Hey Steemers, I'm back with my very first blogpost in Cardiology. I'm going to write about the infamous and yet a daunting cardiovascular disease, the heart attack. The title of this blog post is taken from the chorus of a song by the distinguished Demi Lovato. The song projects her desires for not wanting to fall in love again and if she does, she might get a heart attack. Well, heart breaks are painful. True enough. I've experienced it once and I don't wish to go through the miserable process again. However I'm not going to discuss about relationship tips or etc because I ain't a love doc, unfortunately. Hahaha. Okay, enough with the unrelated jokes. Let's get back to business.
How does Heart Attack happens?
Heart Attack occurs when the blood flow that brings the essential oxygen supply to the heart is severely reduced or stopped, a condition which is medically termed as “ischaemia”. Prolonged ischaemia will lead to a condition known as infarction. Infarction is the word to describe the death of any organ cells. Myocardial is the heart muscles and thus, heart attack is called as Myocardial Infarction.
There are many great arteries that supplies the heart and the main two arteries are the right and left coronary arteries which then terminate to many other branches that help to supply the whole heart. The coronary arteries or its branches might be clogged by fats, cholesterols, or plaques. The process is called as the atherosclerosis. These substances might get itself detached from the vessels and blood clots will form. The blood clots might totally clog up the artery, which will then lead to the ischaemia of the myocardial cells.
There are several terms to describe heart attacks, namely:
- STEMI – ST-Elevation Myocardial Infarction
- NSTEMI – Non ST-Elevation Myocardial Infarction
- Unstable Angina
These terms or conditions are slightly different to each other and placed to one big umbrella, which is the acute coronary syndrome (ACS).
What are the symptoms of heart attack?
- Chest pain/discomfort
- Pain or discomfort in one or both arms, jaw, neck, back or stomach
- Shortness of breath
- Dizzy or lightheadedness
- Nausea
- Sweating
How to diagnose Myocardial Infarction?
The American Heart Association suggested that ACS are diagnosed based on careful medical history, physical examination and two tests, namely the ECG (Electrocardiogram) and blood test for cardiac biomarkers.
Risks that predisposes an individual to get Myocardial Infarction:
- Smoking
- Hypertension
- High Cholesterol Level
- Diabetes
- Sedentary Lifestyle
- Overweight/Obese
- Family history of chest pain, heart diseases, or stroke
To understand how to diagnose heart attack, it is important to know the structures of the heart as well as the blood supply that provides nutrition and oxygen supply to the heart.
The heart is a hollow muscular pump which lies in the chest. The heart has four chambers, namely the right atrium, right ventricle, left atrium and left ventricle.
So how does the blood flow in the heart?
First and foremost, do not get confused between the blood supply of the heart and the blood flow in the heart. The blood supply of the heart is a network of small blood vessels that help to provide oxygen to the heart. The blood flow in the heart is the blood that passes through all the atria and ventricles, pumped to either the lung circulation or to the whole body. Blood from the systemic circulation, arrives to the heart from all the other body parts via the vena cava and enters the right atrium of the heart. Similar to those atria in shopping malls, an atrium is the main entrance of the blood when it reaches the heart. The blood flows to the left ventricle and passes through a valve which permits only one way movement of the blood. The valve that is situated between the right atrium and ventricle is the tricuspid valve. The blood is then pumped via the right ventricle to the pulmonary or lung circulation, passing through the pulmonary valve. After those blood gets re-oxygenated in the lungs, they return to the heart via the pulmonary veins, and enters the left atrium. Similar to the right side, the blood from the left atrium travels to the left ventricle by passing through the biscuspid/mitral valve. The left ventricle is a strong pump as it needs to pump blood to the whole body. The left ventricle pushes the blood to the aorta by passing through the aortic valve.
So now, what are the blood supply of the heart?
So before I explain about the blood supply of the heart, I’ll explain the importance of why do we need to know about it. Remember that I have explained regarding the Myocardial Infarction earlier? Yes, the necrosis or myocardial cell death is usually not extensive, as in it does not commonly involves ALL THE HEART. It could be at the septal, lateral, inferior, anterior, or posterior parts of the heart. By knowing which part of the heart is involved, we can actually point out the most likely culprit artery that has been clogged by the plaque. A blockage in the coronary artery can be quickly identified by performing a coronary angiography .
This procedure involves the introduction of a catheter into the aorta, via the femoral artery. Take note that the femoral artery is located nearby our hips. Quite a long journey to the heart huh. A contrast dye is then injected and an x-ray based imaging is used to visualize the blockage. This procedure is awesome as it is a life-saving one. Why is that so? It is because that the blockage can be treated via coronary angioplasty, which involves the inflation of the balloon within the problematic artery. This balloon interestingly pushes the plaque and restores back the blood loss, relieving the ischaemia. The artery may be supported further via the insertion of stents to enlarge it, making it difficult to be clogged again.
There are two main coronary arteries that supplies the heart muscles. They are named as right and left coronary arteries and arises from the aortic sinuses. Aortic sinuses are mini-openings located in the aorta, specifically behind the aortic valve flaps. The left coronary artery (LCA) initially branches to the left anterior descending artery (LAD) and the left marginal artery (LMA) at the anterior surface of the heart. The remnant parts of the LCA gives off the left circumflex artery (Cx) at the left posterior surface of the heart.
The right coronary artery (RCA) gives off a branch to the right marginal artery (RMA) to supply the anterior heart. The RMA moves along the right and inferior border of the heart, towards the apex. The remaining part of the RCA continues posteriorly and give rise to the posterior interventricular artery (PIv) towards the apex of the heart.
Summary:
Inferior – RCA
Anteroapical – Distal RAD
Anteroseptal – LAD
Anterolateral – Cx
Extensive Anterior – Proximal LCA
True Posterior –** RCA**
ECG
ECG (Electrocardiogram) or EKG, is the method of recording the electrical activity of the heart by using electrodes placed on the chest. These electrodes will detect if there’s any deviation from the usual electricophysiologic pattern during each heartbeat. To understand how ECG works, let’s appreciate how the electrical activities works in the heart.
The pictures above depict the electrodes placement on a person
It begins in the Sinoatrial (SA) Node which is located at the upper wall of right atrium. These are pacemaker cells that could spontaneously generate electrical impulse and spreads to the both atria, resulting in atrial contractions which is also known as the atrial systole. These contractions allow the blood to flow from the atria to the ventricles, both left and right atria simultaneously. After the electrical current spread across the atria, they converge and activate the Atrioventricular (AV) node. This node acts to delay the electrical current to allow more time for the atria to eject its blood to the ventricles.
After the atrial systole ends, the atrioventricular bundles (bundle of His) transmits the electrical current from the AV node to the Purkinje fibres of the ventricles. This bundle divides into right and left bundle branches and transmits the impulse to the right and left Purkinje fibres of each ventricles, respectively. Purkinje fibres are network of specialized cells that are located in the subendocardial surface of the ventricular walls and able to transmit impulse to the ventricles rapidly, causing ventricular contractions or ventricular systole.
How to interpret ECG?
ECG is very complex. It requires a lot of reading and practices. Even for myself as a medical student, I am still not confident in reading a patient’s ECG but practice makes perfect so I’ll try my best to explain about what I understood about the graph that shows the heart’s electrical activity.
There are four types of waves in a typical ECG, namely the P, Q, R, S, and T waves. Depolarization means the membrane potential is more positive than usual and repolarization means the membrane is in its usual negative state. Depolarization basically means that there is higher electrical activity on that area.
- P wave represents atrial depolarization and it is the first positive deflection on the ECG
- Q wave is any negative deflection that precedes an R wave
- R wave is the first upward deflection after the P wave and it represents early ventricular depolarization
- S wave is the first downward deflection after the R wave and may not be present in all ECG leads. In the ECG, there is a large S wave in V1 and progressively becomes smaller in V6.
- T wave is the positive deflection after each Q,R,S complex and represents ventricular repolarization
It starts with the heart rate:
1mm (small square) = 0.04 sec
5mm (big square) = 0.2 sec
To estimate the heart rate, there are two ways to calculate it:
- Rate = 300/number of large squares in each consecutive R wave
- Rate = number of complexes x 6 (this gives the average rate over a ten second period)
Normal range:
- Adult - 60-100 beats/min
- Newborn – 110-150 beats/min
- 2 years – 85-125 beats/min
- 4 years – 75-115 beats/min
Rhythms are best analyzed by looking at a 10 second record of the Lead II. Patterns of QRS complex should be checked whether it is regular or irregular. Narrow complex indicates sinus, atrial or junctional origin and broad complex shows the ventricle origin. P waves could be absent in Atrial Fibrillation. The relationship of P and QRS complex should be checked as it is related to the AV association.
Axis Deviation of the electrical activity can be interpreted via the ECG. There are left and right axis deviations. The deviation shows which side does the wave of depolarization travels to. This is important as it might indicate several diseases such as right/left ventricular hypertrophy, myocardial infarction, and left bundle branch block. There are two effective methods to estimate the axis deviation. The first one is the quadrant method.
The Q, R, S complex of lead I and avF should be seen and determine whether it is Positive, Isoelectric or Negative. First we have to understand the directions of avL, avR, avF, and leads I, II, III. Positive means R wave is > than S, Equiphasic means R=S and Negative means R<S. A positive QRS in lead I puts it at the same direction as lead I. Positive QRS in lead avF puts it at the same direction as lead avF, which is inferiorly. Hence, QRS is lead I is positive and avF is negative, the current might flow more towards the left side of the heart, indicating a possible left axis deviation. If the lead I is negative and avF is positive, it indicated more flow towards the right side of the heart, indicating a possible right axis deviation. To confirm it further, we can use the second method which is by adding another lead to the estimation process, namely lead II. The location of direction of lead II is shown in the picture. The lead II direction is almost parallel with lead avF.
So now if both leads II and avF are negative and lead I is positive, it further supports the fact that the current moves more towards lead I (left side of the heart), indicating a left axis deviation. If both lead II and avF are positive and lead I is negative, it indicates a high possibility of right axis deviation as the picture above shows. If all the values are positive, the axis is normal. Usually left axis deviation indicates a left ventricular hypertrophy (which could be caused by long standing hypertension as the left ventricular needs to become more muscular in order to pump the higher systemic blood pressure) and right axis deviation might indicate a right ventricular hypertrophy (which could be caused by pulmonary circulation hypertension, which is the same concept as the left ventricular hypertrophy)
Okay guys, there is so much to learn in an ECG. There are so many websites that can help you guys to understand ECG better but I’m going to focus specifically on myocardial infarction.
STEMI or the ST-Elevated Myocardial Infarction which is diagnosed by history taking, an elevated ST segment of the ECG and a positive cardiac biomarker result from the blood test. The ST segment is the flat, isoelectric section of the ECG situated between the S wave and the beginning of T wave. It represents the interval between ventricular depolarization and repolarization. There are at least 10 causes of ST elevation apart from Myocardial Infarction including the pericarditis, benign early repolarization, left bundle branch block, left ventricular hypertrophy, and a few others. Since we have understood the blood supply of each part of the heart, the ST elevation on each leads too represents the location of which area is infarcted.
The picture above shows a possible inferior myocardial infarction. Notice the ST elevation of leads II, III and avF?
Septal – V1, V2
Anterior – V3, V4
Lateral – 1 + avL, V5, V6
Inferior – II, III, avF
Posterior – V7-V9
Heart disease is very common, undeniably. About 610, 000 people in the USA die of this condition every year. One of every four deaths in the USA is due to heart disease and 1 death happens in 4 seconds, which is quite an alarming rate. Frightening isn’t it? Cardiovascular diseases claim more lives each year compared to cancers, and the risk factors of CVS diseases are mostly modifiable compared to cancers. Smoking, Diabetes, Hypertension, Hypercholesterolemia, and excessive alcohol ingestions are pretty much avoidable or at least controllable to begin with.
Worldwide, coronary heart disease is the leading cause of death with more than 17.3 million deaths per year in 2013, and the number is expected to grow to a staggering 23.6 million by 2030. All the other co-morbidities that can lead to Heart Attack are mostly modifiable, as in we have the power to avoid it from happening. Healthy lifestyle, healthy lifestyle and healthy lifestyle. With that, thank you for reading :)
References
- The Heart. Teach Me Anatomy. Retrieved April 11, 2018, from http://teachmeanatomy.info/thorax/organs/heart/
- ECG library. Life in the fast lane. Retrieved April 11, 2018, from https://lifeinthefastlane.com/ecg-library/
- Heart Disease facts. Centers for Disease Control and Prevention. Retrieved April 11, 2018, from https://www.cdc.gov/heartdisease/facts.htm
- Survived A Heart Attack? Welcome Home. American Heart Association. Retrieved April 11, 2018, from http://www.heart.org/HEARTORG/Conditions/HeartAttack/Heart-Attack_UCM_001092_SubHomePage.jsp