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Disappearing His deflection. Electrophysiological evidence for conduction defect within the His bundle
Insights
Changes in the His bundle deflection voltage and character during electrophysiological studies indicate His bundle conduction disturbances. This phenomenon complicates precise localization of atrioventricular block.
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.
Abstract:
A change in the voltage and character of the His bundle deflection following premature atrial stimuli was observed and analysed in 5 of 95 patients having intracardiac conduction studies because of AV conduction disturbances. Of these 5 patients, 3 had spontaneous block within the His bundle, 2 of them showing block in other segments of the conduction system. With increasing prematurity of programmed atrial stimuli, there was a progressive decrease in the voltage of the His deflection, followed by a split His deflection, and finally disappearance of the His deflection. The voltage of the His deflection was also reduced in sinus beats following spontaneous His bundle premature beats. Similarly, during atrial stimulation at increasing rates, the His deflection decreased in voltage, split, and finally disappeared, but when Wenckebach periods appeared the His deflection reappeared in the first paced beat after the dropped beat. The preceding H-H interval was the only electrophysiological variable consistently related to the changes in the His deflection. These changes in His deflection can be explained electrophysiologically as the result of a conduction disturbance within the His bundle. The clinical significance of the phenomenon is discussed. The occurrence of this phenomenon during a conduction study makes it difficult or even impossible to localise the AV block precisely.