Long QT Syndrome

The QT interval describes the depolarization and repolarization of the cardiac cycle. Increase in this interval is associated with onset of Torsades de Pointes, a specific type of polymorphic ventricular tachycardia. This disorder is more common than previously supposed.

Symptoms:

· palpitations

· syncope

· seizures

· sudden cardiac death

Etiology:

· inherited (genetic)

· medications or overdose

· acquired and metabolic abnormalities

· bradyarrhythmias

Diagnosis:

· Measurement of QTc (corrected QT interval) on resting ECG. Anything over 440 ms. is considered prolonged. 440 to 470 is borderline. This measurement usually appears on the computerized ECG readout. Above 470 in males and 480 in females is abnormal

· Recorded evidence of Torsades.

· Presence of family history of syncope or sudden death.

· Presence of triggering medication with suggestive symptoms.

· Presence of illness severe enough to produce electrolyte abnormalities should prompt ECG looking for this disorder

· Ambulatory ECG can be helpful

Treatment:

· Acquired causes usually triggered by a bradycardia.

· Congenital causes usually triggered by a catecholamine surge. Beta blockers can be used to reduce triggering.

· Amiodarone, lidocaine and procainamide contraindicated – prolong QT interval.

· Correct electrolyte abnormalities

· Discontinue triggering or toxic medications

· For unstable Torsades, treat promptly with nonsynchronized defibrillation.

· For a conscious patient who is more stable, IV magnesium sulfate is first line therapy, and works even if serum Mg. is normal. Benefit occurs without shortening of the QT interval.

· Look for an eating disorder.

· Occasionally pacing is required.

Sources:

1. Unrecognized killers on ECG. Audio Digest Emergency Medicine 2007. 24(1)

2. Warnica W. A tale of two “synching” teenagers: What is LQTS anyway? Perspectives in Cardiology 2007; 23(2): 21-24.