How to read ecg report in india?

This guide demonstrates how to read an ECG using a systematic approach. If you want to put your ECG interpretation knowledge to the test, check out our ECG quiz on the Geeky Medics quiz platform.

Before beginning ECG interpretation, you should check the following details:

If a patient has a regular heart rhythm their heart rate can be calculated using the following method:

If a patient’s heart rhythm is irregular the first method of heart rate calculation doesn’t work (as the R-R interval differs significantly throughout the ECG). As a result, you need to apply a different method:

A patient’s heart rhythm can be regular or irregular.

Irregular rhythms can be either:

Mark out several consecutive R-R intervals on a piece of paper, then move them along the rhythm strip to check if the subsequent intervals are similar.

Cardiac axis describes the overall direction of electrical spread within the heart.

In a healthy individual, the axis should spread from 11 o’clock to 5 o’clock.

To determine the cardiac axis you need to look at leads I, II and III.

Read our cardiac axis guide to learn more.

Typical ECG findings for normal cardiac axis:

Typical ECG findings for right axis deviation:

Typical ECG findings for left axis deviation:

The next step is to look at the P waves and answer the following questions:

1. Are P waves present?

2. If so, is each P wave followed by a QRS complex?

3. Do the P waves look normal? – check duration, direction and shape

4. If  P waves are absent, is there any atrial activity?

The PR interval should be between 120-200 ms (3-5 small squares).

A prolonged PR interval suggests the presence of atrioventricular delay (AV block).

First-degree heart block involves a fixed prolonged PR interval (>200 ms).

Second-degree AV block (type 1) is also known as Mobitz type 1 AV block or Wenckebach phenomenon.

Typical ECG findings in Mobitz type 1 AV block include progressive prolongation of the PR interval until eventually the atrial impulse is not conducted and the QRS complex is dropped.

AV nodal conduction resumes with the next beat and the sequence of progressive PR interval prolongation and the eventual dropping of a QRS complex repeats itself.

Second-degree AV block (type 2) is also known as Mobitz type 2 AV block.

Typical ECG findings in Mobitz type 2 AV block include a consistent PR interval duration with intermittently dropped QRS complexes due to a failure of conduction.

The intermittent dropping of the QRS complexes typically follows a repeating cycle of every 3rd (3:1 block) or 4th (4:1 block) P wave.

Third-degree (complete) AV block occurs when there is no electrical communication between the atria and ventricles due to a complete failure of conduction.

Typical ECG findings include the presence of P waves and QRS complexes that have no association with each other, due to the atria and ventricles functioning independently.

Cardiac function is maintained by a junctional or ventricular pacemaker.

Narrow-complex escape rhythms (QRS complexes of <0.12 seconds duration) originate above the bifurcation of the bundle of His.

Broad-complex escape rhythms (QRS complexes >0.12 seconds duration) originate from below the bifurcation of the bundle of His.

If the PR interval is shortened, this can mean one of two things:

When assessing a QRS complex, you need to pay attention to the following characteristics:

Width can be described as NARROW (< 0.12 seconds) or BROAD (> 0.12 seconds):

Height can be described as either SMALL or TALL:

To assess morphology, you need to assess the individual waves of the QRS complex.

The mythical ‘delta wave‘ is a sign that the ventricles are being activated earlier than normal from a point distant to the AV node. The early activation then spreads slowly across the myocardium causing the slurred upstroke of the QRS complex.

Note – the presence of a delta wave does NOT diagnose Wolff-Parkinson-White syndrome. This requires evidence of tachyarrhythmias AND a delta wave.

Isolated Q waves can be normal.

A pathological Q wave is > 25% the size of the R wave that follows it or > 2mm in height and > 40ms in width.

A single Q wave is not a cause for concern – look for Q waves in an entire territory (e.g. anterior/inferior) for evidence of previous myocardial infarction.

Assess the R wave progression across the chest leads (from small in V1 to large in V6).

The transition from S > R wave to R > S wave should occur in V3 or V4.

Poor progression (i.e. S > R through to leads V5 and V6) can be a sign of previous MI but can also occur in very large people due to poor lead position.

The J point is where the S wave joins the ST segment.

This point can be elevated resulting in the ST segment that follows it also being raised (this is known as “high take-off”).

High take-off (or benign early repolarisation to give its full title) is a normal variant that causes a lot of angst and confusion as it LOOKS like ST elevation.

Key points for assessing the J point segment:

The ST segment is the part of the ECG between the end of the S wave and the start of the T wave.

In a healthy individual, it should be an isoelectric line (neither elevated nor depressed).

Abnormalities of the ST segment should be investigated to rule out pathology.

ST-elevation is significant when it is greater than 1 mm (1 small square) in 2 or more contiguous limb leads or >2mm in 2 or more chest leads.

It is most commonly caused by acute full-thickness myocardial infarction.

ST depression ≥ 0.5 mm in ≥ 2 contiguous leads indicates myocardial ischaemia.

T waves represent repolarisation of the ventricles.

T waves are considered tall if they are:

Tall T waves can be associated with:

T waves are normally inverted in V1 and inversion in lead III is a normal variant.

Inverted T waves in other leads are a nonspecific sign of a wide variety of conditions:

Around 50% of patients admitted to ITU have some evidence of T wave inversion during their stay.

Observe the distribution of the T wave inversion (e.g. anterior/lateral/posterior leads).

You must take this ECG finding and apply it in the context of your patient.

Biphasic T waves have two peaks and can be indicative of ischaemia and hypokalaemia.

Flattened T waves are a non-specific sign, that may represent ischaemia or electrolyte imbalance.

U waves are not a common finding.

The U wave is a > 0.5mm deflection after the T wave best seen in V2 or V3.

These become larger the slower the bradycardia – classically U waves are seen in various electrolyte imbalances, hypothermia and secondary to antiarrhythmic therapy (such as digoxin, procainamide or amiodarone).

You should document your interpretation of the ECG in the patient’s notes (check out our guide to documenting an ECG).

ECG is the abbreviated term for an electrocardiogram. It is used to record the electrical activity of the heart from different angles to both identify and locate pathology. Electrodes are placed on different parts of a patient’s limbs and chest to record the electrical activity.

Check out our ECG quiz on the Geeky Medics quiz platform to put your knowledge to the test.

P waves represent atrial depolarisation.

In healthy individuals, there should be a P wave preceding each QRS complex.

The PR interval begins at the start of the P wave and ends at the beginning of the Q wave.

It represents the time taken for electrical activity to move between the atria and the ventricles.

The QRS complex represents depolarisation of the ventricles.

It appears as three closely related waves on the ECG (the Q, R and S wave).

The ST segment starts at the end of the S wave and ends at the beginning of the T wave.

The ST segment is an isoelectric line that represents the time between depolarisation and repolarisation of the ventricles (i.e. ventricular contraction).

The T wave represents ventricular repolarisation.

It appears as a small wave after the QRS complex.

The RR interval begins at the peak of one R wave and ends at the peak of the next R wave.

It represents the time between two QRS complexes.

The QT interval begins at the start of the QRS complex and finishes at the end of the T wave.

It represents the time taken for the ventricles to depolarise and then repolarise.

The paper used to record ECGs is standardised across most hospitals and has the following characteristics:

It is important to understand the difference between an ECG electrode and an ECG lead.

An ECG electrode is a conductive pad that is attached to the skin to record electrical activity.

An ECG lead is a graphical representation of the heart’s electrical activity which is calculated by analysing data from several ECG electrodes.

A 12-lead ECG records 12 leads, producing 12 separate graphs on a piece of ECG paper.

Only 10 physical electrodes are attached to the patient, to generate the 12 leads.

An ECG electrode is a conductive pad that is attached to the skin to record electrical activity.

The data gathered from these electrodes allows the 12 leads of the ECG to be calculated (e.g. lead I is calculated using data from the electrodes on both the right and left arm).

The electrodes used to generate a 12 lead ECG are described below.

There are six chest electrodes:

There are four limb electrodes:

An ECG lead is a graphical representation of the heart’s electrical activity which is calculated by analysing data from several ECG electrodes.

Each individual lead’s ECG recording is slightly different in shape. This is because each lead is recording the electrical activity of the heart from a different direction (a.k.a viewpoint).

When the electrical activity within the heart travels towards a lead you get a positive deflection.

When the electrical activity within the heart travels away from a lead you get a negative deflection.

In reality, electrical activity in the heart flows in many directions simultaneously.

Each deflection (a.k.a. wave) on the ECG represents the average direction of electrical travel (which is calculated using mathematical formulae by the ECG machine).

The height of the deflection represents the amount of electrical activity flowing in that direction (i.e. the higher the deflection, the greater the amount of electrical activity flowing towards the lead).

The lead with the most positive deflection is most aligned with the direction the heart’s electrical activity is travelling.

If the R wave is greater than the S wave it suggests depolarisation is moving towards that lead.

If the S wave is greater than the R waves it suggests depolarisation is moving away from that lead.

If the R and S waves are of equal size it means depolarisation is travelling at exactly 90° to that lead.

It’s important to understand which leads represent which anatomical territory of the heart, as this allows you to localise pathology to a particular heart region.

For example, if there is ST elevation in leads V3 and V4 it suggests an anterior myocardial infarction (MI). You can then combine this with some anatomical knowledge of the heart’s blood supply, to allow you to work out which artery is likely to be affected (e.g. left anterior descending artery).

In healthy individuals, the electrical activity of the heart begins at the sinoatrial node then spreads to the atrioventricular (AV) node. It then spreads down the bundle of His and then Purkinje fibres to cause ventricular contraction.

Whenever the direction of electrical activity moves towards a lead, a positive deflection is produced.

Whenever the direction of electrical activity moves away from a lead a negative deflection is produced.

The cardiac axis gives us an idea of the overall direction of electrical activity.

In healthy individuals, you would expect the cardiac axis to lie between -30°and +90º. The overall direction of electrical activity is therefore towards leads I, II and III (the yellow arrow below). As a result, you see a positive deflection in all these leads, with lead II showing the most positive deflection as it is the most closely aligned to the overall direction of electrical spread. You would expect to see the most negative deflection in aVR. This is due to aVR providing a viewpoint of the heart from the opposite direction.

Right axis deviation (RAD) involves the direction of depolarisation being distorted to the right (between +90º and +180º).

The most common cause of RAD is right ventricular hypertrophy. Extra right ventricular tissue results in a stronger electrical signal being generated by the right side of the heart. This causes the deflection in lead I to become negative and the deflection in lead aVF/III to be more positive.

RAD is commonly associated with conditions such as pulmonary hypertension, as they cause right ventricular hypertrophy. RAD can, however, be a normal finding in very tall individuals.

Left axis deviation (LAD) involves the direction of depolarisation being distorted to the left (between -30° and -90°). This results in the deflection of lead III becoming negative (this is only considered significant if the deflection of lead II also becomes negative). LAD is usually caused by conduction abnormalities.

We have several other articles relevant to ECGs:

Consultant Interventional Cardiologist

• Each small square represents 0.04 seconds.
• Each large square represents 0.2 seconds.
• 5 large squares = 1 second.
• 300 large squares = 1 minute.