53.6 Arrhythmias in pregnancy

The incidence of supraventricular tachycardia during pregnancy is low. The tachyarrhythmias are often well tolerated but may become more frequent, refractory, and symptomatic, and may even manifest for the first time during pregnancy even in the absence of structural heart disease. Arrhythmia requiring treatment develops in up to 15% of patients with structural heart disease during pregnancy. Ventricular arrhythmias and symptomatic bradycardia are rare.

The incidence of supraventricular tachycardia (SVT) during pregnancy is low.¹ The tachyarrhythmias are often well tolerated^2,3 but may become more frequent, refractory, and symptomatic,⁴ and may even manifest for the first time during pregnancy even in the absence of structural heart disease.⁵ Arrhythmia requiring treatment develops in up to 15% of patients with structural heart disease during pregnancy. Ventricular arrhythmias and symptomatic bradycardia are rare.¹

Although some therapies have potential toxicity and side effects to the fetus, safe and effective alternatives are available for most cases.

For the majority of antiarrhythmic drugs there is not enough data to ensure safety during pregnancy. The risk of teratogenic effects is highest during the first 8–10 weeks of pregnancy. The lowest recommended dose should be used with close monitoring. Attention should be paid to symptoms of heart failure and to ruling out pregnancy-induced cardiomyopathy. Worsening factors, such as electrolytic imbalance, hyperthyroidism, and anaemia, should be corrected.

Vagal manoeuvers is the first line of treatment to terminate episodes of SVT, followed by adenosine intravenously (IV), which can be used safely⁶ (Table 53.6.1). Intravenous metoprolol or propranolol is the second choice. Verapamil IV may cause maternal hypotension. Direct current cardioversion is recommended for all sustained tachycardia with haemodynamic compromise and can safely be performed at all stages of pregnancy.⁷ It is a second option in well-tolerated SVT if drug therapy fails. Fetal rhythm monitoring is recommended since transient fetal arrhythmia has been reported.⁸ Transoesophageal overdrive pacing is an alternative for cardioversion.

Prophylactic antiarrhythmic drugs should be used with caution if symptoms are intolerable or if tachycardia causes haemodynamic compromise (Table 53.6.1).

Beta blockers, metoprolol, propranolol, and acebutolol, are the first-line treatment, preferably after the first trimester.⁹ Long-term use of atenolol has been associated with intrauterine growth retardation and is not recommended.¹⁰ Metoprolol and acebutolol have β₁-selective properties and are less likely to interfere with β₂-mediated uterine relaxation.¹¹ Verapamil is considered to be relatively safe.¹² For refractory cases or for patients with Wolff–Parkinson–White syndrome, Vaughan Williams class I or III antiarrhythmic drugs may be considered. Flecainide appears to be well tolerated and reasonably safe. The experience with propafenone and disopyramide is limited, the latter associated with uterus contractions.

Focal atrial tachycardia is rare during pregnancy. Beta blockers or digoxin are drugs of choice.

Catheter ablation has been reported to be effective with minimal maternal and fetal complications,¹³ but should be restricted to drug-refractory, poorly tolerated SVT and avoided in the first trimester. The radiation should be minimized by using non-fluoroscopic mapping systems and intracardiac echocardiography. Ablation should only be performed in experienced centres and by skilled operators.

New onset of ventricular tachycardia should prompt an investigation to rule out a structural abnormality. Ventricular premature beats during pregnancy are, as a rule, benign.⁵ For symptomatic ventricular premature beats, beta blockers may be used.

Idiopathic right ventricular outflow tract tachycardia is the most common and usually well-tolerated ventricular tachycardia (VT).¹⁴ If severe symptoms or haemodynamic compromise occur, beta blockers or verapamil should be tried.¹⁵ Catheter ablation can be performed in drug-refractory cases.¹⁵

Long QT syndrome patients, especially long QT syndrome type 2, have a higher risk for cardiac events postpartum.^{16,17,18,19,20} Beta blockers reduce the risk of arrhythmia and are highly recommended.^15,18,20 Brugada syndrome does not seem to aggravate arrhythmias during pregnancy.²¹ For catecholaminergic polymorphic ventricular tachycardia, close monitoring and beta blockers are recommended.^22,23,24 In arrhythmogenic right ventricular cardiomyopathy, pregnancy has been well tolerated.^{25,26,27,28,29,30,31}

Acute therapy is outlined in Table 53.6.1. Direct current cardioversion is the first choice in sustained VT with haemodynamic compromise. In well-tolerated VT, IV antiarrhythmic drugs or overdrive pacing can be considered (Table 53.6.1). In recurrent or refractory VT, amiodarone may be tried.¹⁵ Long-term therapy with cardioselective beta blockers is considered safe (Table 53.6.1). Class IC drugs are a second choice in the absence of structural heart disease. Amiodarone should only be used in therapy-resistant VT.¹⁵

Implantable cardioverter defibrillators may be implanted safely during pregnancy.^32,33 The experience of implantable cardioverter defibrillator implantation during pregnancy is limited. The presence of an implantable cardioverter defibrillator does not itself contraindicate future pregnancy.

Asymptomatic bradycardia may become symptomatic, especially with structural heart disease. In patients without structural heart disease, bradycardia usually implies no fetal or maternal complications.

Sinus bradycardia may occur during delivery. Rare cases of sinus bradycardia during pregnancy have been attributed to the supine hypotensive syndrome of pregnancy. It should be managed by changing the position of the mother. For persistent symptoms, a temporary pacemaker may be necessary.

First-degree atrioventricular block may occur and usually does not progress. Second-degree atrioventricular block is rare, and usually associated with structural heart disease or drug therapy. The majority of cases are asymptomatic second-degree Wenckebach block. In patients with congenital heart disease, second-degree block may occur in repaired tetralogy of Fallot or after repair of a ventricular septal defect.

Acquired complete heart block is rare. Isolated congenital complete heart block has a favourable outcome during pregnancy, especially if the QRS complexes are narrow. Supportive pacing is usually not necessary, but close surveillance is warranted since some patients can develop heart failure. Vaginal delivery carries no extra risks for a mother with congenital complete heart block.

Temporary pacing during delivery is recommended in selected women with complete heart block and symptoms. Since complete heart block usually has a favourable outcome, implantation of a permanent pacemaker before pregnancy is, in general, not indicated. Implantation can be performed safely, preferably beyond 8 weeks’ gestation. Echocardiography guidance may be helpful for implantation.¹⁵ Obstetrical management of a pregnant woman with an already implanted permanent pacemaker is of low risk.