The ECG Rhythms content is currently under development and is being updated by medical professionals.
Long QT syndrome (LQTS) is a heart rhythm disorder characterized by a prolonged QT interval on the electrocardiogram (ECG).194 This prolongation indicates a delay in the repolarization of the ventricles, making the heart more susceptible to dangerous and potentially life-threatening arrhythmias.194 LQTS can be either congenital, due to genetic mutations affecting ion channels in the heart, or acquired, often caused by certain medications, electrolyte imbalances, or underlying medical conditions.194
Analogy: “A prolonged echo in the heart’s electrical activity, making it vulnerable to disruptions.”
The primary ECG finding in Long QT syndrome is a prolonged QT interval, specifically a corrected QT interval (QTc) that is greater than 440 milliseconds in males and greater than 460 milliseconds in females.194 The QT interval is measured from the beginning of the QRS complex to the end of the T wave.194 The morphology of the T wave may also be abnormal and can vary depending on the specific type of LQTS. These abnormalities can include broad-based T waves, notched T waves, peaked T waves, or inverted T waves.196 A particularly dangerous arrhythmia associated with LQTS is Torsades de Pointes, a polymorphic ventricular tachycardia characterized by QRS complexes that appear to twist around the isoelectric baseline.194
The most common symptom of Long QT syndrome is syncope, or fainting spells, which can occur suddenly and with little to no warning.194 These fainting episodes are often triggered by factors such as exercise, emotional stress, or sudden startling events in congenital LQTS, or by rest or auditory stimuli in acquired forms.194 Some individuals may experience palpitations or seizures.194 The most severe complication of LQTS is sudden cardiac death due to the development of life-threatening ventricular arrhythmias like Torsades de Pointes or ventricular fibrillation.194 Some individuals with LQTS may remain asymptomatic, with the prolonged QT interval being discovered incidentally during an ECG performed for another reason.194
“Like a stretched rubber band taking longer to return to its original shape, the ventricles take longer to repolarize, making them susceptible to abnormal rhythms.”