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Myth #1

The heart stops beating when a heart attack strikes. 

False! During a heart attack, the heart does not always stop beating. But the blood supply to the heart, through coronary arteries (blood vessels that supply oxygen to heart muscles; read more here), is severely compromised because of the sudden blockage. The rapid loss of oxygen supply to the heart muscle, because of that blockage, is what causes chest pain. The heart attack is therefore a problem of blood supply to the heart.

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Image 1. Normal heart vs Heart during a heart attack. Blood supply to the heart is severely compromised during a heart attack, represented by the incomplete red arrows. I

If the blockage is in a major coronary artery (read more here), and if the blockage is not re-opened quickly enough, then the heart may lose its capability to function and stop beating. When the heart stops beating, it is a condition known as cardiac arrest. A cardiac arrest can also sometimes occur due to an irregular heart rhythm, instead of blocked coronary arteries. When the heart stops beating, blood is no longer effectively pumped to the rest of the body. This results in death unless CPR and the defibrillator are used quickly and successfully. Cardiac arrest is an electrical problem.

What causes a heart attack?

 

Obstruction of blood flow in coronary arteries (and also other arteries) is most commonly caused by atherosclerosis, which is the buildup of substances (i.e. a plaque made up of fat, cholesterol, etc) along the arterial walls. A sudden heart attack occurs when the plaque ruptures, and a clot builds up rapidly inside the narrow space of the vessel lumen (if we think of vessels as a hose, the lumen is where water flows through), and the heart is unable to get its oxygen-rich blood supply.

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Image 2. Atherosclerosis. 

Often, atherosclerotic plaques (or buildup along arterial walls) are also built up gradually over long periods of time of months and years. When plaques cause sufficient narrowing themselves, this also causes chest pain, but this form of chest pain usually occurs only when the person exerts himself/herself, and gets better when the person stops to rest. The chest pain that occurs on exertion is called ‘angina’, while the sudden (acute) chest pain is called a “myocardial infarction”. Myocardial infarction is also known as a form of “Acute Coronary Syndromes” (an umbrella term for coronary artery diseases that are associated with sudden plaque rapture). Myocardial infarction and acute coronary syndromes are what is commonly known as heart attacks.

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Image 3. Blood flow is blocked during a heart attack. 

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Image 4. Scar tissue forms after a heat attack. 

What happens during a heart attack?

 

Blood flow to the heart through the coronary arteries is totally blocked. Nutrients and oxygen flow to the heart stop, resulting in serious damage to the heart muscle. The extent of damage is dependent on many factors including the size of heart muscle whose blood supply was cut, how long the stop in blood flow was, and how quickly the blockage is re-opened.

 

What happens after a heart attack?

 

Complications might arise. A heart attack could result in irregular heartbeats which could be followed by a cardiac arrest. A heart attack can be massive so that inadequate functioning muscle is left for the pump to work. If there are no complications, and the damage is not lethal, the damaged heart muscle will start to heal by forming scar tissues. Unlike heart muscle tissues, scar tissues cannot contract and hence cannot help the heart with pumping blood. So the heart function starts to go downhill because it is working only on a reduced portion of functioning heart muscle.

As you age, damage to your heart accumulates. This is because of accumulated damage from small heart attacks, or other conditions such as hypertension or diabetes, whether you know it or not (See Myth #3: No symptoms mean no heart disease). This is why the heart gets weaker and stiffer with age. An ageing heart also has an accumulation of buildup along the arteries, and these also cause arteries to become stiffer. Over the decades, partially blocked blood flow, and stiffer arteries also cause heart muscles to suffer damage. Since the heart is already weakened, a heart attack is more deadly in the elderly. 

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Image 5. Ageing heart. .

Written by: Kellie Wong

References

  • North, B. J., & Sinclair, D. A. (2012). The intersection between ageing and cardiovascular disease. Circulation research, 110(8), 1097-1108. 

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  • Saleh, M., & Ambrose, J. A. (2018). Understanding myocardial infarction. F1000Research, 7. 

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