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Pharmacological characterization of conduction over a Mahaim fiber: evidence for adenosine sensitive conduction
K A Ellenbogen1, R Rogers, W Old
1Department of Medicine, Medical College of Virginia, Richmond.
Insights
Mahaim fibers, a type of accessory pathway, are sensitive to adenosine, which blocks conduction. This suggests calcium-independent mechanisms are involved in accessory pathway conduction.
Area of Science:
- Cardiology
- Electrophysiology
- Cardiac Anatomy
Background:
- Mahaim fibers (nodoventricular pathways) explain unique ECG and electrophysiological findings.
- These pathways exhibit decremental conduction properties.
Discussion:
- This case study examines Mahaim fiber response to various drugs including adenosine and verapamil.
- Adenosine effectively blocked Mahaim fiber conduction, unlike verapamil.
Key Insights:
- Mahaim fibers are adenosine-sensitive accessory pathways with decremental conduction.
- Adenosine-induced block in Mahaim fibers differs in timing from AV nodal block.
Outlook:
- Findings challenge the role of calcium channels in accessory pathway conduction with decremental properties.
- Further research into non-calcium channel mechanisms is warranted.
Abstract:
The presence of a nodoventricular pathway (Mahaim fiber) has been invoked to explain certain distinctive electrocardiographic and electrophysiological observations. The presence of an atrioventricular or atriofascicular fiber with decremental conduction properties has been documented in many of these patients. We report the case of a patient with a Mahaim fiber and the response to conduction over this pathway after adenosine, procainamide, encainide, verapamil, edrophonium, phenylephrine and isoproterenol. Conduction over the Mahaim fiber was blocked by adenosine, but not verapamil. The time course of adenosine induced block over the Mahaim fiber differed from adenosine induced AV nodal block. Mahaim fibers are decrementally conducting pathways that are adenosine sensitive. These findings support the concept that conduction in accessory pathways manifesting decremental properties is not mediated by the calcium channel.