Catecholaminergic Polymorphic Ventricular Tachycardia
Description
Catecholaminergic polymorphic ventricular tachycardia (CPVT) is a genetic disorder characterized by arrhythmia (abnormal heart rhythm). As the patient encounters physical activity or emotional stress, the increase in heart rate can trigger an abnormally fast and irregular heartbeat called ventricular tachycardia. This can cause light-headedness, dizziness, and fainting (syncope). These episodes typically begin in childhood.
Prevalence
The prevalence of CPVT is estimated to be about one in every 10,000 people. The true prevalence is unknown.
Causes
CPVT is caused by mutations in the RYR2 gene or the CASQ2 gene. Mutations in the RYR2 gene account for about half of all cases while mutations in the CASQ2 gene account for about 1 percent to 2 percent of all cases. In the remaining cases, the genetic cause of the disorder is unknown. These two genes provide instructions for making proteins that maintain a regular heartbeat. The proteins are involved in handling calcium within myocytes (heart muscle cells), which is critical for the regular contraction of these cells.
When CPVT results from mutations in the RYR2 gene, it has an autosomal dominant pattern of inheritance. Autosomal dominant inheritance means that one copy of the altered gene in each cell is sufficient to cause the disorder. In about half of cases, an affected person inherits an RYR2 gene mutation from one affected parent. The remaining cases result from new mutations in the RYR2 gene and occur in people with no history of the disorder in their family. When CPVT is caused by mutations in the CASQ2 gene, the condition has an autosomal recessive pattern of inheritance. Autosomal recessive inheritance means that both copies of the gene in each cell have mutations. The parents of an individual with an autosomal recessive condition each carry one copy of the mutated gene, but they typically do not show signs and symptoms of the condition.
When CPVT results from mutations in the RYR2 gene, it has an autosomal dominant pattern of inheritance. Autosomal dominant inheritance means that one copy of the altered gene in each cell is sufficient to cause the disorder. In about half of cases, an affected person inherits an RYR2 gene mutation from one affected parent. The remaining cases result from new mutations in the RYR2 gene and occur in people with no history of the disorder in their family. When CPVT is caused by mutations in the CASQ2 gene, the condition has an autosomal recessive pattern of inheritance. Autosomal recessive inheritance means that both copies of the gene in each cell have mutations. The parents of an individual with an autosomal recessive condition each carry one copy of the mutated gene, but they typically do not show signs and symptoms of the condition.
Symptoms
The symptoms typically start between 7 and 9 years of age. The first symptom observed are frequently syncopal spells brought on by exercise or acute emotion. Sudden death can also be the first manifestation of the disease in 10 to 20 percent of patients. Major symptoms include arrhythmia and episodes of ventricular tachycardia which lead to lightheadedness, dizziness, and fainting (syncope).
Diagnosis
In terms of diagnosis, subjects with a family history of CPVT or sudden death during stress or syncope induced by exercise/emotion should undergo exercise stress test and Holter monitoring. Graded exercise is of utmost diagnostic relevance because arrhythmias are usually reproducible. Holter monitoring is also indicated for rarer cases where acute emotion is a more powerful trigger. Resting electrocardiogram (ECG) is usually unremarkable and cardiac imaging (echocardiogram and MRI) is typically normal. The principal differential diagnoses are Long QT Syndrome (LQTS), arrhythmogenic right ventricular cardiomyopathy (ARVC), and Andersen-Tawil Syndrome.
Diagnostic Tests
Diagnostic tests include genetic testing. Screening for the RYR2 mutation (which follows an autosomal dominant pattern of inheritance) is indicated in all patients. In the case of negative RYR2 screening and in the case of parental consanguinity, screening of CASQ2 is indicated with evidence of recessive inheritance.
Treatments
Beta blockers (nadolol and propranolol) are the first treatment option for patients and the maximum tolerated dose should be administered to control arrhythmias. Recently, flecainide (a sodium channel blocker), has shown good results in suppressing arrhythmias in CPVT patients. Implantable cardioverter defibrillators (ICDs) are recommended in patients with recurrent syncope (despite full dose beta blockers and flecainide therapy) to prevent cardiac arrest and sudden death. Left cardiac sympathetic denervation was successful in eliminating arrhythmias in a few cases. Possible drugs include Betapace® (Bayer HealthCare Pharmaceuticals) (Sotalol HCl) which is used for the treatment of life-threatening ventricular tachyarrhythmias and Cordarone® (Wyeth Pharmaceuticals, Inc.) (Amiodarone HCl) which is used for initiation of treatment and prophylaxis of frequently recurring ventricular fibrillation and hemodynamically unstable ventricular tachycardia in patients refractory to other therapy.
Prognosis
Although CPVT is a severe and often deadly disease, early diagnosis and proper treatment can greatly increase life expectancy. Exercise restriction along with beta-blocker therapy and ICD implants in patients has resulted in a favourable prognosis. However, if it is not recognized and treated, an episode of ventricular tachycardia may lead to sudden death. This may be a significant cause of sudden death in children and young adults without recognized heart abnormalities.
Tips
Physical activity is to be strongly limited.
Other Names
- bidirectional tachycardia induced by catecholamines
- Catecholamine-induced polymorphic ventricular tachycardia
- CPVT
- familial polymorphic ventricular tachycardia
- FPVT