Electrocardiography: Overview, ECG Indications and Contraindications, Preparation (2022)

The initial review of the 12-lead electrocardiogram (ECG) should encompass the following: heart rate and rhythm, P-QRS-T morphology, presence of ST segment, and PR-QRS-QT intervals (see the image below). Each ECG should be thoroughly analyzed ("read") in a systematic fashion to avoid overlooking important abnormalities.The following steps are important to consider:

  1. Rate: Normal versus tachycardia versus bradycardia
  2. Rhythm: Abnormal versus normal sinus
  3. Intervals: PR, QRS, QT
  4. Axis: Normal versus left deviation versus right deviation
  5. Chamber abnormality: Atrial enlargement, ventricular hypertrophy
  6. QRST duration: Q waves, poor R-wave progression, ST-segment depressions/elevations, or T-wave changes

Electrocardiogram waves, intervals, and segments.

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The ECG grid

In the image below, the ECG is recorded on standard paper with large boxes in heavy lines of 0.5 cm on the sides. On the horizontal axis, each large box represents 0.2 seconds at a typical paper speed of 25 mm per second, which is then divided into five smaller boxes that each represent 0.04 seconds. On the vertical axis, the large box consists of five subdivisions, each of which is 1 mm in height. In standard calibration, each 10 mm equals 1 mV. The normal heart rate ranges from 60 to 100 per minute; rates below 60 per minute and, occasionally, lower than 50 per minute are routinely seen in seasoned athletes.

On standard calibration, each large box has sides of 0.5 cm. On the horizontal axis, each large box represents 0.2 seconds, and each smaller box represents 0.04 seconds. On the vertical axis, each small box is 1 mm in height; 10 mm = 1 mV.

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Heart rate

When the cardiac rhythm is regular, the heart rate can be determined by the interval between two successive QRS complexes. On standard paper with the most common tracing settings, the heart rate is calculated by dividing the number of large boxes (5 mm or 0.2 seconds) between two successive QRS complexes into300. For example, if the interval between two QRS complexes is two large boxes, then the rate is 150 beats per minute (bpm) (300 ÷ 2 = 150 bpm). See the following images.

Heart rates associated with each of the large boxes in the following order are 300, 150, 100, 75, 60, 50, 43, 37, 33 beats per minute (bpm).

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Heart rate boxes.

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If the heart rate is irregular, count the number of QRS complexes on the ECG and multiply by 6 to obtain the average heart rate in bpm (the ECG displays a period of 10 seconds; thus, 6 × 10 seconds = 60 seconds [1 minute]).

The P wave

The P wave represents atrial depolarization. The normal P wave morphology is upright in leads I, II, and aVF, but it is inverted in lead aVR. The P wave is typically biphasic in lead V1 (positive-negative), but when the negative terminal component of the P wave exceeds 0.04 seconds in duration (equivalent to one small box), it is abnormal.

Left atrial enlargement should be suspected when the P wave duration is increased; it is associated with being more than one small box deep (>1 mm2) in lead V1 and a bifid P wave in lead II with a duration that is longer than 110 milliseconds. [19] Right atrial enlargement is associated with a peaked P wave taller than 2.5 mm in the inferior leads and more than 1.5 mm tall in leads V1 and V2. [20]

The PR interval

The PR interval incorporates the time from the depolarization of the sinus node to the onset of ventricular depolarization. The measurement starts from the beginning of the P wave to the first part of the QRS complex, with a normal duration between 0.12 to 0.20 seconds. [6]

The QRS complex

The QRS duration represents the time for ventricular depolarization. The duration is normally 0.06 to 0.10 seconds. Q waves are inscribed when the initial QRS vector is directed away from the positive electrode. The R wave is the first positive deflection of the QRS complex; its amplitude varies by age, race, and cardiac pathology, and it should increase across the precordium from leads V1 to V5. The negative deflection after the R wave is the S wave.

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The ST segment

The ST segment is an interval between ventricular depolarization and ventricular repolarization. It is identified as the end of the QRS complex to the beginning of the T wave.

The end of the T wave to the beginning of the P wave is described as the TP segment, which is the zero potential or isoelectric point. The amount of elevation or depression in millimeters is relative to the TP segment.

The J point is located at the junction between the end of the QRS complex and the beginning of the ST segment. J-point elevation is known as an Osborne wave, which represents distortion of the earlierst phase of membrane repolarization, and it is associated with hypothermia.

Myocardial ischemia diagnosed by ECG is an integral part of the acute coronary syndrome (ACS) treatment pathway and allows patient stratification into ST-segment elevation ACS (STE-ACS) and non-ST-segment elevation ACS (NSTE-ACS). [4, 21, 22] ST-segment wave changes may be in association with disease states such as acute ischemia, myocardial injury, pericarditis, and intraventricular conduction delays.

In the absence of left ventricular hypertrophy (LVH) and left bundle branch block (LBBB), new ST-segment elevation in upward convexity are signs of myocardial infarction (typically 60 msec following the J point in two contiguous leads [with cut-off points in leads V2-V3 of ≥0.2 mV in men ≥40 years, ≥0.25 mV in men ˂40 years, or ≥0.15 mV in women, and/or 0.1 mV in other leads for both men and women]). [23] New horizontal or down sloping ST depression that is 0.05 mV or more in two contiguous leads and/or T-wave inversion that is 0.1 mV or more in two contiguous leads, with a prominent R wave or an R/S ratio over 1, are also signs of myocardial infarction.

Coronary spasm may be associated with angina (Prinzmetal) and with transient ST-segment elevation in a coronary artery branch distribution that has the spasm.

Pericarditis is associated withECG manifestations of diffuse upward concave ST-segment elevation with PR depressions.

See the following images.

ST depression.

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ST elevation.

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The QT interval

The QT interval measures the depolarization and repolarizationof the ventricles. QT prolongation is associated with development of ventricular arrhythmias and sudden death. [24] It is commonly caused by various medications or can be a manifestation of an underlying ion channelopathy.

The QT interval is dependent on the heart rate. A faster heart rate leads to a shorterQT interval, whereas a slower heart rate leads to a longer QT interval. A corrected QT interval (QTc) corrects for the variations in heart rate. QTcb is the QT interval divided by the square root of the RR interval in seconds when using the Bazett formula. The normal value of for QTcb in men is 0.44 seconds or less; in women, it is 0.46 seconds or less. [25]

The ECG axis

The QRS axis represents the major vector of ventricular activation, which is the overall direction of electrical activity. The electrical activity in healthy individuals starts at the sinoatrial node and spreads to the atrioventricularnode down the Bundle of His, followed by conduction through the left and right bundle branches,and then to the Purkinje fibers to cause ventricular contraction. A positive deflection is when the direction of the overal electrical activity is toward that lead. Therefore, the cardiac axis may provide the overall direction of electrical activity when the ventricles depolarize. The normal cardiac axis is expected to lie between-30º and 90º, which means the overall direction of electrical activity is towardleads I, II, and III.

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Electrocardiographic axis. Normal axis is between -30º and 90º; left axis deviation (LAD) is between -30º and - 90º; right axis deviation (RAD) is between 90º and 180º; extreme axis deviation (EAD) (left or right) is between -90º and -180º.

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The electrical axis can be estimated from the standard frontal leads. There are shortcut methods to determine the axis.For example, if the QRS complex is upright in both leads I and II, then the axis must fall somewhere between -30º and 90º and the axis is normal.

If the complexes are negative in lead I and positive in lead aVF, then the axis is rightward. If the complexes are positive in lead I but negative in lead II, then the axis is leftward. If the complexes are negative in both leads I and aVF, then the axis is extreme.

The causes of left axis deviation include normal variation, left ventricular hypertrophy, left anterior fascicular block, congenital heart disease with primum atrial septal defect or endocardial cushion defect, ventricular ectopic beats, and preexcitation syndromes. [26]

The causes of right axis deviation include normal variation, right ventricular hypertrophy, left posterior fascicular block, ventricular ectopic beats, preexcitation,and dextrocardia. [26]

R wave progression

The R wave should progress in size across leads V1 to V6. Normally, in lead V1, there is a small R wave with a deep S wave; the R-wave amplitude should increase in size with the transition zone, normally in leads V2 to V4. Poor or late R-wave progression consists of a transition zone in lead V5 or V6, and it can be a sign of a previous anterior myocardial infarction. [27]


What are the indications for an ECG? ›

A health care provider might use an electrocardiogram to determine or detect: Irregular heart rhythms (arrhythmias) If blocked or narrowed arteries in the heart (coronary artery disease) are causing chest pain or a heart attack. Whether you have had a previous heart attack.

What are contraindications for ECG monitoring? ›

There are no absolute contraindications for an electrocardiogram.

What are the 3 types of ECG monitoring? ›

3 Types Of Electrocardiogram Monitoring
  • Holter Monitor. A Holter Monitor is a portable EKG device. ...
  • Cardiac Event Monitor. Like the Holter Monitor, the Cardiac Event Monitor is a portable EKG device. ...
  • Stress Test.
24 Aug 2019

What are the 5 components of an ECG? ›

Components of ECG

Each ECG cycles consists of 5 waves: P, Q, R, S, T corresponding to different phases of the heart activities.

How do you prepare for an ECG? ›

You do not have to restrict what you eat or drink before your ECG, although it is recommended that you not smoke just before the test. You will be asked to remove your jewelry and wear a hospital gown.

What is ECG medical term? ›

A line graph that shows changes in the electrical activity of the heart over time. It is made by an instrument called an electrocardiograph.

How do you measure ECG? ›

Simply identify two consecutive R waves and count the number of large squares between them. By dividing this number into 300 (remember, this number represents 1 minute) we are able to calculate a person's heart rate. Rate = 300 / number of large squares between consecutive R waves.

What are normal ECG results? ›

If the test is normal, it should show that your heart is beating at an even rate of 60 to 100 beats per minute. Many different heart conditions can show up on an ECG, including a fast, slow, or abnormal heart rhythm, a heart defect, coronary artery disease, heart valve disease, or an enlarged heart.

Which type of ECG is best? ›

Resting 12-lead EKG: This type of electrocardiogram is the standard test for measuring your heart's electrical function.

What is a 5 lead ECG? ›

An electrocardiogram (ECG) is a non-invasive method of monitoring the electrophysiology of the heart. Electrodes are placed on the patient's torso, and the electrical activity of the heart is measured from several leads (voltage difference between electrodes). 5-lead monitoring uses five electrodes.

What are the 4 types of waves seen in an ECG? ›

The waves on an ECG include the P wave, Q wave, R wave, S wave, T wave and U wave. Interval: The time between two specific ECG events. The intervals commonly measured on an ECG include the PR interval, QRS interval (also called QRS duration), QT interval and RR interval.

How many ECG leads are there? ›

The 12 ECG leads are therefore divided into two sets: the six extremity leads (three unipolar and three bipolar), which record voltages on the frontal plane of the body, and the six chest (precordial) leads, which record voltages on the horizontal plane.

How do ECG leads work? ›

The electrodes are connected to an ECG machine by lead wires. The electrical activity of the heart is then measured, interpreted, and printed out. No electricity is sent into the body. Natural electrical impulses coordinate contractions of the different parts of the heart to keep blood flowing the way it should.

What are the parts of an ECG? ›

There are three main components to an ECG: the P wave, which represents depolarization of the atria; the QRS complex, which represents depolarization of the ventricles; and the T wave, which represents repolarization of the ventricles.

What is an abnormal ECG? ›

An abnormal ECG can mean many things. Sometimes an ECG abnormality is a normal variation of a heart's rhythm, which does not affect your health. Other times, an abnormal ECG can signal a medical emergency, such as a myocardial infarction /heart attack or a dangerous arrhythmia.

How long is an ECG test? ›

An ECG usually takes between five and ten minutes. You will usually be able to go home straight after the test. An ECG is a quick, safe and painless test. No electricity is put into your body while it's carried out.

When preparing a patient for an ECG leads should be placed? ›

Patient Positioning for 12-Lead ECG Placement

Place patient in supine or Semi-Fowler's position. If both positions are impossible, you can perform ECG with the patient in a more elevated position. With arms lying flat on the side, ask the patient to relax the shoulders and keep the legs uncrossed.

Who invented ECG? ›

Willem Einthoven found the beat and built a machine that could measure the electrical current a heart creates. It weighed 600 pounds. An electrocardiogram — called informally an ECG or EKG — measures the small electric waves that a human heart creates. It's been doing it for more than a century.

Is ECG test painful? ›

It's a test that records the electrical activity of your ticker through small electrode patches that a technician attaches to the skin of your chest, arms, and legs. EKGs are quick, safe, and painless. With this test, your doctor will be able to: Check your heart rhythm.

Where are ECG leads placed? ›

12 Lead ECG Placement Guide
ElectrodePlacement Area
V1Fourth intercostal space to the right of the sternum.
V2Fourth intercostal space to the left of the sternum.
V3Directly between leads V2 and V4.
V4Fifth intercostal space at midclavicular line.
2 more rows
6 Mar 2019

What is 1st degree heart block? ›

First-degree atrioventricular (AV) block is a condition of abnormally slow conduction through the AV node. It is defined by ECG changes that include a PR interval of greater than 0.20 without disruption of atrial to ventricular conduction. This condition is generally asymptomatic and discovered only on routine ECG.

What is a normal QRS? ›

The normal duration (interval) of the QRS complex is between 0.08 and 0.10 seconds — that is, 80 and 100 milliseconds. When the duration is between 0.10 and 0.12 seconds, it is intermediate or slightly prolonged. A QRS duration of greater than 0.12 seconds is considered abnormal.

What is normal and abnormal ECG? ›

The signals with heart rates outside the range of 60–100 beats per minute and QRS durations outside the range of 0.08 sec to 0.12 sec are considered as abnormal signals. The ECG signals with heart rates and QRS durations within the range are considered as normal signals.

What type of electrodes are used in ECG? ›

Leads I, II, III, aVF, aVL and aVR are all derived using three electrodes, which are placed on the right arm, the left arm and the left leg. Given the electrode placements, in relation to the heart, these leads primarily detect electrical activity in the frontal plane.

What equipment is used for an ECG? ›

Electrodes (sensors) Gauze and skin prep solution (as approved by your facility) Razor or clippers and a roll of tape (for hair removal) Skin adhesive and or antiperspirant.

Which ECG lead is most important? ›

The most useful lead is V4R, which is obtained by placing the V4 electrode in the 5th right intercostal space in the mid-clavicular line.

What is heart PR? ›

The PR interval is the time from the beginning of the P wave (atrial depolarization) to the beginning of the QRS complex (ventricular depolarization). The normal PR interval measures 0.12-0.20 seconds (120-200 milliseconds). A prolonged or shortened PR interval can indicate certain disease.

What is a 3 lead ECG? ›

3-lead ECGs are used most often for recording a 24-hour reading. A 24-hour reading is a frequently used tool for the diagnosis of heart problems and is reimbursed as a long-term reading. 3 vertical and 0 horizontal visual axes.

What are 3 reasons a person would get an EKG? ›

8 reasons to get an EKG
  • Get a baseline measurement of heart activity.
  • Determine the cause of chest pain.
  • Diagnose arrhythmias.
  • Evaluate possible heart-related problems, including severe tiredness, shortness of breath, dizziness, or fainting.
  • Diagnose inflammation of the heart or its lining (endocarditis)

Who needs ECG? ›

When are ECGs needed? In some cases, it can be important to get this test. You should probably have an ECG if you have risk factors for an enlarged heart such as high blood pressure or symptoms of heart disease, such as chest pain, shortness of breath, an irregular heartbeat or heavy heartbeats.

Is ECG enough to detect heart problems? ›

An ECG is pretty accurate at diagnosing many types of heart disease, although it doesn't always pick up every heart problem. You may have a perfectly normal ECG, yet still have a heart condition.

Can ECG detect heart problems? ›

An electrocardiogram (ECG) is a medical test that detects cardiac (heart) abnormalities by measuring the electrical activity generated by the heart as it contracts. The machine that records the patient's ECG is called an electrocardiograph.

What is an abnormal ECG? ›

An abnormal ECG can mean many things. Sometimes an ECG abnormality is a normal variation of a heart's rhythm, which does not affect your health. Other times, an abnormal ECG can signal a medical emergency, such as a myocardial infarction /heart attack or a dangerous arrhythmia.

What happens in an ECG? ›

The ECG is a simple test, with 10 electrodes used to record 12 different views of your heart's electrical activity. You don't need to do anything to prepare for it. An electrode is attached to each ankle and wrist with sticky pads and six more are attached to the chest.

What are the different types of heart tests? ›

Also on NHS inform
  • Blood tests.
  • Angiography.
  • CT scan.
  • Echocardiogram.
  • Electrocardiogram (ECG)
  • MRI scan.
  • X-ray.
  • Cardiac catheterisation and coronary angiography.
13 Feb 2020

How do you measure ECG? ›

Simply identify two consecutive R waves and count the number of large squares between them. By dividing this number into 300 (remember, this number represents 1 minute) we are able to calculate a person's heart rate. Rate = 300 / number of large squares between consecutive R waves.

How long is an ECG test? ›

An ECG usually takes between five and ten minutes. You will usually be able to go home straight after the test. An ECG is a quick, safe and painless test. No electricity is put into your body while it's carried out.

Why is ECG used for high blood pressure? ›

Electrocardiogram (ECG or EKG).

This painless noninvasive test records the electrical signals in the heart. This test can help determine whether a heart problem might be causing secondary hypertension. In this test, sensors (electrodes) are attached to the chest and sometimes to the limbs.

Does blood pressure affect ECG? ›

High blood pressure

Other aspects of heart disease may lead to an abnormal EKG. For example, people with high blood pressure are more likely to have an abnormal EKG reading.

What is full form of echo? ›

An echocardiogram (echo) is a test that uses high frequency sound waves (ultrasound) to make pictures of your heart. The test is also called echocardiography or diagnostic cardiac ultrasound.

Can ECG detect stroke? ›

In the present study, the most common ECG abnormalities associated with stroke were T-wave abnormalities, prolonged QTc interval and arrhythmias, which were respectively found in 39.9%, 32.4%, and 27.1% of the stroke patients and 28.9%, 30.7%, and 16.2 of the patients with no primary cardiac disease.

Can ECG detect lung problems? ›

The ECG findings were found to be 35.7% sensitive and 95.6% specific in diagnosis of COPD among patients having respiratory problems.


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