ESSENTIALS OF DIAGNOSIS
Includes long QT syndrome, Brugada syndrome, arrhythmogenic RV cardiomyopathy, and catecholaminergic polymorphic ventricular tachycardia.
Genetic testing for patients with suspected congenital long QT syndrome based on family history, ECG or exercise testing, or severely prolonged QT interval (greater than 500 msec) on serial ECGs.
Patients with long QT syndrome or catecholaminergic polymorphic ventricular tachycardia should be treated long term with an oral beta-blocker (nadolol or propranolol). ICD is indicated for patients with ventricular arrhythmia or syncope despite medical treatment.
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 is an uncommon disease (1 in 2500 live births) that is characterized by a long QT interval (usually greater than 470 msec) and ventricular arrhythmia, typically polymorphic ventricular tachycardia. It may occur in the presence of congenital deafness (Jervell-Lange-Nielsen syndrome) with autosomal recessive inheritance. Acquired long QT syndrome is usually secondary to use of antiarrhythmic agents (sotalol, dofetilide), methadone, antidepressant medications, or certain antibiotics; electrolyte abnormalities; myocardial ischemia; or significant bradycardia (eFigures 10–73 and 10–74). Brugada syndrome accounts for up to 20% of sudden cardiac death in the absence of structural heart disease and is most often due to a defect in a sodium channel gene. Arrhythmogenic RV cardiomyopathy is an inherited cardiomyopathy that predominantly affects the right ventricle and is characterized by areas of myocardial replacement with fibrosis and adipose tissue that frequently causes ventricular arrhythmia. Catecholaminergic polymorphic ventricular tachycardia is a rare but important cause of sudden cardiac death associated with exercise.
An example of drug-induced long QT syndrome. A common feature is a pause (often after an ectopic beat) with deranged repolarization in the following cycle. A 12-lead ECG recorded from a 79-year-old patient with advanced heart disease who had recently begun taking dofetilide. The abnormal QT interval is followed by a pause (star) and then four beats of polymorphic ventricular tachycardia (torsades de pointes). Sustained torsades de pointes then occurs after another pause. (Reproduced, with permission, from Kannankeril P et al. Drug-induced long QT syndrome. Pharmacol Rev. 2010;62(4):760–81.)
Prolonged QT interval. Sinus bradycardia with deep T wave inversions is concerning for ischemia. Note markedly prolonged QT segment. (Used, with permission, from Jose Sanchez, MD.)
Patients with an inherited arrhythmia syndrome have a variable clinical presentation; they 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. A 12-lead ECG should be performed with careful attention to ...