Review Question - QID 106985

This patient's clinical presentation is consistent with second-degree heart block, Mobitz I (Wenckebach), which is caused by atrioventricular node dysfunction.

Second degree heart block is divided into Mobitz I and Mobitz II. Mobitz I is characterized by increasing PR intervals culminating in a dropped beat. It is typically asymptomatic and does not require urgent intervention, however medications that slow cardiac conductivity should be discontinued. Mobitz II is characterized by a fixed PR interval with dropped beats, often in a 2:1 or 3:1 ratio. Symptoms of Mobitz II include dizziness and syncope, and urgent placement of a cardiac pacemaker is warranted.

Gregoratos discusses the pathophysiology of heart block. He notes that Mobitz I is a result of atrioventricular nodal dysfunction, regardless of the QRS duration. Mobitz II is typically a result of infranodal dysfunction, but may have additional AV nodal dysfunction if the QRS is noted to be narrow.

Barold and Padeletti discuss Mobitz II heart block in young, seasoned athletes. Although it is known that Mobitz I is more common in seasoned athletes, several case reports suggested that Mobitz II is also common in athletes. However, the authors review the available literature and conclude that there is no increased risk of Mobitz II in young athletes.

Figure A is an EKG showing Mobitz I heart block, with increasing PR intervals followed by a dropped beat. Illustration A shows Mobitz II heart block with a fixed PR interval with dropped beats.

Incorrect Answers:
Answer 1: Mobitz type II heart block is usually the result of dysfunction in the His-Purkinje system.
Answer 2: Sick sinus syndrome is associated with sinoatrial node dysfunction.
Answer 4: Rheumatic heart disease is associated with mitral valve dysfunction.
Answer 5: Intravenous drug use and fetal lithium exposure are associated with tricuspid valve dysfunction.