Tag Archives: defibrillator

Let’s straighten a few things out

While perusing various media outlets looking for stories that may be of interest I’ve noticed a few wild inaccuracies that I desperately want to correct.  Some of these examples aren’t really appropriate to critique each article but as concepts I’m happy to correct as you’ll see further down the page.  However if the media can’t report  basic things correctly how can we have confidence in their ability to report larger issues well?

If you’re a medical professional, please be kind.  I’ve tried to keep things as simple as possible and remove as much medical jargon as I can – this may have led to a little over simplification in places but is necessary.

The first thing I’ve noticed is that some papers think that the terms ‘cardiac arrest’ and ‘heart attack’ are interchangeable.  This is blatantly incorrect.  

A heart attack is where one of the arteries supplying the muscle of the heart becomes blocked.  This blockage is when a plaque breaks off from fatty deposits lining the blood vessels and then blocks smaller vessels further along.  Depending on where the blockage is will determine how much heart muscle is damaged.  If sufficient damage is caused then cardiac arrest will follow, conversely if the blockage is small enough then the patient may not even be away that damage has occurred.  

Cardiac arrest is where the heart ceases beating entirely or beats in such an erratic way as to prevent blood from being pumped around the body.  

As you can now see these two terms are clearly not the same thing.  While a heart attack can lead to cardiac arrest not every one will, additionally not every cardiac arrest is caused by a heart attack – a cardiac arrest can be reversible which is why it’s so important to start CPR as soon as a cardiac arrest is evident.  The reversible causes of cardiac arrest are a lack of oxygen, a significant loss of blood, hypothermia, extreme low blood sugar and issues with salts and minerals in the blood.  Additional reversible causes are collapsed lungs, fluid around the heart, some poisons and blood clots that have blocked blood flow to vital organs.  This doesn’t mean that every case of these is absolutely reversible, in some cases the damage is too great too quickly or because of the distances involved it just takes too long to get the patient to the help required by which point it is too late and the patient unfortunately dies.

Obviously not every cardiac arrest is reversible, I’m sure you don’t need me to run through that particular list.

Talking about cardiac arrest leads me nicely onto my next topic, defibrillators.

Here’s something that will suprise an awful lot of people, a defibrillator does not restart a heart, it stops it.  Before I get rotten tomatoes thrown at me, here’s the explanation, starting with some basic physiology.

As I’m sure you’re aware the heart pumps blood to the lungs so that it can pick up oxygen, once the blood is oxygen rich it returns to the heart so that it can be pumped to the body so that this oxygen can be used by the body.  To do this the heart needs to beat in a very organised way and in the human four chambered heart the top two chambers beat first then the bottom two beat.  The top two chambers job is essentially to properly fill the bottom two chambers and it’s the bottom chambers that push the blood to either the lungs or to the rest of the body.  Because of an inbuilt electrical system in the heart this process, when working properly, follows a nice steady rhythm and this gives you the nice regular trace you see on an ECG.  Should the inbuilt electrical system of the heart fail then what can happen (not every time, depends on the problem) is that each cell starts to beat independently of each other.  This process is called fibrillation and if it effects the bottom two chambers of the heart then the heart will no longer pump blood around the body.  It is possible to attempt to reset the heart into a normal rhythm by passing electricity across the heart with a defibrillator.  The hope is that by stopping the heart it will allow the normal electrical system to regain control and for a normal heartbeat to resume.

There is another rhythm that can be successfully shocked called ventricular tachycardia, while a different disease process it can also be shocked – for the purposes of using a defibrillator they’re treated in the same way.

As you can see there are only two heart rhythms that can be shocked with a defibrillator, this means that when someone is ‘flat lining‘ there is already no electrical activity in the heart, so trying to stop the heart with a defibrillator has no benefit and no shock will be given.  There is another heart rhythm called ‘pulseless electrical activity‘ this is where essentially the electrical system is already working properly but for whatever reason the muscle of the heart isn’t responding.  It’s common sense to not pass electricity across this rhythm as the electrical system is already working so stopping that will bring no benefit to the patient.

The final inaccuracy I want to work on today is as follows, I see time and again various articles where the reporter triumphantly reports that a person ‘died of a cardiac arrest’.  Everyone dies of a cardiac arrest, it’s what caused the arrest that needs to be explained: merely stating a person died of a cardiac arrest is like saying your car stopped because it broke down rather than saying the alternator broke, it ran out of fuel or an oil leak caused the engine to seize.

I think that’s all the pedantry anyone can take for today.  As and when other things annoy me there may be more ‘media corrections’ coming out.