Figure 1 - Torsades de pointes. Top figure: Normal heart rhythm. Bottom figure: Torsades de pointes. "Torsades de pointes" means torsion around a point. In this arrhythmia, the heart rhythm is extremely rapid, and the shape of the complexes on the ECG are constantly changing, often resembling a sine-wave pattern as in this picture. When the heart's electrical system behaves in this way, effective pumping is impossible
People with LQTS have prolonged QT intervals on their ECGs. The QT interval is a reflection of how long it takes to “recharge” heart cells after they have been stimulated to beat. The abnormalities in the QT interval produce the arrhythmias.
Figure 2 - The QT interval. The QT interval represents repolarization, or "recharge," of a cardiac cell. After the heart's electrical impulse stimulates a heart cell (thus causing it to beat), recharging must occur in order for the cell to be ready for the next electrical impulse. The QT interval is measured from the beginning of the QRS complex to the end of the T wave. In LQTS, the QT interval is prolonged.
What causes LQTS?
LQTS is an inherited disorder. Several genes have been identified that affect the QT interval, so several varieties of LQTS exist. Some families have a very high incidence of LQTS.How common is LQTS?
LQTS is present in approximately one of 5000 people. LQTS is one of the more common causes of sudden death in young people, resulting in between 2000 and 3000 deaths per year.What are the symptoms?
The symptoms of LQTS occur only when the patient develops an episode of torsades de pointes, and the degree of symptoms depends on the length of time the arrhythmia persists. If it lasts only momentarily, a few seconds of extreme dizziness may be the only symptom. If it persists for more than 10 seconds or so, syncope occurs. And if it lasts for more than a few minutes, the victim never regains consciousness.In those with inherited LQTS, episodes are often triggered by sudden bursts of adrenaline – such as might occur during physical exertion, when startled, or when extremely angry.
Fortunately, many people with LQTS have a mild form, and never experience life-threatening symptoms.
How is LQTS diagnosed?
Doctors should think of LQTS in anyone who has had syncope or cardiac arrest, and in family members of a person with known LQTS. Any young person with syncope that occurs during exercise or in any other circumstance in which a surge of adrenaline levels was likely to have been present should have LQTS specifically ruled out. The diagnosis of LQTS is made by seeing an abnormally prolonged QT interval on the ECG. Sometimes a treadmill test is necessary to bring out the ECG abnormalities.How is LQTS treated?
In patients with inherited LQTS, the most common treatment is to use beta blockers. Beta blockers blunt the surges of adrenaline that trigger episodes of torsades de pointes in these patients. Unfortunately, it has not yet been proven that beta blockers significantly reduce the incidence of syncope and sudden death in these patients.It is important for individuals with LQTS to avoid the many drugs that cause a prolongation of the QT interval. In these people, such drugs are very likely to provoke episodes of torsades de pointes. (Indeed, these drugs can produce torsades de pointes even in some people who do not have LQTS.)
The major offenders are, ironically, the antiarrhythmic drugs quinidine, procainamide, disopyramide, ibutilide, dofetilide, and sotalol; several antidepressant medications, and the antibiotic erythromycin.
Here is a sitee from the University of Arizona that lists drugs that have been associated with sudden death from QT interval prolongation.
For many people with LQTS, the implantable defibrillator is the best treatment. This device should be used in patients who have survived cardiac arrests, and probably in patients who have had syncope due to LQTS – especially if syncope occurs while already taking beta blockers.
