What is the significance of a prolonged QT interval?

• A. It increases risk of arrhythmias, particularly Torsades de Pointes
• B. It indicates acute myocardial infarction
• C. It indicates hyperkalemia
• D. It is a normal variant in well-conditioned athletes

Answer: (A)

Prolonged QT interval means the ventricles take longer to repolarize after each beat, which sets the stage for dangerous ventricular rhythms. The key danger is early afterdepolarizations during the extended repolarization period, which can trigger Torsades de Pointes, a chaotic, twisting form of ventricular tachycardia that may progress to ventricular fibrillation and cardiac arrest.

In practice, this is a warning sign that the patient may be at risk for sudden destabilization. Identify and remove any medications known to prolong the QT interval, correct electrolyte imbalances (notably low potassium and low magnesium), and monitor closely. If Torsades de Pointes occurs, the immediate management includes administering magnesium sulfate and optimizing heart rate—often with temporary pacing or medications that increase rate—to shorten the QT interval and suppress the arrhythmia. Maintain continuous monitoring and protect the patient from further QT-prolonging factors.

Hyperkalemia does not cause this pattern; it tends to shorten the QT interval and produce other ECG changes. Acute myocardial infarction has different ECG and biomarker patterns and is not defined by a prolonged QT. A prolonged QT is not a normal variant in well-conditioned athletes.