Torsades de pointes

A 55 year old female with a history of depression presents to the emergency department after an episode of syncope. She reports lightheadedness and palpitations prior to transient loss of consciousness, followed by spontaneous recovery. She was recently treated for a urinary tract infection with ciprofloxacin and is taking citalopram. On examination, findings are unremarkable. Vital signs show blood pressure 100/60 mmHg, pulse 55/min, respiratory rate 18/min, oxygen saturation 98% on room air, and temperature 97.9°F. ECG shows prolonged QT interval (QTc > 500 ms) and polymorphic ventricular tachycardia with twisting of QRS complexes around the isoelectric line. Diagnosis?

Diagnosis is Torsades de pointes.

1. Definition

Torsades de pointes is a polymorphic ventricular tachycardia that occurs in the setting of a prolonged QT interval, characterized by cyclic twisting of QRS complexes around the baseline.

2. Pathophysiology

1. Prolonged QT interval due to delayed ventricular repolarization
2. Caused by inhibition of delayed rectifier potassium currents (IKr)
3. Leads to early afterdepolarizations
4. Often triggered by R on T phenomenon
5. May be pause dependent, occurring after a long RR interval

3. Etiology

3.1 Acquired Causes

1. QT prolonging drugs
• Antiarrhythmics such as class IA and class III
• Antibiotics such as macrolides and fluoroquinolones
• Antidepressants such as SSRIs (citalopram) and TCAs
• Antipsychotics
• Antiemetics such as ondansetron
2. Electrolyte abnormalities
• Hypokalemia
• Hypomagnesemia
• Hypocalcemia
3. Bradycardia

3.2 Congenital Causes

1. Congenital long QT syndrome
• Romano Ward syndrome
• Jervell and Lange Nielsen syndrome

4. Clinical Features

1. Palpitations
2. Dizziness
3. Syncope
4. May progress to ventricular fibrillation and sudden cardiac death

5. ECG Findings

1. QTc > 500 ms significantly increases risk
2. Polymorphic ventricular tachycardia
3. Twisting QRS complexes around isoelectric line

6. Management

6.1 Immediate Measures

1. Discontinue offending drugs
2. Correct electrolyte abnormalities, especially potassium and magnesium

6.2 Hemodynamically Unstable

1. Immediate unsynchronized defibrillation

6.3 Hemodynamically Stable

1. Intravenous magnesium sulfate (2 g IV) is first line therapy
2. Effective even if serum magnesium is normal

6.4 Refractory Cases

1. Increase heart rate to shorten QT interval
2. Isoproterenol for acquired torsades
3. Overdrive pacing

7. Special Considerations

1. Avoid QT prolonging drugs
2. Maintain potassium in high normal range
3. Avoid isoproterenol in congenital long QT syndrome
4. Consider implantable cardioverter defibrillator (ICD) in recurrent or high risk cases

8. Key Clinical Insight

Syncope + QTc > 500 ms + polymorphic VT with twisting QRS + QT prolonging drugs = Torsades de pointes

9. Exam Level Pearls

1. Magnesium sulfate is first line regardless of serum level
2. QT prolonging drugs are the most common cause
3. Bradycardia increases risk
4. Pause dependent arrhythmia is characteristic
5. Combination of citalopram and ciprofloxacin increases risk