Teaching topics from the New England Journal of Medicine - Vol. 358, No. 2, January 10, 2008
The most common cause of sudden death in a young person is the long-QT syndrome characterized by abnormal QT prolongation and increased risk of ventricular fibrillation. Common presentations of the long-QT syndrome are palpitations, presyncope, syncope, and cardiac arrest. The differential diagnosis of syncope in a young patient ranges from benign conditions such as vasovagal syncope to serious genetic conditions such as hypertrophic cardiomyopathy and catecholaminergic polymorphic ventricular tachycardia.
Long-QT Syndrome Genetic Testing and Treatment
Genetic testing for the long-QT syndrome is most useful in two settings. First, when a clinical diagnosis is relatively certain, knowing the specific gene (or the site of the mutation within the gene) may clarify the prognosis and guide therapeutic choices. Second, in a family with an affected proband and a known genetic defect, the genotyping can help rule out the diagnosis in some family members. The major therapeutic options for the long-QT syndrome are beta-blockers and implantable cardioverter defibrillators (ICDs).
Morning Report Questions
Q: What would the physical examination and echocardiography reveal in a patient with long-QT syndrome?
A: The physical examination and echocardiography (or magnetic resonance imaging, if performed) generally show no abnormalities in patients with this syndrome; thus, they are helpful only in ruling out other diagnoses such as hypertrophic cardiomyopathy.
Q: What can cause acquired QT prolongation?
A: Acquired causes of QT prolongation include hypocalcemia and hypothyroidism, as well as drugs such as sotalol, dofetilide, haloperidol, methadone, and pentamidine. The QT interval, the surface ECG representation of ventricular repolarization, is affected by the patient's heart rate and sex; the upper limits of the QT interval corrected for heart rate (the QTc) are below 460 msec for women and below 440 msec for men.