Nifedipine tocolysis associated atrial fibrillation responds to DC cardioversion

Case reportA 38-year-old woman presented at 33 weeks of gestation with threatened preterm labour.Her obstetric history included two normal vaginal deliveries at term and a miscarriage at 19 weeks, the details of which were not known.She had conceived with a copper intrauterine contraceptive device, which was removed at 6 weeks of gestation.She reported low backache and uterine tightenings occurring every 2 minutes.She had no vaginal bleeding, rupture of membranes or dysuria.On examination, she had a pulse rate of 80 per minute, blood pressure 106/72 mmHg and was apyrexial.Speculum examination revealed a closed os with no shortening of the cervix.She received two doses of betamethasone 12 mg intramuscularly 12 hours apart.Tocolysis was commenced with nifedipine.She received nifedipine 30 mg followed by three doses of 20 mg slow-release nifedipine tablets given 8 hourly.Within 4 hours of the last dose, she experienced palpitations and left-sided chest pain radiating to the left shoulder and upper arm.Her pulse was irregular at about 190 beats per minute and blood pressure was 100/70 mmHg.Heart sounds were normal with no murmurs.Thyroid function was normal.The serum magnesium was normal and serum potassium was 3.4 mmol/l (normal range: 3.5-5.5 mmol/l).Electrocardiography confirmed atrial fibrillation with a rapid ventricular response.Transthoracic echocardiography showed no major structural cardiac abnormality.The left atrium was not dilated.Direct current (DC) cardioversion was undertaken under a short general anaesthetic due to the symptoms and hypotension with a rapid ventricular rate.Anticoagulation was avoided since atrial fibrillation was of recent onset.She reverted from atrial fibrillation to sinus rhythm with a single, synchronised, biphasic, 100 joules DC shock.She was discharged 5 days later.