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Lown-Ganong Levine Lown-Ganong-Levine (Example 1) Lown-Ganong-Levine (Example 2) Lown-Ganong-Levine (LGL) syndrome falls into the category of "pre-exitation" syndromes such as Wolff-Parkinson-White (WPW) syndrome. In WPW syndrome, an "accessory pathway" is present which electrically connects the atria to the ventricular myocytes. Thus when the sinus node fires, the electrical activation does not need to travel through the AV node like in a normal person (which usually delays the impulse from getting to the ventricles), instead it can travel down the accessory pathway and activate the venticles quite fast. This short duration between the sinus node firing and the ventricles being depolarized results in a short PR interval. Since the depolarization in the ventricles is going from myocyte to myocyte (since the accessory pathway in WPW connects to the ventricular myocardium), the QRS duration can be somewhat prolonged (remember it takes longer for conduction through the myocytes compared to the normal conduction pathways of the heart such as the bundle of His). In LGL syndrome, the theory is that the accessory pathway connects the atria directly to the bundle of His, resulting in a narrow QRS complex. The time from sinus node firing to conduction to the ventricles is again short since the AV node is bypassed, thus the PR interval is short in LGL syndrome as well. This abnormal connection can result in SVTs specifically AVRT and AVNRT. Treatment of LGL syndrome, unlike WPW syndrome, does not usually consist of ablation, since ablating the bundle of His would require a permanent pacemaker. |
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