Cardiovascular · Year 1 · from Cardiovascular
Case 3: Long QT Syndrome with Torsades de Pointes
Patient Presentation
Demographics: 18-year-old female
Chief Complaint: Cardiac arrest during swimming
History of Present Illness: An 18-year-old female was found unresponsive at the bottom of a swimming pool during swim practice. Bystander CPR was initiated immediately. Upon EMS arrival, the cardiac monitor showed polymorphic ventricular tachycardia (torsades de pointes). She was defibrillated once with return of spontaneous circulation. She had experienced several "fainting spells" over the past 2 years, including one episode while startled by a loud noise. Her maternal uncle died suddenly at age 25 during exercise.
Physical Examination (post-resuscitation):
- Vital Signs: BP 105/65 mmHg, HR 68 bpm, RR 14/min (intubated), Temp 36.2°C
- General: Intubated, sedated
- Cardiovascular: Regular rhythm, no murmurs
- Neurological: Purposeful movements to stimulation
Workup
- ECG: Sinus rhythm with markedly prolonged QTc interval (520 ms), notched T waves in lateral leads
- Echocardiogram: Normal LV function, no structural abnormalities
- Labs: Electrolytes normal (K+ 4.0, Mg 2.1, Ca 9.2)
- Genetic testing: KCNQ1 mutation identified (LQT1)
- Family screening: Mother has prolonged QTc (480 ms)
Diagnosis
Congenital Long QT Syndrome Type 1 (LQT1) with aborted sudden cardiac death due to torsades de pointes
Electrophysiology Correlation: Long QT syndrome results from mutations in cardiac ion channels that prolong repolarization. LQT1 is caused by mutations in KCNQ1 gene encoding the IKs potassium channel (slow delayed rectifier). Prolonged repolarization creates heterogeneity in refractoriness and increases risk of early afterdepolarizations (EADs), which can trigger torsades de pointes. LQT1 is characteristically triggered by exercise, especially swimming, and emotional stress (catecholamine-mediated).
The action potential prolongation is due to:
- Reduced IKs current → delayed phase 3 repolarization
- EADs during plateau phase → triggered activity
- Dispersion of refractoriness → reentry
Treatment
- Beta-blocker therapy (nadolol preferred for LQT1) - reduces catecholamine triggers
- ICD implantation (indicated after cardiac arrest)
- Avoid QT-prolonging medications (www.crediblemeds.org)
- Avoid strenuous exercise, especially swimming
- Family screening with ECG and genetic testing
- Magnesium repletion and potassium optimization
Clinical Image
Image Description: ECG showing torsades de pointes, a polymorphic ventricular tachycardia characterized by QRS complexes that appear to twist around the isoelectric baseline. The characteristic "twisting of the points" pattern with undulating axis is visible.
Source: Wikimedia Commons - Torsades de pointes ECG License: CC BY-SA 3.0 URL: https://commons.wikimedia.org/wiki/File:Torsades_de_Pointes.svg