Fetal ventricular tachycardia secondary to long QT syndrome treated with maternal intravenous magnesium: case report and review of the literature

Abstract

CASE REPORTA 35-year-old woman presented to our center at 30 weeks' gestation because of reduced fetal movements. A fetal arrhythmia, skin edema and ascites were detected on admission, prompting referral to the fetal cardiology unit. The initial fetal echocardiogram confirmed ventricular tachycardia with a ventricular rate of 220 beats per min (bpm) compared with an atrial rate of 130 bpm (Figure 1). There was little beat-to-beat variation in the rate of the ventricular contractions (Figure 1). Ventricular function was judged to be poor, with mitral valve regurgitation, tricuspid valve regurgitation and hydrops. Maternal and paternal electrocardiograms showed normal sinus rhythm with corrected QT intervals of 423 ms and 438 ms, respectively. Maternal anti-Ro/La antibodies were negative.The fetus was treated by administration of 100 mg oral maternal flecainide three times daily because this is an accepted treatment of ventricular arrhythmias during postnatal life and has a rapid onset of action based on our experience of managing other types of fetal arrhythmias 1 . After 48 h, the ventricular rate had accelerated to 270 bpm with worsening cardiac failure. The flecainide level at this time was 300 µg/L (therapeutic range, 300-700 µg/L). An intravenous magnesium sulfate infusion at 2-4 g/h was commenced in an attempt to gain rapid control of the fetal arrhythmia 2 and flecainide therapy was continued. The pretreatment maternal magnesium level was 0.78 mmol/L (normal range, 0.65-1.05 mmol/L), which increased to 1.47-1.71 mmol/L during the infusion. Within 12 h of commencing the magnesium infusion, fetal ventricular tachycardia resolved, revealing variable atrioventricular block with an atrial rate of 140-150 bpm and a ventricular rate of 90 bpm. The magnesium infusion was continued for 4 days, during which time the hydrops resolved completely. Flecainide was discontinued and propranolol was administered at a dose of 80 mg three times daily, given the likelihood of an underlying long QT syndrome, and to evaluate whether intravenous magnesium could be stopped. During propranolol therapy, after withdrawal of intravenous magnesium, there were short bursts of ventricular tachycardia only, intermittent sinus rhythm and atrioventricular block.On repeat scan in our fetal medicine unit, 10 days after instituting therapy, marked dilatation of the lateral and third cerebral ventricles was observed (Figure 2), which had not been evident on previous scans. There was a very poor neurological prognosis and, following parental

Diagnosis and Treatment of Fetal Cardiac Disease

“…325,330 Maternal intravenous magnesium is recommended as first-line treatment for fetal VT at rates >200 bpm, but its use should be limited to <48 hours duration. 348,434,461 Redosing may be considered in cases of recurrent VT as long as maternal magnesium levels are <6 mEq/L 462 and there are no signs of maternal toxicity. In addition to short-duration magnesium, treatment for VT includes intravenous lidocaine, particularly with associated hydrops, or oral propranolol or mexiletine.…”

Fetal Presentation of Long QT Syndrome – Evaluation of Prenatal Risk Factors: A Systematic Review

“…The search terms ‘long QT syndrome’, ‘fetal arrhythmia’ and ‘congenital heart disease’ were used. The 30 reports were classified into three categories according to content: 20 reports [2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21] describing 21 patients with LQTS documented abnormal cardiac findings found in utero (table 1); 5 reports [23,24,25,26,27] described series of LQTS patients and included prenatal cardiac findings for some of the fetuses (table 2), and 5 reports [28,29,30,31,32] described series of fetuses, some of whom were subsequently diagnosed as having LQTS, for whom echocardiography examinations had been performed because of abnormal cardiac findings detected incidentally during antenatal care (table 3). …”

“…LQTS accounts for more than 10% of the causes of sudden infant death syndrome [1]. Although several reports have described the prenatal cardiac findings of single or multiple cases of LQTS [2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21], some patients with LQTS show only a slightly reduced baseline fetal heart rate (FHR) of 110–120 bpm in utero, as shown in figure 1. Since some fetuses with LQTS die in utero or during the neonatal period and because effective measures exist that are capable of preventing life-threatening episodes, such as syncope and ventricular tachycardia [1], antenatal diagnosis or a suspicion of LQTS may be helpful for improving the outcomes of fetuses with LQTS.…”

Fetal Echocardiography and Prenatal Cardiovascular Interventions – An Update (2012)

“…Fetal supraventricular tachyarrhythmias can now be classified as long and short V-A (ventricular-atrial, corresponding with electrophysiological long and short R-P) tachycardias, atrial flutter or junctional ectopic tachycardia. Ventricular tachycardia, which accounts for 1-2% of all fetal tachyarrhythmias and may occur in isolation, the setting of long QT syndrome, fetal cardiomyopathy and cardiac tumors, is typically suspected where there is a fast ventricular rate and a slower atrial rate with V-A dissociation [47]. Recognition of the specific mechanism of tachycardia contributes to improved prenatal counseling and more appropriate, targeted pharmacotherapy.…”

“…For instance, in contrast to short V-A supraventricular tachycardias (accessory pathway mediated), we have learned that atrial flutter [48] and certain long V-A supraventricular tachycardias [45] do not respond as well to digoxin, and thus use of a more potent antiarrhythmic medication such as sotalol may be warranted. For ventricular tachycardia, use of amniodorone, beta blockade therapy, lidocaine and magnesium, the latter particularly for long QT syndrome, among other largely maternally-administered medications have all been reported with variable success [47].…”