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September 25, 2018 Circulation. 2018;138:e272–e391. DOI: 10.1161/CIR.0000000000000549 e328

CLINICAL STATEMENTS AND GUIDELINES syndrome type. In long QT syndrome type 3, ranolazine, mexiletine, and flecainide shorten the QTc and have been used to reduce recurrent arrhythmias.S7.9.1.1-6,S7.9.1.1-7,S7.9.1.1-10

4.	 Genetic testing for disease-causing mutations in long QT syndrome offers important diagnostic, prognostic, and therapeutic information in addition to the clinical evaluation, and a positive test can facilitate establishing risk for family members. The yield of genetic testing in long QT syndrome phenotype-positive patients is 50% to 86%, with the higher range present in patients with marked QT prolongation or positive family history of SCD.S7.9.1.1-17,S7.9.1.1-21,S7.9.1.1-53 A negative genetic test does not exclude the diagnosis of long QT syndrome, which relies on the clinical evaluation. In asymptomatic patients with otherwise unexplained prolonged QTc  ≥480 ms on serial ECGs, genetic testing may help confirm the diagnosis and supplement prognostic information in addition to clinical symptoms and QTc duration.S7.9.1.1-5,S7.9.1.1-18–S7.9.1.1-20,S7.9.1.1-30,

S7.9.1.1-35,S7.9.1.1-54–S7.9.1.1-56 5.	 In a prospective, observational study of patients with suspected long QT syndrome, patients with a history of syncope or cardiac arrest and either an affected first-degree relative or a borderline or prolonged QTc interval underwent exercise treadmill testing and bicycle exercise, with ECGs recorded before, during, and after exercise, as well as in different positions.S7.9.1.1-27 long QT syndrome was confirmed by genetic testing in all affected individuals. Among patients with borderline-to-normal resting QTc intervals, prolongation of the 4-minute recovery QTc ≥445 ms had high sensitivity for correctly identifying patients with long QT syndrome.S7.9.1.1-27 A study in younger patients demonstrated QTc prolongation >460 ms at 7 minutes of recovery predicted long QT syndrome type 1 or long QT syndrome type 2 patients versus controls.S7.9.1.1-23 In a study using burst bicycle exercise, patients with latent long QT syndrome had a significantly greater increase in QTc with exercise than either controls or those with QTc prolongation at baseline.S7.9.1.1-24 These findings can be useful in establishing whether long QT syndrome is present. Monitoring adequacy of beta-blocker therapy using exercise testing can be beneficial, particularly in schoolaged patients.S7.9.1.1-26,S7.9.1.1-28 Beta-blocker therapy may be associated with a decrease in supine and peak exercise QTc, with the exception of long QT syndrome type 1 patients with C-loop mutations.S7.9.1.1-25 6.	 Approximately 10% to 36% of genotype-positive patients with long QT syndrome have QTc intervals ≤440 ms, most commonly patients with long QT syndrome type 1.S7.9.1.1-31,S7.9.1.1-35 Patients with long QT  syndrome and normal QTc have a lower risk of VA and SCD compared to those with prolonged QTc,S7.9.1.1-35 but still have an increased risk of SCA or SCD compared with genotype-negative, age- and sex-matched general patients.S7.9.1.1-31 Beta blockers reduce the risk of adverse cardiac events substantially.S7.9.1.1-1–S7.9.1.1-5,

S7.9.1.1-30,S7.9.1.1-36,S7.9.1.1-38,S7.9.1.1-41,S7.9.1.1-57 During the periods of highest risk in the first 3 decades of life,S7.9.1.1-11,S7.9.1.1-18 treatment with a beta blocker may reduce risk of SCA.S7.9.1.1-26,S7.9.1.1-28,S7.9.1.1-36, S7.9.1.1-38 Changes in QTc occur over time, particularly during puberty and during and after pregnancy, indicating the need for assessment of QTc on ECG annually or with medication changes, and assessing medication efficacy with exercise testing as feasible. Asymptomatic adult (male) long QT syndrome patients with normal QTc intervals may choose to decline beta-blocker therapy.S7.9.1.1-11,S7.9.1.1-34 7.	 The risk of adverse cardiac events from VA is influenced by the patient’s resting QTc interval, age, sex, and long QT syndrome genotype/ mutation. For asymptomatic males with long QT syndrome, the risk of cardiac events is highest in childhood,S7.9.1.1-2,S7.9.1.1-8,S7.9.1.1-11,S7.9.1.1-30 during a time when medication compliance is challenging. Young women  with LQT2 and  QTc >500 ms are at increased risk of SCAS7.9.1.1-2,S7.9.1.1-11,

S7.9.1.1-18–S7.9.1.1-20,S7.9.1.1-30,S7.9.1.1-35 especially in the 9 months postpartum, and may be candidates for primary prevention ICD placement or use of a wearable cardioverter-defibrillator.S7.9.1.1-30 8.	 The risk of adverse events increases in patients with long QT syndrome with prolongation of the QTc >500 ms.S7.9.1.1-2,S7.9.1.1-12,S7.9.1.1-26,S7.9.1.1-35,S7.9.1.1-41,S7.9.1.1-58 QT-prolonging medications (www.crediblemeds. org)S7.9.1.1-59 should not be used in patients with long QT syndrome unless there is no suitable alternative; careful monitoring of the QTc during therapy is recommended, with consideration for discontinuing therapy with marked QTc prolongation. Concurrent use of stimulant or nonstimulant attention deficit/hyperactivity medications was associated with an increased risk of syncope/ cardiac arrest in long QT syndrome, particularly males, in 1 study,S7.9.1.1-34 but it did not appear to be associated with increased risk in another retrospective study.S7.9.1.1-60 Episodes of torsades de pointes can be precipitated by exposure to a QT prolonging medication, or hypokalemia induced by diuretics or gastrointestinal illenss. Attention to maintaining normal potassium and magnesium balance when medications or situations

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