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Mahaim conduction producing left axis deviation and normal QRS
Insights
This study describes Mahaim conduction, a rare accessory pathway, in a patient with atrioventricular block. Electrophysiology revealed unique conduction patterns without the typical Wolff-Parkinson-White syndrome delta wave.
Area of Science:
- Cardiology
- Electrophysiology
- Cardiac Electrophysiology
Background:
- Mahaim fibres are accessory pathways that can cause conduction abnormalities.
- Atrioventricular (AV) block, specifically AH block, can present with varying electrophysiological findings.
- Left anterior hemiblock is a common intraventricular conduction defect.
Observation:
- An unusual case of Mahaim conduction was identified in a patient with a history of left anterior hemiblock who developed advanced AV block.
- Electrophysiological studies showed short HV intervals and left anterior hemiblock QRS patterns during AV nodal conduction.
- Junctional escape beats exhibited normal HV intervals and normal intraventricular conduction, with His bundle pacing confirming these findings.
Findings:
- The findings strongly suggest an accessory pathway (Mahaim fibres) connecting the His bundle to the left bundle branch.
- Unlike typical Wolff-Parkinson-White syndrome, the surface electrocardiogram did not display a delta wave.
- Conduction via Mahaim fibres can manifest solely as an intraventricular conduction defect.
Implications:
- This case highlights that Mahaim conduction may not always present with the characteristic delta wave.
- Understanding these atypical presentations is crucial for accurate diagnosis of accessory pathway syndromes.
- Further research into Mahaim fibre conduction is warranted to elucidate its full spectrum of clinical manifestations.
Abstract:
An unusual patient is described in whom electrophysiological studies strongly suggest the occurrence of Mahaim conduction. The patient whose electrocardiogram previously showed a left anterior hemiblock pattern then developed advanced atrioventricular (AV) block (AH block). Beats conducted through the atrioventricular node always had a short HV interval (20 ms) and QRS complexes of left anterior hemiblock pattern. Junctional escape beats always had a normal HV interval (50 ms) with normal intraventricular conduction. His bundle pacing showed the StV interval and QRS contour of escape beats. These findings suggest the existence of an accessory pathway (Mahaim fibres) passing from the area of block, presumably the uppermost portion of the His bundle, to the posteroinferior division of the left bundle-branch. The surface electrocardiogram did not show the characteristic delta wave of the Wolff-Parkinson-White syndrome. Our observations suggest that patients in whom there is conduction along Mahaim fibres may show only the pattern of intraventricular conduction defect without a delta wave.