Sudden Cardiac Arrest




Introduction

Sudden cardiac arrest, also referred to as sudden cardiac death, is the sudden, unexpected loss of heart function, breathing and consciousness. It's a medical emergency that, if not treated immediately, is fatal. With fast, appropriate medical care, survival is possible.

You may assume that sudden cardiac arrest is the same as a heart attack, but the conditions are different. Sudden cardiac arrest usually results from a severely abnormal heart rhythm that interferes with the pumping action of your heart and causes the immediate cessation of blood flow from the heart to the rest of your body. A heart attack, on the other hand, occurs when a sudden blockage in the coronary artery prevents blood flow to part of your heart muscle, causing dysfunction in the affected part and possible tissue death.

Sudden cardiac arrest almost always occurs in the context of other underlying heart problems, particularly coronary artery disease. A heart attack can lead to cardiac arrest by triggering an unstable heart rhythm. In many cases, sudden cardiac arrest may be the first indication of heart problems.

Survival of sudden cardiac arrest depends on prompt emergency care. This generally involves administration of cardiopulmonary resuscitation (CPR), shock treatment to your chest to reset your heart's rhythm (defibrillation) and advanced life support. Restoring circulation as fast as possible improves your chances of survival.

Signs and symptoms

With sudden cardiac arrest, signs and symptoms are sudden and drastic:
  • Sudden collapse
  • No pulse
  • No breathing
  • Loss of consciousness
Sometimes, other signs and symptoms precede sudden cardiac arrest. These may include fatigue, fainting, blackouts, dizziness, chest pain, shortness of breath, palpitations or vomiting. But sudden cardiac arrest often occurs with no warning.

Causes

The immediate cause of sudden cardiac arrest is usually an abnormality in your heart rhythm (arrhythmia), the result of a malfunction in your heart's electrical system.

Unlike other muscles in your body, which rely on nerve connections to receive the electrical stimulation they need to function, your heart has its own electrical stimulator — a specialized group of cells called the sinus node, located in the upper right chamber (right atrium) of your heart. The sinus node, a natural pacemaker, generates electrical impulses that flow in an organized, orderly fashion through your heart to synchronize heart rate and coordinate the pumping of blood from your heart to the rest of your body.

If something goes wrong with the sinus node or the flow of electric impulses through your heart, an arrhythmia can result, causing your heart to beat too fast, too slow or in an irregular fashion. Often, these interruptions in rhythm are momentary and harmless. But some types of arrhythmia can be serious and lead to sudden cardiac arrest. These more serious arrhythmias include:
  • Ventricular tachycardia. The cause of this type of arrhythmia is faulty electrical signals arising from your heart's lower chambers (ventricles). With ventricular tachycardia, your ventricles beat regularly but very fast. Sometimes, this arrhythmia lasts only a few seconds, but if it's sustained, it can rapidly degenerate into ventricular fibrillation, which is the most common cause of cardiac arrest.
  • Ventricular fibrillation. With ventricular fibrillation, rapid, erratic electrical impulses cause your ventricles to quiver uselessly instead of pumping blood. Without an effective heartbeat, your blood pressure plummets, cutting off blood supply to your vital organs.
  • Bradycardia. On occasion, a very slow heartbeat, caused by problems with the sinus node or by blockages in your heart's electrical pathways, can lead to sudden cardiac arrest.
Most of the time, cardiac-arrest-inducing arrhythmias don't occur on their own. In a person with a normal, healthy heart, a sustained arrhythmia is unlikely to develop without some outside trigger, such as an electrical shock or the use of illicit drugs.

Predisposing heart conditions
More often, a life-threatening arrhythmia develops in a person with a pre-existing heart condition. Virtually any heart condition may lead to sudden cardiac arrest, but more common examples are:

Coronary artery disease. More than 80 percent of cases of sudden cardiac arrest occur in people who have coronary artery disease. In coronary artery disease, your arteries become clogged with cholesterol and other deposits, reducing blood flow to your heart. This can alter the ability of your heart to conduct electrical impulses smoothly.

If a heart attack occurs, often as a result of severe coronary artery disease, it can precipitate ventricular fibrillation and sudden cardiac arrest. In addition, a heart attack can leave behind areas of dead scar tissue. Electrical short circuits around the scar tissue can lead to abnormalities in your heart rhythm, including ventricular tachycardia or ventricular fibrillation.

Cardiomyopathy. This occurs primarily when your heart's ventricular walls stretch and enlarge (dilated cardiomyopathy) or when your left ventricular wall thickens (hypertrophic cardiomyopathy). In both cases, your heart's muscle is abnormal, a condition that often leads to heart tissue damage.

The cause of dilated cardiomyopathy is unclear — it may be viral, autoimmune, genetic or environmental. Hypertrophic cardiomyopathy is a genetic disorder and is the most common cause of sudden cardiac arrest in young athletes, triggered perhaps by vigorous exertion, although the mechanism isn't completely understood.

A condition called arrhythmogenic right ventricular dysplasia is an uncommon type of genetic cardiomyopathy that develops in your right ventricle. The muscular wall of the right ventricle is replaced by fat and fibrous tissue. In people with this disorder, fainting or sudden cardiac arrest is often triggered by exercise.

Valvular heart disease. Leaking or narrowing of your heart valves can lead to stretching or thickening of your heart muscle, or both. When the chambers become enlarged or weakened because of stress caused by a tight or leaking valve, there's an increased risk of developing arrhythmia. An example of valvular heart disease that may lead to sudden cardiac arrest is aortic stenosis. This is a condition in which your aortic valve — the valve leading to the largest artery in your body, the aorta — becomes narrowed, obstructing blood flow from your heart to the rest of your body.



Congenital heart disease. When sudden cardiac arrest occurs in children or adolescents, it's more often due to a heart condition that was present at birth (congenital). Examples are:
  • Hypertrophic cardiomyopathy
  • Aortic stenosis
  • Pulmonary stenosis, obstruction of the flow of blood from the right ventricle to the pulmonary artery
  • Tetralogy of Fallot, a condition marked by a set of four defects in the heart
  • Transposition of the great arteries, in which the positions of the aorta and the pulmonary artery (the great arteries) are reversed
Doctors treat many of the above conditions with surgery. Most people remain at increased risk of cardiac arrest even after surgery. The degree of risk depends on a variety of factors including the nature of the defect as well as the type of operation performed.

  • Electrophysiological abnormalities. In some people, the problem is in the heart's electrical system itself, instead of a problem with the heart muscle or valves. For example, some people have primary ventricular tachycardia or fibrillation, unrelated to another heart condition. Other primary heart rhythm abnormalities include:
    • Long QT syndrome. An electrocardiogram (ECG) is a test that measures the electrical activity of your heart. It produces a characteristic wave form. Different points on the wave form are represented by different letters.
      The letter "Q" marks the point where an electrical impulse signals your ventricles to contract. The letter "T" marks the point where the cells of your ventricles have electrically recharged for the next heartbeat. When the QT interval is prolonged, ventricle cells may not have recovered in time to properly conduct the next heartbeat. This can lead to arrhythmias and potentially sudden cardiac arrest.
      Long QT syndrome may be an inherited condition or it may occur as a side effect of certain medications, as a complication of stroke, or as a result of nutritional deficiencies or metabolic problems.
    • Wolff-Parkinson-White syndrome (WPW). This is a type of arrhythmia that's caused by an extra electrical pathway between the heart's upper chambers (atria) and the ventricles. This may lead to short circuits and rapid heartbeats. WPW is a rare cause of sudden cardiac arrest.
    • Brugada syndrome. This is a genetic condition marked by specific abnormal electrical patterns on an ECG. Having Brugada syndrome may place you at high risk of ventricular fibrillation and sudden cardiac arrest.
    Treatment

    Immediate cardiopulmonary resuscitation (CPR) is critical to treating sudden cardiac arrest. By maintaining a flow of oxygen-rich blood to the body's vital organs, CPR can provide a vital link until more advanced emergency care is available.

    Defibrillation
    Advanced care for ventricular fibrillation typically includes delivery of an electrical shock through the chest wall to the heart. The procedure, called defibrillation, momentarily stops the heart and the chaotic rhythm. This often allows the normal heart rhythm to resume.

    The shock may be administered by emergency personnel or by a trained citizen if a public-use defibrillator, the device used to administer the shock, is available. If you're not trained to use an automatic external defibrillator (AED), a 911 operator may be able to guide you in its use. Trained staff members at many public places are able to provide and use an AED.

    Defibrillators are available in a small, portable form and come with built-in automated instructions to ensure proper use. They're programmed to recognize ventricular fibrillation and send a shock only when it's appropriate. These portable defibrillators are available in an increasing number of public places, including airports, shopping malls, casinos, health clubs, and community and senior citizen centers.

    Prevention

    There's no sure way to know your risk of sudden cardiac arrest, so primary prevention — methods to stop first-time development of a condition — consists mostly of regular checkups, including screening for heart disease, and living a heart-healthy lifestyle with the following approaches:
    • Eat a nutritious, well-balanced diet.
    • Don't smoke.
    • Stay physically active.
    If you know you have heart disease or conditions that make you more vulnerable to an unhealthy heart, your doctor may recommend that you take appropriate steps to improve your health, such as taking medications for high cholesterol or carefully managing diabetes.

    In some people with a known high risk of sudden cardiac arrest — such as those with a heart condition and an ejection fraction of less than 35 percent — doctors may recommend anti-arrhythmic drugs or an ICD as primary prevention.

    If you have a high risk of sudden cardiac arrest, you may also wish to consider purchasing an automatic external defibrillator (AED) for home use. Before purchasing one, discuss the decision with your doctor; the devices can be expensive and aren't always covered by health insurance.

    If you live with someone who is vulnerable to sudden cardiac arrest, it's important that you be trained in CPR. The American Red Cross offers courses in CPR and defibrillator use to the public. Being trained will help not only your loved one but also those in your community. The more people who know how to respond to a cardiac emergency, the more the survival rate for sudden cardiac arrest can be improved.

    Informations obtained from National Institute of Health.
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