What Actually Happens in Cardiac Arrest, What Does CPR Do, & Why Must We Defibrillate?
Sudden Cardiac Arrest SCA, the big one, nothing trumps it!!
In Australia 30,000 suffer SCA each year
Without effective CPR, and defibrillation, the chance of survival decreases by 10% every minute.
Only about 9%-10% of SCA survive
NSW Ambulance survival rate figures are about 3% (This is due to the time taken to arrive and commence treatment)
But what is actually happening to the heart and the brain???
Firstly, let’s look at the heart and what it does.
Simply put, the heart is pump that pumps blood around the body. It has four chambers, or holding tanks, two on top, the left and right atriums, and two on the bottom, the left and right ventricles. It has two systems, electrical and plumbing.
Our body is made up of cells, and every cell, especially the brain, needs oxygen and sugars to survive.
Now think of blood as a semi trailer driving around the body through the arteries and veins, being propelled by the pumping heart, delivering oxygen, and sugars to all the cells of the body, especially the brain. The blood does a lot more, but for now let’s keep it simple.
When the brain receives a good supply of oxygen and sugar, it sends an electrical signal to the heart to beat. This is good, we like this.
However, if the heart has plumbing problems, like blocked pipes (arteries, veins) caused by cholesterol, or plaque, or other plumbing issues, and does not pump enough blood to the brain, the electrical signal the brain sends to the heart to beat can become distorted, meaning the heart is now beating in a different rhythm. This is called an arrhythmia.
This can lead to a rhythm called Ventricular Fibrillation (VF). This means the heart is now shaking like a jelly on a plate, and not pumping any blood around the body. This is SCA.
The other arrhythmia that can cause SCA is Ventricular Tachycardia (VT). This is where the heart is beating too fast. Think Tachy (tacho on a car) and cardia (heart) = fast heart.
This means the rate at which the heart squeezes is so fast, it hasn’t got a chance to refill with blood, so it only pumps a small amount of blood, therefore a small amount of oxygen and sugar. This in turn means the brain doesn’t receive enough oxygen to survive. This can also cause SCA
When someone is in Cardiac Arrest, we must start Cardiopulmonary Resuscitation (CPR).
But will CPR bring someone back to life? The short answer is NO!!!
The patient must be defibrillated. CPR buys you time so the patient can be defibrillated.
Think shaking heart = fibrillating heart, so we must defibrillate the heart
The reason we do CPR is because the heart is shaking like that “jelly on a plate” we spoke of, and not pumping. This means the brain, which runs the whole body is not getting any blood, which in turn means, no oxygen is being transported to the brain. The brain is now hypoxic, and dying, and once it dies, it’s all over.
So by doing CPR, we manually push on the heart to squeeze the blood out into the pipes towards the brain. Although not near as effective as a natural heart beat, we are now manually trying to keep the brain alive by pushing on the patient’s chest / heart, propelling oxygenated blood to the brain.
But we can only keep the brain alive with effective CPR for a short period of time. The patient needs to be defibrillated.
Think of defibrillation as rebooting your computer. Your computer is playing up with incorrect electrical activity, so you press a button to momentarily stop your computer, and it starts again in normal mode.
This is exactly the same as defibrillating a heart! The heart is in arrhythmia, either VF, or VT (both incorrect electrical rhythms), we shock the heart, momentarily stopping it, and hopefully it starts again in a correct electrical rhythm; called sinus rhythm.
This is just a brief overview, and by no means covers all the possibilities. But is a simple overview about SCA, and how CPR / defibrillation helps to maybe save a life.