From the Guidelines
A long QT interval on an EKG is a significant finding that requires prompt attention as it indicates delayed ventricular repolarization, which can predispose patients to a potentially fatal arrhythmia called Torsades de Pointes. The normal QT interval is typically less than 450ms in men and 460ms in women when corrected for heart rate (QTc) 1. Management includes immediate identification and correction of reversible causes such as electrolyte abnormalities (particularly low potassium, magnesium, or calcium), discontinuation of QT-prolonging medications, and cardiac monitoring.
- Common QT-prolonging medications include:
- Certain antiarrhythmics (amiodarone, sotalol)
- Antibiotics (macrolides, fluoroquinolones)
- Antipsychotics (haloperidol, quetiapine)
- Antiemetics (ondansetron) Electrolyte replacement should target potassium levels of 4.5-5.0 mEq/L and magnesium levels above 2 mg/dL 1.
- Long QT can be acquired or congenital (Long QT Syndrome), with congenital cases potentially requiring:
- Beta-blockers (such as nadolol 40-80mg daily or propranolol 10-40mg three times daily)
- Avoidance of triggers like intense exercise or loud noises
- Consideration of an implantable cardioverter-defibrillator for high-risk patients The physiological basis for this concern is that prolonged repolarization creates vulnerability to early afterdepolarizations, which can trigger life-threatening ventricular arrhythmias 1. Treatment should be stopped if the QTc is > 500 ms on monitoring, and conditions known to provoke torsades de pointes, especially hypokalaemia and extreme bradycardia, should be avoided in patients with drug-induced QT prolongation 1.
From the Research
Significance of Long QT Interval on EKG
The long QT interval on an electrocardiogram (EKG) is a significant indicator of an increased risk of torsades de pointes (TdP), a life-threatening arrhythmia 2.
Risk Factors for TdP
Several risk factors contribute to the development of TdP, including:
- Hypokalemia
- Female sex
- Drug-drug interactions
- Advancing age
- Genetic predisposition
- Hypomagnesemia
- Heart failure
- Bradycardia
- Corrected QT (QTc) interval prolongation 2, 3, 4
Drugs Associated with QT Prolongation
Various drugs, including antipsychotic medications and cardiovascular agents, can cause QT interval prolongation, increasing the risk of TdP:
- Antipsychotic drugs: amisulpride, clozapine, flupenthixol, fluphenazine, haloperidol, melperone, olanzapine, perphenazine, pimozide, quetiapine, risperidone, sulpiride, thioridazine, and ziprasidone 3, 5
- Cardiovascular drugs: class Ia antiarrhythmic agents, sotalol, and amiodarone 4
Monitoring and Prevention
To prevent TdP, careful and regular monitoring of EKG and electrolytes is necessary, especially in patients at risk for QT interval prolongation 2.
- Patients should be educated to seek immediate medical attention if they experience symptoms such as palpitations, lightheadedness, dizziness, or syncope 2.
- Close monitoring for QTc prolongation is necessary, and dose reduction or discontinuation of the offending drug should be considered if the QTc interval is prolonged 2.