Long QT syndrome

Long QT syndrome is a disorder of cardiac electrical repolarization that prolongs the QT interval and can trigger torsades de pointes, fainting, or sudden cardiac arrest.

Cardiac action potential: The sequence of electrical changes across a heart cell’s membrane that drives contraction and recovery. Its ventricular-cell recovery phase is prolonged in long QT syndrome.
Electrocardiogram: A recording of the heart’s electrical activity from electrodes placed on the skin. It measures the QT interval used to identify the syndrome.
Schwartz score: A clinical scoring system that combines electrocardiographic, clinical, and family-history findings to assess long-QT syndrome probability. It organizes evidence when a single QT measurement does not settle diagnosis.
LQT1: The long-QT syndrome subtype caused by pathogenic variants in KCNQ1. Exercise, especially swimming, is a characteristic trigger for arrhythmias in this subtype.
Syncope: A brief loss of consciousness caused by transient inadequate blood flow to the brain. A self-terminating ventricular arrhythmia can cause abrupt fainting in long-QT syndrome.
QT interval: The electrocardiographic interval from the start of ventricular depolarization to the end of repolarization. Its abnormal prolongation defines the syndrome’s central electrical finding.
Corrected QT interval: An estimate of the QT interval adjusted for heart rate, commonly reported as QTc. Rate correction helps compare QT measurements across different heart rates.
Beta blocker: A medication that blocks beta-adrenergic receptors and reduces the effects of adrenaline and noradrenaline. Nonselective beta blockers reduce arrhythmic risk in many patients with inherited long-QT syndrome.
LQT2: The long-QT syndrome subtype caused by pathogenic variants in KCNH2. Sudden sounds or emotional stress can trigger events in this subtype.
Sudden cardiac death: An unexpected death caused by loss of cardiac function, usually following a sudden arrhythmia. Untreated malignant ventricular arrhythmias create the syndrome’s most serious outcome.

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