From the Guidelines
A QTc interval of 440 msec is considered borderline prolonged and warrants monitoring, but does not necessarily require immediate intervention. This finding is particularly relevant in women, where normal QTc intervals are typically less than 460 msec, and in men, where normal QTc intervals are less than 450 msec 1. I recommend reviewing the patient's medication list for QT-prolonging drugs, such as certain antipsychotics, antibiotics (macrolides, fluoroquinolones), antiarrhythmics, and antiemetics, and considering alternatives when possible 1. Checking electrolytes, particularly potassium, magnesium, and calcium, is also crucial, as deficiencies can prolong the QT interval 1.
Key Considerations
- Regular ECG monitoring is advisable, especially if starting new medications, to assess for any changes in the QTc interval 1.
- Patients should be educated about symptoms of arrhythmias, including palpitations, dizziness, and syncope, which warrant immediate medical attention 1.
- The risk of cardiac events, such as torsades de pointes, increases significantly with QTc values above 500 msec 1.
- According to the 2017 AHA/ACC/HRS guideline, beta blockers should be used with caution in patients with long QT syndrome, and careful monitoring of the QTc during therapy is recommended 1.
Management
- Avoidance of QT-prolonging drugs and correction of electrolyte abnormalities are recommended in all patients with a diagnosis of long QT syndrome 1.
- Beta-blockers are recommended in patients with a clinical diagnosis of long QT syndrome, and ICD implantation with the use of beta-blockers is recommended in patients with previous cardiac arrest 1.
- Monitoring and management should be individualized based on the patient's specific risk factors and clinical presentation.
From the Research
QTc Interval Prolongation
- A QTc interval of 440 msec is considered prolonged, which signifies an increased risk of the life-threatening arrhythmia torsades de pointes (TdP) 2.
- Risk factors for drug-induced TdP include hypokalemia, female sex, drug-drug interactions, advancing age, genetic predisposition, hypomagnesemia, heart failure, bradycardia, and corrected QT (QTc) interval prolongation 2.
- The study suggests that when the QTc interval is 470-500 ms for males, or 480-500 ms for females, or the QTc interval increases 60 ms or more from pretreatment values, dose reduction or discontinuation of the offending drug should be considered where possible, and electrolytes corrected as needed 2.
Management of QTc Interval Prolongation
- Close monitoring for QTc prolongation is necessary to prevent TdP 2.
- Patients at risk for QT interval prolongation should be educated to go directly to the emergency room if they experience palpitations, lightheadedness, dizziness or syncope 2.
- The use of certain antipsychotic agents, such as ziprasidone and iloperidone, can significantly prolong the QTc interval, while others, such as brexpiprazole, cariprazine, olanzapine, and clozapine, are considered lower risk 3.
Assessment of QTc Interval
- Assessment of the heart rate-corrected QT-interval on the 12-lead electrocardiogram is a common part of consultation-liaison psychiatry practice 4.
- In patients with ventricular conduction delay due to bundle branch block (BBB) and ventricular pacing, the QT-interval must be adjusted for QRS duration, and multiple formulae have been proposed to account for wide QRS complex in this setting 4.