Pathophysiology and management of syncope in Kearns-Sayre syndrome.

A 20-year-old woman with known Kearns-Sayre syndrome was transferred to the emergency department due to syncopal episodes. The electrocardiogram on admission showed complete atrioventricular block. The diagnosis of mitochondrial encephalomyopathy was made when she was 14 years old. At the time of the initial diagnosis, she displayed a normal electrocardiogram pattern. At the age of 17, electrocardiogram recordings demonstrated right bundle branch block with left anterior fascicular block and a prolonged QTc interval of 485 milliseconds (Figure). She was taking coenzyme Q10, oral nicotinamide adenine dinucleotide (reduced), piribedil, amantadine, and primidone. Transthoracic echocardiography revealed normal wall motion of both ventricles and mitral valve prolapse without regurgitation. A permanent dual-chamber pacemaker was immediately implanted.