A 52-year-old woman with a history of recurrent syncope is referred for evaluation. Her 12-lead ECG shows a prolonged QT interval (QTc 480 ms on repeated measurements) with normal QRS duration and no ST-segment abnormalities. She denies chest pain and has normal troponin levels. What is the most appropriate next investigation to identify the underlying structural or functional abnormality?

Explanation

## Investigation of Choice in Prolonged QT Interval with Syncope **Key Point:** In a patient with ECG evidence of prolonged QT interval and recurrent syncope, transthoracic echocardiography is the most appropriate next investigation to exclude structural heart disease (left ventricular hypertrophy, cardiomyopathy, valvular disease) that may predispose to arrhythmias and sudden cardiac death. ### Rationale for Echocardiography 1. **Structural screening:** Identifies left ventricular dysfunction, hypertrophy, or cardiomyopathy that may prolong QT and precipitate torsades de pointes. 2. **Non-invasive and readily available:** Can be performed in outpatient clinic without delay. 3. **Risk stratification:** Ejection fraction and wall motion assessment guide prognosis and need for ICD. 4. **First-line in syncope evaluation:** Guidelines recommend echocardiography in all patients with syncope and abnormal ECG findings. ### Differential Diagnosis: Causes of Prolonged QT | Cause | ECG/Clinical Feature | Investigation | |---|---|---| | **Long QT syndrome (congenital)** | Family history, syncope with emotion/exercise, normal echo | Genetic testing; EPS if diagnosis unclear | | **Acquired QT prolongation** | Drugs (antiarrhythmics, antipsychotics, antibiotics), electrolyte abnormalities | Medication review; serum K^+^, Mg^2+^, Ca^2+^ | | **Structural heart disease** | LVH, DCM, HCM, valvular disease | **Echocardiography** | | **Myocarditis/cardiomyopathy** | Chest pain, dyspnea, reduced EF | **Echocardiography** ± CMR | **High-Yield:** In syncope with prolonged QT on ECG, always exclude structural heart disease first with echocardiography before pursuing genetic testing or EPS. This is the standard initial approach per ACC/AHA guidelines. **Clinical Pearl:** Torsades de pointes (polymorphic VT) is the life-threatening arrhythmia associated with prolonged QT. Risk is increased by structural disease, female sex, bradycardia, and electrolyte abnormalities. Echocardiography helps identify modifiable structural factors. **Mnemonic: "ECHO First in Long QT" — Exclude structural disease before Genetic/Electrophysiology studies.**