Spontaneous changes in atrioventricular conduction in a pilot with intermittent concealed preexcitation syndrome.

A case of a 36-year-old pilot with a left sided accessory pathway (Kent bundle) is presented. The electrophysiological study revealed spontaneous changes in atrioventricular conduction in both the accessory and physiological pathways, lack of retrograde conduction via accessory pathway, and constant ventriculoatrial block in the atrioventricular node during the pacing tests of the right ventricular apex. We point out the influence of the autonomic nervous system on the accessory pathway conduction as well as the clinical and electrophysiological aspects of the phenomenon observed.

The influence of the autonomic system upon atrio-ventricular accessory pathways conductive performance.

In this report, the influence of the autonomic nervous system on the accessory pathway (Kent and Mahaim fibers) is discussed, based on electrophysiological and centrifuge examination results in two military pilots. We demonstrated that catecholamines reduce the effective refractory period (ERP) and improve conductivity in both the atrio-ventricular node (A-V node) and the accessory pathway. We concluded that the pattern of intermittent preexcitation may be connected with phenomenon of the 3rd and 4th phase block of the functional potential in the accessory pathway, and that in some cases the +Gz gravitoinertial tolerance test performed on the human centrifuge may help in distinguishing subjects with the intermittent preexcitation syndrome. Finally we concluded that all pilots with preexcitation syndrome should be dismissed from flying.

Relationship between the value of the Wenckebach point and +Gz tolerance.

The +Gz acceleration tolerance in a homogeneous group of 21 male clinically healthy pilots or candidates to airservice was evaluated. The +Gz acceleration tolerance was compared with the Wenckebach point, i.e., the lowest rate of atrial stimulation needed to produce constant Wenckebach or Mobitz II atrio-ventricular (AV) block. The Wenckebach point was used as an autonomic nervous system activity index. It was demonstrated that the degree of +Gz acceleration tolerance depends greatly upon autonomic nervous system activity, and is lower in people with enhanced parasympathetic tone. The possibility of pharmacological correction of +Gz acceleration tolerance was discussed.