Torsades de pointes

Torsades de pointes (i.e. twisting of the QRS complexes around an isoelectric line) is a polymorphic ventricular tachycardia associated with congenital or acquired long QT interval (i.e. long QT interval >0.45 in male and >0.47 in female); Tdp can progress to ventricular fibrillation; "R-on-T phenomenon" (i.e. ventricular depolarization coincides with vulnerable period of ventricular repolarization).

Pathogenesis:- Long QT interval → inhibition of the delayed rectifier potassium current → early after depolarization → polymorphic ventricular tachycardia.

Etiologies:- Drugs, hypokalemia, hypocalcemia, hypomagnesemia, and congenital long QT interval syndrome (e.g. Romano-Ward syndrome and Jervell and Lange Nielsen syndrome).

Drugs are ABCDE:-
1. AntiArrhythmic(e.g. Class IA, Class III)
2. AntiBiotics (e.g. macrolides, fluoroquinolones)
3. Antipsychotics (e.g. haloperidol)
4. AntiDepressants (e.g. TCA)
5. AntiEmetics (e.g. ondansetron)

Presents with dizziness, palpitations, syncope, and sudden cardiac death.

ECG shows long QT interval and polymorphic ventricular tachycardia.

Management:-
1. Immedicated DC cardioversion in hemodynamically unstable patients.
2. Intravenous magnesium (2 g IV) is the 1st line therapy for hemodynamically stable patients.
3. Isoproterenol (Beta agonist) is used in Torsades de Pointes with prolonged QT that is refractory to magnesium by increasing heart rate; Contraindicated in congenital QT prolongation syndrome.
4. Overdrive pacing.

Figure:- Torsades de pointes (TdP)