Long QT Syndrome

Definition:
The long QT syndrome (LQTS) is a rare inborn heart condition in which delayed repolarization of the heart following a heartbeat increases the risk of episodes of torsade de pointes (TDP, a form of irregular heartbeat that originates from the ventricles). These episodes may lead to palpitations, fainting and sudden death due to ventricular fibrillation. Episodes may be provoked by various stimuli, depending on the subtype of the condition.
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You can be born with a genetic mutation that puts you at risk of long QT syndrome. In addition, certain medications and medical conditions may cause long QT syndrome.

The condition is so named because of the appearances of the electrocardiogram (ECG/EKG), on which there is prolongation of the QT interval.

Long QT syndrome is treatable. You may need to limit your physical activity, avoid medications known to cause prolonged Q-T intervals or take medications to prevent a chaotic heart rhythm. Some people with long QT syndrome need surgery or an implantable device.

Symptoms :
Many people with long QT syndrome don’t have any signs or symptoms. They may be aware of their condition only from results of an electrocardiogram (ECG) performed for an unrelated reason, because they have a family history of long QT syndrome or because of genetic testing results.

For people who do experience signs and symptoms of long QT syndrome, the most common symptoms include:

*Fainting. This is the most common sign of long QT syndrome. In people with long QT syndrome, fainting spells (syncope) are caused by the heart temporarily beating in an erratic way. These fainting spells may happen when you’re excited, angry or scared, or during exercise. Fainting in people with long QT syndrome can occur without warning, such as losing consciousness after being startled by a ringing telephone.

Signs and symptoms that you’re about to faint include lightheadedness, heart palpitations or irregular heartbeat, weakness and blurred vision. However, in long QT syndrome, such warning signs before fainting are unusual.

*Seizures. If the heart continues to beat erratically, the brain becomes increasingly deprived of oxygen. This can then cause generalized seizures.

*Sudden death. Normally, the heart returns to its normal rhythm. If this doesn’t happen spontaneously and paramedics don’t arrive in time to convert the rhythm back to normal with an external defibrillator, sudden death will occur.Signs and symptoms of inherited long QT syndrome may start during the first months of life, or as late as middle age. Most people who experience signs or symptoms from long QT syndrome have their first episode by the time they reach age 40.

Rarely, signs and symptoms of long QT syndrome may occur during sleep or arousal from sleep.

Causes:
Your heart beats about 100,000 times a day to circulate blood throughout your body. To pump blood, your heart’s chambers contract and relax. These actions are controlled by electrical impulses created in the sinus node, a group of cells in the upper right chamber of your heart. These impulses travel through your heart and cause it to beat.

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After each heartbeat, your heart’s electrical system recharges itself in preparation for the next heartbeat. This process is known as repolarization. In long QT syndrome, your heart muscle takes longer than normal to recharge between beats. This electrical disturbance, which often can be seen on an electrocardiogram (ECG), is called a prolonged Q-T interval.

Prolonged Q-T interval
An electrocardiogram (ECG, also called an EKG) measures electrical impulses as they travel through your heart. Patches with wires attached to your skin measure these impulses, which are displayed on a monitor or printed on paper as waves of electrical activity.

An ECG measures electrical impulses as five distinct waves. Doctors label these five waves using the letters P, Q, R, S and T. The waves labeled Q through T show electrical activity in your heart’s lower chambers.

The space between the start of the Q wave and the end of the T wave (Q-T interval) corresponds to the time it takes for your heart to contract and then refill with blood before beginning the next contraction.

By measuring the Q-T interval, doctors can tell whether it occurs in a normal amount of time. If it takes longer than normal, it’s called a prolonged Q-T interval. The upper limit of a normal Q-T interval takes into account age, sex, and regularity and speed of the heart rate.

Long QT syndrome results from abnormalities in the heart’s electrical recharging system. However, the heart’s structure is normal. Abnormalities in your heart’s electrical system may be inherited or acquired due to an underlying medical condition or a medication.

Inherited long QT syndrome
At least 12 genes associated with long QT syndrome have been discovered so far, and hundreds of mutations within these genes have been identified. Mutations in three of these genes account for about 70 to 75 percent of long QT syndrome, and cause the forms referred to as LQT1, LQT2 and LQT3.

Doctors have described two forms of inherited long QT syndrome:

*Romano-Ward syndrome. This more common form occurs in people who inherit only a single genetic variant from one of their parents.

*Jervell and Lange-Nielsen syndrome. Signs and symptoms of this rare form usually occur earlier and are more severe than in Romano-Ward syndrome. It’s seen in children who are born deaf and have long QT syndrome because they inherited genetic variants from each parent.

Additionally, scientists have been investigating a possible link between SIDS and long QT syndrome and have discovered that about 10 percent of babies with SIDS had a genetic defect or mutation for long QT syndrome.

Acquired long QT syndrome
More than 50 medications, many of them common, can lengthen the Q-T interval in otherwise healthy people and cause a form of acquired long QT syndrome known as drug-induced long QT syndrome.

Medications that can lengthen the Q-T interval and upset heart rhythm include certain antibiotics, antidepressants, antihistamines, diuretics, heart medications, cholesterol-lowering drugs, diabetes medications, as well as some antifungal and antipsychotic drugs.

People who develop drug-induced long QT syndrome may also have some subtle genetic defects in their hearts, making them more susceptible to disruptions in heart rhythm from taking drugs that can cause prolonged Q-T intervals.

Risk Factors:
People at risk of long QT syndrome include:

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*Children, teenagers and young adults with unexplained fainting, unexplained near drownings or other accidents, unexplained seizures, or a history of cardiac arrest

*Family members of children, teenagers and young adults with unexplained fainting, unexplained near drownings or other accidents, unexplained seizures, or a history of cardiac arrest

*Blood relatives of people with known long QT syndrome

*People taking medications known to cause prolonged Q-T intervals

Long QT syndrome often goes undiagnosed or is misdiagnosed as a seizure disorder, such as epilepsy. However, researchers believe that long QT syndrome may be responsible for some otherwise unexplained deaths in children and young adults. For example, an unexplained drowning of a young person may be the first clue to inherited long QT syndrome in a family.

People with low potassium, magnesium or calcium blood levels — such as those with the eating disorder anorexia nervosa — may be susceptible to prolonged Q-T intervals. Potassium, magnesium and calcium are all important minerals for the health of your heart’s electrical system.

Diagnosis:
The diagnosis of LQTS is not easy since 2.5% of the healthy population have prolonged QT interval, and 10–15% of LQTS patients have a normal QT interval. A commonly used criterion to diagnose LQTS is the LQTS “diagnostic score”. The score is calculated by assigning different points to various criteria (listed below). With four or more points, the probability is high for LQTS; with one point or less, the probability is low. A score of two or three points indicates intermediate probability.

*QTc (Defined as QT interval / square root of RR interval)
#>= 480 msec – 3 points
#460-470 msec – 2 points
#450 msec and male gender – 1 point

*Torsades de pointes ventricular tachycardia – 2 points

*T wave alternans – 1 point

*Notched T wave in at least 3 leads – 1 point

*Low heart rate for age (children) – 0.5 points

*Syncope (one cannot receive points both for syncope and torsades de pointes)
#With stress – 2 points
#Without stress – 1 point

*Congenital deafness – 0.5 points

*Family history (the same family member cannot be counted for LQTS and sudden death)
#Other family members with definite LQTS – 1 point
#Sudden death in immediate family (members before the age 30) – 0.5 points
Treatment options:
Those diagnosed with long QT syndrome are usually advised to avoid drugs that would prolong the QT interval further or lower the threshold for TDP.  In addition to this, there are two intervention options for individuals with LQTS: arrhythmia prevention and arrhythmia termination.

Arrhythmia prevention:
Arrhythmia suppression involves the use of medications or surgical procedures that attack the underlying cause of the arrhythmias associated with LQTS. Since the cause of arrhythmias in LQTS is after depolarizations, and these after depolarizations are increased in states of adrenergic stimulation, steps can be taken to blunt adrenergic stimulation in these individuals. These include:

*Administration of beta receptor blocking agents which decreases the risk of stress induced arrhythmias. Beta blockers are the first choice in treating Long QT syndrome.
In 2004 it has been shown that genotype and QT interval duration are independent predictors of recurrence of life-threatening events during beta-blockers therapy. Specifically the presence of QTc >500ms and LQT2 and LQT3 genotype are associated with the highest incidence of recurrence. In these patients primary prevention with ICD (Implantable cardioverter-defibrillator) implantation can be considered.

*Potassium supplementation. If the potassium content in the blood rises, the action potential shortens and due to this reason it is believed that increasing potassium concentration could minimize the occurrence of arrhythmias. It should work best in LQT2 since the HERG channel is especially sensitive to potassium concentration, but the use is experimental and not evidence based.

*Mexiletine. A sodium channel blocker. In LQT3 the problem is that the sodium channel does not close properly. Mexiletine closes these channels and is believed to be usable when other therapies fail. It should be especially effective in LQT3 but there is no evidence based documentation.

*Amputation of the cervical sympathetic chain (left stellectomy). This may be used as an add-on therapy to beta blockers but modern therapy mostly favors ICD implantation if beta blocker therapy fails.

Arrhythmia termination:
Arrhythmia termination involves stopping a life-threatening arrhythmia once it has already occurred. One effective form of arrhythmia termination in individuals with LQTS is placement of an implantable cardioverter-defibrillator (ICD). Alternatively, external defibrillation can be used to restore sinus rhythm. ICDs are commonly used in patients with syncopes despite beta blocker therapy, and in patients who have experienced a cardiac arrest.

It is hoped that with better knowledge of the genetics underlying the long QT syndrome, more precise treatments will become available.
Prognosis:
The risk for untreated LQTS patients having events (syncopes or cardiac arrest) can be predicted from their genotype (LQT1-8), gender and corrected QT interval.

*High risk (>50%)
QTc>500 msec LQT1 & LQT2 & LQT3 (males)

*Intermediate risk (30-50%)
QTc>500 msec LQT3 (females)

QTc<500 msec LQT2 (females) & LQT3

*Low risk (<30%)
QTc<500 msec LQT1 & LQT2 (males)

Disclaimer: This information is not meant to be a substitute for professional medical advise or help. It is always best to consult with a Physician about serious health concerns. This information is in no way intended to diagnose or prescribe remedies.This is purely for educational purpose

Resources:
http://www.bbc.co.uk/health/physical_health/conditions/longqt1.shtml
http://www.mayoclinic.com/health/long-qt-syndrome/DS00434
http://en.wikipedia.org/wiki/Long_QT_syndrome
http://paramedicine101.blogspot.com/2009/09/long-qt-syndrome-part-iii.html
http://www.itriagehealth.com/disease/long-qt-syndrome-(qt-prolongation)

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