Lown-Ganong-Levine syndrome
Encyclopedia
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-entrant tachycardia (AVRT). The syndrome is named after Bernard Lown
, William Francis Ganong, Jr.
, and Samuel A. Levine
.
A short PR is seen.
(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).
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:
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...
due to an accessory pathway providing an abnormal electrical communication from the atria
Atrium (anatomy)
In anatomy, the atrium , sometimes called auricle , refers to a chamber or space. For example, the term is used for a portion of the lateral ventricle in the brain and the blood collection chamber of the heart...
to the ventricles. It is grouped with Wolff–Parkinson–White syndrome as an atrioventricular re-entrant tachycardia (AVRT). The syndrome is named after Bernard Lown
Bernard Lown
Bernard Lown, M.D. is the original developer of the defibrillator and is an internationally known peace activist. International Physicians for the Prevention of Nuclear War, an organization he helped to create, was awarded the 1985 Nobel Peace Prize for its work against nuclear proliferation...
, William Francis Ganong, Jr.
William Francis Ganong, Jr.
William Francis Ganong, Jr. was a Harvard-educated American physiologist, and was one of the first scientists to trace how the brain controls important internal functions of the body...
, and Samuel A. Levine
Samuel A. Levine
Samuel Albert Levine was an influential American cardiologist.Levine's sign is named for him.The Samuel A. Levine Cardiac Unit at Brigham and Women's Hospital is named in his honor.-References:...
.
A short PR is seen.
Pathophysiology
In normal individuals, electrical activity in the heart is initiated in the sinoatrialSinoatrial node
The sinoatrial node is the impulse-generating tissue located in the right atrium of the heart, and thus the generator of normal sinus rhythm. It is a group of cells positioned on the wall of the right atrium, near the entrance of the superior vena cava...
(SA) node (located in the right atrium
Right atrium
The right atrium is one of four chambers in the hearts of mammals and archosaurs...
), propagates to the atrioventricular
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...
(AV) node, and then through the 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...
to the ventricles of the heart. (See electrical conduction system of the heart
Electrical conduction system of the heart
The normal intrinsic electrical conduction of the heart allows electrical propagation to be transmitted from the Sinoatrial Node through both atria and forward to the Atrioventricular Node. Normal/baseline physiology allows further propagation from the AV node to the ventricle or Purkinje Fibers...
).
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
Atrial fibrillation
Atrial fibrillation is the most common cardiac arrhythmia . It is a common cause of irregular heart beat, identified clinically by taking a pulse. Chaotic electrical activity in the two upper chambers of the heart result in the muscle fibrillating , instead of achieving coordinated contraction...
or atrial flutter
Atrial flutter
Atrial flutter is an abnormal heart rhythm that occurs in the atria of the heart. When it first occurs, it is usually associated with a fast heart rate or tachycardia , and falls into the category of supra-ventricular tachycardias. While this rhythm occurs most often in individuals with...
), 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
Pulse
In medicine, one's pulse represents the tactile arterial palpation of the heartbeat by trained fingertips. The pulse may be palpated in any place that allows an artery to be compressed against a bone, such as at the neck , at the wrist , behind the knee , on the inside of the elbow , and near the...
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
Electrocardiogram
Electrocardiography is a transthoracic interpretation of the electrical activity of the heart over a period of time, as detected by electrodes attached to the outer surface of the skin and recorded by a device external to the body...
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
Ventricular fibrillation
Ventricular fibrillation is a condition in which there is uncoordinated contraction of the cardiac muscle of the ventricles in the heart, making them quiver rather than contract properly. Ventricular fibrillation is a medical emergency and most commonly identified arrythmia in cardiac arrest...
) – leading to sudden cardiac death
Sudden Cardiac Death
Sudden cardiac death is natural death from cardiac causes, heralded by abrupt loss of consciousness within one hour of the onset of acute symptoms. Other forms of sudden death may be noncardiac in origin...
(SCD).
Diagnosis
LGL syndrome is commonly diagnosed on the basis of the surface EKGElectrocardiogram
Electrocardiography is a transthoracic interpretation of the electrical activity of the heart over a period of time, as detected by electrodes attached to the outer surface of the skin and recorded by a device external to the body...
in an asymptomatic
Asymptomatic
In medicine, a disease is considered asymptomatic if a patient is a carrier for a disease or infection but experiences no symptoms. A condition might be asymptomatic if it fails to show the noticeable symptoms with which it is usually associated. Asymptomatic infections are also called subclinical...
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.
See also
- Wolff–Parkinson–White syndrome
- Premature ventricular contractionPremature ventricular contractionA premature ventricular contraction , also known as a premature ventricular complex, ventricular premature contraction , ventricular premature beat , or extrasystole, is a relatively common event where the heartbeat is initiated by the heart ventricles rather than by the sinoatrial node, the...
- Cardiac electrophysiologyCardiac electrophysiologyCardiac electrophysiology is the science of elucidating, diagnosing, and treating the electrical activities of the heart. The term is usually used to describe studies of such phenomena by invasive catheter recording of spontaneous activity as well as of cardiac responses to programmed electrical...
- Electrical conduction system of the heartElectrical conduction system of the heartThe normal intrinsic electrical conduction of the heart allows electrical propagation to be transmitted from the Sinoatrial Node through both atria and forward to the Atrioventricular Node. Normal/baseline physiology allows further propagation from the AV node to the ventricle or Purkinje Fibers...
- ElectrocardiogramElectrocardiogramElectrocardiography is a transthoracic interpretation of the electrical activity of the heart over a period of time, as detected by electrodes attached to the outer surface of the skin and recorded by a device external to the body...
- Electrophysiology studyElectrophysiology studyAn electrophysiology study is a minimally invasive procedure which tests the electrical conduction system of the heart to assess the electrical activity and conduction pathways of the heart. The study is indicated to investigate the cause, location of origin, and best treatment for various...