Disappearing His deflection. Electrophysiological evidence for conduction defect within the His bundle

Area of Science:

• Electrophysiology
• Cardiac Electrophysiology
• Cardiology

Background:

• Intracardiac conduction studies are crucial for diagnosing atrioventricular (AV) conduction disturbances.
• The His bundle deflection provides key information about conduction through the AV node and His-bundle.

Observation:

• A subset of patients (5/95) with AV conduction disturbances exhibited altered His bundle deflection voltage and character.
• Progressive prematurity of atrial stimuli led to decreased His deflection voltage, splitting, and disappearance.
• Sinus beats following His bundle premature beats and increasing atrial stimulation rates also showed reduced His deflection voltage.

Findings:

• Changes in His bundle deflection are directly correlated with the preceding H-H interval.
• These observed alterations suggest an underlying conduction disturbance within the His bundle itself.
• The His deflection reappeared after dropped beats during Wenckebach periods.

Implications:

• These His bundle deflection changes can be electrophysiologically explained by His bundle conduction disturbances.
• The phenomenon complicates the precise localization of atrioventricular block during electrophysiological studies.
• Understanding these changes is vital for accurate interpretation of intracardiac conduction studies.