I hope I am not patronising anyone, but I for one never used to know that there was a difference between a heart attack and a cardiac arrest so I just wanted to do a quick blog post to clear it up because I would like to think I was not alone in being confused.
One important thing to mention before the explanations is that a heart attack is the leading cause of cardiac arrest.
|Chaotic Ventricular Activity Seen in VF|
The consequences of a cardiac arrest are immediate with loss of consciousness, respiratory arrest (erratic or no breathing) and permanent neurological damage setting in after just 4 minutes. If there is no effort to resuscitate the patient (CPR/Defibrillation) pressure in the arteries and veins equalizes before circulatory standstill and death occur.
To Treat Cardiac Arrest
|Image Credit http://www.ruralgp.com/|
Circulatory support through chest compressions (CPR) helps circulate blood around the body. When you push down on the chest you are ‘squashing’ the heart and forcing its contents (blood) out around the body. You are mimicking a heart beat – though it is less efficient it can hold off the organ damage until further medical assistance is available.
Further medical assistance involves External Cardiac Defibrillation and reversal of the initial cause of the cardiac arrest- for example if a heart attack has occurred clearing the obstructed artery.
Heart Attack (Myocardial Infarction) and Angina
Like all organs and muscles the heart has its own blood supply, the larger of these vessels are called the Coronary Arteries. Over time (depending on diet, lifestyle and genetics) plaque called atheroma builds up in these arteries – a few examples of a range of plaque build up is shown in the picture below.
|Image Credit http://www.cvtsa.com/|
When a partial blockage (like the ones shown above) are flow limiting this can cause angina. By flow limiting we mean that the narrowing of the artery, caused by the atheroma, is significant enough that it hampers the supply of blood to the muscle (heart). When a muscle has insufficient blood supply this can cause cramp. Essentially angina is a cramp of the heart caused by inadequate blood supply.
Imagine that the heart is a city with one big 4 lane road that runs into it. Over the years and due to poor council budgeting, the main road has started to crumble at the sides and pot holes are every where. Essentially the road is now down to just one lane it has a 75% blockage. Every year the city holds a music festival (exercise) and 1000’s of people try to enter the city on the same weekend. Sufficient traffic can no longer get in to the city when the city needs it most! The music festival is a complete failure with bands and fans stuck in a huge slow moving traffic jam.
When the demand for blood is at its maximum, this is when narrowed arteries can restrict blood flow – this simple analogy explains why angina most commonly presents itself during exertion/exercise or music festivals.
A heart attack or myocardial infarction occurs when one of these blood vessels blocks completely. The most common reasons for this is a total build up of plaque blocking the artery and not just restricting flow or a rupture of the plaque that causes a clot (scab) that blocks the artery. When the artery is totally blocked, no blood reaches the heart muscle that is downstream to the blockage. If the blood supply is not returned then that area of the muscle is permanently damaged.
|Image Credit http://heart.stonybrookmedicine.edu/|
This helps to explain how some heart attacks can be major and how some can be minor. If it is a blood vessel responsible for a huge part of the cardiac tissue that is blocked it will be much more serious than if one of the smaller end vessels was blocked.
Treatment for narrowing includes medications, stents and bypass surgery which I will explain at a later date. In Heart Attacks stents, angioplasty or more invasive surgery can be used to regain blood supply to the tissue.
I hope this has explained the difference between Cardiac Arrest and a Heart Attack.
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