Symptoms of QT Prolongation
QT prolongation most commonly presents with palpitations, dizziness, syncope, or sudden cardiac arrest, though many patients remain completely asymptomatic until a life-threatening arrhythmia occurs. 1, 2
Clinical Presentations
Symptomatic Manifestations
- Palpitations are a common presenting symptom, occurring when patients experience episodes of torsades de pointes (TdP), the characteristic polymorphic ventricular tachycardia associated with QT prolongation 1, 2
- Syncope (fainting) represents the most frequent clinical manifestation in congenital long QT syndrome, with first occurrence typically between ages 5-15 years, and serves as a warning sign of potentially fatal arrhythmias 1, 3
- Dizziness or lightheadedness occurs during episodes of TdP, particularly when the arrhythmia is self-limited and does not progress to cardiac arrest 1, 4, 5
- Seizures can occur due to cerebral hypoperfusion during arrhythmic episodes, sometimes leading to misdiagnosis as primary seizure disorders 3
- Sudden cardiac arrest or sudden cardiac death may be the first and only presentation, particularly in patients with undiagnosed congenital long QT syndrome or those exposed to QT-prolonging medications without appropriate monitoring 1, 4
Asymptomatic Presentation
- Many patients remain completely asymptomatic despite significant QT prolongation, with approximately 10-36% of genotype-positive long QT syndrome patients having normal QTc intervals (≤440 ms) at baseline 1
- Incidental discovery on routine ECG is common, particularly during pre-operative screening, employment physicals, or evaluation for unrelated cardiac symptoms 1
Trigger-Specific Symptoms
Exercise-Related Symptoms
- LQT1 patients (Romano-Ward syndrome with KCNQ1 mutations) are at highest risk during exercise, particularly swimming, experiencing syncope or cardiac arrest during physical exertion 1
Auditory-Triggered Symptoms
- LQT2 patients are particularly sensitive to loud noises, especially when asleep or resting, with sudden auditory stimuli triggering arrhythmic events 1
Rest/Sleep-Related Symptoms
- LQT3 patients typically experience events during sleep or rest, representing the most malignant variant with higher mortality despite beta-blocker therapy 1
Warning Signs Requiring Immediate Evaluation
- Any patient experiencing palpitations, lightheadedness, dizziness, or syncope while taking QT-prolonging medications should proceed directly to the emergency department for immediate ECG evaluation and continuous cardiac monitoring 5
- Recurrent syncope in children or adolescents, particularly if exercise-related or associated with emotional stress, warrants urgent evaluation for congenital long QT syndrome 1
Critical Clinical Pitfall
The absence of symptoms does not exclude significant QT prolongation or risk of sudden death—asymptomatic patients with QTc >500 ms remain at substantial risk for life-threatening arrhythmias and require aggressive risk factor modification and close monitoring 1, 2.