Management of Prolonged QT Syndrome
Beta blockers are the cornerstone of treatment for patients with Long QT Syndrome (LQTS), especially those with a resting QTc greater than 470 ms. 1
Diagnosis and Risk Stratification
Diagnostic tools:
- 12-lead ECG (measure QTc interval)
- Ambulatory ECG monitoring
- Exercise stress testing (particularly useful for diagnosing LQTS type 1 and 2)
- Postural ECG changes (recording ECG lying and immediately on standing)
- Genetic testing for confirmed cases
High-risk features:
- QTc >500 ms
- Genotypes LQTS type 2 and 3
- Females with genotype LQTS type 2
- Age <40 years
- Symptom onset at <10 years of age
- History of syncope or cardiac arrest
- Postpartum period (especially for LQTS type 2)
Treatment Algorithm
1. First-line therapy:
- Beta blockers for all patients with LQTS with QTc >470 ms (Class I recommendation)
- Nadolol is preferred by many centers (especially for LQTS type 2)
- Propranolol and atenolol are also effective
- Metoprolol appears less effective and should be avoided
- Dosing should be maximally tolerated with regular monitoring of QTc and beta blockade adequacy
2. For asymptomatic patients with QTc <470 ms:
- Beta blocker therapy is reasonable (Class IIa recommendation)
- Monitor QTc interval regularly
3. For symptomatic patients with inadequate response to beta blockers:
- Treatment intensification is recommended (Class I recommendation):
- Additional medications based on LQTS type:
- LQTS type 1: Beta blockers (most effective)
- LQTS type 2: Beta blockers + mexiletine (mexiletine can shorten QT interval)
- LQTS type 3: Consider mexiletine (may be more effective than beta blockers)
- Left cardiac sympathetic denervation
- ICD implantation for high-risk patients
- Additional medications based on LQTS type:
4. For patients with recurrent ICD shocks despite beta blockers:
- Intensify medical therapy (Class I recommendation):
- Additional medications based on LQTS type
- Left cardiac sympathetic denervation
5. For asymptomatic patients with QTc >500 ms despite beta blockers:
- Consider treatment intensification (Class IIb recommendation):
- Additional medications based on LQTS type
- Left cardiac sympathetic denervation
- ICD implantation
Critical Preventive Measures
Avoid QT-prolonging medications (Class III: Harm) 1, 2, 3
- Check all medications against updated databases (www.crediblemeds.org)
- Common offenders include:
- Antiarrhythmics (class IA and III)
- Antibiotics (macrolides, fluoroquinolones)
- Antipsychotics (haloperidol, phenothiazines)
- Antidepressants (tricyclics, SSRIs)
- Antiemetics (ondansetron)
Maintain normal electrolyte balance 1
- Correct hypokalemia, hypomagnesemia, and hypocalcemia
- Monitor electrolytes during diuretic use or gastrointestinal illness
Additional preventive measures:
- Reduce fever with antipyretics (fever can prolong QT in LQTS type 2)
- Avoid competitive sports and strenuous exercise (especially in LQTS type 1)
- Avoid sudden loud noises (especially in LQTS type 2)
- Avoid swimming without supervision (especially in LQTS type 1)
Special Considerations
Genetic testing and counseling:
- Recommended for all patients with clinically diagnosed LQTS (Class I)
- Should be offered to first-degree relatives of patients with LQTS
- Approximately 10-36% of genotype-positive patients have normal QTc intervals (≤440 ms)
Pregnancy and postpartum:
- Continue beta blockers during pregnancy
- Women with LQTS type 2 have increased risk of cardiac events postpartum
- Consider wearable cardioverter-defibrillator in high-risk postpartum women
Common pitfalls:
- Misdiagnosing Torsades de Pointes as VT and administering amiodarone (which can worsen QT prolongation) 3
- Inadequate monitoring of QTc during medication changes
- Failing to recognize drug interactions that may prolong QT
- Overlooking modifiable risk factors (electrolyte abnormalities, bradycardia)
By following this algorithmic approach to management, clinicians can significantly reduce morbidity and mortality in patients with prolonged QT syndrome while improving quality of life.