A 31-year-old woman presents to the emergency department at 35-weeks gestation with acute shortness of breath, chest pressure, and sudden onset of palpitations for the preceding 30 minutes. Her medical history is notable for a history of hyperthyroidism for which she received radioactive iodine ablation. She takes levothyroxine 75 mcg by mouth daily, which was recently increased in the first trimester. Six years ago, she had presented to the emergency department with thyrotoxicosis and a supraventricular tachycardia. Her initial vital signs demonstrate a heart rate of 164 beats per minute, blood pressure of 109/56 mmHg, and respiratory rate of 26 respirations per minute. An electrocardiogram is shown in Fig. 1. Laboratory values are not yet obtained. Carotid sinus pressure is applied at the bedside, which decreases the rate to 146 beats per minute (bpm) briefly. Adenosine 6 mg IV once is administered, with a two-second pause and termination of the arrhythmia with conversion to sinus rhythm at 83 bpm. Her shortness of breath and chest discomfort resolve. She is admitted for further monitoring on telemetry, but she remains in sinus rhythm for 24 hours (h) and is discharged home without medication changes. Twelve days later, she re-presents with recurrent symptoms and is found to have a supraventricular tachycardia at 157 bpm. She is given adenosine 6 mg IV once, with resolution of the tachycardia and reestablishment of sinus rhythm. During the preceding 10 days, she noted intermittent palpitations for 1–2 min before resolving either on their own or with vagal maneuvers. She is admitted for monitoring and started on digoxin 0.125 mg daily. She undergoes induction of labor on hospital day three, with placement of an epidural, and delivery of a healthy baby boy at 37 0/7 weeks gestation. On hospital day six, she undergoes an electrophysiology study and atrioventricular nodal reentrant tachycardia (AVNRT) ablation. She is discharged on hospital day seven in stable condition.

Premature extra beats and atrial tachyarrhythmias are more frequent and may even manifest for the first time, during pregnancy. The sensation of palpitations is common in pregnancy, with sinus tachycardia, premature atrial contractions, and premature ventricular complexes representing the most common findings [10, 11]. Premature beats manifest most frequently during the second trimester. They are not associated with adverse maternal or fetal outcomes and require treatment only if symptoms are intolerable to the mother. The occurrence of atrial fibrillation or atrial flutter is relatively rare during pregnancy and is usually associated with hyperthyroidism or structural cardiac disease [1], such as underlying valvular disease, congestive heart failure, or congenital heart disease.

AVNRT is the most common supraventricular arrhythmia in pregnant and nonpregnant women. In patients with a preexisting history of supraventricular tachycardia, the incidence of recurrence during pregnancy is as high as 20–44 % in case studies [12, 13]. Previously highly symptomatic tachyarrhythmias should be treated with catheter ablation prior to pregnancy, when possible. During pregnancy, as in our patient, most supraventricular arrhythmias represent a WHO class II risk category, with a small increase in maternal mortality and a moderate increase in morbidity.

Typically, supraventricular tachyarrhythmias are not well tolerated in pregnancy, if rapid and sustained. Thus, the general preference is to restore sinus rhythm. AVNRT or atrioventricular reentrant tachycardia (AVRT) involving an accessory pathway can often be terminated by successful vagal maneuvers, such as having the patient perform the Valsalva maneuver and cough vigorously or by applying carotid sinus pressure. If vagal maneuvers fail, adenosine is the first drug of choice and can be administered safely and intravenously in pregnancy for diagnostic and therapeutic purposes [13, 14]. Adenosine interrupts conduction down the accessory atrioventricular nodal pathway by prolonging the refractory period of the atrioventricular (AV) node and revealing the underlying atrial arrhythmia. Intravenous metoprolol can be used if adenosine fails and serves to slow the ventricular rate to control symptoms but will not typically convert the rhythm to sinus. Direct current synchronized cardioversion is also safe in all stages of pregnancy [13] and is used typically in situations of hemodynamic instability or arrhythmias refractory to medical therapy.

Digoxin is considered safe in pregnancy and can be used to control the ventricular rate but is not an effective medication to use in the acute setting [13]. Other agents, such as specific medications acting on the AV node (beta-blockers, non-dihydropyridine calcium channel blockers; most class C agents) (Table 5), may also be safe and tolerated during pregnancy to treat the symptoms of the arrhythmia. Antiarrhythmic drug therapies can be toxic to the developing fetus and should be discontinued prior to conception [13]. Major controlled studies of antiarrhythmic drugs during pregnancy are lacking. Typically, antiarrhythmic therapy is reserved for hemodynamic compromise or refractory or recurrent arrhythmia. Specific antiarrhythmic medications are considered safer to use in pregnancy, such as sotalol (class B), flecainide (class C), and ibutilide (class C) [13]. They have not demonstrated any adverse fetal effects, but experience with these medications in pregnancy is limited. Amiodarone is usually recommended against in pregnancy. It is a pregnancy class D medication and its use in pregnancy should be restricted to arrhythmias that are resistant to other drugs or are life threatening [15]. Bypass tract or atrioventricular nodal ablation is possible during pregnancy if necessary and is best performed during the second trimester when the fetus has undergone initial development and the mother and fetus can still be adequately shielded from radiation exposure.

A 28-year-old Indian American woman presents for evaluation at 8-weeks gestation with a recent diagnosis of rheumatic mitral stenosis (MS). This is her second pregnancy, and the first was an uncomplicated pregnancy with vaginal delivery and home birth three years ago with a midwife while living in India. She was noted to have a murmur on exam by her current midwife and referred for further evaluation. She underwent a transthoracic echocardiogram one week ago which demonstrated mild dilation of the left atrium and a characteristic rheumatic deformity of the mitral valve with severe mitral stenosis and a calculated mitral valve area of 1.3 cm². Prior to her pregnancy, she did not experience dyspnea on exertion, orthopnea, paroxysmal nocturnal dyspnea, or peripheral edema. She does note occasional palpitations that she describes as “skipped beats” for the last four weeks, occurring approximately every other day. She does not exercise regularly and is able to care for her three-year-old son, cook, and clean the home without limitations.