Introduction
Background
Torsade de pointes, literally meaning twisting of points, is a distinctive form of polymorphic ventricular tachycardia (VT) characterized by a gradual change in the amplitude and twisting of the QRS complexes around the isoelectric line. Torsade de pointes (torsade) is associated with a prolonged QT interval, which may be congenital or acquired. It usually terminates spontaneously but frequently recurs and may degenerate into sustained VT and ventricular fibrillation.
Pathophysiology
The association between torsade and a prolonged QT interval has long been known, but the mechanisms involved at the cellular and ionic levels have been made clearer in approximately the last decade. The abnormality underlying both acquired and congenital long QT syndromes is in the ionic current flow during repolarization, which affects the QT interval. Various studies support the concept that prolongation of the repolarization delays the inactivation of the ion channels responsible for the inward flow of positive depolarizing currents. This leads to a further delay in repolarization and causes early after depolarization (EAD), the triggering event for torsade. The following phases are described:
- Phase 1: During initial upstroke of action potential in a normal cardiac cell, a rapid net influx of positive ions (Na+ and Ca++) occurs, which results in the depolarization of the cell membrane. This is followed by a rapid transient outward potassium current (Ito), while the influx rate of positive ions (Na+, Ca++) declines. This represents the initial part of the repolarization, or phase 1.
- Phase 2 is characterized by the plateau, the distinctive feature of which is the cardiac repolarization. The positive currents flowing inward and outward become almost equal during this stage.
- Phase 3 of the repolarization is mediated by activation of the delayed rectifier potassium current (IK) moving outward while the inward positive current decays. If a slow inactivation of the Ca++ and Na+ currents occurs, this inward "window" current can cause single or repetitive depolarization during phases 2 and 3 (ie, EADs). These EADs appear as pathologic U waves on a surface ECG, and, when they reach a threshold, they may trigger ventricular tachyarrhythmias.
These changes in repolarization do not occur in all myocardial cells. The deep endocardial region and midmyocardial layer (composed of M cells) of the ventricle are more prone to prolongation of repolarization and EADs because they have a less rapid delayed rectifier potassium current (IKr), while other regions might have short or normal cycles. This heterogeneity of repolarization in the myocardial cells promotes the spread of triggered activity, which is initiated by EADs by a reentrant mechanism and currently is thought to be responsible for the maintenance of torsade.
Mortality/Morbidity
Torsade is a life-threatening arrhythmia and may present as sudden cardiac death in patients with structurally normal hearts.
Race
For both sexes, the corrected QT interval is longer in white persons than in black persons, thus explaining the lower susceptibility to acquired torsade in black persons.
Sex
Females are more prone to the development of torsade than males because they have longer QT intervals.
Age
Torsade occurs in patients of a wide age range, from newborn to 86 years. If it occurs at an early age, the cause usually is due to congenital long QT syndrome. In later years, the cause usually is due to acquired long QT syndrome.
Clinical
History
Patients with torsade usually present with recurrent episodes of palpitations, dizziness, and syncope; however, sudden cardiac death can occur with the first episode. Nausea, cold sweats, shortness of breath, and chest pain also may occur but are nonspecific and can be produced by any form of tachyarrhythmia.
- In a young patient with torsade, a diagnosis of congenital long QT syndrome should be considered, especially if a family history of sudden cardiac death or sudden infant death syndrome is present. In these patients, episodes of torsade are triggered by adrenergic stimulation such as stress, fear, or physical exertion, but other predisposing factors also should be considered.
- Patients with Jervell and Lange-Nielsen syndrome commonly have congenital sensorineural deafness representing an autosomal dominant pattern of inheritance for cardiac abnormalities, whereas deafness usually is autosomal recessive.
- Another form of familial or congenital long QT syndrome is Romano-Ward syndrome, in which hearing is normal and an autosomal dominant pattern of inheritance is observed.
- Patients with acquired long QT syndrome usually develop torsade during periods of bradycardia.
- The most common causes of acquired long QT syndrome are medications and electrolyte disorders (eg, hypokalemia, hypomagnesemia).
- Risk factors for torsade include the following:
- Congenital long QT syndrome
- Acquired long QT syndrome (causes of which include medications and electrolyte disorders such as hypokalemia and hypomagnesemia)
- Bradycardia
- Female sex
Physical
The physical findings in torsade depend on the rate and duration of tachycardia and the degree of cerebral hypoperfusion.
- Findings include rapid pulse, low or normal blood pressure, or transient or prolonged loss of consciousness. This could be preceded by bradycardia or premature ventricular contractions (leading palpitations).
- Pallor and diaphoresis may be noted, especially with a sustained episode.
- Other physical signs depend on the etiology of torsade.
Causes
- Congenital long QT syndromes (adrenergic-dependent)
- Jervell and Lange-Nielsen syndrome
- Romano-Ward syndrome
- Acquired long QT syndromes
- Antiarrhythmic drugs
- Class 1A - Quinidine, disopyramide, procainamide
- Class III - Sotalol, amiodarone (rare), ibutilide, dofetilide, almokalant
- Histamine1-receptor antagonists - Terfenadine, astemizole
- Cholinergic antagonists - Cisapride, organophosphates (pesticides)
- Antibiotics - Erythromycin, clarithromycin, trimethoprim-sulfamethoxazole, clindamycin, pentamidine, amantadine, chloroquine, halofantrine
- Antifungals - Ketoconazole, itraconazole
- Diuretics - Indapamide
- Psychotropic agents - Haloperidol, phenothiazines, thioridazine, trifluoperazine, sertindole, zimeldine, fluoxetine (possible)
- Tricyclic and tetracyclic antidepressants
- Antihypertensives - Bepridil, lidoflazine, prenylamine, ketanserin
- Other drugs - Oral hypoglycemics, citrate (massive blood transfusions), vasopressin (possible), carbamazepine (possible), cocaine
- Electrolyte abnormalities - Hypokalemia, hypomagnesemia, hypocalcemia
- Endocrine disorders - Hypothyroidism, hyperparathyroidism, pheochromocytoma, hyperaldosteronism
- Cardiac conditions - Myocardial ischemia, myocardial infarction, myocarditis, bradyarrhythmia, complete atrioventricular (AV) block
- Intracranial disorders - Subarachnoid hemorrhage, thalamic hematoma, cerebrovascular accident, encephalitis, head injury
- Nutritional disorders - Anorexia nervosa, starvation, liquid protein diets, gastroplasty and ileojejunal bypass, celiac disease
- Antiarrhythmic drugs
More on Torsade de Pointes |
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| Multimedia: Torsade de Pointes |
| References |
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Further Reading
Keywords
torsade de pointes, quinidine syncope, polymorphic ventricular tachycardia, VT, prolonged QT interval, arrhythmia, TdP, torsade de pointes ventricular tachycardia, TdPVT, ventricular fibrillation, early after depolarization, EAD, afterdepolarization, arrhythmia, torsades de pointes, torsades, torsade, sudden cardiac death, SCD, sudden death, ventricular fibrillation, tachyarrhythmia
