhythmias, but serum concentrations and clinical response must be interpreted carefully during pregnancy because pharmacokinetics change.

Drugs With Greater Concern Or Narrower Roles

Amiodarone is generally avoided when alternatives are effective. It crosses the placenta and has a long half-life; exposure has been associated with fetal and neonatal thyroid dysfunction, growth problems, bradycardia and possible neurodevelopmental concerns. It may still be justified for life-threatening maternal or fetal arrhythmia when other approaches fail. Such use calls for specialist oversight, detailed fetal monitoring and neonatal thyroid assessment.

Quinidine and procainamide have historical roles in selected ventricular or atrial arrhythmias, but their adverse-effect profiles and monitoring requirements limit routine use. Class IC medicines may be appropriate in carefully defined cases, while class III medicines can prolong the QT interval and increase the risk of torsades de pointes. A medication that is reasonable in one patient may be hazardous in another with hypokalaemia, congenital long-QT syndrome or interacting medicines.

The available evidence rarely permits a simple “safe” or “unsafe” label. Apparent associations can reflect the underlying maternal illness, co-medications or the severity of the arrhythmia. Shared decision-making should document why treatment is needed, what alternatives were considered, how the fetus will be monitored and what signs require immediate review. The Journal of Arrhythmia articles provide clinicians and trainees with access to current research and clinically relevant electrophysiology literature.

Non-Drug Treatment And Acute Rescue

Electrical cardioversion is an important alternative when an arrhythmia is unstable, poorly tolerated or resistant to medication. It can be performed during pregnancy when clinically necessary, using the lowest effective energy and standard precautions. Fetal monitoring before and after the procedure is commonly arranged, with obstetric support based on gestation and local capability.

Catheter ablation may be considered for drug-refractory, poorly tolerated recurrent supraventricular tachycardia, especially when repeated admissions or medication exposure would carry greater risk. When possible, ablation is postponed until after delivery or performed during the second trimester by an experienced team. Modern approaches may reduce or avoid fluoroscopy, using three-dimensional mapping and intracardiac guidance.

A pre-pregnancy ablation can be especially valuable for people with a known re-entry circuit and frequent symptomatic episodes. In Australia, referral pathways differ between metropolitan centres such as Sydney, Melbourne, Brisbane, Adelaide and Perth and smaller regional hospitals. A written plan should identify the nearest emergency department, the accepting cardiology service and transport arrangements for patients who live far from an electrophysiology laboratory.

Monitoring The Pregnancy And Newborn

Monitoring depends on the rhythm, drug, gestational age and maternal cardiac substrate. It may include serial ECGs, ambulatory monitoring, echocardiography, renal and liver tests, electrolytes, drug levels and fetal growth scans. Medicines that affect conduction or repolarisation warrant particular attention to the maternal QT interval and to other prescribed or over-the-counter products.

The obstetric team may assess fetal heart rate, growth, amniotic fluid and signs of fetal arrhythmia. If a beta blocker is continued late in pregnancy, the newborn team should know in advance so that heart rate and blood glucose can be observed. Amiodarone exposure may require neonatal thyroid testing, while digoxin and other medicines may need an individualised postnatal review.

Breastfeeding decisions should be planned before birth rather than made during a sleep-deprived postnatal admission. Many medicines enter breast milk to some degree, but the clinical relevance varies with dose, timing, infant maturity and renal function. A cardiologist, pharmacist, paediatrician and obstetric team can coordinate a practical feeding and medication plan.

Special Situations Inherited And Structural Disease

Pregnancy can be high risk when arrhythmia occurs with cardiomyopathy, repaired congenital heart disease, significant valve disease, pulmonary hypertension or an inherited electrical disorder. Long-QT syndrome, Brugada syndrome and catecholaminergic polymorphic ventricular tachycardia require specialist risk assessment because hormonal and haemodynamic changes may alter arrhythmia susceptibility. Fever, electrolyte disturbance and QT-prolonging medicines should be managed carefully.

An implantable cardioverter-defibrillator generally remains in place during pregnancy when indicated; pregnancy alone is not a reason to deactivate appropriate protection. Device interrogation can confirm lead function and arrhythmia burden. For broader device-related electrophysiology context, the clinical discussion of lead-related tricuspid regurgitation is relevant when assessing structural and lead-associated complications.

Patients with atrial fibrillation may also need anticoagulation, which is a separate but connected issue. Warfarin, heparins and direct oral anticoagulants have different pregnancy considerations, and the choice depends on valve disease, stroke risk and timing. Anticoagulation should never be started, stopped or substituted without advice from the treating team.

Planning Before Conception And Around Delivery

A preconception consultation allows clinicians to confirm the rhythm diagnosis, review all medicines, correct electrolyte or thyroid abnormalities and consider definitive ablation. It is also an opportunity to assess ventricular function, inherited disease and the need for an implantable device. People should be advised not to stop an antiarrhythmic suddenly, since rebound arrhythmia may be more dangerous than supervised continuation.

As delivery approaches, the plan should cover medication timing, monitoring, analgesia, fluid management and escalation if an arrhythmia occurs. Most patients do not require caesarean birth solely because they take an antiarrhythmic medicine. The mode and place of birth depend on obstetric indications, maternal cardiac risk and access to appropriate monitoring.

Australian prescribing information, Therapeutic Goods Administration updates, specialist pharmacy advice and local hospital protocols can support decision-making, but they do not replace an individual assessment. The evidence base changes as pregnancy registries and post-marketing data expand. Clinicians can also follow emerging themed research through the journal’s arrhythmia collections.

Every treatment plan should leave the patient with clear instructions about palpitations, fainting, breathlessness, chest pain and reduced fetal movement. Emergency symptoms warrant urgent assessment rather than waiting for a routine appointment. For clinicians, documenting the indication, gestational age, alternatives, monitoring schedule and neonatal plan creates continuity across general practice, cardiology, maternity and emergency services.

Patients planning pregnancy or already pregnant should seek an early review with their cardiologist and maternity team, bringing a complete list of prescriptions, supplements and previous ECGs. Clinicians can use a coordinated, evidence-based pathway to select the lowest-risk effective strategy, arrange timely non-drug treatment when appropriate and protect both maternal rhythm stability and fetal wellbeing.