Mahaim fibre tachycardia

Mahaim fibre tachycardia

Mahaim fibres [1] are a type of accessory pathways connecting the atria to the fascicular conduction system in the ventricles. Nodofascicular pathways have also been described. They have decremental conduction properties like the AV (atrioventricular) node. No delta wave is usually seen in sinus rhythm with Mahaim fibres, though it is a form of pre-excitation. Mahaim fibres do not conduct retrogradely. So Mahaim fibre tachycardia is always with wide QRS complexes – antidromic with  LBBB pattern. The fibres are usually located around the tricuspid annulus [2]. The fibres are peculiar in that loss of conduction can occur even with trauma due to the electrophysiology (EP) catheter used for EP study. Specific Mahaim potentials (M potential) generated by the accessory pathway can be recorded in certain cases is useful in guiding successful radiofrequency (RF) ablation. Mahaim junctional acceleration occurs during RF ablation as in case of AV nodal re-entrant tachycardia (AVNRT). Mahaim acceleration during RF ablation has been considered as a predictor of successful ablation [3]. Slow spontaneous automaticity of the distal Mahaim fibre during RF ablation has also been reported [4].

Left sided Mahaim fibres

Rare cases of left sided atriofascicular pathways have appeared in literature. In one case the Mahaim pathway (with decremental antegrade conduction) was located in the mitral annulus – aorta junction, between the left and right fibrous trigones [5]. Thus it was situated in the supero-septal aspect of the mitral annulus rather than along the tricuspid annulus.

ECG in Mahaim fibre tachycardia

Typical Mahaim fibre tachycardia has a left bundle branch block (LBBB) morphology, with left axis deviation and a late precordial R/S transition [3]. Baseline ECG may not show any significant change in case of Mahaim fibre, though an LBBB pattern with normal PR interval may be seen sometimes [6].

References

1. 1. Benatt Mahaim I. Nouvelles recherches sur les connexions superiors de la branche gauche du faisceau de His-Tawara avec cloison interventriculaire. Cardiologia. 1938;1:61–120.
   2. Bohora S, Dora SK, Namboodiri N, Valaparambil A, Tharakan J. Electrophysiology study and radiofrequency catheter ablation of atriofascicular tracts with decremental properties (Mahaim fibre) at the tricuspid annulus. Europace. 2008 Dec;10(12):1428-33.
   3. Ma FS, Ma J, Chu JM, Fang PH, Wang FZ, Chen X, Zhang S. The automaticity of Mahaim fibre and its response to effective ablation. Chin Med J (Engl). 2004 Dec;117(12):1768-71.
   4. Pavlović N, Kühne M, Sticherling C. Slow automaticity of a Mahaim fibre after radiofrequency ablation. Europace. 2014 Dec;16(12):1705.
   5. Francia P, Pittalis MC, Ali H, Cappato R. Electrophysiological study and catheter ablation of a Mahaim fibre located at the mitral annulus-aorta junction. J Interv Card Electrophysiol. 2008 Nov;23(2):153-7.
   6. Heald SC, Davies DW, Ward DE, Garratt CJ, Rowland E. Radiofrequency catheter ablation of Mahaim tachycardia by targeting Mahaim potentials at the tricuspid annulus. Br Heart J. 1995 Mar; 73(3):250-7.