Sudden Cardiac Arrest ~ SCA

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.

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:

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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.
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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.
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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:

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Hypertrophic cardiomyopathy
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Aortic stenosis
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Pulmonary stenosis, obstruction of the flow of blood from the right ventricle to the pulmonary artery
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Tetralogy of Fallot, a condition marked by a set of four defects in the heart
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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:

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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.
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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.
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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.

Risk factors

Because sudden cardiac arrest is so often intertwined with coronary artery disease, the same factors that put you at risk of coronary artery disease may also put you at risk of sudden cardiac arrest. These include:

• A family history of heart disease
• Smoking
• High blood pressure
• High blood cholesterol
• Obesity
• Diabetes
• A sedentary lifestyle

In addition to a personal or family history of heart disease — including heart rhythm disorders, congenital heart defects, congestive heart failure and cardiomyopathy — other factors that may increase your risk of sudden cardiac arrest include:

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Low output of blood from you heart (ejection fraction)
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Previous episode of cardiac arrest
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Previous heart attack
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Markedly changed blood levels of potassium or magnesium — minerals called electrolytes that need to be properly balanced in order to maintain vital organ functions, including that of the heart
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Hyperthyroidism, a condition in which your thyroid gland produces too much of the hormone thyroxine, speeding up your metabolism and potentially causing arrhythmia
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Pulmonary hypertension, a type of high blood pressure that affects the arteries in your lungs
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Taking drugs that affect your heart rhythm, such as prescription anti-arrhythmic or pro-arrhythmic drugs, or over-the-counter medications, such as pseudoephedrine-containing cold medicines
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Using illicit drugs, such as cocaine or amphetamines

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.

When to seek medical advice

If you have frequent episodes of heart palpitations, irregular or rapid heartbeats, unexplained wheezing or shortness of breath, fainting or near fainting, or feeling lightheaded, dizzy or weak, or if you have chest pain or discomfort, see your doctor promptly.

If someone near you collapses unconscious, take immediate action:

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Call the Emergency number in your area.
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Administer CPR, or if you don't know how, find someone nearby to do it. Keep administering CPR until a defibrillator is available to deliver an electric shock to the person's chest.
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Use a portable defibrillator, if one is available. If you're not trained to use a portable defibrillator, an Emergency (911) operator may be able to guide you in its use.

Portable automatic external defibrillators (AEDs) are available in an increasing number of places, including airports, casinos and shopping malls. You can also purchase them for your home. AEDs come with built-in instructions for their use. They're programmed to allow a shock only when appropriate.

Screening and diagnosis

It isn't always easy to predict who might experience sudden cardiac arrest. In many cases, the affected person may have appeared healthy. Regular checkups with your doctor can help identify risk factors you might have for conditions that might lead to cardiac arrest. Treating and monitoring these conditions, as well as making healthy life choices, can help reduce your risk of sudden cardiac arrest.

If you experience an episode of sudden cardiac arrest without warning and survive, your doctor will want to investigate what caused the cardiac arrest. Identifying the underlying problem may help prevent future episodes of cardiac arrest.

Tests your doctor may recommend include:

Electrocardiogram
A test commonly given after cardiac arrest is an electrocardiogram (ECG). During an ECG, sensors (electrodes) that can detect the electrical activity of your heart are attached to your chest and sometimes to your limbs. An ECG measures the timing and duration of each electrical phase in your heartbeat and can reveal disturbances in heart rhythm. Because injured heart muscle doesn't conduct electrical impulses normally, the ECG may show that a heart attack has occurred.

Blood tests - Blood tests may include:

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Cardiac enzyme test. Certain heart enzymes leak into your blood if your heart has been damaged by a heart attack. Because a heart attack can trigger sudden cardiac arrest, it's important to know whether you've had a heart attack. Testing a blood sample for these enzymes may help indicate whether a heart attack has indeed occurred.
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Electrolyte test. A sample of your blood may also be tested for levels of electrolytes, such as potassium, calcium and magnesium. Electrolytes are minerals in your blood and body fluids that participate in the creation of electrical impulses. An imbalance in the levels of these substances can increase your risk of arrhythmia and sudden cardiac arrest.
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Drug test. Your doctor may check your blood for evidence of drugs that have the potential to induce arrhythmia, including certain prescription and over-the-counter drugs and illicit drugs.
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Hormone test. Testing for hyperthyroidism may indicate this condition as the trigger for your cardiac arrest.

Imaging tests - These may include:

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Chest X-ray. An X-ray image of your chest allows your doctor to check the size and shape of your heart and its blood vessels. It may also indicate whether you have congestive heart failure.
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Nuclear scan. This test, usually done in conjunction with a stress test, helps identify blood flow problems to your heart. Trace amounts of radioactive material, such as thallium, are injected into your bloodstream. Special cameras can detect the radioactive material as it flows through your heart and lungs.
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Echocardiogram. This test uses sound waves to produce an image of your heart. During an echocardiogram, sound waves are directed at your heart from a wand-like device (transducer), held on your chest. The sound waves bounce off your heart and are reflected back through your chest wall and processed electronically to provide video images of your heart. An echocardiogram can help identify whether an area of your heart has been damaged by a heart attack and isn't pumping normally or at peak capacity (ejection fraction), or whether there are valvular abnormalities.

Other tests - Other tests that are often done include:

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Electrophysiological testing and mapping. This test is usually done later, after you have recovered and any underlying problems have been identified. With this type of test, your doctor may try to actively induce an arrhythmia while closely monitoring your heart. The test can also help locate where in the heart the arrhythmia originates.

During the test, thin, flexible tubes (catheters) tipped with electrodes are threaded through your blood vessels to a variety of spots within your heart. Once in place, the electrodes can precisely map the spread of electrical impulses through your heart. In addition, your cardiologist can use the electrodes to stimulate your heart to beat at rates that may trigger — or halt — an arrhythmia. This allows your doctor to observe the location of the arrhythmia and the mechanisms that may be causing it.

The ability to start and stop your arrhythmia also may be used to test various treatment methods for effectiveness. If your cardiologist determines that radiofrequency catheter ablation — a catheter-based treatment option for many arrhythmias — is appropriate, he or she can perform this procedure during an electrophysiological test.
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Ejection fraction testing. One of the most important predictors of your risk of sudden cardiac arrest is how well your heart is able to pump blood. Your doctor can determine your heart's pumping capacity by measuring what's called the ejection fraction. This refers to the percentage of blood that is pumped out of a filled ventricle with each heartbeat. A normal ejection fraction is 55 percent to 70 percent. An ejection fraction of less than 35 percent is associated with a high risk of sudden cardiac arrest. Your doctor can measure ejection fraction in several ways, such as with an echocardiogram, magnetic resonance imaging (MRI) of your heart, a nuclear medicine scan (multiple gated acquisition, or MUGA) of your heart or a computerized tomography (CT) scan of your heart.
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Coronary catheterization (angiogram). This test can show if your coronary arteries are narrowed or blocked. Along with ejection fraction, the number of obstructed blood vessels is another important predictor of sudden cardiac arrest.

During the procedure, a liquid dye is injected into the arteries of your heart through a long, thin tube (catheter) that's advanced through an artery, usually in your leg, to arteries in your heart. As the dye fills your arteries, the arteries become visible on X-ray and videotape, revealing areas of blockage.

Additionally, while the catheter is in position, your doctor may treat a blockage by performing an angioplasty, also known as coronary artery balloon dilation, balloon angioplasty and percutaneous coronary intervention. Angioplasty uses tiny balloons threaded through a blood vessel and into a coronary artery to widen the blocked area. In most cases, a mesh tube (stent) is also placed inside the artery to hold it open more widely and prevent re-narrowing in the future.

Complications

When sudden cardiac arrest occurs, your brain is the first part of your body to suffer because, unlike other organs, it doesn't have a reserve of oxygen-rich blood. It's completely dependent on an uninterrupted supply of blood. Reduced blood flow to your brain results in unconsciousness.

If your heart rhythm doesn't rapidly return to its normal rhythm, irreversible loss of brain function occurs and death results. A delay in defibrillation of more than 10 minutes reduces the survival rate to less than 5 percent. Survivors of cardiac arrest may show signs of brain damage.

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.

At the emergency room
Once you arrive in the emergency room, the medical staff will work to stabilize your condition and treat possible heart attack, heart failure or electrolyte imbalances. You may be given medications to stabilize your heart rhythm.

The degree of recovery after cardiac arrest varies. Some people may be in a coma for days, weeks or indefinitely. Others may recover only partial function. After you recover, your doctor will discuss with you or your family what additional tests you may need to determine the cause of the cardiac arrest. Your doctor will also discuss preventive treatment options with you, to reduce your risk of another cardiac arrest.

Therapies may include:

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Medications. Doctors use various anti-arrhythmic drugs for emergency or long-term treatment of arrhythmias or potential arrhythmia complications. Most anti-arrhythmic medications work to slow your heart rate in one of two ways. One way suppresses the activity of pacemaking tissue that's initiating impulses too quickly. The other slows the transmission of fast impulses inside the heart. Doctors commonly use a class of medications called beta blockers in people at risk of sudden cardiac arrest, but they may also use angiotensin-converting enzyme (ACE) inhibitors, calcium channel blockers or a drug called amiodarone (Cordarone).

Anti-arrhythmic drugs may have certain potential side effects. For example, an anti-arrhythmic drug may cause your particular arrhythmia to occur more frequently — or even cause a new arrhythmia to appear that's as bad as or worse than your pre-existing condition. Side effects not related to your heart also may occur.
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Implantable cardioverter-defibrillator (ICD). After your condition stabilizes, your doctor is likely to recommend implantation of an ICD. An ICD is a battery-powered unit that's implanted near your left collarbone. One or more electrode-tipped wires from the ICD run through veins to your heart.

The ICD constantly monitors your heart rhythm. If it detects a rhythm that's too slow, it paces your heart as a pacemaker would. If it detects ventricular tachycardia or ventricular fibrillation, it sends out low- or high-energy shocks to reset your heart to a normal rhythm. An ICD may be more effective than preventive drug treatment at reducing your chance of having a fatal arrhythmia.
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Coronary angioplasty. This procedure is for the treatment of severe coronary artery disease. It opens blocked coronary arteries, letting blood flow more freely to your heart, which may reduce your risk of serious arrhythmia. Doctors insert a long, thin tube (catheter) that's passed through an artery, usually in your leg, to a blocked artery in your heart. This catheter is equipped with a special balloon tip.

Once in position, the balloon tip is briefly inflated to open up a blocked coronary artery. At the same time, a metal mesh stent may be inserted into the artery to keep it open long term, restoring blood flow to your heart. Coronary angioplasty may be done at the same time as a coronary catheterization (angiogram), a procedure that doctors do first to locate narrowed arteries to the heart.
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Coronary bypass surgery. Another procedure to improve blood flow is coronary bypass surgery. Bypass surgery involves sewing veins or arteries in place at a site beyond a blocked or narrowed coronary artery (bypassing the narrowed section), restoring blood flow to your heart. This may improve the blood supply to your heart and reduce the frequency of ventricular tachycardia, similar to angioplasty.
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Radiofrequency catheter ablation. This procedure works best to block a single abnormal electrical pathway, which is the cause of arrhythmias such as Wolff-Parkinson-White syndrome. In this procedure, one or more catheters are threaded through your blood vessels to your inner heart. They're positioned along electrical pathways identified by your doctor as causing your arrhythmia. Electrodes at the catheter tips are heated with radiofrequency energy. This destroys (ablates) a small spot of heart tissue and creates an electrical block along the pathway that's causing your arrhythmia. Usually, this stops your arrhythmia.
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Corrective heart surgery. If you have a congenital heart deformity, a faulty valve or diseased heart muscle tissue due to cardiomyopathy, surgery to correct the abnormality may improve your heart rate and blood flow, reducing your risk of fatal arrhythmias.
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Heart transplantation. Some people with severe congestive heart failure who've experienced cardiac arrest may be eligible for a heart transplant. But given the limited number of donor hearts, this may be available to few people.

Courtesy of: Mayo Clinic