What is the difference between a heart attack and a cardiac arrest?
By Safiya Zaloum
The terms cardiac arrest and heart attack are often used interchangeably. However these are actually two different things! A heart attack happens when blood flow to the heart is blocked. This is a problem with circulation. A cardiac arrest occurs when the heart suddenly stops beating – this is an electrical problem. Let’s explore this a bit more – we are going to look at heart attacks and cardiac arrests, what happens in the heart, how you can recognize them and what you can do if you see one.
To better understand what a heart attack is, we need to understand why a blockage of the vessels supplying the heart muscle is bad. The blood vessels that supply the heart muscle are called coronary arteries.The coronary arteries supply blood to the heart muscle, also called cardiac muscle. The heart pumps blood all around the body, including to itself! In this blood there is oxygen and nutrients which are essential for the muscles to be able to function properly. Like any other muscle, without this, cardiac muscle cells will die. Heart muscle is special though, it is myogenic. This means it causes its own contractions and this is what makes the heart beat. Therefore, if part of the muscle dies, that part of the heart cannot beat properly.
This is what causes a heart attack. Heart attacks are usually caused by a sudden blockage of a coronary artery. Usually this happens because the artery has been narrowing over time. The endothelium is a thin layer of cells that lines blood vessels, and damage to this layer can lead to coronary artery disease. There are many ways in which the endothelium can become damaged, including smoking and diabetes. Many people have coronary artery disease, where the coronary arteries narrow over time. Here, fatty deposits build up and over many years cause the vessel to become narrower and narrower. This itself doesn’t usually cause a heart attack though. The fatty deposit that causes the narrowing of the coronary artery is called a plaque, and the plaque has a cap on it. This can be torn off or ripped, which exposes the fatty mixture that lies underneath. This attracts platelets, which are responsible for your blood clotting. This is what happens when you get a cut on your knee for example, and it forms a scab. The same thing happens in the coronary artery except the platelets pile up and block the whole artery, suddenly causing the vessel to be blocked. Now there is no blood being delivered to one part of the heart and the heart muscle cells will die if they do not have a blood supply for long enough.
This is an emergency, and blood flow needs to be restored to that part of the heart muscle to prevent it dying. Some common symptoms of a heart attack are chest pain or feeling like there is pressure in the chest, sweating, feeling sick, feeling fatigued, feeling lightheaded and shortness of breath. If you are with someone who has these symptoms, they may be having a heart attack. However, not everyone is in a lot of pain. Often the pain can be mild and feel like indigestion. The pain may also radiate to the jaw or the left arm.
For someone who thinks they are having a heart attack, the first and most important thing to do is to call 999 as they need to go to hospital. Whilst waiting for an ambulance, the 999 operator may tell them to chew some aspirin – this medicine thins the blood so can help to improve blood flow to the heart muscle. Once the person gets to hospital they will either be given medication that dissolves the clot, or taken to surgery to have a procedure that restores blood flow to the heart, by opening up the blocked coronary artery.
To better understand what happens in a cardiac arrest, we need to explore the electrical signalling in the heart. The heart’s rhythm is controlled by electrical signalling. The electrical system controls the heart rate – the number of times the heart beats per minute, and the heart rhythm – the synchronised beating of all 4 chambers of the heart. The timing of the heartbeat is controlled by electrical signals that are conducted through specialised heart cells that are responsible for carrying this electrical signal.
The electrical signal originates at one point on the heart called the SA node. The SA node produces the impulse which spreads across the atria, causing them to contract. The electrical signal then crosses a bridge to the ventricles at the AV node. The electrical signal then spreads out across the ventricles, causing them to contract, pumping blood out of the heart to the body. The diagram above shows how the electrical impulse travels through the heart.
A cardiac arrest usually happens suddenly and without warning. When the heart stops beating, this is a cardiac arrest. One cause of this is when the heart starts beating in an abnormal rhythm which can be due to a heart attack, often causing the ventricles to not contract properly.
The signs that someone has gone into cardiac arrest are:
- They appear to not be breathing
- They are not moving
- They are unconscious – they don’t respond to you when you speak to or touch them
They will not be breathing or moving as the heart has stopped pumping blood around the body.
If someone is having a cardiac arrest you need to call 999 straight away. Whilst waiting for an ambulance, you or an adult who knows how should immediately start CPR. You should aim to do 100-120 compressions a minute. Interlock your fingers and use the heel of your lower hand to press straight down in the middle of the chest, roughly between the person’s armpits, keeping your arms straight and using your body weight. This page explains how to do CPR. Don’t worry if you don’t know what you should do, the 999 phone operator will tell you and guide you through the steps. You should do CPR until the ambulance arrives and takes over.
If an automated external defibrillator (AED) is available, the 999 operator will tell you where your nearest one is located, if the person needs it. You do not have to be trained to be able to use an AED as they all come with clear instructions. They do not work on a heart that is beating normally. They are located in most public places and places of work. This machine helps to establish a regular heart rhythm and gives the person an electric shock if needed. AEDs increase survival rate above CPR alone. Once the person arrives in hospital, the healthcare staff will try to restore the heart to a normal rhythm if this has not been done already. Following successful restoration of a normal heartbeat, the person will recover in hospital and doctors will try to figure out exactly what caused the cardiac arrest, to try to avoid it happening again.