The diagnosis of Mobitz II (second-degree, atrioventricular [AV]) heart block implies a primary disorder of conduction localized to the His-Purkinje system and the potential for sudden progression to complete heart block.1 However, an ectopic focus located in the His bundle or a bundle branch may, with proper timing, partially penetrate the conduction system and collide with normal sinus impulses, causing either slowing or complete blockage of the sinus impulse. This phenomenon, a manifestation of concealed conduction, may mimic first- or second-degree AV block, including a Mobitz II pattern, resulting in what has been termed pseudoatrioventricular block.2 Pseudoatrioventricular and true AV blocks have different therapeutic and prognostic implications. Therefore, identification of pseudoatrioventricular block is clinically important.
REPORT OF A CASE
A 29-year-old woman was admitted to the hospital for elective repair of an ostium primum atrial septal defect. Her admission ECG disclosed normal sinus rhythm, a left-axis deviation, and