What are the causes of prolonged QT interval?
The QT interval is prolonged when the corrected QT interval (QTc) is more than 440 msec in men and 460 msec in women.
Idiopathic long QT interval syndrome:
- The Jervell-Lange-Nielson Syndrome: Accompanied by sensorineural deafness. Autosomal recessive.
- The Romano-Ward Syndrome: Autosomal dominant
- Sporadic long QT Syndrome
- (5% per year risk for syncope, symptomatic patients 10 year mortality rate = 50%)
- Syncope due to torsades de points polymorphic v tach, triggered by adrenergic arousal.
Secondary(acquired) types of QT interval prolongation:
- Coronary artery disease – myocardial ischemia and infarction (most common, QT interval is an independent risk factor post MI)
- Metabolic disturbances – electrolyte imbalance; e.g. hypocalcemia, liquid protein diet, intracoronary contrasts
- Cardiac drugs – quinidine, procainamide, disopyramide, propafenone, sotolol, amioderone
- Psychotropic drugs – phenothiazines, tricyclic antidepressants
- Antihistamine – terfenadine overdose or used in combination with antifungal agent e.g. ketoconazole or erythromycin
- Pentamidine used in AIDs
- Central nervous system, esp. intracranial hemorrhage
- Autonomic nervous system dysfunction secondary to radical neck dissection, carotid endartectomy, transabdominal truncal vagotomy
- Mitral valve prolapse, cardiomyopathy
- Misc. – severe bradycardia, high degree AV block, post Stroke-Adams seizures, hypothyroidism, hypothermia, pheochromocytoma, organophosphate poisoning.