Heart Attack or Sudden Cardiac Arrest

October is Sudden Cardiac Arrest Awareness Month, so let’s take a look at the differences between heart attack and sudden cardiac arrest (SCA).

Most people have heard of a person who “dropped dead” unexpectedly of something like “massive coronary”. A lot of people know about coronary artery disease and its association with chest pains, which can lead to heart attacks. However, what people rarely know about and what has not had much publicity is a truly deadly syndrome known as Sudden Cardiac Arrest.

Heart attack is a problem with the plumbing to the heart, or the coronary arteries. When these vessels start to narrow due to plaque buildup and abruptly close off, either because, in the area of the narrowing, there is a buildup of blood forming a clot or because plaque rich with cholesterol becomes frail and ruptures, that leads to a blockage of blood flow. That event leads to starvation of the heart muscle downstream of the blockage, and eventually, to permanent damage and death of the heart muscle. The area of the permanent damage is then replaced with scar tissue, essentially a patch which does not contribute to the pump function of the heart.

When such a situation is occurring, patients often experience some warning signs, such as chest pains, sweating, nausea, dizziness, and shortness of breath. There is a crucial time of about 90 minutes to interrupt the heart attack, in which blood flow has to be restored to the endangered heart muscle, in order to prevent permanent damage. These days, it is most commonly done by inserting a stent (an expandable sleeve) across the area of the blockage. In some hospitals where such technology and interventional skill may not available, the patient can then be given an infusion of a clot dissolving medication called thrombolytics.

Although the symptoms described can be very severe and the diagnosis is very grave, it infrequently leads to immediate death, and survival rates are improving.

Sudden cardiac arrest, on the other hand, is caused by a dysfunction of the electrical system of the heart. Most often, there are no warning signs. The patient usually unexpectedly collapses and the chances for spontaneous recovery are slim. The problem occurs when the heart suddenly loses the electrical impulse which makes it rhythmically squeeze, usually around 70 to 80 beats per minute. When Sudden Cardiac Arrest occurs, the electrical system goes into complete chaos and the heart muscle, instead of squeezing, it starts to quiver, a process called ventricular fibrillation. Thus, all circulation and pump function instantaneously cease. Within several seconds, the brain shuts down and the patient loses consciousness. The window of opportunity to reset the heart back to a meaningful contractility, which would sustain life, is only about four minutes before permanent brain damage threatens to ensue.

Termination of ventricular fibrillation, which is not compatible with life, has to be done through delivery of an electrical shock to the heart, which is called defibrillation. This can be done by medical personnel or even by a bystander with access to the automatic external defibrillator (AED). AEDs are often found in public places these days. Additionally crucial to survival is chest compressions. CPR should be started immediately while awaiting the final defibrillation rescue. There is no other life-saving approach.

Patients at greatest risk are those who have previously sustained a large amount of heart damage from either a heart attack or other processes leading to heart muscle damage or weakness, such as congestive heart failure or other causes of cardiomyopathies.

Let's put Sudden Cardiac Arrest in perspective with numbers:

Sudden cardiac arrest claims 350,000 lives each year. That is one life every two minutes. It is more than lives taken by breast cancer, lung cancer or AIDS. (Source: HRS).

It is therefore imperative that physicians have an awareness of the risks leading up to sudden cardiac arrest and are familiar with prevention strategies. The sooner a patient at risk is referred to a cardiologist, the better the chances of preventive measures being taken.

The Heart Rhythm Society has published a poster, (see photo), which graphically depicts the two processes: the plumbing, leading to a Heart Attack, and the electrical system, leading to Sudden Cardiac Arrest, making them as similar as apples and oranges.

In a future blog, we will review what approaches we have to dramatically reduce the risk of sudden cardiac arrest. For now, the take-home message is that apples are apples and oranges are oranges and the only commonality they have is that they are fruit. Aside from being part of heart disease, Sudden Cardiac Arrest and Heart Attack have nothing in common.

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