Congenital Long QT Syndrome Recommendations for Long QT Syndrome References that support the recommendations are summarized in Online Data Supplement 40. COR LOE Recommendations I B-NR In patients with long QT syndrome with a resting QTc greater than 470 ms, a beta blocker is recommended.S7.9.1.1-1 S7.9.1.1-5 I B-NR In high-risk patients with symptomatic long QT syndrome in whom a beta blocker is ineffective or not tolerated, intensification of therapy with additional medications (guided by consideration of the particular long QT syndrome type), left cardiac sympathetic denervation, and/or an ICD is I B-NR In patients with long QT syndrome and recurrent appropriate ICD shocks despite maximum tolerated doses of a beta blocker, intensification of medical therapy with additional medications (guided by consideration of the particular long QT syndrome type) or left cardiac sympathetic denervation, is recommended.S7.9.1.1-6, I B-NR In patients with clinically diagnosed long QT syndrome, genetic counseling and genetic testing are recommended.S7.9.1.1-17 S7.9.1.1-21 IIa B-NR In patients with suspected long QT syndrome, ambulatory electrocardiographic monitoring, recording the ECG lying and immediately on standing, and/or exercise treadmill testing can be useful for establishing a diagnosis and monitoring the response to therapy.S7.9.1.1-22 S7.9.1.1-29 IIa B-NR In asymptomatic patients with long QT syndrome and a resting QTc less than 470 ms, chronic therapy with a beta blocker is IIb B-NR In asymptomatic patients with long QT syndrome and a resting QTc greater than 500 ms while receiving a beta blocker, intensification of therapy with medications (guided by consideration of the particular long QT syndrome type), left cardiac sympathetic denervation or an ICD may be III: Harm B-NR In patients with long QT syndrome, QT- prolonging medications are potentially Recommendation-Specific Supportive Text 1. 