How to Read an ECG?
An electrocardiogram (EKG or ECG) is a diagnostic tool to assess the heart activity. Interpreting an EKG provides valuable insights into heart health and helps detect abnormalities. Mastering EKG interpretation requires a firm grasp of foundational concepts and practice.
Reading an ECG report seems difficult, but it provides valuable information about heart health. This EKG interpretation will help you understand the basics of reading and analyzing EKGs.
From identifying heart rhythms to recognizing arrhythmias and abnormalities, the guide offers a step-by-step approach to interpreting EKG.
What is an ECG Report?
Our heart relies on electrical impulses to pump blood to our body. An ECG report is a detailed interpretation of these electrical signals. It helps healthcare professionals to diagnose and monitor heart conditions like arrhythmias and heart attacks. ECG also monitors the treatments and tracks changes in a patient's heart health.
Small electrodes are attached to the skin on the chest, arms, and legs. These electrodes detect the electrical signals generated by the heart with each beat and transmit them to a machine that records the impulses. The report represents the electrical activity of the heart on a graph.
A normal ECG report shows a regular rhythm and consistent spacing between the waves and tracings. However, irregular rhythms, changes in a wave shape, or variations in spacing indicate heart problems that require further evaluation.
How to Read an ECG Report?
Reading an ECG test result seems difficult; by dividing the report into smaller sections, it becomes easy to read. Here we learn how to interpret ECG test report in detail:
Checking for patient details
- Review the patient data, which includes the name, date of birth, and day and time of the test. It must be accurate and pertain to the patient being reviewed.
- Then, you should check other details like heart rate, rhythm, and waveform.
- At first, we need to check if the paper speed and amplitude values are normal. A standard EKG has a speed of 25mm/s, and its amplitude is 1 mV by 10 mm.
Assuming the ECG is correctly performed. We start the reading in the following sequence.
Heart Rate
The number of times a heart beats is the heart rate.
- Normal heart rate is 60 to 100 times per minute for a healthy individual.
- Tachycardia: More than 100 beats per minute.
- Bradycardia: Less than 60 beats per minute.
Regular heart rhythm
If the patient has a regular heart rhythm, the heart rate can be calculated in the following way.
Count the large squares present within the one PR interval.
Divide 300 by this number.
Irregular heart rhythm
In irregular heart rhythms above-mentioned may not work as the R-R interval may differ significantly. Here, it is done in the following manner.
We can count the number of complexes on the rhythm strip. Each rhythm strip is 10 seconds long. Multiply the number of complexes by 6. It gives an average number of complexes in one minute.
Heart rhythm
The patient's heart rhythm may be Regular or irregular.
Irregular rhythms can be
- Regularly regular: This has a recurrent pattern of irregularity.
- Irregularly irregular: This is completely disorganized.
Notice several consecutive R-R intervals on the paper. Along the rhythm strip, check if subsequent intervals are similar. Measure R-R intervals to check if rhythms are regular or irregular.
Cardiac axis
The cardiac axis tells us about the direction of electric impulses spread in the heart.
In healthy individuals, the axis should spread from 11 o’clock to 5 o’clock.
Leads I, II, and III show the cardiac axis.
Normal cardiac axis
Lead II shows the most positive deflection compared to leads I and III.
Right axis deviation
- Lead III shows the most positive deflection, and lead I is negative.
- Right axis deviation represents right ventricular hypertrophy.
Left axis deviation
- Lead I show the most positive deflection.
- Leads II and III are negative.
- The left axis deviations are associated with hard conduction abnormalities.
P Waves
The P wave represents the electrical activity of the atria.
The next step is to
- Look for P waves
- If present, the P wave is followed by the QRS complex
- Do they appear normal in duration, direction, and shape
- If absent, is there any atrial activity?
It should be uniform in shape and smooth.
Irregularities in the atria, such as atrial hypertrophy or obstruction, are diagnosed by changed waves.
- A Sawtooth baseline represents flutter waves.
- A chaotic baseline represents fibrillation waves.
- The flat line shows no atrial activity.
PR Interval
The PR interval should be between 120 - 200 ms. It should cover 3 to 5 small squares.
Prolonged PR interval
- It is more than 0.2 seconds.
- A prolonged PR interval is indicative of atrioventricular delay or block.
First-degree heart block AV block
It involves a fixed, prolonged PR interval that is more than 200 ms.
Second-degree heart block
Second-degree heart block, Type1
It is Mobitz Type 1 AV block or the Wenckebach phenomenon. It shows progressive prolongation of PR interval until the atrial impulse does not conduct and the QRS complex gets dropped.
Conduction in the AV node resumes with the next beat, and the sequence of progressive PR Interval is prolonged, causing the dropping of the QRS complex to repeat itself.
Second-degree AV block type 2 or Mobitz type 2 AV block
A consistent PR interval duration with intermittently dropped QRS complexes caused by conduction failure.
The intermittent dropping of the QRS complex follows a repeated cycle of every 3rd (3:1) or 4th (4:1) P Wave.
Third-degree heart block or complete heart block
Whenever there is no electrical communication between atria and ventricles, there is a 3rd degree AV block. It occurs due to complete conduction failure. ECG findings include the presence of P waves and QRS complexes without any association with each other. It happens as both atria and ventricles function independently.
Junctional or ventricular pacemakers maintain cardiac functions. Above the bundle of His bifurcation narrow, complex escape rhythms (QRS complexes of less than 0.12 seconds duration) originate. Below the bundle of His broad, complex escape rhythms (QRS complex is more than 0.12 seconds duration) originate.
Shortened PR interval
It means
- P wave originates close to the AV node as a result, conduction takes less time. The SA node. It is not in a fixed place or the size of Atria is small.
- Atrial impulse. Takes a shortcut. To the ventricle. Instead of conducting slowly across the arterial wall. This accessory pathway forms a Delta wave.
QRS complex
Height, Width, and morphology are the important characteristics we must consider in assessing a QRS complex.
Width
Narrow when it is less than 0.12 seconds or broad if it is more than 0.12 seconds. A narrow QRS complex forms when the impulse is conducted down the bundle of His. And the Purkinje fibers to the ventricles. It is smooth, well organized, synchronized, ventricular depolarization.
A broad QRS complex occurs when there is an abnormal depolarization. For example. Ventricular ectopic in which the impulse spreads down across the myocardium from the focus in the ventricle. An atrial ectopic results in a narrow QRS complex because it would conduct down the normal conduction system of the heart. Bundle branch block results in abroad QRS complex. The impulse reaches the ventricle through the conduction system and spreads across the myocardium to the other ventricles.
Height
Described as small or tall
- Small complexes are less than 5 mm in limb leads or 10 mm in chest leads.
- Tall complexes usually imply Ventricular hypertrophy. However, they are even found. In tall, slim people.
Morphology
To know about the morphology, we need to learn about individual waves in the QRS complex.
Delta wave
Delta wave indicates ventricles are activated earlier than normal from a point far away from a point distant from the AV node. The early activation spreads across the myocardium and is represented as a QRS complex slurred upstroke.
Q wave
Isolated single Q waves can be normal. The presence of Q waves over a widespread region suggests an old myocardial infarction.
A pathological Q wave is usually more than 25% the size of an R wave or greater than 2 mm in height and 40 mm in width.
R and S waves
- Observe R wave progression across chest leads (from small in V1 to large V6).
- S>R wave progression to R>S wave should occur in V3 or V4.
- S>R progression through leads V5 and V6 indicates a previous MI.
J point Segment
It is where the S wave joins the ST segment. The J point can be elevated, showing the ST segment that follows to be raised. It is known as the high take-off (Benign early repolarization).
Key points to assess J point segment
- Benign early repolarization occurs below the age of 50. Over the age of 50, ischemia is more common.
- A raised J point with widespread ST elevation makes ischemia unlikely.
- T waves are also raised (in contrast to ST elevation MI, STEMI when the T wave remains the same size, and the ST segment is raised.
ST segment
- The part of ECG between the end of the S wave and the start of the T wave
- In a healthy individual, it is neither elevated nor depressed.
- Any abnormality in the ST segment should be investigated to rule out pathology.
ST Elevation
It is significant when it is greater than 1mm. or one small square in 2 or more limb leads, or 2 mm. in 2 or more chest leads. It usually occurs in myocardial infarction.
ST Depression
ST depression is more than or equal to 0.5 mm. in more than two or equal to 2 leads. It indicates myocardial ischemia.
T wave
It represents the repolarization of the ventricles.
Tall T waves
- More than 5 mm. in the limb leads
- More than 10 mm. in the chest leads.
They are associated with hyperkalemia and hyperacute STEMI.
Inverted T wave
- T waves are normally inverted in V1.
- Inversion in lead 3 is a normal variant.
Inverted T waves Occur in. The following conditions
- Ischemia
- Bundle branch block (V4-V6 in LBBB and V1- V3 in RBBB)
- Pulmonary embolism.
- Left ventricular hypertrophy
- Hypertrophic cardiomyopathy.
- General illness.
T wave inversion in anterior, lateral, and posterior leads must be observed and correlated clinically.
Biphasic T waves
They have two peaks and indicate schema and hypokalemia.
Flattened T waves
There are non-specific signs that show ischemia or electrolyte imbalance.
U waves
- They are not a common finding.
- A U wave is a more than 0.5 mm deflection after the T wave and is seen in V2 or V3.
- They are large and slow in bradycardia.
- Visible when there is an electrolyte imbalance, hypothermia, or are secondary to anti-arrhythmic therapy
Report Assessment
A normal ECG report
A normal ECG Presents the following characteristics.
- An adult has a heart rate between 60 to 100 beats per minute.
- Heart rhythm is regular. And there are consistent intervals between the R waves.
- A uniform P Wave shows before every PQRS complex.
- A consistent narrow QRS complex.
- A flat ST segment with no deviation from the baseline.
- An upright T wave with consistent shape and duration.
- Intervals like PT and QT intervals are within the normal range.
- A good ECG report shows normal activity of the heart without significant abnormalities.
Understanding abnormal ECG results
- An abnormal ECG may not indicate a serious heart condition, but it certainly does warrant further investigation.
- Abnormal ECG results may range from minor issues to potentially life-threatening conditions.
- Heart attack, heart rhythm disorders, heart valve problems, and congenital heart diseases may be the common causes of some abnormal ECG results.
- An abnormal ECG result always does not mean that your heart is failing. Often, people with abnormal ECG results. Live healthy and active lives with proper care and management. Do not panic; instead, take charge of your heart health and work with your healthcare provider. Create a plan for further testing and treatment if needed.
Some common heart conditions causing ECG abnormalities
- Atrial fibrillation: It is arrhythmia where the upper heart chamber atria beat irregularly and cause blood clots and stroke.
- Bradycardia: It is a slow heart rate. Some medications or conditions, such as hypothyroidism, can cause it.
- Tachycardia: Condition where the heart beats very fast. It causes palpitations, shortness of breath, and chest pain.
- Bundle branch block: It occurs when the electrical signals in the heart travel abnormal pathways which indicates damage to the heart.
- Myocardial infarction: Also called a heart attack. Occurs when the blood flow of the heart is blocked. This results in damage to the heart muscles.
Misconceptions and ECG reports
An ECG is a valuable tool, to assess the condition of your heart. Often, interpreting the results gives birth to certain misconceptions. Some of them are-
- An abnormal ECG always means a serious problem.
- ECG can diagnose all hard problems.
- Only older adults need ECG.
- ECG is painful.
When to consult a doctor?
You can consult a doctor if you experience any of the following.
- Chest pain: Get medical help immediately if you develop it.
- Family history of heart disease: An ECG will help you identify heart disease symptoms and prevent a crisis.
- High blood pressure: Heart strain and heart disease raise blood pressure.
- Shortness of breath: Indicates heart or lung problems. An ECG helps to diagnose it.
- Irregular heartbeat: If you have palpitations or a rapid heart rate.
Conclusion
An ECG interprets the electrical activity of the heart. Only a healthcare provider can accurately interpret ECG. He is the best guide for identifying normal or abnormal variations and for guiding you in matters of your heart health.
