A 52-year-old man with hypertension presents to the emergency department with palpitations and chest discomfort for 2 hours. His vital signs are stable (BP 148/92 mmHg, HR 102/min, RR 18/min, SpO₂ 98% on room air). A 12-lead ECG shows a prolonged QT interval (QTc 520 ms) with normal sinus rhythm and no ST-segment changes. Serum electrolytes are normal. He is not on any QT-prolonging medications. What is the most appropriate next step in management?

Explanation

## Clinical Approach to Prolonged QT Interval **Key Point:** A prolonged QTc (>460 ms in women, >450 ms in men) in a stable patient with normal electrolytes and no obvious precipitant requires systematic evaluation for underlying causes before empiric treatment. ### Differential Diagnosis of Prolonged QT | Cause | Mechanism | Management Focus | |-------|-----------|------------------| | Long QT syndrome (congenital) | Ion channelopathy | Genetic testing, family screening, beta-blockers | | Acquired QT prolongation | Drug-induced, electrolyte, structural | Identify and remove offending agent | | Myocardial ischemia | Acute coronary syndrome | ECG changes, troponin, angiography | | Hypokalemia/Hypomagnesemia | Electrolyte depletion | Electrolyte replacement | | Bradycardia | Slower heart rate increases QT | Pacing if symptomatic | **High-Yield:** In a hemodynamically stable patient with isolated QT prolongation and normal electrolytes, the priority is identifying the underlying etiology (congenital long QT syndrome vs. acquired cause) rather than empiric antiarrhythmic therapy. ### Rationale for Next Step This patient requires: 1. **Detailed drug history** — screen for QT-prolonging agents (antipsychotics, macrolides, fluoroquinolones, antiarrhythmics, antiretrovirals) 2. **Family history** — syncope, sudden cardiac death, or deafness (Jervell and Lange-Nielsen syndrome) 3. **Echocardiography** — exclude structural heart disease (cardiomyopathy, left ventricular hypertrophy from hypertension) 4. **Genetic testing** — if clinical suspicion for congenital long QT syndrome (family history, recurrent syncope, QTc >500 ms) **Clinical Pearl:** Torsades de pointes is the life-threatening arrhythmia associated with prolonged QT. However, in a stable patient without active arrhythmia, investigation for cause takes precedence over empiric drug therapy. --- ### Why Other Options Are Premature **Magnesium sulfate** is indicated for acute torsades de pointes (polymorphic VT), not for asymptomatic QT prolongation. This patient has normal electrolytes and stable rhythm. **Amiodarone** can paradoxically prolong QT and increase torsades risk in some settings; it is not first-line for asymptomatic QT prolongation without active arrhythmia. **Coronary angiography** is not indicated in the absence of ECG ischemic changes, elevated troponin, or clinical features of acute coronary syndrome. [cite:Harrison 21e Ch 226]