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| Pre-excitation syndrome | |
|---|---|
 | |
| Electrical conduction system of the heart (accessory pathways not shown) | |
| Specialty | Cardiology |
Pre-excitation syndrome is a heart condition in which part of thecardiac ventricles are activated too early.[1] Pre-excitation is caused by an abnormal electrical connection oraccessory pathway between or within thecardiac chambers. Pre-excitation may not cause any symptoms but may lead topalpitations caused byabnormal heart rhythms. It is usually diagnosed using anelectrocardiogram, but may only be found during anelectrophysiological study.[2] The condition may not require any treatment at all, but symptoms can be controlled using medication orcatheter ablation.
Several types of pre-excitation syndrome have been described.[3]
| Type | Conduction pathway | PR interval | QRS interval | Delta wave |
|---|---|---|---|---|
| Wolff–Parkinson–White syndrome | Bundle of Kent (atria to ventricles) | short | long | yes |
| Lown–Ganong–Levine syndrome | "James bundle" (atria to bundle of His) | short | normal | no |
| Mahaim-type | Mahaim fibers | normal | long | no |
Normally, the atria and the ventricles are electrically isolated, and electrical contact between them exists only at the "atrioventricular node". In all pre-excitation syndromes, at least one more conductive pathway is present. Physiologically, the normal electrical depolarization wave is delayed at theatrioventricular 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, and the ventricles are depolarized (excited) before (pre-) normal conduction system.
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