THERE often is confusion in the lay public as to the difference between a heart attack and a cardiac arrest. As physicians we sometimes contribute to this confusion by using these terms imprecisely when speaking to our patients.

A heart attack (or myocardial infarction) is the death of heart muscle because of impairment of blood flow usually resulting from acute rupture of a plaque, causing abrupt stoppage of blood flow in the coronary vessel. A cardiac arrest can be thought of as the cessation of the pumping function of the heart. A cardiac arrest can occur because of a heart attack but often occurs in the absence of a heart attack in patients who do not have coronary artery disease. Cardiac arrests are important as once the heart stops pumping, the organs of the body cease receiving the blood flow that they need to stay alive. Some organs of the body are relatively resistant to temporary disruptions in blood flow. For example, the muscle of the heart can recover normal function if flow is interrupted for less than two hours. In contrast, brain tissue starts to die within minutes of an absence of blood flow. Given this and the fact that absence of electrical activity in the brain is the gold standard for the definition of death, cardiac arrests that are untreated will almost uniformly lead to death. For some patients, cardiac arrest is expected as they are experiencing rapid progression of heart disease in a hospital setting. Most cardiac arrests, however, take place at home and are unexpected. This is called sudden cardiac death and in many developed and developing countries constitutes a significant percentage of total mortality.

Why does the heart stop pumping?

As we have discussed in previous articles, the heart has different systems that work together in synchrony to ensure that the heart can pump blood to meet the needs of the body. Simply put the heart beats because an electrical signal runs through it from the upper chambers to the lower chambers. This electrical signal results in muscle contraction which generates the force for pumping blood. Cardiac arrest almost always results from disturbances in the electrical activity of the heart. These disturbances can be divided into rapid heart rhythms abnormalities or rhythms with slowing/absence of the electrical signals. Rapid heart rhythms particularly involving the bottom chambers of the heart account for almost 90 per cent of cardiac arrest while slow heart rhythms or an absent heart rhythm account for the remainder. The fact that rapid heart rhythms are such a dominant cause does open the possibility for treatment to “restart the heart” and allow the return of a normal cardiac rhythm. If this is done before the brain and other organs suffer significant damage, then the patient can return to a normal life.

What are the possible outcomes of cardiac arrest?

The outcomes of sudden cardiac arrest tend to be best in places where the patient is being closely monitored and there is the ability to rapidly deliver an electric shock to the heart muscle. Of secondary importance is the ability to continue delivery of blood flow to the body in the absence of the pumping action of the heart. This is known as cardiac pulmonary resuscitation or basic life support. Patients who experience cardiac arrest in the emergency room, in the ICU or in procedure suites have relatively high rates of survival with normal neurological function. This improved outcome is related to the fact that cardiac arrest is quickly identified, personnel are available who can provide life support and cardiac rhythm abnormalities can be identified and treated. Studies have found survival after cardiac arrest of greater than 70 per cent in the coronary care unit and greater than 50 per cent in medical intensive care unit. In contrast, patients who have cardiac arrest at home normally have poor outcomes. Some studies have suggested that only six out of 100 patients survive a cardiac arrest at home. The percentage of patients who survive and are neurologically intact is even lower. Data from the Unites States of America suggests that some of the poor outcomes for patients at home is the fact that cardiac pulmonary resuscitation is performed only 40 per cent of the time.

What leads to cardiac arrest?

Most cardiac arrests occur in patients who have some form of cardiovascular disease. The risk of heart disease increases with age and thus so does the risk of cardiac arrest. Coronary artery disease is the most common heart disease that is seen in developed countries and many developing countries. Coronary disease can lead to cardiac arrest in several circumstances. If an individual is having a heart attack, the absence of blood flow to the heart will often cause the heart muscle to be irritable and to develop arrhythmias. These tend to be most common early in the heart attack course and are what the layman thinks of when someone is said to “drop dead” from a heart attack. Cardiac arrest can also commonly occur in patients who have sustained a heart attack in the past. When a heart attack heals the muscle tissue of the heart is replaced by scar or fibrous tissue which can serve as a focus for the development of abnormal heart rhythms particularly if the pumping function of the heart is reduced.

Patients who have heart failure, particularly when the main pumping chamber of the heart is enlarged and does not pump effectively, are at high risk of developing cardiac arrest. This risk increases when the pumping function of the heart is severely reduced. Other forms of heart muscle disease or cardiomyopathies are at risk including those with abnormally increased thickness of the heart muscle “hypertrophic cardiomyopathy”, genetic abnormalities that increase the risk of heart arrhythmias, valvular heart disease and congenital heart disease.

How common is cardiac arrest?

The exact scope of the problem can be difficult to determine. Cardiac arrest is easy to diagnose in a medical setting where rhythm monitoring is available. Most cardiac arrests, however, occur outside of medical facilities. In these scenarios an exact diagnosis can be challenging even in those limited cases in which autopsy is performed. For epidemiologic studies sudden cardiac death is often defined as death occurring within an hour of symptoms. For example, someone falls to the ground and cannot be resuscitated. It is important to note that many deaths can take place where there are no witnesses to the events and the best that can be said is that the patient was alive last night. In the United States it is estimated that 36,500 cardiac arrests take place outside hospitals each year. The numbers for Europe are estimated to be approximately 340,000 per year. For the United States it is estimated that this represents 20 per cent of total mortality.

Can anything be done to lower the rates of cardiac arrest and to improve survival?

Lowering the rates of cardiac arrest and improving survival is a common goal of heart foundations and organisations worldwide, including our own Jamaica Heart Foundation. Research, improved diagnosis/management of cardiovascular disease, educational outreach at a population level and policy changes at the national level have the potential to improve the outcomes in this challenging clinical area. We will address some of these matters in future articles

Dr Ernest Madu, MD, FACC and Dr Paul Edwards, MD, FACC are consultant cardiologists for Heart Institute of the Caribbean (HIC) and HIC Heart Hospital. HIC is the regional centre of excellence for cardiovascular care in the English-speaking Caribbean and has pioneered a transformation in the way cardiovascular care is delivered in the region. HIC Heart Hospital is registered by the Ministry of Health and Wellness and is the only heart hospital in Jamaica. Correspondence to info@caribbeanheart.com or call 876-906-2107