Torsades de Pointes (TdP)

A 34 year old female presents with recurrent episodes of palpitations, dizziness, and syncope. She recently started erythromycin for pneumonia and has been taking ondansetron for nausea. On examination, pulse is irregular and blood pressure is 92/58 mmHg. ECG demonstrates prolonged QT interval followed by polymorphic ventricular tachycardia with twisting QRS complexes around the baseline. Diagnosis?

Diagnosis is torsades de pointes (TdP).

1. Definition

Torsades de pointes is a polymorphic ventricular tachycardia associated with prolonged QT interval.

It is characterized by cyclical twisting of QRS complexes around the isoelectric line and may deteriorate into ventricular fibrillation.

2. Pathophysiology

1. Prolonged QT interval delays ventricular repolarization
2. Inhibition of delayed rectifier potassium current prolongs action potential duration
3. Early afterdepolarizations develop during repolarization
4. Triggered activity initiates polymorphic ventricular tachycardia
5. “R-on-T phenomenon” may precipitate TdP:
• Ventricular depolarization occurs during vulnerable ventricular repolarization

3. QT Interval Prolongation

Prolonged QT Interval

1. QTc >450 ms in males
2. QTc >470 ms in females

Markedly prolonged QT interval significantly increases risk of TdP

4. Etiology

4.1 Electrolyte Abnormalities

1. Hypokalemia
2. Hypomagnesemia
3. Hypocalcemia

4.2 Congenital Long QT Syndromes

Romano-Ward Syndrome

• Autosomal dominant

Jervell and Lange-Nielsen Syndrome

• Autosomal recessive
• Associated with sensorineural deafness

4.3 Drug-Induced QT Prolongation

ABCDE Mnemonic

Antiarrhythmics

1. Class IA:
• Quinidine
• Procainamide
2. Class III:
• Sotalol
• Dofetilide
• Amiodarone may prolong QT but is less torsadogenic than other class III agents

Antibiotics

1. Macrolides
2. Fluoroquinolones

Antipsychotics

1. Haloperidol
2. Ziprasidone

Antidepressants

1. Tricyclic antidepressants
2. SSRIs such as citalopram

Antiemetics

1. Ondansetron

5. Clinical Features

1. Palpitations
2. Dizziness
3. Syncope
4. Seizure-like episodes due to cerebral hypoperfusion
5. Sudden cardiac death

Episodes may be self-terminating or may progress to ventricular fibrillation

6. ECG Findings

1. Prolonged QT interval
2. Polymorphic ventricular tachycardia
3. Twisting of QRS complexes around the isoelectric line
4. Beat-to-beat variation in QRS amplitude and axis

7. Diagnosis

Diagnosis is based on:

1. Characteristic ECG findings
2. Presence of prolonged QT interval
3. Identification of precipitating factors such as drugs or electrolyte abnormalities

8. Management

8.1 Hemodynamically Unstable or Pulseless TdP

1. Immediate unsynchronized defibrillation

8.2 Hemodynamically Stable Patient

Intravenous Magnesium Sulfate

1. First-line therapy even if serum magnesium level is normal
2. Typical dose:
• Magnesium sulfate 2 g IV

8.3 Correction of Underlying Causes

1. Discontinue QT-prolonging drugs
2. Correct hypokalemia
3. Correct hypomagnesemia
4. Correct hypocalcemia
5. Maintain serum potassium >4.0–4.5 mEq/L when possible

8.4 Refractory or Recurrent TdP

Isoproterenol

1. Beta-agonist that increases heart rate and shortens QT interval
2. Used in acquired pause-dependent TdP refractory to magnesium
3. Contraindicated in congenital long QT syndrome

Overdrive Pacing

1. Increases heart rate and shortens repolarization time
2. Useful in refractory or recurrent TdP

8.5 Congenital Long QT Syndrome Management

1. Beta-blockers are first-line long-term therapy
2. ICD may be required in patients with recurrent arrhythmias or prior cardiac arrest

9. Complications

1. Ventricular fibrillation
2. Sudden cardiac death
3. Recurrent syncope
4. Hemodynamic collapse

10. Prognosis

1. Prognosis depends on rapid recognition and correction of underlying cause
2. Untreated TdP may rapidly progress to ventricular fibrillation
3. Congenital long QT syndromes carry risk of recurrent arrhythmia and sudden death

11. Key Clinical Insight

Patient with syncope or palpitations who is taking QT-prolonging medications and demonstrates polymorphic ventricular tachycardia with prolonged QT interval likely has torsades de pointes

12. Key Exam Points

1. TdP is a polymorphic ventricular tachycardia associated with prolonged QT interval
2. Early afterdepolarizations are the underlying electrophysiologic mechanism
3. “R-on-T phenomenon” can precipitate TdP
4. Hypokalemia, hypomagnesemia, and QT-prolonging drugs are common causes
5. Magnesium sulfate is first-line therapy even with normal magnesium levels
6. Hemodynamically unstable TdP requires immediate unsynchronized defibrillation
7. Isoproterenol and overdrive pacing may be used in refractory acquired TdP
8. Congenital long QT syndromes include Romano-Ward and Jervell-Lange-Nielsen syndromes
9. TdP may degenerate into ventricular fibrillation
10. ECG shows twisting QRS complexes around the isoelectric baseline