Camille Borland Medical Physiology Dr. Tolunimi Adedeji

The Heart

Next to the brain, the heart is the most important organ in the human body for life. It is

simply a muscular pump which single-handedly generates the driving force that allows the

blood to circulate throughout the body. The heart pumps blood for many important reasons.

The following are a list of these reasons:

Distribution of substrates and oxygen to the body cells of the tissues, muscles, etc.

Collection of carbon dioxide and waste products from the tissues and carries it to their

sites of excretion.

Distribution of hormones

Aids in the body’s immune response mechanism by delivering antibodies, platelets,

and leukocytes.

All four of these processes are preformed with one main purpose, maintaining

homeostasis. Homeostasis is kept constant in order to achieve a physical and chemical balance

in the body with its external environment. In simpler terms, the heart pumps blood through the

body, the blood aids in maintaining homeostasis, homeostasis’ intentions are to sustain a

balance throughout the body, and this balance will preserve the body’s physiology.

Regardless of how important the heart is, many people develop heart diseases and the

most common of these diseases is one called, Myocardial infarction.

What is myocardial infarction?

Myocardial infarction or MI is the medical term for a type of cardiovascular disease more

commonly known as a “Heart Attack.” A heart attack occurs when there is damage or death to a

part of the heart, causing it to cease its work (beating/pumping blood). A heart attack or cardiac

arrest or myocardial infarction (MI) happens mainly because of two activities:

Myocardial Ischemia

Cardiac Hypoxia

In order for these activities to cause a cardiac arrest they must be prolonged.

Myocardial Ischemia is caused by a clot formation or plaque buildup which occludes the

blood vessel (coronary artery) which supplies the heart with blood. This will result in

coronary vasospasm.

Cardiac Hypoxia occurs by the blockage of oxygen supply to the heart. Without sufficient

oxygen the cell tissues of the heart with die.

Plaque is a hard substance made up of crystallized cholesterol and other cells. When plaque

builds up it will crack or tear the blood vessel. Platelets in the blood with adhere to the ripped

fibers and for a blood clot. This clot can form big enough to completely blood oxygen-rich blood

from flowing to the heart. If the plaque does not cause a crack of tear in the blood vessel, it will

instead just increase in bulk and still end up blocking the coronary artery, leading to not enough

oxygen getting to the heart. In the two instances, cells in the portions of the heart which has

insufficient oxygen supply will die out and a heart attack can and will arise.

Types of Myocardial Infarctions

There are 5 different classifications of myocardial infarctions, type1, type2, type3, type4 (a & b)

and type5. The following table will further explain each type and what it consists of.

Types Description Image

Type 1

Plaque erosion, rupture,

fissuring or dissection causing

ischemia and produces a

spontaneous myocardial

infarction.

Type 2

There is an increase in oxygen

demand or decreased supply

causing Myocardial infarction

secondary to ischemia.

(coronary artery spasm,

coronary embolism, anaemia,

arrhythmias, hypertension, or

hypotension)

Type 3Myocardial ischemia causing

sudden and unexpected

cardiac death with cardiac

arrest. Usually seen with new

ST elevation of indication of

thrombus in the coronary

artery by angioplasty or

autopsy.

Type 4 Interrelated with coronary

angioplasty or stents.

-Type 4a Percutaneous Coronary

Intervention (PCI) causing a

Myocardial Infarction.

-Type 4b

A Myocardial Infarction

caused by an angioplasty with

a stent thrombosis

Type 5

Coronary Artery Bypass

Grafting (CABG-

“CABBAGE”) producing a

Heart Attack.

Almost all cases of MIs are caused by some underlying condition of Coronary Heart

Disease, more specifically (atherosclerosis and angina). Atherosclerosis is the hardening and

narrowing of the blood vessels, in this case, the coronary artery. This will lead to myocardial

ischemia and cardiac hypoxia causing damage of the myocardial tissues. This will result in a lost

of contractility of the cardiac muscle i.e. systolic and diastolic dysfunction.

A heart attack can either be gradually, within minutes but never suddenly. Some symptoms

include:

Chest pain (angina). The pain may radiate into the jaw/teeth, shoulders, arm or

back.

Bad indigestion

Shortness of breath (dypsnea)

Fainting (syncope)

Tightness or squeezing sensation in the center of the chest.

Anxiety, nervousness, cold sweaty skin (diaphoresis), paleness.

Fatigue and weakness

Recent clinical research has concluded that signs and symptoms differ in males and

females. It is less common for women to experience angina but more likely to have weakness,

fatigue and dyspnea (PhD. Klabunde R.E, 2007). Others who have not experienced chest pain

would be non-caucasians, older than 75 and those who have diabetes or suffered from a stroke.

Furthermore, about 50% of patients have warning symptoms but an MI usually occurs in the

early mornings or upon strenuous physical activities.

Once symptoms have been sighted the following test can be done to diagnose a heart attack.

ECG/EKG (Electrocardiogram) – this machine monitors and depict the electrical

activities of the heart on a special graph paper. Whenever a heart attack is inevitable the

ECG will depict abnormally shaped waves patterns. There are two types of MIs when

interpreting the ECG.

o STEMI – ST elevated myocardial infarction. Where the ST segment of

the ECG wave is prominently high. (see image below)

o NSTEMI – non-ST elevated myocardial infarction. Since it cannot be

identified by an elevated ST segment then a blood test should be done

to further clarify heart attack suspicions. (see image below)

Blood test – this test is done by testing for cardiac enzyme proteins or biomakers

(creatine phosphokinase and tropin) which are secreted into the blood by dying heart

muscles. These enzymes will be in high levels in the blood several hours after the onset

of a heart attack. (see graph below)

Depending on the classified

type of MIs, treatment can be administered.

Pain medications:

Nitroglycerin is given either in IV (intravenous line) of under the tongue to relieve the

pain. Also, Morphine can also be administered for pain and anxiety. These will relax the

individual and allows the heart to work less, possibly dilating the arteries of the heart and causes

reduced workload.

Anti-clotting agents:

At the first sight of a heart attack a simple over the counter medication such as aspirin

can be given to the patient. This will help prevent further blood clot from forming and has a great

reduction effect on the mortality of the heart attack. Other anti-clot medications include

intravenous herapin or warfarin (blood thinners). Person who may be allergic to aspirin can take

other anti-clot agents such as colpidogrel or ticlopidine. These can also be taken after having a

heart attack, so as to prevent another incident.

Medical Procedures:

Early catheterization - This is a blood vessel procedure, preformed within the first

hours of being hospitalized, where a cardiac catheterization (a small plastic tube)

is threaded through an artery (usually in the groin region) leading to the coronary

artery. When or if a blockage is found then another procedure called percutaneous

coronary intervention (angioplasty or stenting) is

done. Next a tiny catheter with an inflatable

balloon at the end will progress into the

blocked/narrowed coronary artery. The balloon is

then inflated and causes the narrowed artery to

open up. To prevent narrowing from reoccurring

again, an expandable metal tube (stent) is placed in the artery.

(Balloon Angioplast, 2007)

Coronary artery bypass graft surgery (CABG) - this procedure is done if blockage

cannot be opened using the previous procedure (angioplasty or stent). In the

operation, a blood vessels, which can either be a vein or artery, is taken from the

leg or chest and is used to be detoured around the blocked coronary artery. This

procedure will allow blood flow to be completely diverted from its original path

through the coronary artery and through a unblocked blood vessel.

Clot-bursting agents:

These are alternatives whenever the medical procedures cannot be performed on hand.

Drugs such as thrombolytic or fibrinolytic agents must be given upon arrival at the hospital,

within 30 minutes. Take in consideration that not all patients can be given these types of drug,

including those who has a high blood pressure reading, who have active bleeding, recent trauma

of history of having strokes. Patients with NSTEMIs are prohibited from taken clot-bursting

agents also.

Other drugs:

(Turner M. 2011)

Usually taken after having a heart attack. Beta blockers will be taken by the patient in

order to slow the heart and its demand for oxygen. Such medications include metoprolol,

propranolol or timolol. These also cause the heart to work less and reduce the amount of

damaged tissue which can result from ischemia. This will protect the heart. Also oxygen is

administered to the patient through nasal prong or a face mask will also minimize the amount of

damaged tissue.

Life style:

The patient’s life style should change. This means there should be a close monitoring

blood pressure, blood sugar and blood cholesterol levels. If the patient is a smoker, they will

need to quit smoking. Their diet should be of more fruits, vegetables and whole grain, a more

healthy eating habit, which includes low fat intake. Healthy diet also consist of intake of alcohol,

which should be limited to one a day for women and two a day for men. Exercise should be a

daily routine, at least 30 minutes a day.

Prevention:

Once a heart attack has been evident, it is impossible to reverse its damage, regardless of

treatment. Sequentially, prevention is better than cure. So if it is desired to thwart the occurrence

of a heart attack, measures should be taken in one’s health.

There are many medications that can be taken to prevent an episode of heart attack,

including aspirin, as mentioned before, but in this case it will prevent the happening of blood

clots rather than disable existing ones. It was researched that it reduces the risk of having a heart

attack or a second episode by 15 to 30 %.

Other drugs such as lipid-lowering drugs also reduce the risk of death from a heart attack. This

drug would be taken with people at high risk like those who are obese with diabetes.

After a heart attack, to help prevent the development of heart failure, angiotensin converting

enzyme inhibitors are given to them. This ACE inhibitor can reduce the enlargement of the heart,

thus increasing the chance of survival after a MI incident.

But the most important factor that can lower the threat and prevent a heart attack all together is

an individual’s lifestyle, with the right diet (low-fat, whole grains, fruits and vegetables), limit

alcohol intake to one or two a day (depending on sex), moderate amounts of exercise ( 30

minutes a day for 5 days a week) and smoking cessation. By quitting smoking a person can

reduce his chances of undergoing another MI by 50%. As a side note, smoking cessation also

lowers the risk of many other pathological diseases such as lung failure, and lung diseases.

Heart Attack Complications

Whenever a person has a heart attack scar tissue will be left behind from in the area of the

oxygen deprived heart muscles. Evidently the scar tissue will no longer function and leaves the

heart weaker and less able to meet the circulation needs of the body. The other working parts of

the heart will need to be over worked to compensate, which leads to intolerance to strenuous

exercises and the person will supper from early fatigue and dyspnea on exertion.

Also, because the muscles have lost its contractible strength less blood will be supplied to

the heart making it electrically irritable and cause ventricular fibrillation, which is when

ventricles do not undergo systole and diastole as of normal beating of the heart (abnormal

beating-arrhythmias). An electrical shock should be performed on the patient in order to reset the

heart’s beating rhythm.

The weakening can also cause ventricular aneurysms, where a thin bulge forms on the

damaged muscle. This thin bulge can burst and in that case large blood clots can be formed in the

heart chamber. The aneurysm should be surgically removed before it ruptures.

Epidemiology (risk factors)

Myocardial infarctions are thought to be one of the leading causes of death worldwide. In

2002, 12.6% of worldwide deaths were from ischemia heart disease, with most cases in

developed countries such as the United States of America, with the highest numbers. There are

more than 3 million people with STEMIs and about 4 million with NSTEMI a year worldwide.

Coronary heart disease is the cause of every 1 in 5 deaths in the United States,

approximately 500,000 – 700,000 deaths each year and about 600 cases per every 100,000

person is specifically linked to Myocardial Infarction. The United Stated ranked number 1 with

the most deaths while Belize came in at number 58 with only about 35 deaths per year. This is to

say that more industrialized and developed nations with higher populations have more deaths

caused by MIs than undeveloped or developing nations. Evidently this is so because in

industrialized nations there are a higher number of people with diabetes, hypertension or high

cholesterol (factors contributing to cardiovascular diseases).

Epidemiology of Heart Attacks in Belize

“Diseases of the heart and circulation are the leading causes of death in Belize, with heart

attacks being a major cause of morbidity and mortality” (Crawford J.I, 2011)

Risk factors include: age, sex, hereditary, smoking, diet, ethnicity or previous relaying diseases.

Diet and Obesity

People who have poor eating habits or eating disabilities such as obesity have a higher

rate to experience a myocardial infarction than people who exercise regularly, watch what they

what and how much they eat and.

Poor eating habits would include a diet high in sugar, cholesterol and fats (animal fat) and

not enough whole grain, fruits or vegetables.

Sex and Age

It was found that males with an age range of 35 to 70 are more likely to have a heart

attack episode which for females the age range is higher, 45 to 80. The age for females is higher,

the post-menopausal period of their lives, due to some protection from atherosclerosis possible

because of the estrogen present in females. Approximately about 85% of patients who have a

heart attack have died.

Rate of mortality due to acute myocardial infarction by age and sex 1999

Smoking

As seen in the pie chart to the left, that in the

United States, approximately 126,000 people die

from ischemia heart disease which was

contributed by cigarette smoking. This number

is very close to the amount of people who have

died from Lung disease alone.

Interesting facts:

46% more men are killed than women.

10% of that amount dies from second

hand smoke. So when smoking

consideration for others should be taken.

Ethnicity

According to research done by the

California Department of Public Health it was

found that for some unknown reason

black/African American are the most likely to be

hospitalized for cardiac arrest.

Hereditary

When ever a heart disease such as arteriosclerosis is cause by a genetic fact, there is a

more likely chance that the individual will have a higher chance of incident of cardiac arrest.

Bibliography

Annual Deaths Attributable to Cigarette Smoking – United states, 2000-2004 (2010) Center for

Disease Control and Prevention. Retrieved on October 16, 2011 from website :

http://www.cdc.gov/tobacco/data_statistics/tables/health/attrdeaths/index.htm

Balloon Angioplast.(2007) In Encyclopædia Britannica. Retrieved on October 16, 2011 from

website: http://www.britannica.com/EBchecked/media/95218/Balloon-angioplasty-and-

stent-insertion-In-a-coronary-artery-where

Bolooki H.M et.al (2011) Acute Myocardial Infarction. Cleveland Clinic. Retrieved on October

19, 2011 from website:

http://www.clevelandclinicmeded.com/medicalpubs/diseasemanagement/cardiology/

acute-myocardial-infarction/#s0055

Crawford J.I. (2011) Belizeans to benefits from fully-equip cath lab. Amandala “online”.

Retrieved on October 16, 2011 from website: http://www.amandala.com.bz/index.php?

id=10741

Heart disease, a disabling yet preventable disease (2000) National Academy on an Aging

Society. (pdf) Retrieved on October 19, 2011 from website:

http://www.agingsociety.org/agingsociety/pdf/heart.pdf

PhD. Klabunde R.E (2007) The Pathophysiology of Myocardial Infarction.Cardiovascular

Pharmacology Concepts retrieved on October 15, 2011 from website:

http://www.cvpharmacology.com/clinical%20topics/myocardial%20infarction.htm

Myocardial Infarction (2011). Wikipedia. Retrieved on October 16, 2011 from website:

http://en.wikipedia.org/wiki/Myocardial_infarction

Reynen D.J. et.al (2009) Heart Attack: Who is at risk? California department of Public Health.

Retrieved on October 19, 2011 from website: http://www.ehib.org/page.jsp?

page_key=40#MI_genderdisparities

Turner .M (2011) Cardiology: Bypass surgery (CABG). MD Notes. Free Medical Revision Notes

for Medical Students. Retreieved on October 16, 2011 from website:

http://medicalnotesonline.blogspot.com/2011/01/cardiology-bypass-surgery-cabg.html

M.D. Warnica J.W. (2008) Acute Coronary Syndromes (Heart attack; Myocardial Infarction;

Unstable Angina). The Merck Manual Home Health Handbook. Retrieved on October

15,2011 from website :

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coronary_artery_disease/

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qt=&sc=&alt=

Table of contents

Topic page #

Introduction (The heart and its importance).................................................................. 1

What is Myocardial Infarction.......................................................................................1

Types of MIs.................................................................................................................3

Sign and symptoms........................................................................................................5

Diagnostic test...............................................................................................................5

Treatment.......................................................................................................................6

Prevention......................................................................................................................9

Complication..................................................................................................................10

Epidemiology.................................................................................................................10

Risk Factor.....................................................................................................................11

Bibliography..................................................................................................................13