Delayed ventricular repolarization due to congenital ion channel mutation or acquired causes is identified by prolongation of the QT interval on ECG. Prolongation is generally defined as QT interval > 450 msec, although some use different thresholds depending on patient population (eg, 440 msec in men and 460 msec in women). Prolongation carries an increased risk of ventricular arrhythmias, primarily torsades de pointes, resulting in recurrent syncope and/or sudden cardiac arrest.
Most patients present with incidental findings on ECG.
Symptomatic patients will present with syncope and potentially sudden cardiac death.
QT prolongation can be categorized as congenital or acquired, although there is likely interaction between the two, eg, genetic mutations may predispose certain individuals who are more sensitive to certain stressors.
Congenital – Genetic condition affecting the channels that regulate the flow of sodium, potassium, and calcium in cardiac cells. At least 10 genes have been identified thus far with a spectrum of different clinical features. Age of onset is variable, most often occurring in adolescence.
Acquired – Results from external factors altering sodium, potassium, or calcium currents in cardiac cells, eg, certain medications, cardiac disease, intracranial hemorrhage, electrolyte abnormalities, hypothyroidism, cirrhosis, or hypothermia.
ICD10CM: I45.81 – Long QT syndrome
SNOMEDCT: 111975006 – Prolonged QT interval
Differential Diagnosis & Pitfalls
When QT prolongation is identified, the underlying cause should be sought. This includes taking a very thorough family and medication history from the patient.
Medications that may cause prolonged QT intervals include amiodarone, tricyclic antidepressants, antibiotics (ie, fluconazole and erythromycin), metoclopramide, quinidine, haloperidol, droperidol, methadone, ondansetron, selective serotonin reuptake inhibitors, and diphenhydramine.
Below is a list of drugs with literature evidence indicating an adverse association with this diagnosis. The list is continually updated through ongoing research and new medication approvals. Click on Citations to sort by number of citations or click on Medication to sort the medications alphabetically.