What is Catecholaminergic Polymorphic Ventricular Tachycardia?

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Illustration of heart with Catecholaminergic Polymorphic Ventricular Tachycardia

Introduction

Catecholaminergic polymorphic ventricular tachycardia or CPVT, also called catecholamine-induced polymorphic ventricular tachycardia, familial polymorphic ventricular tachycardia or FPVT, is a rare inherited disturbance in the rhythm of the heart that is found in children and young individuals. It accounts for 15% of unexplained sudden cardiac deaths in children and young individuals.

Proteins in the heart cells control the release of calcium ions. If the proteins don’t function well, it can result in an increased level of calcium inside the heart cells. The increase in calcium can result in arrhythmia. CPVT is caused by mutations in the genes encoding a calcium channel or proteins that are related to this calcium channel. All modified proteins take part in regulating calcium ion flow in and out of the cardiac or heart cells’ sarcoplasmic reticulum. Having a decreased electrical stability of cardiomyocytes can result in a life-threatening state of ventricular tachycardia as feedback to the natural release of catecholamines from the adrenal glands into the circulation and from the nerve endings on the heart muscle. The disturbance in rhythm hinders the heart from correctly pumping blood.

Causes of CPVT

CPVT can be brought about by mutations in one of at least 5 genes. 4 of these genes are currently known. The mutations in 2 of these genes are inherited in an autosomal dominant fashion while the rest are passed on through families in an autosomal recessive fashion. The 4 genes affected by CPVT are RYR2, CASQ2, CALM1, and TRDN. Mutations in these genes can cause CPVT.

RYR2 takes part in intracardiac Ca2+ handling and the overload of Ca2+ triggers abnormal cardiac activity. CASQ2 is the sarcoplasmic reticulum’s calcium buffering protein.

Symptoms of CPVT

The frequent symptom of this disease is syncope or dizziness that normally occurs as a reaction to emotional stress or during exercise. Heightened emotions and strenuous physical activity can result in an increase in the amount of adrenaline running through the blood. Other symptoms may include:

  • Atrial fibrillation
  • Atrial standstill
  • Autosomal dominant inheritance
  • Blackouts
  • Palpitations
  • Seizures
  • Sudden cardiac death
  • Sudden death
  • Syncope
  • Ventricular tachycardia
  • Vertigo

The symptoms felt may vary from one person to another. CPVT starts to develop during an individual’s first or second decade of living. An estimated 60% of individuals affected by CPVT experience their first episode of cardiac arrest or syncope when they are between 12 to 20 years of age. The symptoms are usually triggered by ventricular arrhythmias that are exercise-induced and which occur during periods of acute emotional stress or periods of physical activity.

Diagnosis of CPVT

It is challenging to make a diagnosis of rare and genetic diseases. Doctors usually conduct a short interview to know about the patient’s medical and family history. Afterwards, he/she administers a physical exam to check for symptoms of the disease. Laboratory tests are also performed and the results from these laboratory tests enable to doctor to make a diagnosis.

Individuals with CPVT don’t show signs of structural heart problems when using CT scan, MRI, or echocardiographic imaging because the symptoms are only triggered when the body is subjected to heightened emotion and physical stress.

The diagnosis of CPVT on those who have a structurally normal heart is based on a normal resting electrocardiogram and an exercise stress test. The exercise stress test is performed by using ECG to record the heart’s electrical rhythm while exercising. Any abnormal rhythm of the heart can be seen in the ECG. The stress test is the most important test to diagnose CPVT because it can show the type of ventricular tachycardia present on an individual during exercise and when with acute emotion. The ECG exercise stress testing reproduces irregularly shaped ventricular arrhythmias.

Since this disease is a genetic condition, it is also advised to go for a genetic testing to check for possible mutations in the specific genes that are usually affected by this disease especially if someone in the family has already been diagnosed with CPVT or other heart conditions. This is a precautionary measure even if the individual does not show any signs or symptoms of CPVT. Identification of pathogenic variants in the 5 genes can help establish a diagnosis.

Treatment of CPVT

These are the medications that are approved by the Food and Drug Administration or FDA to treat this condition:

  • Sotalol HCI – treats life-threatening ventricular tachyarrhythmias
  • Amiodarone HCI – for prophylaxis and treatment of the hemodynamically unstable ventricular tachycardia and often recurring ventricular fibrillation in patients who are rigid to other treatments
  • IV Sotalol – treats ventricular tachycardia and ventricular fibrillation and maintains sinus rhythm when oral intake is not possible
  • Beta-blockers
  • Verapamil
  • Flecainide – slows down or hinders the release of the cardiac ryanodine receptor-mediated Ca2+ which treats the underlying molecular cause of CPVT.

Implantable cardioverter-defibrillator prevents sudden death.

Sympathectomy is used to control the symptoms that cannot be controlled by beta blockers. Bilateral thoracoscopic sympathectomy and left cardiac sympathetic denervation have both shown promising results in treating CPVT.