cardiovascular disorders
Catecholaminergic Polymorphic Ventricular Tachycardia
Introduction
Catecholaminergic polymorphic ventricular tachycardia is a genetic disorder affecting intracellular calcium regulation in cardiac tissue. Patients are predisposed to ventricular tachyarrhythmias (less commonly atrial tachyarrhythmias) and sudden cardiac death, particularly during increased adrenergic activity (eg, from exercise). Diagnosis is by exercise testing. Treatment is exercise restriction, beta blockade, and sometimes an implantable cardioverter-defibrillator (ICD). (See also Overview of Arrhythmias and Catecholaminergic polymorphic ventricular tachycardia (CPVT) results from mutations affecting proteins related to intracellular calcium regulation (particularly upregulation of the sarcoplasmic reticulum ryanodine receptor) in the heart. The abnormalities increase release of calcium from the sarcoplasmic reticulum in response to adrenergic stimulation. The resulting myocyte calcium overload causes delayed after-depolarizations and a propensity to atrial and/or ventricular tachyarrhythmias. Sudden cardiac death may occur. The tachyarrhythmias are usually precipitated by the adrenergic stimulation of physical or emotional stress. The most characteristic ventricular tachyarrhythmia is bidirectional ventricular tachycardia which appears on ECG as two QRS complexes of opposite polarity in an alternating pattern. Nevertheless, any polymorphic ventricular tachycardia (VT), or ventricular fibrillation (VF) may occur. The incidence of CPVT is about 1 in 10,000 and is equally common in males and females. It is usually inherited as an autosomal dominant mutation of the gene encoding the cardiac ryanodine receptor, but it may be inherited as an autosomal recessive mutation of cardiac calsequestrin (CASQ2). 