Basic Facts

• Sudden cardiac death refers to death that occurs unexpectedly and presumably due to a heart condition.
• In sudden cardiac death the heart may have a) an electrically chaotic rhythm, called ventricular fibrillation, b) no electrical beat at all, called asystole, or c) be so weak that it is unable to mechanically pump any blood.
• There are many causes for sudden cardiac death, which include severe heart failure, heart attack and certain inherited heart conditions.
• It is imperative for bystanders to perform cardiopulmonary resuscitation (CPR) to improve the chances for survival for the victim.
• Survivors of sudden cardiac death may require an implantable cardioverter defibrillator (ICD)  to prevent the future possibility of sudden death.
  
  

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A More Detailed Explanation

Sudden cardiac death (SCD) is a term used to describe death that occurs unexpectedly and presumably due to a heart related problem.  Victims of SCD may not have any symptoms to suggest an illness, or may exhibit symptoms for only a short period (i.e. an hour or less) before death.  An estimated 500,000 cases of SCD occur per year in the United States.

In sudden cardiac death the heart may:

a) exhibit an electrically chaotic rhythm called ventricular fibrillation 

b) have no electrical beat at all (“flat line” or “asystole”)

c) be so weak that it cannot pump any blood despite the presence of electrical activity

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Causes of Sudden Cardiac Death

The causes of sudden cardiac death are many (Table 1).  However, in this country the most common cause is  coronary atherosclerosis  – plaque in the heart arteries. This process may lead to a heart attack (“myocardial infarction”), where a portion of the heart muscle is so extremely deprived of oxygen and nutrients that it becomes permanently damaged. Sudden cardiac death may occur if the oxygen-starved heart muscle becomes electrically unstable causing ventricular fibrillation to develop. In ventricular fibrillation the heart rhythm is chaotic and there is no effective mechanical heartbeat.  Death occurs within minutes unless cardiopulmonary resuscitation (CPR) is performed and the heart is shocked back to a normal beat.  Most heart attacks which result in SCD do so because ventricular fibrillation has occurred.  However if a very large heart attack occurs resulting in extensive heart muscle damage, just the overall weakness of the heart muscle itself may lead to SCD.

Sudden cardiac death can also occur in the absence of a heart attack. It may occur in people who have diminished heart function – a weakness in the heart muscle from whatever cause. The “ejection fraction” is a number that is used to describe how much blood is pumped out by the heart with every heart beat; normally the heart can eject at least 50% of its contents with every heart beat. Heart function is considered severely diminished if the ejection fraction is less than 35%, and under these circumstances patients can also be at increased risk for SCD (again, most frequently as a result of ventricular fibrillation).  Most diminished heart function develops as a result of coronary artery disease and heart attacks, but some people have diminished heart function despite having normal coronary arteries.

In rare circumstances, sudden cardiac death, presumably due to ventricular fibrillation, can occur in individuals who seem perfectly healthy. Tragic stories of athletes dying during competition are in this category. Some of these athletes are later found out to have abnormal hearts and various unusual heart conditions that may be genetic. One such condition is called “hypertrophic cardiomyopathy” where there is an abnormal thickness of the heart muscle.  Other individuals may have normal appearing hearts but have a genetic predisposition to various electrical disorders. The most common electrical diseases include “long QT syndrome” and “Brugada syndrome”.  Another rare cause of sudden death can occur if a blow to the chest occurs during a vulnerable portion of the heart beat; this situation can potentially affect anyone and is called “commotio cordis”. 

Table 1

Causes of Sudden Cardiac Death

1.  Severely Reduced Heart Function

2.  Heart Attack

3.  Inherited heart muscle diseases (including “hypertrophic cardiomyopathy”)

4.  Heart electrical diseases (such as “Long QT syndrome”or “Brugada syndrome”)

5.  Commotio cordis (blow to the heart during a vulnerable portion of the heart beat)

Hypertrophic cardiomyopathy, long QT syndrome, Brugada syndrome, and commotio cordis are all rare conditions.  However, because SCD related to these underlying problems can affect young, otherwise healthy individuals, having life-saving resources available in areas where such people are concentrated makes sense.  As a result, many schools and sports venues now have automated external defibrillators (“AEDs”) that can be used in these rare life-threatening situations.   Having AEDs available in any setting where people congregate makes sense in general, and they are fortunately becoming more and more commonplace.

While sudden cardiac death is unexpected,  it is potentially survivable. However, this requires that bystanders be able to react quickly and responsibly to the emergency. It is not enough to merely call 911 and wait for paramedics to arrive. It is imperative to start CPR, which involves compressing the chest and to apply an AED to shock the heart. A victim has the best chances for good survival if witnesses act quickly.  Victims that do survive sudden cardiac death require testing to determine if the cause for sudden death can be reversed. If it is determined that the risk for another cardiac arrest is high, then an implantable cardioverter defibrillator (ICD) is needed. This is a device, similar to a pacemaker,  that can shock the heart within seconds if a dangerous heart rhythm is detected.  Many patients are implanted with ICDs before a cardiac arrest has ever occurred if they are identified as having high risk characteristics, such as severe heart dysfunction for example.

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