Cardiac arrest: what makes the heart stop?

Resource post for June

The King of Pop Michael Jackson was said to have suffered from cardiac arrest but the actual cause of death is unknown. This statement confused many people – why can’t cardiac arrest be the cause of death? To answer this question, we have to brush up a bit on what we know about cardiac arrest.

What is cardiac arrest?

According to the National Heart Lung and Blood Institute

Sudden cardiac arrest (SCA) is a condition in which the heart suddenly and unexpectedly stops beating. When this happens, blood stops flowing to the brain and other vital organs.

If the heart does not start beating within a few minutes, death occurs.

There many things that can cause the heart to stop or “arrest” and sometimes it doesn’t even have anything to do with heart disease. The heart runs on an internal electrical system that regulates the rate and rhythm of the heart beat. From time to time, the electrical system can have problems, causing abnormal rhythms called arrhythmias. These abnormal heart rhythms can be too slow (bradycardia) or too fast (tachycardia) or it can complete stop. Some arrhythmias can cause the heart to stop pumping blood, causing sudden cardiac arrest.

Now, it is important for us to know that cardiac arrest is not synonymous to a heart attack or myocardial infarction in doctor speak. However, a cardiac arrest may be a complication of a heart attack. Although, people with heart problems have a high risk of SCA, most SCAs happen in completely healthy people with no history of heart disease.

What causes cardiac arrest?

So what can cause the heart to stop beating and lead to cardiac arrest? There are many things that can interfere with the heart’s electrical system and these are:

Coronary heart disease (CAD)/Heart attack. Blocked coronary arteries can lead to heart attacks but also interfere with the electrical system of the heart. A large number of SAC cases are due to CAD or heart attack.
Electric shock/electrocution. A strong electrical shock can stop the heart. Electrocution and lighting strikes can easily lead to SAC.
Respiratory arrest. This can happen when people choke, or drown or can’t breath, cutting off the oxygen supply to the heart.
Overdose on certain drugs. It is a know fact that certain drugs can interfere with heart rhythms. This is why new drugs are screened for pro-arrhythmic effects before approval. When taken in excessive amounts, certain drugs complete halt the heart, resulting in SAC.
Trauma. A strong sudden blow to the heart, or an injury that damages the heart can also lead to cardiac arrest.
Unknown causes. Some cases of SAC cannot be explained, unless an autopsy is conducted.

What are the signs of SAC?

According to the American Heart Association (AHA), the warning signs for SAC are

Loss of consciousness
Cessation of normal breathing
Absence of pulse
Absence of blood pressure

Death occurs within 4 to 6 minutes after cardiac arrest. It is estimated that 95% of SAC cases result in death.

How can cardiac arrest be reversed?

In SAC, every second counts. To save the patient, it is imperative that the heart be restarted as soon as possible. It can happen that heart function is restored but brain death has already set in due to interruption of blood and oxygen supply.

There are several ways to restore a normal heartbeat:

Electric shock using defibrillators, a scene that we often see in emergency rooms. In settings away from hospitals, the use of automated external defibrillators (AEDs) has saved many lives.
Cardiopulmonary resuscitation (CPR) is to manually restore the heart beat by applying pressure on the chest region.

According to the AHA

Cardiac arrest can be reversed if it’s treated within a few minutes with an electric shock to the heart to restore a normal heartbeat. This process is called defibrillation. A victim’s chances of survival are reduced by 7 to 10 percent with every minute that passes without CPR and defibrillation. Few attempts at resuscitation succeed after 10 minutes… It’s estimated that more than 95% of cardiac arrest victims die before reaching the hospital. In cities where defibrillation is provided within 5 to 7 minutes, the survival rate from sudden cardiac arrest is as high as 30-45 percent.

Because SAC is very time critical, wait ing for emergency services to arrive may be too late. This is why AEDs are available in crowded public places, e.g. airports, sports stadiums, public events where people gather. In Zurich, Switzerland, AEDs are strategically located in telephone booths in the city center. Equally important is bystander awareness. AEDs are designed to be used by almost anybody, even without any medical training. Yet, many people are hesitant to “get involved.” Health groups, including the AHA are campaigning for more active bystander involvement in the prevention of SAC.