Pre-excitation syndrome

Pre-excitation syndrome is a condition where the the ventricles of the heart become depolarized too early, which leads to their partially premature contraction. Normally, the atria (chambers taking venous blood) and the ventriculi (chambers propulsing blood towards organs) are electrically isolated, and only electrical passage exists at "atrioventricular node". In all pre-excitation syndromes, there is at least one more conductive pathway is present. Physiologically, the electrical depolarization wave 'waits' in atrioventricular node to allow atria contract before ventriculi. However, there is no such property exists in abnormal pathway, so electrical stimulus passes to ventricule by this tracts far before normal atrioventricular-his system, and ventricules are depolarized (excitated) before (pre-) normal conduction system. The term pre-excitation derives from this condition.

It is usually caused by a secondary conduction pathway (other than the bundle of His):