(See also Overview of Arrhythmias Overview of Arrhythmias The normal heart beats in a regular, coordinated way because electrical impulses generated and spread by myocytes with unique electrical properties trigger a sequence of organized myocardial... read more and Overview of Channelopathies Overview of Channelopathies Channelopathies are a group of genetic, autoimmune, or inflammatory conditions that alter cardiomyocyte ion channel function in a manner that predisposes to bradyarrhythmias or tachyarrhythmias... read more .)
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).
Symptoms and Signs of CPVT
Some patients are asymptomatic and identified only on family screening. When symptoms occur, they usually develop at a young age (ie, childhood or adolescence). The tachyarrhythmias may cause palpitations, syncope, or cardiac arrest. Events are typically triggered by emotional or physical stress.
Diagnosis of CPVT
Screening of first-degree family members
Diagnosis should be considered in patients with unexplained cardiac arrest or syncope or a family history of such in the absence of structural heart disease.
Resting ECG is normal. Diagnosis is confirmed by exercise testing–induced polymorphic VT (especially bidirectional VT) that also reproduces the patient's symptoms. Genetic testing should then be done; it has a yield of approximately 50%.
First-degree family members of patients have a significant risk of disease. They should have clinical evaluation (ie, to detect symptoms suggestive of arrhythmia) and exercise testing performed every 1 to 3 years. If the initial patient has a causative mutation identified, family members without the index mutation are then freed of the need follow-up investigations.
Treatment of CPVT
Sometimes an implantable cardioverter-defibrillator (ICD)
Rarely left cardiac sympathetic denervation
All patients are advised to avoid strenuous exercise (eg, competitive sports). Particularly those who will not accept exercise restrictions should be counseled on the need for appropriate cautions (eg, availability of an automated external defibrillator during training and competition).
For patients who have had symptoms (eg, syncope, cardiac arrest) or who have demonstrated VF or sustained VT, the primary treatment is high doses of a long-acting beta-blocker, preferably one without intrinsic sympathomimetic activity (eg, nadolol, slow-release propranolol). If beta blockade is ineffective, flecainide may be useful both for its sodium channel and ryanodine receptor blocking effects. Implantable cardioverter-defibrillators (ICDs) are used for patients with CPVT who survived cardiac arrest or who have VT despite antiarrhythmic drug therapy. Refractory cases are treated with left cardiac sympathetic denervation and/or arrhythmia substrate ablation.
Follow-up typically involves repeated exercise testing, but the predictive value is only moderate.
Asymptomatic patients (including relatives identified by genetic testing) should also moderate their physical activity and receive beta-blocker therapy.
Drugs Mentioned In This Article
|HEMANGEOL, Inderal, Inderal LA, Inderal XL, InnoPran XL