From the Guidelines
Beta-blockers are recommended as the first-line treatment for patients with a clinical diagnosis of Long QT Syndrome (LQTS) to reduce the risk of sudden cardiac death and improve quality of life. According to the 2015 ESC guidelines for the management of patients with ventricular arrhythmias and the prevention of sudden cardiac death 1, beta-blockers are recommended in patients with a clinical diagnosis of LQTS. The guidelines also suggest that patients with LQTS should avoid QT-prolonging drugs, correct electrolyte abnormalities, and avoid genotype-specific triggers for arrhythmias.
Key Recommendations
- Avoidance of QT-prolonging drugs is crucial in managing LQTS, as these medications can increase the risk of torsades de pointes and sudden cardiac death 1.
- Correction of electrolyte abnormalities, such as hypokalemia, hypomagnesemia, and hypocalcemia, is essential to prevent arrhythmias in patients with LQTS 1.
- Genotype-specific triggers should be avoided, such as strenuous swimming in patients with LQT1 and exposure to loud noises in patients with LQT2 1.
- ICD implantation may be considered in patients with LQTS who have experienced cardiac arrest or syncope while receiving beta-blockers 1.
Treatment Approach
The treatment approach for LQTS depends on the severity of the condition and the presence of symptoms. For asymptomatic patients with a resting QTc less than 470 ms, chronic therapy with a beta blocker may be reasonable 1. However, for patients with a resting QTc greater than 500 ms, intensification of therapy with medications, left cardiac sympathetic denervation, or an ICD may be considered 1. It is essential to individualize treatment based on the patient's specific condition and genotype.
From the FDA Drug Label
Mexiletine did not prolong ventricular depolarization (QRS duration) or repolarization (QT intervals) as measured by electrocardiography.
Mexiletine does not cause QT prolongation syndrome. The drug label explicitly states that mexiletine did not prolong QT intervals, making it a potentially useful treatment option for ventricular arrhythmias associated with a prolonged QT interval 2.
- Key points:
- Mexiletine does not prolong QT intervals
- It may be useful in treating ventricular arrhythmias with a prolonged QT interval
- The drug's effect on QT intervals was measured by electrocardiography in clinical trials 2
From the Research
Qt Prolong Syndrome
- Qt prolong syndrome, also known as long QT syndrome (LQTS), is a familial disorder characterized by a prolongation of the QT interval on the ECG and occurrence of life-threatening cardiac arrhythmias 3.
- The syndrome is caused by congenital genetic mutations, and results in increased occurrence rates of polymorphic ventricular tachyarrhythmias and sudden cardiac death (SCD) 4.
- Twelve LQTS genes have been identified, and most of them encode cardiac ion channels 3.
Causes and Risk Factors
- Antipsychotic drugs can prolong the QT interval, usually by blocking the potassium IKr current, and may increase the risk of sudden death in psychiatric patients 5.
- Other factors that may contribute to QT interval prolongation and torsades de pointes include errors in the use of medications, hypokalemia, and genetic predisposition 5, 6.
- The risk of torsades de pointes should be assessed in patients who are about to begin taking a QT-prolonging medication, and proper monitoring of the QT interval is recommended 6.
Treatment and Management
- Beta-blockers, such as propranolol and nadolol, are effective in reducing the risk of cardiac events in patients with LQTS 3, 4, 7.
- Nadolol is recommended as a relatively effective strategy for LQT2, and propranolol is the least effective drug in patients who have had a prior cardiac event while taking beta-blockers 4, 7.
- Left Cardiac Sympathetic Denervation (LCSD) is a highly effective therapy that can complement any other therapy, but its availability is limited to a few selected centers 3.
- Implantation of a cardioverter defibrillator (ICD) may be considered in patients who have had an aborted cardiac arrest or who continue to have syncope despite LCSD, but it is burdened by a high rate of adverse events 3.