In the last two posts, I discussed vasovagal syncope and adrenal insufficiency. In this post, we move on to a more complex topic, Ischemic heart disease.
Ischemia is the condition in which a tissue such as brain or muscle is subjected to hypoxia or low oxygen because of an obstruction of the blood supply.
Ischemic Heart Disease include Stable Angina, Unstable Angina, Prinzmetal Angina and Myocardial Infarction.
So lets get on with the discussion.
Introduction
In this article, we have already established that blood is the transport medium of the body.
Blood is responsible for the supply of oxygen to different part of the body.
Hence, ischemia leads to hypoxia (reduction of oxygen supply) of a tissue.
Ischemic Heart Disease, as the name suggests, is the reduction of blood supply to heart tissue leading to hypoxia (oxygen deficiency), leading to chest pain. (We will go in details of this in some time)
Before diving into the details of the Ischemic Heart Disease, we should first know how our heart functions.
Back to the Basics
Human heart is a muscular organ. Its function is to pump blood to various tissue and organs of the body.
Through the blood, our heart pumps the necessary nutrients and oxygen to those tissues and organs. Oxygen and these nutrients are required for the tissues to stay alive and function properly.
The human heart functions throughout our lifespan. It pumps almost 200,00,00,000 (200 million) litres of blood in our lifetime.
Heart is mostly made up of muscle (myocardium).
Myocardium is in constant need of an uninterrupted supply of the necessary nutrients and oxygen to function properly.
Oxygen is especially necessary as muscles throughout the body rely on Aerobic metabolism (Glycolysis or Kreb’s cycle, remember Biochemistry??) for production of Adenosine Tri-Phosphate (ATP).
Adenosine Tri-Phosphate is the biological currency of energy in all forms of life.
When oxygen is not available or is in shortage, the muscles shift to Anaerobic (without oxygen) metabolism for a short duration.
So, the heart pumps the oxygenated blood to itself via the Coronary arteries.
When the heart pumps the blood out to various parts of the body, it pumps the blood to its myocardium at the same time via these coronary arteries.
Pathophysiology
If this balance tilts towards demand side due to some reason (either demand increases or supply decreases or both), it will lead to chest pain.
Hence the heart rate and cardiac output is a little towards the lower side or in the normal resting range.
So, the oxygen and energy demand of Myocardium is also on the lower side or in the normal resting range.
In stressful (physical or psychological) condition, our body goes in to the Fight or Flight response and there is a sudden increase in demand for energy.
So, the heart starts to beat at a higher rate and it also contracts more forcefully to increase the cardiac output.
For the heart to maintain this increased cardiac output, its myocardium is in constant need of a high supply of oxygen and energy.
If, for some reason, myocardium does not receive the adequate amount of oxygen, it shifts to anaerobic (without oxygen) metabolism for its energy requirements.
Our cells cannot sustain on anaerobic metabolism alone for a longer duration. This leads to the death of muscle cells (myocytes).
Another thing you need to remember is that by-product of anaerobic metabolism is Lactic acid. (click on the link to watch the video)
If there is oxygen deficiency for a longer duration and myocardium derives its energy from anaerobic metabolism, then there is an accumulation of Lactic acid in the myocardium.
This lactic acid, and not cell death, is responsible for the chest paint that the patient experiences. And this chest pain is called Angina.
Now that you know how the chest pain in Ischemic Heart Disease arises, let us discuss various scenarios where it may arise.
As mentioned earlier, there exists a delicate balance between the demand and supply of oxygen to the myocardium.
In a normal individual, when oxygen demand of myocardium increases, it causes an increase in blood supply leading to an increased oxygen supply.
For example, if we keep continuing weight training at a gym for weeks or months gradually increasing the weight of barbell or dumbell, our body adapts to the increased demands gradually.
This change is not sudden. It is gradual over a period of time.
In some conditions, there is a sudden increase in demand for oxygen to the myocardium and the oxygen supply is not able to keep up with the demand then it leads to chest pain.
These conditions include physically stressful condition like sudden heavyweight workout or a psychologically stressful condition like a dental procedure.
This condition is called Stable Angina or Angina Pectoris.
The pain in this condition is relieved by resting and removal of stress.
Another condition that may lead to chest pain, is when there may or may not be increased oxygen demand but the oxygen supply is hampered.
These conditions include Atherosclerosis, Intraarterial Thrombosis, and Arterial spasm.
Atherosclerosis is cholesterol deposition in the vessel walls leading to narrowing of the Lumen of the coronary arteries.
This atherosclerotic plaque may sometimes cut through the vessel wall and enter the lumen of the artery.
This leads to an accumulation of platelets on this plaque and clot formation. In Intra-Arterial Thrombosis, a clot may form even in the absence of plaque.
This clot will occlude the lumen of the coronary artery leading to partial or complete blockage of blood supply to a portion of the myocardium supplied by that artery.
When there is a narrow lumen because of Atherosclerosis or partial blockade by a clot, the patient might experience chest pain even on slight stress or physical activity.
The pain does not go away even after resting and removing the stress. The pain stays for a longer duration as compared to Stable Angina.
This condition is called as Unstable Angina.
If complete blockade persists for a longer duration, it leads to muscle cell death (necrosis).
This condition that leads to death of muscle tissue is called as Myocardial Infarction.
Infarction is tissue death due to the inadequate blood supply to the affected area.
In some patients, the artery walls go into spasm (vasospasm) spontaneously.
When this happens, it leads to hampering of blood supply to a portion of the myocardium supplied by that artery.
This condition is called as Prinzmetal Angina or Variant Angina.
It can occur even when the patient is at rest.
Pain in Angina Pectoris and Prinzmetal Angina is relieved by Oral Nitroglycerin.
In contrast to this, pain in Unstable Angina and Myocardial Infarction is not relieved by the use of Oral Nitroglycerin.
So now you know, how Angina and Myocardial Infarction are different from each other.
In angina, there is no blockade of the artery and no tissue death occurs.
In Myocardial Infarction, there is a blockade of the artery and tissue death occurs.
Now that you know what Angina Pectoris and Myocardial Infarction are, I will talk about how these conditions affect dental treatment in the next post.