Pre-excitation syndrome
Encyclopedia
Pre-excitation syndrome is a condition where the ventricles
of the heart become depolarized too early, which leads to their partial premature contraction.
". In all pre-excitation syndromes, at least one more conductive pathway is present. Physiologically, the normal electrical depolarization wave is delayed at the atrioventricular node
to allow the atria to contract before the ventricles. However, there is no such delay in the abnormal pathway, so the electrical stimulus passes to the ventricle by this tract faster than via normal atrioventricular/bundle of His
system, so the ventricles are depolarized (excited) before (pre-) normal conduction system.
Ventricle (heart)
In the heart, a ventricle is one of two large chambers that collect and expel blood received from an atrium towards the peripheral beds within the body and lungs. The Atria primes the Pump...
of the heart become depolarized too early, which leads to their partial premature contraction.
Pathophysiology
Normally, the atria (chambers taking venous blood) and the ventricles (chambers pumping blood towards organs) are electrically isolated, and electrical contact between them exists only at the "atrioventricular nodeAtrioventricular node
The atrioventricular node is a part of the electrical control system of the heart that coordinates heart rate. It electrically connects atrial and ventricular chambers...
". In all pre-excitation syndromes, at least one more conductive pathway is present. Physiologically, the normal electrical depolarization wave is delayed at the atrioventricular node
Atrioventricular node
The atrioventricular node is a part of the electrical control system of the heart that coordinates heart rate. It electrically connects atrial and ventricular chambers...
to allow the atria to contract before the ventricles. However, there is no such delay in the abnormal pathway, so the electrical stimulus passes to the ventricle by this tract faster than via normal atrioventricular/bundle of His
Bundle of His
The bundle of His, known as the AV bundle or atrioventricular bundle, is a collection of heart muscle cells specialized for electrical conduction that transmits the electrical impulses from the AV node to the point of the apex of the fascicular branches...
system, so the ventricles are depolarized (excited) before (pre-) normal conduction system.
Types
Several different types have been described.| Type | Conduction pathway | PR interval | QRS interval | Delta wave? >- | Wolff-Parkinson-White syndrome Wolff-Parkinson-White syndrome Wolff–Parkinson–White syndrome is a disorder of the heart in which the ventricles of the heart contract prematurely due to an accessory pathway known as the bundle of Kent. This accessory pathway is an abnormal electrical communication from the atria to the ventricles... |
Bundle of Kent (atria to ventricles) | short | long | >- | "James bundle" (atria to bundle of His) | short | normal | >- | Mahaim fibers Mahaim fibers Mahaim fibers are portions of the electrical conduction system of the heart which connect to the interventricular septum, though there is some disagreement about their exact insertion.They can be associated with forms of pre-excitation syndrome.... |
normal | long | yes |