Postoperative supraventricular tachycardia and polymorphic ventricular tachycardia due to a novel SCN5A variant: a case report of a rare comorbidity that is difficult to diagnose

BACKGROUND: Loss-of-function mutations of human cardiac sodium channel gene SCN5A induce a wide range of arrhythmic disorders. Mutation carriers with co-existing conditions such as congenital heart diseases and histories of cardiac surgeries, could develop complex arrhythmic events that are difficult to diagnose. CASE PRESENTATION: A 41-year-old Japanese male with a history of a surgical closure of an ASD presented impairment of consciousness by wide QRS tachycardia. Because the patient’s baseline ECG in sinus rhythm showed similar QRS axis with right bundle brunch block morphology, we suspected supraventricular tachycardia (SVT). During hospitalization, the patient developed polymorphic ventricular tachycardia that was induced by bradycardia. In an electrophysiological study, the SVT was identified as right atrial incisional tachycardia circulating around the scar in the right atrium. The genetic analysis revealed a heterozygous SCN5A c.4037–4038 del TC, p. L1346HfsX38 variant. We diagnosed this patient as having progressive cardiac conduction disorder (PCCD) and polymorphic VT caused by the mutation. Incisional tachycardia with wide QRS morphology was a by-standing comorbidity related to the history of cardiac surgery which could miss lead the diagnosis. The patient’s SVT was eliminated by radiofrequency catheter ablation. An implantable cardioverter defibrillator (ICD) was implanted for the secondary prevention of polymorphic VT. Cardiac pace-making therapy by the ICD to avoid bradycardia effectively suppressed the patient’s arrhythmic events. CONCLUSIONS: We treated a patient with a sodium channel gene variant. Co-existing SVT originated by a scar in the right atrium made the diagnosis extremely difficult. A multilateral diagnostic approach using an ECG analysis, an electrophysiological study, and genetic screening enabled effective combination therapy comprised of catheter ablation and an ICD.