CONGRESS ABSTRACT

Background Mahaim type tachycardia is an Atrioventricular re-entrant antidromic tachicardia  in which an accessory pathway establish a direct connection between the atrial tissue and the infra-His conduction tissue (at the level of the right branch of the bundle of His). The accessory pathways is characterized by anterograde decremental conduction and a lack of retrograde conduction. The association of this supraventricular tachycardia with congenital Long QT syndrome (LQTS) has never been reported. Case A newborn boy (12th days of life) with a significant family history of congenital LQTS (including two second-degree relatives with Jervell and Lange-Nielsen syndrome and several relatives with Romano-Ward syndrome) presented to the Emergency Room due to the onset of diarrhea. Due to the presence of ventricular extrasystoles with left bundle branch morphology he was subsequently referred to our cardiology department for a complete evaluation. Physical examination was unremarkable. Electrocardiogram and echocardiogram resulted normal. Telemetric monitoring showed episode of QT interval prolongation and a progressive increase in the arrhythmic burden with appearance of sustained episodes of wide complex tachycardia with complete left bundle branch morphology. The tachycardia displayed: Heart rate 145 beat for minute Left bundle branch morphology negative P wave (p axis – 90°) PR interval > RP interval (RP interval > 80 ms) QRS axis -30° QRS duration 110 ms dominant R wave in lead I rS in precordial lead V1 QRS transition in lead V4. The tachycardia started always in the same way with a shorter PR interval (100 ms) and a wider QRS (incomplete bundle branch morfology) followed by the onset of a supraventricular tachycardia at a heart rate of 145 bpm. These ECG findings meet the diagnostic criteria for Mahaim fiber tachycardia. Beta-blocker therapy (propranolol) was promptly started, leading to a gradual reduction in arrhythmic episodes until the reentrant tachycardia was completely controlled. Due to the familial history of LQTS, otoacoustic emissions test was diagnostic for sensorineural hearing loss. A Schwartz-score = 4 outlined a definite LQTS. Conclusion This was the first description of a Mahaim fiber tachycardia associated with congenital LQTS. Actual knowledge is not able to explain if this was a random association or the result of a genetic condition.