If you are a medical student, paramedic or a doctor, the Electrocardiogram (ECG) is one of the most fascinating and often misunderstood tool in modern medicine. At first glance, an ECG seems like a squiggly lines on a paper. It is a simple yet comprehensive test that can reveal a ton of information about the heart and is useful in detecting a heart attack or arrhythmias.
In this crash course we will break down how to read an ECG like a pro without any medical degree. All you need is curiosity and willingness to learn. At the end of this blog you will have the skills to recognize common patterns, spot warning signs and understand what your heart might be trying to tell you.
What is ECG?
An Electrocardiogram records the electrical activity of heart over time. This electric activity is recorded with the help of electrodes placed on the skin at different locations. Each time the heart beat it triggers an electrical impulse and the electrocardiogram captures these impulses as waves.
Doctors use this test to assess heart rhythm and rate, structural abnormalities, ischemia (lack of blood flow), signs of past or present heart attacks, electrolyte imbalances and drug effects.
According to the American Heart Association, Electrocardiograms are the most common cardiac tests performed. Millions are conducted every year across hospitals, clinics and emergency rooms.
What Does The ECG Waves Mean?
I will explain the basics in a very simplified way. Each and every ECG consists of five main parts:
P wave: Atrial depolarization (electrical activity in the atria)
QRS complex: Ventricular depolarization (electrical activity in the ventricles)
T wave: Ventricular repolarization (resetting of the ventricles)
PR interval: Time between atrial and ventricular activity
ST segment: Important for identifying ischemia or infarction.
ECG shows the pattern of heart electrical activity. Any out syncing from the normal rhythm will suggest abnormality in heart.
How To Read ECG:
There is a six step method to read an ECG that is foolproof and covers all the aspects. Step by step explanation is given below:
1. Check the Rate:
In order to check the heart rate, whether it’s normal, low or high you need to count the number of QRS complexes in a 10 second strip. Now multiply the value by 6.
The normal heart rate is between 60 to 100 beats per minute. If the heartrate is less than 60 bpm it is called bradycardia and if the heart rate is more than 100 bpm it is called tachycardia.
2. Asses the Rhythm:
Is the rhythm regular or irregular? You can use clippers to measure the distance between R waves. Heart problems like atrial fibrillation or heart blocks are seen as irregular rhythms on ECG.
3. Look at The P Wave:
You can look at points like, is there a p wave before every QRS complex? Are the p waves upright in lead ll and aVF?. If the p wave is abnormal it suggests atrial enlargement or ectopic beats.
4. Measure PR Interval:
The normal PR interval is 120 to 200 ms (about 3 to 5 small squares). Prolonged PR interval is suggestive of 1st degree AV block. Short PR indicates Wolff-Parkinson-White syndrome.
5. Examine the QRS complex:
In the ECG of a normal healthy patient the QRS complex occupy 2 small sqaures (less than 120 ms). If the QRS complex is wide, it suggest bundle branch block, ventricular rhythm or hyperkalemia.
6. Analyze the ST Segment and T Waves:
If the ST segment of an ECG is elevated it arises the suspension of Myocardial Infarction (Heart Attack). ST depression is suggestive of Ischemia of the heart. Inverted T waves may indicate electrolyte imbalance, ischemia or drug effects.
Common Patterns in ECG:
1. Atrial Fibrillation (AFib):
Whenever the atrial chambers of the heart beats irregularly you will not see clear p waves in ECG. The rhythm will be irregular. People with Atrial fibrillation are at risk of stroke and heart failure. Patients usually present with the complaint of palpitations. Seen in older people with uncontrolled high blood pressure.
2. Myocardial Infarction (MI or Heart Attack):
Heart supplies blood to every organ of the body but did you know, heart also needs blood for its proper functioning? Heart is supplied with many arteries. If these vessels are blocked the blood flow to heart will be compromised leading to a heart attack. In an ECG you will notice ST elevation in more than two contiguous leads. T wave will be inverted or you will see pathological Q waves. Make sure to use STEMI criteria for diagnosing heart attacks.
3. Bundle Branch Block:
Bundle branches are specialized muscle fibers capable of transmitting electrical impulses needed for the contraction of ventricles. If the impulses are blocked partially or completely, you will see a wide QRS complex with a specific pattern called RSR’ in V1 or V6.
Now let’s practice some scenarios to help you apply the knowledge you just learned.
Scenario 1:
A 24 year old women faints suddenly during a lecture. She looks pale and wake up quickly after fainting. She went to her doctor and did an ECG. The ECG reports showed that her heart rate is 48 beats per minute with normal rhythm. PR interval is 220 ms and QRS complex appears normal? What could be the possible diagnosis?
There is no abnormality in rhythm, P wave, PR interval, QRS complex or ST segment. The only problem in her ECG is bradycardia that lead to fainting. So not every fainting is dangerous, heart rate can drop below the normal levels even in healthy individuals especially athletes.
Scenario 2:
A 58 year old diabetic man comes to the OPD with a chief complaint of severe chest pain. He is also hypertensive. His ECG findings shows ST elevation in Lead ll, lll, aVF and reciprocal changes in l and aVL. What could be the possible diagnosis?
As mentioned above ST elevation is suggestive of Myocardial Infarction (STEMI). The patient is having a heart attack. If you are a pro and have past experience with ECGs you will also be able to tell where the MI is happening. In this scenario from the rest of the information I can say it with confidence that the inferior wall of the heart is involved
Scenario 3:
A 35 year old man presented to the OPD with complaint of palpitation and light headedness after consuming energy drinks. His ECG reports revealed heart rate of 180 bpm and a very narrow QRS complex. P wave is not visible with a regular rhythm. What is the probable diagnosis?
A fast yet regular rhythm is suggestive of Supraventricular Tachycardia (SVT). Such a patient can be treated either with vagal maneuvers or medications like adenosine.
Myths About ECG:
Myth 1:
Only cardiologists can interpret ECG; It is true that no one can interpret an ECG like a cardiologists but it does not mean that only cardiologists can interpret it. Anyone including nurses, EMTs and even patients can, if they know the basics of ECG and the 6 steps method I just described.
Myth 2:
A normal ECG means your heart is fine; ECG shows the electrical activity of your heart. It fails to give us any idea about structural problems of heart. Many serious valves disease can be reported with a normal ECG.
Researches:
A study was conducted in 2019, that got publish in the BMJ Open found that early ECG interpretation in emergency settings reduces time required from treatment of STEMI patients, significantly improves the outcomes.
According to the European Society of Cardiology (ESC), ECGs are essential in risk stratification for arrhythmias and sudden cardiac death.
Conclusion:
ECG is no doubt one of the most important test advised in cardiac centers. It is also the most common heart test performed that shows the electrical activity of heart. Reading an ECG for the first time might seem like a difficult thing to do, but just with focus and a little practice you can read an ECG like a pro. You don’t need medical degrees or years of experience you just need to know the basics and you are good to go.
Anyone working in an emergency department or cardiac centers should master this worthwhile skill. Reading it becomes easier if you start using the 6-step method. This way you won’t miss anything and will timely and accurately recognize life threatening patterns of diseases like Myocardial Infarction and Atrial Fibrillation. Your heart has a story to tell and now you know how to read it. If you liked this blog and want to know more about the human body go to my website Medrizz.com.
References:
• European Society of Cardiology Guidelines, 2022
• BMJ Open. 2019;9(5):e028290.
• ECGWaves.com, Life in the Fast Lane ECG Library
FAQs:
What is an ECG and why is it important?
An Electrocardiogram (ECG or EKG) is a test that records the electrical activity of your heart. It’s used to assess heart rhythm, detect heart attacks, identify abnormal rhythms (arrhythmias), and evaluate other heart-related conditions. It’s one of the most common and essential tools in medicine.
What is a normal heart rate on an ECG?
A normal heart rate is between 60–100 beats per minute. Below 60 is bradycardia and above 100 is tachycardia. You can estimate the rate by counting QRS complexes in 10 seconds and multiplying by 6.
What should I look for to identify a heart attack on ECG?
Look for ST segment elevation in at least two contiguous leads. This suggests ST-Elevation Myocardial Infarction (STEMI). Also check for inverted T waves or pathological Q waves depending on the stage of infarction.