Scenario: This electrocardiographic (ECG) strip was recorded for a 3-day-old male newborn after an uncomplicated pregnancy and delivery. Cardiac monitoring was initiated because of a transient episode of cyanosis in which a follow-up ECG showed no signs of congenital heart anomaly. The newborn was deemed otherwise healthy, however there is a well-documented family history of cardiomyopathy.

This ECG shows a first degree atrioventricular (AV) block with right bundle branch block (RBBB), atrial enlargement, and QT prolongation. Isolated hereditary BBB is an autosomal dominant genetic disease of chromosome 19. Affected newborns have various combinations of conduction defects such as RBBB and AV block.

In some neonates this condition is further complicated by long QT syndrome (LQTS) and atrial enlargement. All of these ECG characteristics are seen in this newborn. These conditions are very rare and sometimes are attributed to maternal autoimmune disorders (ie, maternal...

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