[Accessory atrioventricular pathways with decremental conduction (Mahaim connections). 2 case reports].

The so called Mahaim connections form a relatively scarce variant of the preexcitation syndrome. Antidromic atrioventricular reentry tachycardia with wide QRS complex of LBBB morphology represents a typical clinical manifestation of the condition. Nodofascicular and nodoventricular fibres in all the probability do exist, but only rarely. Most of these accessory pathways are located on the firht free wall and conduct only antegradely and decrementally. Majority of these pathways are formed by long bundles inserting in the terminal part of the right bundle branch or in the myocardium near the right ventricular apex. In this setting traditional mapping strategy is of little use and different approaches must be employed. Only minority of these right-sided accessory pathways are short inserting in the ventricular myocardium under the tricuspid annulus. We present two case reports of patients with accessory connections exhibiting the so called Mahaim electrophysiology. In the first case, the pathway was merely an innocent bystander that, however, masked serious low intrahissian conduction disturbance. In the second case, the patient had a long-standing characteristic symptomatology due to the right anterolateral short accessory pathway which was successfully mapped and ablated.