۴٫ کاردیوورتر_دفیبریلاتور قابل کاشت Implantable cardioverter-defibrillator (ICD)
۵٫ دفیبریلاتور Wearable cardiac
Defibrillation is a treatment for life-threatening cardiac dysrhythmias, specifically ventricular fibrillation (VF) and non-perfusing ventricular tachycardia (VT).A defibrillator delivers a dose of electric current (often called a countershock) to the heart. Although not fully understood, this would depolarize a large amount of the heart muscle, ending the dysrhythmia. Subsequently, the body’s natural pacemaker in the sinoatrial node of the heart is able to re-establish normal sinus rhythm.
In contrast to defibrillation, synchronized electrical cardioversion is an electrical shock delivered in synchrony to the cardiac cycle. Although the person may still be critically ill, cardioversion normally aims to end poorly perfusing cardiac dysrhythmias, such as supraventricular tachycardia.
Defibrillators can be external, transvenous, or implanted (implantable cardioverter-defibrillator), depending on the type of device used or needed. Some external .units, known as automated external defibrillators (AEDs), automate the diagnosis of treatable rhythms, meaning that lay responders or bystanders are able to use them successfully with little or no training.
Defibrillation is often an important step in cardiopulmonary resuscitation (CPR).CPR is an algorithm-based intervention aimed to restore cardiac and pulmonary function.Defibrillation is indicated only in certain types of cardiac dysrhythmias, specifically ventricular fibrillation (VF) and pulseless ventricular tachycardia. If the heart has completely stopped, as in asystole or pulseless electrical activity (PEA), defibrillation is not indicated. Defibrillation is also not indicated if the patient is conscious or has a pulse. Improperly given electrical shocks can cause dangerous dysrhythmias, such as ventricular fibrillation.
Survival rates for out-of-hospital cardiac arrests are poor, often less than 10% Outcome for in-hospital cardiac arrests are higher at 20%. Within the group of people presenting with cardiac arrest, the specific cardiac rhythm can significantly impact survival rates. Compared to people presenting with a non-shockable rhythm (such as asystole or PEA), people with a shockable rhythm (such as VF or pulseless ventricular tachycardia) have improved survival rates, ranging between 21-50%.
دفیبریلاتور قلبی قابل کاشت
Manual external defibrillator
Manual external defibrillators require the expertise of a healthcare professional. They are used in conjunction with an electrocardiogram, which can be separate or built-in. A healthcare provider first diagnose the cardiac rhythm and then manually determine the voltage and timing for the electrical shock. These units are primarily found in hospitals and on some ambulances. For instance, every NHS ambulance in the United Kingdom is equipped with a manual defibrillator for use by the attending paramedics and technicians. In the United States, many advanced EMTs and all paramedics are trained to recognize lethal arrhythmias and deliver appropriate electrical therapy with a manual defibrillator when appropriate.
Mechanism of action
The exact mechanism of defibrillation is not well understood. One theory is that successful defibrillation affects a critical mass of the heart, resulting in insufficient remaining heart muscle to continue the arrhythmia. Recent mathematical models of defibrillation are providing new insight into how cardiac tissue responds to a strong electrical shock.
Defibrillators were first demonstrated in 1899 by Jean-Louis Prévost and Frédéric Batelli, two physiologists from University of Geneva, Switzerland. They discovered that small electrical shocks could induce ventricular fibrillation in dogs, and that larger charges would reverse the condition.
In 1933, Dr. Albert Hyman, heart specialist at the Beth Davis Hospital of New York City and C. Henry Hyman, an electrical engineer, looking for an alternative to injecting powerful drugs directly into the heart, came up with an invention that used an electrical shock in place of drug injection. This invention was called the Hyman Otor where a hollow needle is used to pass an insulated wire to the heart area to deliver the electrical shock. The hollow steel needle acted as one end of the circuit and the tip of the insulated wire the other end. Whether the Hyman Otor was a success is unknown.
Society and culture
As devices that can quickly produce dramatic improvements in patient health, defibrillators are often depicted in movies, television, video games and other fictional media. Their function, however, is often exaggerated, with the defibrillator inducing a sudden, violent jerk or convulsion by the patient; in reality, although the muscles may contract, such dramatic patient presentation is rare. Similarly, medical providers are often depicted defibrillating patients with a “flat-line” ECG rhythm (also known as asystole). This is not normal medical practice, as the heart cannot be restarted by the defibrillator itself. Only the cardiac arrest rhythms ventricular fibrillation and pulseless ventricular tachycardia are normally defibrillated. The purpose of defibrillation is to depolarize the entire heart all at once so that it is synchronized, in the hope that it will resume beating normally. Someone who is already in asystole cannot be helped by electrical means, and usually needs urgent CPR and intravenous medication. There are also several heart rhythms that can be “shocked” when the patient is not in cardiac arrest, such as supraventricular tachycardia and ventricular tachycardia that produces a pulse; this more-complicated procedure is known as cardioversion, not defibrillation.