Lown-Ganong-Levine syndrome
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Lown-Ganong-Levine syndrome (LGL) is a syndrome of pre-excitation of the ventricles due to an accessory pathway providing an abnormal electrical communication from the atria to the ventricles. It is grouped with Wolff-Parkinson-White syndrome as an atrioventricular re-entry tachycardia (AVRE).
[edit] Pathophysiology
In normal individuals, electrical activity in the heart is initiated in the sinoatrial (SA) node (located in the right atrium), propagates to the atrioventricular (AV) node, and then through the bundle of His to the ventricles of the heart. (See electrical conduction system of the heart).
The AV node acts as a gatekeeper, limiting the electrical activity that reaches the ventricles of the heart. This is an important function of the AV node, because if the signals generated in the atria of the heart were to increase in rate (such as during atrial fibrillation or atrial flutter), the AV node will limit the electrical activity that conducts to the ventricles. For instance, if the atria are electrically activated at 300 beats per minute, half those electrical impulses are blocked by the AV node, so that the ventricles are activated at 150 beats per minute (giving a pulse of 150 beats per minute). Another important property of the AV node is that it slows down individual electrical impulses. This is manifest on the EKG as the PR interval, the time from activation of the atria (manifest as the P wave) and activation of the ventricles (manifest as the QRS complex).
Individuals with LGL syndrome are thought to have an accessory pathway that connects the atria directly to the bundle of His. As in WPW syndrome, the accessory pathway does not share the rate-slowing properties of the AV node, and may conduct electrical activity at a significantly higher rate than the AV node. For instance, in the example above, if an individual had an atrial rate of 300 beats per minute, the accessory bundle may conduct all the electrical impulses from the atria to the ventricles, causing the ventricles to activate at 300 beats per minute. Because the ventricles are the main pumping chambers of the heart, the body depends on the proper filling and emptying (contraction) of them. When conducted too rapidly (i.e. 300 beats per minute), the body would become hemodynamically unstable. If not corrected quickly, the ventricles can fibrillate causing VF (ventricular fibrillation)- leading to sudden cardiac death (SCD).
[edit] Diagnosis
LGL syndrome is commonly diagnosed on the basis of the surface EKG in an asymptomatic individual. In this case it is manifest as a PR interval less than or equal to 0.12 second (120 ms) with normal QRS complex duration.
It can be distinguished from WPW syndrome because:
- The QRS complexes in LGL syndrome are normal because ventricular contraction is initiated in the normal manner. The broad complexes seen in the asymptomatic individual with WPW are not a feature of LGL.
- The delta waves seen in WPW syndrome are not seen in LGL syndrome as the accessory pathway does not connect to the ventricles and so ventricular contraction does not start early.
