Life-Threatening Neonatal Arrhythmia
Successful Treatment and Confirmation of Clinically Suspected Extreme Long QT-Syndrome-3
Here, we demonstrate the electrophysiological findings for a preterm baby who was referred to our center for therapy of persistent complex arrhythmia with heart rate (HR) varying between 60 and 300 bpm. The ECG showed polymorphic ventricular tachycardia (HR 280 bpm), including short runs of torsade de pointes alternating within a few seconds with bradycardia due to third-grade atrioventricular (AV) block (HR 78 bpm, atrial rate 135 bpm), together with broad QRS complexes of 90 ms1/2 (Figure 1 and Data Supplement). During bradycardia, an extreme prolongation of the normalized QT interval (QTc 760 ms1/2) was present (Figure 2). To control tachycardia, treatment with propranolol was given intravenously, resulting in a predominant 2:1 AV block (HR 68 bpm) and fewer episodes of nonsustained ventricular tachycardia (Figure 3 and Data Supplement), although QTc remained unchanged (740 ms1/2). Because of the persisting unstable hemodynamic condition, the extreme QTc prolongation combined with AV block, and the QRS and T-wave morphology, a sporadic defect in the Na+Ch-encoding SCN5A gene was suspected. Thus, an additional treatment with the Na+Ch blocker mexiletine was initiated. With this medication, sinus rhythm occurred within 90 minutes. Furthermore, within 3 hours, a significant improvement of QTc (760 to 480 ms1/2) and of the intraventricular conduction delay (QRS 90 to 50 ms1/2) occurred (Figure 4). Genetic examination of the child confirmed the suspected long-QT syndrome-3 with proof of a de novo SCN5A gene defect (P1332L) close to the central opening of the Na+ channel.
Our ECG tracings and the child’s clinical course (further details are given in the Data Supplement) confirmed the concept that the Na+Ch blocker mexiletine is capable of shortening the prolonged ventricular refractoriness below the P-P interval in extreme long-QT syndrome-3 with life-threatening arrhythmia.
Movies I and II are available in the online-only Data Supplement at http://www.circulationaha.org.
The editor of Images in Cardiovascular Medicine is Hugh A. McAllister, Jr, MD, Chief, Department of Pathology, St Luke’s Episcopal Hospital and Texas Heart Institute, and Clinical Professor of Pathology, University of Texas Medical School and Baylor College of Medicine.
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