J Formos Med Assoc 2002 • Vol 101 • No 4 291

Long QT Syndrome with Atrioventricular Block

(J Formos Med Assoc2002;101:291–3)

Key words:long QT syndromeatrioventricular blockcongenital heart disease

Department of Pediatrics, National Cheng Kung University Hospital, Tainan.Received: 23 October 2001. Revised: 26 November 2001. Accepted: 8 January 2002.Reprint requests and correspondence to: Dr. Jing-Ming Wu, Department of Pediatrics, National Cheng Kung UniversityHospital, 138 Sheng Li Road, Tainan, Taiwan.

CONGENITAL LONG QT SYNDROME WITH

FUNCTIONALLY IMPAIRED ATRIOVENTRICULAR

CONDUCTION: SUCCESSFUL TREATMENT BY

MEXILETINE AND PROPRANOLOL

Chih-Ta Yao, Jieh-Neng Wang, Yu-Chien Tsai, Chia-Shiang Lin, and Jing-Ming Wu

Congenital long QT syndrome (LQTS) is a geneticdisorder characterized by prolongation of the QT in-terval and polymorphic non-sustained ventriculartachycardias, known as torsades de points, which leadto syncope and even sudden death [1]. LQTS associ-ated with atrioventricular (AV) block usually occurssporadically at a very young age, and carries a poorprognosis [2–7]. We report a case of congenital LQTSassociated with 2:1 AV block that was successfully treatedwith propranolol and mexiletine.

Case Report

A male baby, born at 36 weeks of gestation with a body weightof 2,890 g, was transferred to our hospital due to bradycardia.He had a strong family history of LQTS that manifested withsudden death or syncope (Fig. 1). His elder sister was notedto have bradycardia alternating with AV block and tachycar-dia from the 26th week of gestation. LQTS with intermittentAV block was diagnosed after birth. She died suddenly at theage of 8 months despite propranolol and pacemaker therapy.

On admission, this neonate was well in general appear-ance and without congenital abnormalities. His surface elec-

Abstract: Congenital long QT syndrome (LQTS) with atrioventricular block is a rareand malignant arrhythmia, which usually responds poorly to traditional β-blockertherapy. We describe a male neonate with LQTS with ventricular tachycardia and2:1 atrioventricular block. This patient’s sister had similar presentation and diedsuddenly at the age of 8 months despite β-blocker and pacemaker therapy. Ourpatient responded to a combination of sodium channel blocker (mexiletine) andβ-blocker (propranolol) therapy. He was asymptomatic during a 2-year follow-upperiod. This case suggests that propranolol combined with mexiletine might be usefulin the treatment of patients with LQTS with atrioventricular block.

trocardiogram (ECG) showed a prolonged QT interval (QTc:0.58 s) with early onset broad-based T wave (Fig. 2A). On Day3, continuous rhythm monitoring revealed occasional 2:1 AVconduction with narrow QRS complex (Fig. 2B), whichspontaneously converted into 1:1 AV conduction with pro-gressively increasing T wave amplitude (Fig. 2C), and then aburst attack of torsade de points occurred (Fig. 2D). There was

Fig. 1. Family hereditary chart. Two members died suddenly, two hadsyncopal episodes, and four had prolonged QT interval. The correctedQT interval is given only for the baby (arrow) and key persons.

0.384 sec0.414 sec 0.564 sec0.443 sec

0.40 sec 0.494 sec

0.636 sec 0.58 sec

Syncope

Suddendeath

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occasional right bundle branch conduction block and sinusbradycardia in his ECG tracings (Fig. 2E). He was treated withintravenous propranolol (0.1 mg/kg every 8 hr) but did notrespond, so xylocaine infusion (30 µg⋅kg–1⋅min–1) was addedwhich successfully shortened the QT interval (QTc: 0.48 s),and there were no further episodes of torsade de points or AVblock. He was discharged with a prescription of propranolol(3 mg⋅kg–1⋅d–1) and mexiletine (9 mg⋅kg–1⋅d–1). He was asymp-tomatic during a 2-year follow-up. Neither torsade de pointsnor AV block were observed on repeated ECGs and 24-hourHolter monitoring. The QTc was 0.43 to 0.48 seconds.

Discussion

Due to a markedly prolonged ventricular effectiverefractory period, patients with congenital LQTS canalso have variable degrees of functional AV conductionblock (usually 2:1 block) or intraventricular conduc-tion delay [3]. In this group of patients, the clinicalpresentations are different from those in patients withcongenital LQTS only, including markedly prolongedQT interval, younger age onset, and poor response totraditional therapies [2–7].

Fig. 2. Rhythm strip lead II. A) Sinus rhythm with 1:1 atrioventricu-lar conduction and a prolonged QT interval (QTc: 0.58 s) with earlyonset broad-based T wave. B) Sinus rhythm with 2:1 atrioventricularconduction. C) Peculiar T-wave changes noted with transition from 2:1 to 1:1 atrioventricular conduction. D) Non-sustained polymorphicventricular tachycardia with spontaneous conversion. E) Right bundlebranch conduction block.

Traditionally, β-blocker therapy remains the first-line treatment for patients with LQTS. For patientswith LQTS and bradycardia, combined therapy with aβ-blocker and pacemaker is recommended [1, 8]. Bothour patient and his sister had similar clinical presenta-tions in the perinatal period. They both failed torespond to β-blocker therapy. His sister died in infancydespite a pacemaker implantation. Thus, the standardtreatment for LQTS in this patient and his sister was noteffective.

LQTS is caused by cardiac ion channel defects [8].Different cardiac ion channel mutations can causedifferent subtypes [8]. Thus, the management of LQTSmight be modified based on the specific gene mutationidentified. Mexiletine, a sodium channel blocker,not only shortens the action potential duration of Mcells but can also reduce the transmural dispersionof the ventricular repolarization. These effects, inturn, can prevent the development and inductionof torsade de points [9]. Experimental study hasshown that mexiletine can abbreviate the QT intervalin all patients with LQT3 (sodium ion channel defect)but in fewer than 10% of patients with LQT1 or LQT2(potassium channel defect) [10, 11]. Althoughwe did not perform a genetic study, a diagnosis of type1 LQTS was suggested by the ECG pattern of earlyonset broad-based T waves in the patient and hisfamily members [12]. Mexiletine might possesssome adjunctive effects in shortening the QTinterval and preventing the cardiac arrthymias in suchcases.

LQTS with functional 2:1 AV block has a graveprognosis and more than half of patients die in infancyand early childhood despite the use of different modesof treatment such as beta blockade, pacemakerimplantation, and left ganglion stellectomy [2–7]. Thiscase suggests that, if xylocaine infusion can shorten theQTc interval for patients presenting with LQTS and AVblock, then propranolol combined with mexiletinemight be an alternative outpatient therapy.

ACKNOWLEDGMENT: We are grateful to Dr. Ming-Lon Young (Department of Pediatrics, University ofMiami) for reviewing this manuscript.

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