Sections View Full Chapter Figures Tables Videos Annotate Full Chapter Figures Tables Videos Supplementary Content + Download Section PDF Listen ++ For further information, see CMDT Part 10-38: Inherited Arrhythmia Syndromes + Key Features Download Section PDF Listen +++ +++ Essentials of Diagnosis ++ Includes long QT syndrome, Brugada syndrome, arrhythmogenic right ventricular cardiomyopathy, 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 beta-blocker (nadolol or propranolol) Implantable cardioverter defibrillator (ICD) is indicated for patients with ventricular arrhythmia or syncope despite medical treatment +++ General Considerations ++ 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 Accounts for up to 20% of sudden cardiac death in the absence of structural heart disease Most often due to a defect in a sodium channel gene Arrhythmogenic right ventricular cardiomyopathy Predominantly affects the right ventricle Characterized by areas of myocardial replacement with fibrosis and adipose tissue that frequently causes ventricular arrhythmia Catecholaminergic polymorphic VT is a rare but important cause of sudden cardiac death associated with exercise + Clinical Findings Download Section PDF Listen +++ ++ 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 + Diagnosis Download Section PDF Listen +++ ++ 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 + Treatment Download Section PDF Listen +++ +++ Medications ++ Inherited arrhythmia syndromes Antiarrhythmic medications should be avoided, except when specific genetic abnormalities have been identified and under the direction of a specialist Long-term management depends on the presence of high-risk features Long QT syndrome or catecholaminergic polymorphic VT Use of beta-blockers (particularly propranolol or nadolol) is the mainstay of treatment Intravenous beta-blockers may be effective in treating electrical storm due to long QT syndrome or catecholaminergic polymorphic VT Increasing the heart rate, whether by infusion of beta-agonist (dopamine or isoproterenol) or temporary atrial or ventricular pacing, is an effective approach that can both break and prevent the rhythm Class Ia, Ic, or III antiarrhythmics Prolong QT interval Avoid or withdraw immediately if being used in patients with long QT syndrome Brugada syndrome No reliable medication therapy Focus is on preventing arrhythmias and promptly treating exacerbating triggers, particularly fever +++ Therapeutic Procedures ++ Surgical cervicothoracic sympathectomy should be considered for patients who do not respond to or are intolerant of beta-blockers ICD implantation Recommended for patients with an inherited arrhythmia syndrome in whom sudden cardiac arrest is the initial presentation Should be considered in patients with recurrent sustained ventricular arrhythmias or syncope despite medical therapy + Outcome Download Section PDF Listen +++ +++ When to Refer ++ Any patient with known or suspected inherited arrhythmia syndrome or with severe corrected QT interval prolongation (> 500 ms on serial ECGs) should be referred to a cardiologist or cardiac electrophysiologist Consultation with a genetic counselor and genetic testing is recommended for patients and family members with a high suspicion of an inherited arrhythmia syndrome + References Download Section PDF Listen +++ + +Sharma N et al. A review of long QT syndrome: everything a hospitalist should know. Hosp Pediatr. 2020 Apr;10(4):369–75. [PubMed: 32144177] + +Tang PT et al. Ventricular arrhythmias and sudden cardiac death. Card Electrophysiol Clin. 2017 Dec;9(4):693–708. [PubMed: 29173411]