How to Check if ECG Report is Normal

At the heart of ECG interpretation lies our ability to determine if ECG waves and intervals are normal. In the blog post, we will focus on the ECG waves in terms of morphology (appearance), duration, and intervals.

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We will get to see whether the ECG report is normal or abnormal. An electrocardiogram, ECG, or EKG, is a non-invasive test that monitors and records electrical activity in the heart.

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Abnormalities in the expected electrical pattern are displayed on a graph, which can help to diagnose heart problems such as atrial fibrillation and China and heart attack. ECG also helps to establish if one is at risk of heart disease or monitor if it responds to treatment for a heart condition.

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Purpose of ECG

The ECG provides a consistent pattern of wavy lines on a continuous read-out called tracing. Suppose the pattern is not consistent or is unexpected. It may indicate a heart problem.

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• An ECG helps to determine heart health as in risk factors like smoking, obesity, or a family history of high blood pressure, diabetes, or cholesterol.

• It helps in diagnosing conditions like chest pain, heart palpitation, light-headedness, or fainting.

• It helps to diagnose stroke when there is sudden slurring, numbness, or paralysis on one side of the body.

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Types of ECG

The three main types of ECG.

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• Resting ECG: It is performed while we are lying down. It screens for heart disease and also monitors the heart during surgery.

• Ambulatory monitoring: This involves an ECG device that we wear on our body for 24 hours to detect problems that may happen occasionally, like palpitations.

• Cardiac stress testing involves monitoring heart activity while on a treadmill or stationary bike. It determines the effects of exercise on the heart, detecting problems that do not occur at rest. 

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Overview of the normal ECG

ECG interpretation requires a step-by-step assessment of all the waves and intervals. Before discussing anything, each component in detail. A brief overview of the wave and intervals is described below.

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Risks and limitations of ECG

ECG is one of the most common tests for screening heart conditions. These devices are available in most medical facilities and are safe, simple, and inexpensive to perform. The possible risks from it are-

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• Irritation or allergic reaction due to adhesive electrodes attached to arms and chest.

• Tissue breakdown due to prolonged use of electrodes during ambulatory ECG.

• Lightheadedness, fainting, or other heart-related events while performing stress tests.

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The limitations are-

• A resting ECG detects problems during the tracing only. An ambulatory ECG may be required if a resting ECG fails to detect a suspected problem.

• Often, ECG delivers normal or near-normal readings for many diseases, and other tests like angiography may be required to detect them.

• ECGs are not diagnostic of any condition on their own. Sometimes, they give false positive results, also which have no medical significance.

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How to identify Normal Reading

ECG is used to assess heart rate, rhythm, and other electrical functions, which help doctors detect abnormalities like arrhythmias, heart attacks, and cardiovascular issues.

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Here, we will discuss the critical components of an ECG report and explain how to interpret it. Before identifying heart conditions on ECG, we must understand what a normal ECG is like.

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Components of an ECG report

An ECG has vital components that represent different aspects of the heart’s electrical activity, which must be understood to report accurately.

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• P Wave: Represents atrial depolarization activity that causes atria to contract. Normal P wave should be upright, smooth, and preceed a QRS complex.

• QRS complex: This electrical activity causes the ventricle to contract. The average duration is between 0.06 to 0.10 seconds. It appears as a sharp spike on the ECG.

• T waves: It represents ventricular repolarization after the recovery phase of the ventricles. It should be upright and follow the QRS complex without abnormalities.

• PR Interval: The time between the beginning of the P wave and the of the QRS complex. Reflects the delay between atrial and ventricular depolarization. The average PR interval ranges from 0.12 to 0.20 secs.

• ST segment: It shows ventricular depolarization and repolarization. A flat ST segment indicates normalcy. Deviations - elevation or depression may signal myocardial injury.

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Reading an ECG report

In a standard ECG report

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• The heart rate ideally is between 60 and 100 beats per minute.

• The rhythm should be regular.

• Observe the P wave, QRS complex, and T wave for the correct sequence and shape.

• The intervals between waves should be within standard limits.

• Follow the steps to determine if the ECG report is regular.

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Check the heart rate

The average heart rate varies between 60 to 100 beats per minute. Rates above or below this range indicate tachycardia (fast heart rate) or bradycardia (slow heart rate).

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Assess the heart rhythm 

It should be regular, with consistent intervals between heartbeats. Normal rhythm is the sinus rhythm when every heartbeat originates from the sinoatrial node, the sinus.

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Examine the wave patterns

The shapes and sizes of the P wave, QRS complex, and T wave should appear normal. Abnormal shape, usually large or small, or missing waves indicate a disease pattern.

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P Wave

Shows Atria to contract.

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• Average duration: 0.06-0.12 secs (60-120 milliseconds)

• Average amplitude: Up to 2.5 millimeters high.

• Interpretation: A smooth upright P wave proceeds. Each QRS complex indicates normal atrial depolarization.

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PR Interval

It measures the time taken by electrical signals to travel from the atria to the ventricles. It is an essential marker for heart health. 

• Standard range. 0.12-0.20secs (120-200 milliseconds)

• Interpretation. It reflects the time from atrial to ventricular depolarization. Values within the normal range indicate normal conduction between the atria and ventricles.

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QRS complex

Shows ventricular depolarization. That is how. The Ventricles contract. Its shape and duration are vital for diagnosing heart conditions.

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• Average duration: 0.06-0.10 seconds (60-100millisecs)

• Interpretation: Prolonged duration indicates conduction delay.

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QT Interval

It indicates the time the ventricles take to depolarise and then re-polarise.

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• Standard range: for men is 0.36-0.44 secs(350-450 milliseconds)

                                     for women is 360-460 ms

• Interpretation: total time for ventricular depolarization and repolarization. Prolongation indicates a risk of arrhythmias.

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ST segment

It reflects the recovery phase of the ventricles after contraction. It is flat, signaling average heart recovery.

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• Typical appearance: flat and at baseline (Isoelectric).

• Interpretation. A flat ST segment is suggestive of average ventricular recovery. Elevation or depression indicates myocardial injury.

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T Wave

It represents ventricular repolarization or recovery. And should be upright in most leads.

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• Appearance: Upright in most leads except in aVR and V1, where it can be inverted

• Interpretation: Normal TV wave indicates proper ventricular repolarization. Abnormalities suggest electrolyte imbalance ischemia or cardiac issues.

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Axis

The axis gives insight into the overall direction of electrical signals through the heart.

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• The standard range is from -30 to 90 degrees.

• Interpretation. The heart's electrical axis should fall within a normal range. It reflects the average depolarization direction. Deviations in the axis indicate underlying heart conditions.

• ‍Evaluate intervals and segments. The PR interval, QR duration, and QT interval should fall within the normal range. Abnormal range intervals indicate conduction delays or electrolyte imbalances.

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Let us now dive deep into interpreting ECG

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Understanding the Rhythm Strip

• Paper speed  

• Paper output speed is the rate at which the ECG machine produces a tracing

• The standard output is 25 mm /second.

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When the standard paper speed is 25 mm per second.

• 1 small square (1 mm )= 0.04 seconds or 40 milliseconds.

• 5 Small squares (5mm) = 1large square =0.02secs (200 ms)

• 5 large squares = 1 second

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At the standard paper speed of 25 mm/ second, the rhythm strip consists of

               250 small squares = 50 large squares = 10 seconds.

Rhythm Strip is recorded for one minute

                Therefore, 1500 small squares =  300 large squares = 1minute

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Interpreting Heart Rate

Any of the following three methods can calculate the heart rate.

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Large square method

Recall from above 300 large squares.= 1 minute at paper speed 25 mm per second.

Divide 300 by the number of large squares between each RR interval (space between 2 consecutive R waves = 1 beat ).

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Small square method

1500 is divided by a number of small squares between consecutive R waves.

This method is used for fast heart rates.

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R Wave method

Heart rate = Number of R waves on rhythm strip x 6

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The number of complexes R waves on the rhythm strip gives the average rate over 10 seconds. When this is multiplied by 6, We get average beats per minute(10 secs X 6= 1 minute).

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It is useful in slow and irregular heartbeats.

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Normal Heart rate

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Adults

• Normal. 50 - 100 beats per minute.

• Tachycardia > 100 beats per minute.

• Bradycardia <  50 beats per minute.

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Children

• Newborn 110.-150 bpm.

• 2 years 85 -125 bpm.

• 4 years 75 - 115 bpm.

• 6 years 60 -100 bpm. 

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Bradycardia(Slow heart rate)

A heart rate of less than 60 beats per minute.

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Physiological causes-Athletes have resting bradycardia due to enhanced cardiac efficiency.

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Pathological causes. Heart blocks, Hypothyroidism, Beta blocker medication.

Tachycardia (Fast heart rate)

Heart rate exceeds 100 bpm

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• Physiological causes: Exercise, stress, fever, dehydration.

• Pathological causes: arrhythmia, atrial fibrillation, supraventricular tachycardia. Hyperthyroidism. Heart failure, Anemia. Tachycardia can be a normal reaction to a stressor, but if persistent and symptomatic, it needs evaluation.

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Normal Heart Rhythm

The heart’s normal rhythm is sinus rhythm; the sinus node generates the electrical impulses or signals. These impulses are represented as up and down waves on the electrocardiogram. The patterns so formed are uniform, with high or low impulses falling within the normal parameters.

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                        Normal Sinus Rhythm ECG features

• Regular rhythm at a rate of 60-100 beats per minute. (age-specific for children)
• A normal P wave precedes each QRS complex.
• Normal P wave axis (P waves are upright in lead I and II and inverted in aVR.
• A constant PR interval.
• QRS complex < 100 ms wide.

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ECG rhythm interpretation

• Sinus bradycardia is characterized by heart rhythm originating from the sino-auricular node. Get the heart rate below 60 beats per minute.

• Sinus tachycardia is when the heart rate is above 100 beats per minute.

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Atrial fibrillation(Afib)

It is a common arrhythmia characterized by chaotic and disorganized electrical activity in the atria. It leads to irregular heart rhythm.

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Characteristics. Irregularly irregular rhythm with no distinct P waves. Variable ventricular response rate, fast or slow, and irregular RR intervals.

Significance. It increases the risk of stroke and heart failure.

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• Irregularly irregular rhythm

• No P waves

• Absence of an isoelectric baseline

• Variable ventricular rate

• QRS complexes usually < 120ms unless pre-existing bundle branch block, accessory pathway, or rate-related aberrant conduction

• Fibrillatory waves may be present and can be either fine with an amplitude < 0.5mm or coarse with  an amplitude > 0.5mm

• Fibrillatory waves may mimic P waves, leading to misdiagnosis.

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Atrial Flutter

Atrial flutter has rapid regular atrial contractions at rates between 250 and 350 beats per minute.

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• Narrow complex tachycardia

• Regular atrial activity at ~300 bpm

• Loss of the isoelectric baseline

• “Saw-tooth” pattern - inverted flutter waves in leads II, III, aVF

• Upright flutter waves in V1 that may resemble P waves

• The ventricular rate depends on the AV conduction ratio

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Ventricular tachycardia 

It is a broad, complex tachycardia that originates from the ventricles.

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Ventricular fibrillation

It can be life-threatening.

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• Deflections of varying amplitude are chaotic and irregular.

• No identifiable P waves, QRS complexes, or T waves.

• Heart rate150 to 500bpm

• Amplitude decreases with duration.

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Heart blocks

Hard blocks are disruptions in the conducting system of the heart. They affect the transmission of impulses from material to ventricles.

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Types

• First-degree AV block. Prolonged PR interval. More than 0.20 seconds. With all P waves followed by QRS complexes.

• Second-degree AV block

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Type 1. Wenckebach Gradual lengthening of prior intervals till QRS complex drops.

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Type 2. Intermittent non-conducted P waves with a constant PR interval when conducted.

• Third-degree AB block. No consistent relationship between P waves and QRS complexes. Atria and Ventricles beat independently.

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A step-by-step approach to ECG rhythm analysis.

1. Rate

Tachycardia or bradycardia.

The normal rate is 60 - 100. Beats per minute.

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2. QRS complex pattern

Regular or irregular.

If irregular, is it regularly irregular or irregularly irregular?

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 3. QRS Morphology

Narrow complex. Sinus Atrial or junctional origin.

Wide complex. Ventricular origin or supra ventricular with aberrant conduction.

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4. P waves

• Absent. Sinus arrest, Atrial fibrillation

• Present. Morphology and PR interval suggest sinus. Atrial, junctional, or even retrograde from the ventricles.

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5. Relation between P waves and QRS complexes

• AV Association (difficult to distinguish from isorhythmic dissociation).

• AV Dissociation

            Complete. Atrial and ventricle activity is always independent.

                Incomplete. Intermittent capture.

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6. Onset and termination

• Abrupt. Suggest a re-entrant process.

• Gradual. Suggest increased automaticity.

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P Wave

The atrial waveform relationship to the P wave

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• Atrial depolarization sequentially moves from right to left, with right atrium activation before the left atrium.

• The right and left atrial waveforms together form the P wave.

• The first third of the P wave corresponds to right atrial activation, the final third to left atrial activation, middle third is a combination of the two.

• The right and left atrial waveforms move in the same direction to form a monophasic P wave.

• In V1 lead, the right and left atrial waveforms move in opposite directions causing a biphasic P wave. The initial positive deflection corresponds to the right atrium and the subsequent negative deflection denotes left atrial activation. The separation in V1 lead means abnormalities affecting the atrial waveform can be seen in this lead. The overall shape of the P wave is used to infer atrial abnormality.

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Normal P wave morphology lead to II

The right atrial depolarization wave precedes the left atrium.

The combined depolarization wave P wave. It is less than 120 ms And less than 2.5 mm high. 

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Right atrial enlargement lead II

The right atrial depolarization lasts longer than normal. The waveform extends to the end of left atrial depolarization.

The amplitude of the right atrial depolarization current does not change. Its peak falls on top of the left atrial depolarization wave.

The combination creates a P wave that is taller than normal (>2.5 mm), and the width remains unchanged(< 120ms)

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Left atrial enlargement lead II

Left atrial depolarization last longer than normal and the amplitude remains unchanged.

The height of the resultant P wave is within normal limits, but the duration is longer than 120 ms.

A notch near its peak may or may not be present (P mitrale).

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Normal P wave morphology Lead V1

P wave. It is biphasic in V1 with smaller sizes of positive and negative deflections.

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Right Atrial Engagement leads V1

Right atrial enlargement causes increased height (> 1.5 mm) in  V1 of the initial positive deflection of the P wave.

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Left Atrial Engagement lead V1

Left atrial enlargement causes widening (>40ms wide) and deepening (>1mm Deep.) in V1 of the terminal negative portion of the P wave.

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Bilateral enlargement 

It is when right and left atrial enlargement are present on the same ECG. 

A comparative evaluation of right and left atrial enlargement in II and V1 leads is

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Abnormalities in P wave

P mitrale

A broad notched P wave in lead II is a sign of enlargement due to mitral stenosis.

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P Pulmonale

Tall peaked P waves in the lead II show right atrial enlargement due to pulmonary hypertension.

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Inverted P waves

The inferior leads indicate a non-sinus origin of P waves. When the PR interval is less than 120 ms, the origin is in the AV junction.

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Absent P waves occur in atrial fibrillation.

Sawtooth P waves occur in atrial flutter

Variable P wave morphology indicates ectopic pacemakers within the atria.

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QRS Complex

A QRS complex consists of a Q, R, and S wave. These three waves may not be visible because there is always variation between the leads. The wave that reflects ventricular depolarization is referred to as the QRS complex.

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The following rules apply while naming the waves in the complex.

• Deflection is a wave if it passes the baseline.

• It is a Q wave if the first wave is negative. If the first wave is not negative, then the QRS complex does not have a Q wave regardless of the appearance of the QRS complex.

• All positive waves are R waves. The first positive wave is simply an R wave.

• A negative wave occurring after a positive wave is an S wave.

• Large waves are referred to as QRS by capital letters. Small waves are referred to by the lowercase letters qrs

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Net direction of QRS complex.

QRS complex may be classified as net positive or net negative. It refers to the direction if the QRS complex is net positive; the sum of positive areas above the baseline exceeds that of the negative areas below the baseline.

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Normal QRS Complex

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Abnormal QRS complex

Abnormal QRS patterns indicate cardiac conditions such as bundle branch blocks, ventricular hypertrophy, or myocardial infarction. These patterns are affected by duration, amplitude, abnormal morphology, and axis changes. Suppose the duration is greater than 0.12 seconds then this finding indicates underlying conditions.

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QRS complex width

• Narrow complexes. (QRS is <100 ms) They are supraventricular in origin. They occur in atrial flutter.

• Broad complexes. (QRS > 100 ms) It may be ventricular in origin due to aberrant conduction of supra-ventricular complexes.

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Abnormal broad complexes cause

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Bundle branch block

The Purkinje fibers enable fast impulse conduction so that all impulses can be passed to the myocardium at the same time. A bundle branch block occurs if the bundle branch is dysfunctional and unable to transmit the impulse.

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The ventricle whose bundle is blocked has to wait for electrical impulses from the other ventricle. As a result, the conduction will be slowed, prolonging the QRS duration.

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• Hyperkalaemia. Slows the impulse transmission (in all myocardial conduction cells) and prolongs the QRS duration.

• Drugs Antiarrhythmic drugs and tricyclic antidepressants cause the widening of the QRS complex.

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T-wave

Positive deflection after each QRS complex is the TV. It represents ventricular depolarization.

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Normal T-wave characteristics

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Abnormalities in T-wave 

They are of the following types

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• Peaked T  Waves

• Hyperacute T waves

• Inverted T waves

• Biphasic T waves

• Camel hump, T waves

• Flattened T waves

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Peaked waves

Tall, narrow waves are seen in hyperkalemia

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Hyperacute T waves

They are seen in the early stage of ST Elevation MI.

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Loss of precordial T wave balance

• It occurs when the upright T wave is larger than that in V6. It is a hyperacute T wave.

• A normal T wave in V1 is inverted, while an upright T wave in V1 is abnormal. A tall T wave in V1 and new NTTV1 indicate coronary artery disease. When new, it implies acute ischemia.

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Inverted T waves

They are seen in

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• Normal findings in children

• Persistent juvenile T-wave pattern

• Myocardial ischemia and infarction

• Bundle branch block

• Ventricular hypertrophy

• Pulmonary embolism

• Hypertrophic cardiomyopathy

• Raised intracranial pressure

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T Wave inversion in the lead III is a normal variant. New T wave inversion compared with prior ECGs is always abnormal. Pathological T wave inversion is symmetrical and deep>3mm.

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In children

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MI 

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Left bundle branch block

T wave inversion in the lead I, aVL, V5-6

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Right Ventricular Hypertrophy

T wave inversion in the right precordial leads V1 to V3  and inferior leads II, III, aVF.  

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Pulmonary Embolism

A pattern similar to RVH

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Biphasic T waves

The two main causes are hypokalaemia and myocardial ischemia

The two waves go in opposite directions.

          T waves go up then down.

          T waves go down and then up.

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Camel hump T waves

A term used for T waves with double peaks.

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• Prominent U waves Fuse to the ends of the T wave. Are seen in severe hypokalaemia

• Hidden P waves. Embedded in the T wave seen in sinus tachycardia and heart blocks.

                U waves in hypokalaemia

          Hidden P waves in sinus tachycardia

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Flattened T waves

These are non-specific findings and may represent ischemia or electrolyte abnormality.

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• Anterior ischemia

• Global T wave flattening due to hypokalaemia.

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ST segment

It represents the interval between ventricular depolarization and repolarization. Elevation or depression abnormality of the ST segment Is due to myocardial ischemia or infarction. It helps to assess the heart's electrical stability and recovery after contraction.

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Normal ST segment

• The ST segment should be at the baseline isoelectric line, the flat line that precedes the T wave

• Its deviation from the baseline is of primary concern than its duration.

• The ST segment should be flat or gently sloping towards the T wave without elevation or depression.

• A normal ST segment shows no delay in ventricular repolarization.

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Abnormalities of ST segment

They reveal cardiac issues such as ischemia, infection, or imbalances. And are easily identified by deviation from the baseline.

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Elevation

• St segment elevation indicates MI or myocardial infarction

• The elevations range from 0.1 to. 5 mV or more.

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Depressions

• ST segment depression indicates MI, electrolyte imbalances, or cardiac medications.

• ST segment depression ranges from 0.1 to 5 mV or more.

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A Step-by-Step Guide to Analyzing ECG Reports

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Verify patient details

Ensure all patient details, date, and time are accurately recorded. Ensure proper settings in the ECG machine, paper speed and calibration. The paper speed should be 25 mm/ second, and the calibration should be 10 mm/mV.

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Evaluate the heart rate

Calculate the heart rate, examine the R waves on the ECG strip, and use the methods outlined above.

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Evaluate rhythm

Assess the rhythm by analyzing RR intervals.

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Analyse P waves

Examine P waves for their shape and consistency. Regular P waves show proper atrial depolarization, and abnormalities suggest atrial issues.

Normal P waves indicate proper atrial depolarization; a standard wave is an upright wave in the lead I, II, and aVF, consistent before the QRS complex.

Inverted, absent, or abnormal shape indicates atrial abnormalities. Abnormal P waves signify atrial enlargement or other conditions.

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Analyze the QRS complex

Normal QRS complex indicates effective ventricular depolarization, and abnormalities reveal blockages or hypertrophy. The average QRS is complex is narrow, consistent with a duration of 0.06 to 0.10 seconds. At the same time, wide complexes are more than 0.12 seconds.

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Inspect the ST segment

Check for deviations from the baseline. Proper ST segment morphology reflects ventricular repolarization, and abnormalities indicate cardiac conditions. When elevated, it indicates possible myocardial infarction; when depressed indicates ischemia.

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Analyze the T waves

Analyze the T waves for shape and amplitude. Normal T waves indicate healthy ventricular repolarization. An abnormal T wave reveals electrolyte imbalances or ischemia. Normal T waves are smooth, rounded, and upright in most leads. They may be peaked in hyperkalaemia, inverted in ischemia, or flattened in electrolyte imbalances.

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Look for any additional features

Features such as U waves or abnormal Q waves provide insight into various cardiac conditions and their causes.

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Comparison with previous ECGs

It helps to track the changes or progress in known conditions and assess the effectiveness of the treatment.

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Importance of Consulting a Doctor for ECG Interpretation.

ECG provides valuable information about heart functions. A doctor helps interpret ECG information accurately and ensure diagnosis and effective treatment. A healthcare professional can integrate these results with the overall health and medical history to pinpoint a disease.

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• A doctor helps with an accurate diagnosis and treatment by correctly interpreting the context of the health and prescribing necessary treatment.

• Address symptoms and concerns like chest pain or dizziness and develop a targeted treatment plan.

• Integrate findings with symptoms to evaluate ECG results that align with symptoms and manage potential issues.

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Conclusion

Reading and interpreting in ECG is complex. It requires an understanding of the electrical activity within the heart. A usual ECG shows a heart rate between 60 and 100 beats per minute and a consistent heart rhythm. Abnormal ECG results indicate 

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• Heart conditions

• Changes or damage to heart musculature

• Changes in electrolyte levels

• Abnormal heart rhythms.

• Congenital heart defects

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Gauze, with its AI-powered solutions, simplifies the process for you and helps you to improve the diagnosis.