Implantable Cardiac Defibrillator (cont.)
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What are life-threatening tachycardias?
Two common life-threatening tachycardias are ventricular tachycardia and ventricular fibrillation. Ventricular tachycardia is a rapid regular rhythm caused by electrical signals originating from an area of the ventricle. Ventricular tachycardia can decrease blood delivery by the heart and cause low blood pressure. Ventricular tachycardia can also progress to a more serious heart rhythm called ventricular fibrillation.
Ventricular fibrillation is an irregular rhythm, which is a result of multiple rapid and chaotic electrical signals firing from many different areas in the ventricles. A heart undergoing ventricular fibrillation is in a state of standstill called cardiac arrest. The heart muscles quiver and cease pumping which causes a halt in the delivery of blood to the body. Unless ventricular fibrillation is terminated quickly, irreversible brain damage occurs within minutes of the onset of ventricular fibrillation, leading to death.
Sudden cardiac arrest is the most common cause of death in the United States. About 450,000 Americans suffer cardiac arrest each year. 80 to 90% of these patients die before reaching the hospital. The most frequent causes of cardiac arrest in the United States are ventricular tachycardia and ventricular fibrillation.
What are the causes of ventricular tachycardia and ventricular fibrillation?
Ventricular tachycardia and ventricular fibrillation are most commonly caused by heart attacks (acute myocardial infarctions) or scarring of the heart muscle from previous heart attacks. Less common causes of ventricular tachycardia and ventricular fibrillation include severe weakening of the heart muscles (cardiomyopathy), medication toxicity (such as digoxin toxicity), medication side effects, and blood electrolyte disturbances (such as a low potassium level). Ironically, some medications used in treating heart rhythm abnormalities can cause ventricular tachycardias.
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