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Essentials of Diagnosis
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Includes long QT syndrome, Brugada syndrome, and catecholaminergic polymorphic ventricular tachycardia (VT)
Genetic testing for patients with suspected congenital long QT syndrome based on family history, ECG or exercise testing, or severely prolonged QT interval (> 500 ms) on serial ECGs
Patients with long QT syndrome or catecholaminergic polymorphic VT should be managed long-term with an oral β-blocker (nadolol or propranolol)
Implantable cardioverter defibrillator (ICD) is indicated for patients with ventricular arrhythmia or syncope despite medical treatment
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General Considerations
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Inherited arrhythmia syndromes may result in life-threatening ventricular arrhythmias due to gene mutations in cardiac channels resulting in abnormal electrolyte regulation across the cardiac cell membrane
Congenital long QT syndrome
Uncommon (1 in 2500 live births)
Characterized by a long QT interval (usually > 470 ms) and ventricular arrhythmia, typically polymorphic VT
Acquired long QT syndrome is usually secondary to
Use of antiarrhythmic agents (sotalol, dofetilide), methadone, antidepressant medications, or certain antibiotics
Electrolyte abnormalities
Myocardial ischemia
Significant bradycardia
Brugada syndrome
Catecholaminergic polymorphic VT is a rare but important cause of sudden cardiac death associated with exercise
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Variable clinical presentation
Patients may be asymptomatic or have palpitations, sustained tachyarrhythmia, syncope, or sudden cardiac arrest
In young patients, syncopal episodes may be misdiagnosed as a primary seizure disorder
Personal and family history should be thoroughly reviewed in all patients
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A 12-lead ECG should be performed with careful attention to any abnormality in the ST segment, T wave, and QT interval
A corrected QT interval longer than 500 ms on serial ECGs in the absence of a secondary cause (medication or electrolyte abnormality) identifies a high-risk subset of patients with long QT syndrome
Ambulatory ECG monitoring may be used to evaluate for ventricular arrhythmias as well as dynamic changes to the QT interval or T wave
Exercise ECG testing may be performed in patients with suspected long QT syndrome to assess for lack of appropriate QT interval shortening with higher heart rates
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