James fibers

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Vendhan Ramanujam M.B.B.S [2]

Synonyms and keywords: Atrioventricular bypass fibers

Overview

James fibers are otherwise known as atrioventricular bypass fibers that connect the atrial fibers to bundle of His by penetrating through the AV node. These fibers are categorized as fibers that bypass through the normal conducting system.^[1]^[2]

Historical Perspective

Accessory bypass fibers connecting the atrial fibers to bundle of His by penetrating through the AV node was first described by James in 1961.^[3]

Pathophysiology

James fibers originate in the low atrium and terminate in the low AV node. They connect the above atrial fibers with the below bundle of His. While penetrating the AV node, these fibers run as posterior internodal tract along with other fibers but make contact with the node more distally than the other posterior input fibers. Since they never completely bypass the AV node and found to exist in all hearts, he also described that these fibers may not be actual accessory fibers as we assume. They do not share the rate-slowing properties of the AV node, and may conduct electrical activity at a significantly higher rate than the AV node. This rapid conduction can lead to improper ventricular filling and emptying making the body hemodynamically unstable. If not corrected quickly, the ventricles can fibrillate causing ventricular fibrillation and sudden cardiac death.

Conditions Involving James Fibers

Conduction through James fibers is one of the possibilities for a short PR interval in Lown-Ganong-Levine syndrome. Since these fibers pass through the normal conduction system, QRS complex following the short PR interval in LGL syndrome is found to be normal thus differentiating it from Wolff-Parkinson-White syndrome where the QRS complex is found to be wide and bizzare.

Treatment

When medical therapy fails while treating LGL syndrome, which is rare, radiofrequency ablation of AV node and its accessory fibers may be considered.

References

↑ Rossi L (1975). “A histological survey of pre-excitation syndrome and related arrhythmias”. G Ital Cardiol. 5 (6): 816–28. PMID 1222879.
↑ Anderson RH, Becker AE, Brechenmacher C, Davies MJ, Rossi L (1975). “Ventricular preexcitation. A proposed nomenclature for its substrates”. Eur J Cardiol. 3 (1): 27–36. PMID 1132407. Unknown parameter |month= ignored (help)
↑ JAMES TN (1961). “Morphology of the human atrioventricular node, with remarks pertinent to its electrophysiology”. Am. Heart J. 62: 756–71. PMID 14451029. Unknown parameter |month= ignored (help)