Introduction
How Does Sudden Death Occur?
Do All Types of Arrhythmias Cause Sudden Death?
Do All Cardiac Arrests Lead to Sudden Death?
Who is at Risk for Sudden Cardiac Death?
Treatment to Prevent Sudden Cardiac Death
What Can Society Do to Prevent Sudden Death?
Summary
Sudden death is generally considered any "natural," unexpected death that occurs within one hour after symptoms begin. Sudden death is one of the leading causes of death in the United States, accounting for 300,000 to 500,000 deaths each year. While the threat of sudden death is certainly a frightening prospect, open discussion of the risk factors for sudden death is a crucial step in preventing this all too common problem. It is extremely important for doctors and patients to understand and identify those at risk for sudden death because many actions can be taken to minimize this risk.
The vast majority of sudden death is caused by heart disease, although other illnesses such as massive bleeding, strokes, and pulmonary emboli (a blood clot traveling to the lung) may also cause this problem. Sudden cardiac death frequently occurs in people with known or suspected heart disease, but it may rarely occur in people with no known cardiac abnormalities.
Many sudden deaths occur quite rapidly, oftentimes within seconds or minutes. The choice of one hour between onset of symptoms and death is rather arbitrary. However, this has been adopted as the standard definition. Furthermore, the term "natural" is sometimes included to emphasize that deaths caused by accidents, murder, suicide, or other external circumstances may occur suddenly, but are not considered “sudden deaths” because the cause of death is known and does not directly reflect the individual's pre-existing health condition.
Whenever blood flow to the brain is abruptly and severely decreased, loss of consciousness will occur. This loss of consciousness is called fainting or syncope. A prolonged decrease in blood flow to the brain can cause sudden death. Almost always, this problem is caused by a cardiac arrhythmia, which is any abnormality in the heart’s rhythm or rate. For this reason, I am using the terms sudden death and sudden cardiac death somewhat interchangeably. However, it is important to recognize that the cause of sudden death cannot always be determined with certainty. Moreover, when a death is unwitnessed, it is difficult to be sure whether or not the death occurred suddenly (i.e., within one hour of symptom onset).
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Arrhythmias that cause sudden death do so because they rapidly impair the heart's ability to pump blood. This is different from congestive heart failure, which is a more gradual process in which the heart continues to pump blood, although at less than normal levels of effectiveness.
Do All Types of Arrhythmias Cause Sudden Death?
No. Only arrhythmias that cause cardiac arrest will cause sudden death. Cardiac arrest is the abrupt failure of the heart's pumping function that requires immediate treatment. Most arrhythmias that cause cardiac arrest are fast arrhythmias of the ventricle (the bottom muscular chamber of the heart) such as ventricular tachycardia and ventricular fibrillation. Extremely slow rhythms (called bradycardia or heart block) can also lead to sudden death in some cases.
Your doctor may have told you that you have an arrhythmia. In general, only certain arrhythmias pose a serious risk for sudden death. The most common arrhythmias are atrial arrhythmias such as atrial fibrillation, atrial flutter, single extra beats (such as atrial premature contractions, termed APCs) or SVT (supraventricular tachycardia). In atrial fibrillation, the atria lose the ability to contract properly, producing an irregular and rapid heartbeat. SVT is a fast heart rhythm arising from the upper chambers of the heart. A flutter is similar to atrial fibrillation, but it produces a regular and rapid heartbeat. The simplest arrhythmia is a single extra heartbeat, called a premature beat (or premature contraction). While these disorders may be associated with palpitations or other symptoms, they typically do not impair the heart's ability to pump blood to the extent required to produce a cardiac arrest or sudden death. Ventricular premature beats (commonly called VPCs) may or may not be a significant risk factor for sudden death, depending upon their frequency and pattern.
Do All Cardiac Arrests Lead to Sudden Death?
No. In very rare cases, a cardiac arrest may stop on its own. However the vast majority will result in sudden death unless cardiopulmonary resuscitation (CPR) is provided. CPR is a life-saving technique that both medical professionals and lay persons can provide.
CPR consists of chest compressions and mouth-to-mouth ventilation. By compressing on the victim's chest, you can cause blood to flow through the heart to the body's organs, including the brain. While the amount of blood flow provided by CPR is far below normal levels, it can be enough for survival until more sophisticated medical help arrives. Mouth-to-mouth ventilation may also be helpful in maintaining blood oxygen levels during CPR.
It is important to recognize that CPR is only a temporizing measure, maintaining blood flow to the brain until the heart rhythm and pump function can be restored. Depending on the type of cardiac arrest, restoration of the heart's normal rhythm is attempted using medications, cardiac defibrillation, or both. Cardiac defibrillation refers to the use of paddles that are placed on a patient's chest to deliver an electrical shock to the heart.
Who is at Risk for Sudden Cardiac Death?
While anyone theoretically could die suddenly, the chances are extremely small for most people. In the overall population about one in 500 to 1,000 people will die suddenly each year. While this is a rather high number, the chances are much lower for most healthy people and much greater for certain groups of patients. Those who have survived a previous cardiac arrest are definitely at high risk of having another cardiac arrest. Since each episode of cardiac arrest is associated with a high risk of dying, the risk for sudden death is high in these people (approximately 25 percent risk of death per year).
Past heart disease
The risk is similarly high if you have advanced congestive heart failure or arrhythmias occurring after a myocardial infarction (heart attack). Other heart diseases associated with an elevated risk for sudden death include those with hypertrophic heart disease (thickening of the heart wall as a result of either high blood pressure or genetic factors), some types of valvular heart disease (such as severe aortic stenosis), or previous heart attacks. Even if you have no known heart disease, but many risk factors for heart disease such as diabetes, high blood pressure, tobacco use, high cholesterol, or a strong family history of coronary artery disease, you may be at increased risk for sudden death.
Genetic diseases
Some patients have hearts that appear normal yet are nevertheless at high risk for sudden death. One major group of people in this category is patients with inborn genetic diseases that affect the heart's electrical system. These "electrical" disorders are relatively rare, though medical research efforts are identifying an increasing number of genes that cause lethal arrhythmias. The long-QT syndrome and Brugada's syndrome are important examples of hereditary syndromes that predispose patients to cardiac arrhythmias. Similar genetic disorders probably account for some cases of the sudden infant death syndrome (SIDS). Likewise, a syndrome of premature sudden death exists among apparently healthy southeast Asians and Japanese individuals. Again, inherited electrical diseases of the heart appear to account for many of these deaths.
Medications
Various medications are known to cause lethal arrhythmias and sudden death in rare circumstances. This has been an important topic in recent times, leading to the withdrawal of many drugs from the marketplace. Two recent examples are the anti-histamine allergy medications astemizole (Hismanal) and terfenadine (Seldane). The use of numerous other medications has been severely restricted, such as the antipsychotic medication thioridazine (Mellaril) and the stomach motility medication cisapride (Propulsid). However, many medications remain on the market in situations where the benefits of the medications are judged to outweigh their risks. Some examples include specific antibiotics (such as erythromycin), antifungal medications (such as fluconazole), tricyclic antidepressants (such as amitryptyline, sold as Elavil), and anti-arrhythmic medications (such as sotolol, sold as Betapace). However, the risk can be further increased as a result of drug-drug interactions when specific combinations of medications are used. As always, it is important to review the possibility of drug-drug interactions with your primary care provider and pharmacist.
Blood salt levels
Finally, abnormal blood salt (electrolyte) levels can promote the onset of dangerous arrhythmias. Abnormal potassium, magnesium, and calcium levels are frequently the cause. If you use diuretic medications, you should have your blood electrolyte levels checked periodically. Certain endocrine diseases may also affect the body's electrolyte levels. Some patients require use of potassium or magnesium tablets or adjustment in their other medications to maintain proper blood electrolyte levels.
Treatment to Prevent Sudden Cardiac Death
If your physician has identified that you are at elevated risk for sudden cardiac death, there are several ways that risk can be reduced. First, it is critical to optimally treat any underlying medical conditions that you may have. This includes treatment of congestive heart failure, coronary artery disease, hypertension, and cholesterol. Avoidance of tobacco is also important.
Second, several widely prescribed medications can reduce the risk of sudden death in certain groups of patients. One example is the use of beta-blocking medications in patients with coronary artery disease, congestive heart failure, or the inherited long-QT syndrome. Commonly used beta-blocking medications include propranolol (Inderal), metoprolol (Lopressor or Toprol XL) and atenolol (Tenormin).
Unfortunately, some individuals will remain at extreme high risk for sudden death despite the above treatments. The mainstay of treatment for these patients is the implantable cardiac defibrillator. This device treats ventricular arrhythmias by sensing their occurrence and providing a shock to terminate the arrhythmia before it leads to sudden death. For slow arrhythmias, pacemakers are used. Pacemakers sense the heart rate; when it falls below a set limit, the pacemaker begins to pace the heart at a programmed rate. For certain individuals, anti-arrhythmic medication such as amiodarone (Cordarone) can be useful in preventing life-threatening cardiac arrhythmias.
Evaluation of Risk of Sudden Cardiac Death
There are several tests available that I use to evaluate patients who are at increased risk for sudden death. We already discussed the major patient groups that are at risk for sudden death. However, treating every patient who has had a heart attack or heart failure with an implantable cardiac defibrillator would be extraordinarily expensive and invasive and beneficial to relatively few patients. For this reason, I perform various tests in certain patients at intermediate risk level for sudden death. The results of these tests help determine whether it is most appropriate to recommend an implantable defibrillator, anti-arrhythmic medications, or simply the best medical management of underlying heart disease.
The most frequently used tests include a Holter monitor, which records your electrocardiogram (EKG or ECG) for a 24-hour period. This can detect whether a patient is having dangerous extra heartbeats during a typical day. An electrophysiology study (commonly called an "EP study") is a test in which catheters are placed inside of the heart. We test the ability to provoke abnormal arrhythmias using the catheters. EP study results are very helpful in determining the risk of future arrhythmias for some groups of patients. Other methods are being actively studied as better tests to predict risk of sudden death.
What Can Society Do to Prevent Sudden Death?
Society can play an extremely important role in preventing sudden cardiac death. First, awareness of the problem is a critical step. All individuals should be encouraged to learn CPR. The more people in a community who know CPR, the better the chances of survival for those experiencing a cardiac arrest. If you have a family member or neighbor who has significant heart disease, there is an even greater reason to consider becoming certified in CPR. In many cases, I encourage my patient’s family members to learn CPR.
Second, the emergency medical services in local communities need to continue to work to decrease response times to emergency calls. For example, communities in Seattle, Washington have demonstrated convincingly that this approach improves the odds of survival for those with cardiac arrest.
Finally, many researchers and health policy officials are promoting campaigns for public access cardiac defibrillators. This involves the widespread placement of defibrillators in public places. The defibrillators are specially designed to deliver therapy only when appropriate, making them more user-friendly than standard defibrillators. To date, public defibrillators have been tested and used in airplanes, casinos, shopping malls, and other public places. However, logistical and financial issues have delayed the widespread placement of public access defibrillators. It is likely that this important approach will enjoy greater implementation in the future.
Sudden death is usually the result of a cardiac arrhythmia. The risk of sudden death depends upon the presence of underlying heart disease as well as the result of diagnostic tests. In many cases, optimal treatment of any underlying cardiac disease and risk factors may reduce your chances of experiencing sudden death. The major treatments for patients at very high risk for sudden cardiac death include implantable cardiac defibrillators, pacemakers, and anti-arrhythmic medications. Several public health measures could be extremely valuable in the treatment of cardiac arrest, including increased knowledge of CPR amongst nonmedical professionals, improved response times for local emergency medical services, and more widespread availability of public access defibrillators.
