How to interpret an ECG systematically | EXPLAINED CLEARLY!

Summary

This video tutorial offers a structured approach to interpreting ECGs, essential for medical students and junior doctors. It covers patient details, calibration checks, and a systematic method starting with rate, rhythm, and axis, followed by in-depth analysis of each ECG component. The guide also discusses common abnormalities, such as different types of heart blocks and myocardial infarction, providing a foundation for diagnosing cardiac conditions.

Takeaways

• 🔍 Always verify patient details and ECG calibration before interpretation to avoid errors and ensure accuracy.
• 📈 Calculate the heart rate using either the number of large squares in the RR interval or by counting QRS complexes over a 10-second rhythm strip.
• 💓 Understand the difference between regular and irregular rhythms, and identify specific conditions like second-degree AV block type 1 (Wenckebach phenomenon) and atrial fibrillation.
• 📊 Assess the cardiac axis using leads I, II, and III to determine if there's any left or right axis deviation, which can indicate certain cardiac conditions.
• 👀 Check the presence and appearance of P waves in all 12 leads to identify atrial activity and conditions like atrial fibrillation or atrial enlargement.
• ⏱️ Evaluate the PR interval to determine if there's first-degree heart block or other conduction delays.
• 🔊 Examine the QRS complex for width, height, and morphology to detect abnormalities like bundle branch blocks or myocardial infarctions.
• 📉 Look for ST segment deviations that could signify myocardial ischemia or infarction, distinguishing between STEMI and NSTEMI.
• 🌊 Assess T wave appearance to identify conditions like hyperkalemia, ischemia, or pulmonary embolism.
• ⏲️ Measure the QT interval and consider factors like heart rate and medication effects to identify potential risks for arrhythmias like Torsades de Pointes.

Q & A

What is the first step in interpreting an ECG according to the video?

The first step is checking patient details using three pieces of identification, which is crucial as missing this step in exams could result in zero marks.

What should be the paper speed and amplitude calibration for a standard ECG?

The paper speed should be 25 millimeters per second, with one small square equivalent to 0.04 seconds and one large square to 0.2 seconds. The amplitude calibration should be 10 millimeters per millivolt.

How can one calculate the heart rate on an ECG with a regular rhythm?

For a regular rhythm, you can use the equation 300 divided by the number of large squares in the RR interval to calculate the heart rate.

What is the alternative method to calculate the heart rate if the rhythm is irregular?

If the rhythm is irregular, you count the number of QRS complexes along the rhythm strip and multiply it by six, as the total length of the rhythm strip is 10 seconds.

What does a normal adult heart rate range from?

A normal adult heart rate ranges from 60 to 100 beats per minute, with bradycardia being slower than this and tachycardia being faster.

How can you determine if the ECG rhythm is regular or irregular?

You can determine the rhythm by placing a piece of paper above the start of the rhythm strip and marking three or four R waves, then moving the paper along the strip to see if the lines match up with subsequent R waves.

What does the term 'Wenckebach phenomenon' refer to in the context of ECG interpretation?

The term 'Wenckebach phenomenon' refers to second-degree AV block type 1, where there is a predictable pattern of QRS complexes followed by a pause, often seen as two QRS complexes followed by a pause and then the same again repeated.

What does the cardiac axis represent and what is the normal range for it?

The cardiac axis represents the average direction of electrical depolarization through the ventricles. In healthy individuals, this average direction is between -30 and positive 90 degrees in the coronal plane.

How can you identify if there's left axis deviation or right axis deviation on an ECG?

You can identify axis deviation by comparing the QRS complexes in leads 1, 2, and 3. For a normal axis, lead 2 should be more positive than at least one of the other leads. In right axis deviation, lead 3 is more positive than lead 2 and 1, and in left axis deviation, lead 1 is more positive than lead 3 and 2.

What does the absence of P waves with an irregularly irregular rhythm indicate on an ECG?

The absence of P waves with an irregularly irregular rhythm indicates atrial fibrillation, which is a common finding in medical school exams and clinical practice.

What is the normal duration of the PR interval and what does a prolonged PR interval indicate?

A normal PR interval is 0.12 to 0.20 seconds or 3 to 5 small squares. A prolonged PR interval indicates first-degree heart block, which is caused by the AV node conducting electricity slower than normal.

What does a Delta wave in the QRS complex signify?

A Delta wave in the QRS complex signifies an abnormality and can be seen in conditions such as Wolf Parkinson White syndrome.

What is the significance of a pathological Q wave on an ECG?

A pathological Q wave, which is longer and taller than normal, often represents an old myocardial infarction.

What does ST segment elevation or depression on an ECG indicate?

ST segment elevation or depression can indicate myocardial ischemia. If present in two or more contiguous leads, it suggests ischemia is likely present. ST elevation specifically can indicate a STEMI (ST elevation myocardial infarction).

What does the assessment of T waves on an ECG represent?

The assessment of T waves on an ECG represents ventricular repolarization. Abnormal T waves, such as being tall, normal, or inverted, can indicate conditions like hyperkalemia, myocardial infarction, or pulmonary embolus.

What is the normal QT interval and why is it important to calculate the corrected QT interval?

A normal QT interval is less than 440 milliseconds in men or less than 460 milliseconds in women. The corrected QT interval is calculated to standardize the QT interval to 60 beats per minute, accounting for variations due to heart rate.

Why is it important to assess the ECG components in all 12 leads?

Assessing the ECG components in all 12 leads is important to avoid missing any abnormalities, as different leads provide different views of the heart's electrical activity.

Outlines

00:00

📈 ECG Interpretation Basics

This paragraph introduces the video's focus on a structured approach to ECG interpretation, essential for medical exams and clinical practice. It emphasizes the importance of checking patient details and calibration before diving into the ECG's interpretation. The video script outlines a systematic method to analyze an ECG, starting with rate, rhythm, and axis, followed by a step-by-step examination of the ECG's components. The paragraph also explains how to calculate heart rates in both regular and irregular rhythms, using the RR interval and QRS complexes.

05:03

🔍 Assessing Rhythm and Cardiac Axis

The second paragraph delves into the assessment of cardiac rhythm and axis. It explains how to determine if a rhythm is regular or irregular using the Rhythm strip and a paper method for visual alignment. The paragraph introduces the concept of second-degree AV block type 1, also known as the Wenckebach phenomenon, and contrasts it with atrial fibrillation, an example of an irregularly irregular rhythm. The discussion then shifts to the cardiac axis, detailing how to identify left and right axis deviations by examining the QRS complexes in leads 1, 2, and 3.

10:05

🌡️ ECG Component Analysis

This paragraph provides a comprehensive guide to analyzing individual ECG components, including the P wave, PR interval, QRS complex, ST segment, T waves, and QT interval. It discusses the significance of each component's presence, appearance, and measurements, such as the width and height of the QRS complex and the shape of the P wave. The paragraph also covers abnormalities like bundle branch blocks, Delta waves, pathological Q waves, and conditions that affect the ST segment, such as ischemia and myocardial infarction.

15:06

🛑 Conclusion and Further Learning

The final paragraph wraps up the ECG interpretation process by summarizing the steps taken in the video and encouraging viewers to continue their learning with the third and final video in the series. It reiterates the importance of checking patient details and ECG calibration, followed by a systematic analysis of the ECG's rate, rhythm, axis, and individual components. The paragraph also highlights the need to assess each component in all 12 leads to avoid missing any abnormalities.

Keywords

💡ECG (Electrocardiogram)

An ECG is a graphical representation of the electrical activity of the heart, which is crucial for diagnosing various cardiac conditions. In the video, the ECG is the central focus, with the speaker providing a structured approach to interpreting it from start to finish, which is essential for medical school exams and clinical practice.

💡Calibration

Calibration in the context of an ECG refers to ensuring the paper speed and amplitude are set correctly for accurate readings. The script emphasizes checking the paper speed (25 mm/s) and amplitude (10 mm/mV) as a critical step before interpretation, as incorrect calibration can lead to misinterpretation of the ECG.

💡Heart Rate

Heart rate is the number of times the heart beats per minute and is a fundamental aspect of ECG interpretation. The script explains how to calculate heart rate using the RR interval and QRS complexes, highlighting normal, bradycardic, and tachycardic rates, which are essential for diagnosing rhythm abnormalities.

💡Rhythm

Rhythm in an ECG refers to the regularity of the heartbeats. The video script describes how to assess if the rhythm is regular or irregular using the Rhythm strip and a paper method, which is vital for identifying conditions like second-degree AV block or atrial fibrillation.

💡Cardiac Axis

The cardiac axis represents the average direction of electrical depolarization through the ventricles. The script explains how to determine if there is a normal axis, left axis deviation, or right axis deviation by comparing QRS complexes in leads 1, 2, and 3, which is important for diagnosing conditions like myocardial infarction or hypertrophy.

💡P Wave

The P wave on an ECG indicates atrial depolarization. The video script instructs viewers to check for the presence and normal appearance of P waves in all 12 leads, noting that abnormalities can indicate conditions such as atrial fibrillation, right atrial enlargement (P pulmonale), or left atrial enlargement (P mitrali).

💡PR Interval

The PR interval measures the time from atrial depolarization to ventricular depolarization, reflecting the conduction through the atrioventricular (AV) node. The script explains that a normal PR interval is 0.12 to 0.20 seconds and that prolongation can indicate first-degree heart block or second-degree heart block type 1 (Wenckebach phenomenon).

💡QRS Complex

The QRS complex represents ventricular depolarization. The video script discusses assessing the width, height, and morphology of the QRS complex to identify abnormalities such as bundle branch blocks, left ventricular hypertrophy, or the presence of a Delta wave in conditions like Wolff-Parkinson-White syndrome.

💡ST Segment

The ST segment on an ECG should rest on the isoelectric line, and any elevation or depression can indicate myocardial ischemia or infarction. The script differentiates between ST elevation myocardial infarction (STEMI) and non-ST elevation myocardial infarction (NSTEMI), as well as pericarditis, which can present with a different ST segment pattern.

💡T Wave

T waves represent ventricular repolarization. The video script explains that T waves can be tall, normal, or inverted, with tall T waves potentially indicating hyperkalemia or a STEMI, normal T waves having specific amplitudes, and inverted T waves in certain leads possibly representing an old myocardial infarction or a pulmonary embolus.

💡QT Interval

The QT interval reflects the total time for ventricular depolarization and repolarization. The script mentions that a normal QT interval varies by gender and can be affected by factors such as medications, electrolyte imbalances, or congenital long QT syndrome. Prolongation of the QT interval can increase the risk of serious arrhythmias like Torsades de Pointes.

Highlights

A structured approach to interpreting ECGs for medical exams and practice.

Importance of checking patient details and ECG calibration before interpretation.

Explanation of how to calculate heart rate using RR intervals and QRS complexes.

Distinguishing between regular and irregular heart rhythms using the Rhythm strip.

Identification of second-degree AV block type 1, also known as Wenckebach phenomenon.

Assessment of cardiac axis and its deviation from normal values.

Use of leads 1, 2, and 3 to determine cardiac axis deviation.

Analysis of P waves for atrial depolarization and detection of atrial fibrillation.

Assessment of PR interval for atrial-ventricular node conduction.

Identification of first-degree heart block and second-degree heart block Mobitz type 1.

Evaluation of QRS complex width, height, and morphology for abnormalities.

Explanation of bundle branch blocks and their impact on QRS complex shape.

Assessment of ST segment for signs of myocardial infarction or ischemia.

Differentiation between STEMI and NSTEMI based on ST segment elevation.

Analysis of T waves for signs of hyperkalemia, ischemia, or infarction.

Evaluation of QT interval and its significance in detecting conditions like long QT syndrome.

Introduction to QT correction formulas like Bazett's for standardized assessment.

Summary of the ECG interpretation process from patient details to individual ECG components.

Transcripts

in this video we're going to cover how

to interpret an ECG from start to finish

using a structured and easy to follow

approach that will get you through

Medical School exams and is one that I

still use today as a junior doctor

if you want to learn about the basics of

what ECG components mean then check out

my previous video called ECG basics

the first step to interpreting any ECG

is checking patient details using three

pieces of identification

missing this step in exams could result

in you getting zero marks

step two is checking calibration

this means checking the paper speed

which should be 25 millimeters per

second

this speed will mean that one small

square is equivalent to 0.04 seconds and

one large square is 0.2 seconds

also check the calibration of amplitude

which should be 10 millimeters per

millivolt

now we can move on to our interpretation

to avoid missing any steps it's useful

to follow a structure when interpreting

the ECG

the easiest structure I think to

remember is rate Rhythm and axis

followed by each component of the ECG

complex in the order that it arises

so let's go through each of these steps

in order

first is calculating the heart rate

a normal adult heartbeats at 60 to 100

beats per minute

with bradycardia meaning slower than

this and tachycardia being faster

there are two methods to calculating the

rates

the first way is to use the equation 300

divided by the number of large squares

in the RR interval

feel free to pause the video here and

take a quick moment to calculate the

rates

in this RR interval there are six large

squares which gives us a heart rate of

50 beats per minute

this is bradycardic

this method only works if there's a

regular rhythm otherwise the RR interval

will be changing throughout the ECG

in those cases where the rhythm is

irregular we need to use the second

method

for this we count the number of QRS

complexes along the Rhythm strip and

multiply it by six

this works because the total length of

the Rhythm strip is 10 seconds so

multiplying it by 6 gives us one minute

again feel free to pause the video if

you'd like and take a moment to

calculate the heart rate

14 QRS complexes multiplied by 6 gives

us 84 beats per minute

this particular ECG has a regular rhythm

so you could use either method here

the next step in our interpretation is

the Rhythm which we use the Rhythm strip

to assess

broadly speaking we can classify rhythms

as regular or irregular

the safest method for assessing rhythm

is placing a piece of paper above the

start of the Rhythm strip and marking

three or four R waves

you can then move the paper along the

strip

if the lines match up with the

subsequent R waves then the rhythm is

regular

an irregular Rhythm could be described

as regularly irregular which means it's

irregular but it's quite a predictable

pattern

using the paper method we can see that

this ECG rhythm is irregular since

subsequent R waves do not line up

however there is a predictable pattern

to this ECG with there being two QRS

complexes followed by a pause then the

same again repeated

this particular ECG shows second-degree

AV block type 1. also known as

wankerback phenomenon

I'll cover AV heart block ECGs in more

detail in the next video titled ECG

abnormalities

irregular rhythms can also be

irregularly irregular where there's no

predictable pattern to the QRS complexes

here's an example

this particular ECG shows atrial

fibrillation which is the commonest

irregular irregular rhythm you're likely

to come across

again atrial fibrillation is covered in

more detail in the next video

our next step is assessing the cardiac

axis

at first glance this can be tricky to

get your head around but don't worry it

will eventually make sense

the cardiac axis refers to the average

direction of electrical depolarization

through the ventricles

in healthy individuals this average

direction is somewhere between -30 and

positive 90 degrees in the coronal plane

if the cardiac axis is pointing left of

-30 degrees there is left axis deviation

or if more than positive 90 there's

right Axis deviation

common causes of left axis deviation

include an inferior myocardial

infarction or wolf Parkinson White

syndrome

and right Axis deviation causes include

an anterior lateral myocardial

infarction right ventricular hypertrophy

or PE

now you will not be expected to

calculate the cardiac axis for medical

school exams however you should be able

to identify if there's left access

deviation or right Axis deviation

to do this we're going to use the QRS

complexes in three different leads

the more positive a QRS complex is in a

particular lead I.E the larger the

amplitude of the r wave the more in line

with this lead Direction the cardiac

axis is likely to lie

if a QRS complex is more negative it's

because the cardiac axis is not lined up

with this particular lead

it's these differences that can allow us

to work out the general direction of the

cardiac axis

I'll further illustrate this point by

comparing leads 2 and AVR

which you can see from the diagram on

the right are measuring depolarization

of the heart in complete opposite

directions

the resulting QRS complexes are

therefore inverted with lead 2 being

positive and AVR being negative

now in practice we commonly use leads

one two and three to ascertain if we

have a normal cardiac Axis or a deviated

one

this is because they almost replicate

the normal cardiac axis values between

-30 and positive 90 and they also lie

next to each other on ECG which makes

for easy comparison

so for a normal cardiac axis lead 2

should be more positive than least one

or three

in right Axis deviation

lead 3 will be more positive than lead 2

and 1. since the overall direction of

the polarization has moved clockwise to

the right

conversely in left axis deviation Lead 1

will be more positive than lead three

and two because the overall direction of

depolarization has moved to the left

so to quickly summarize the assessments

of the cardiac axis We compare leads 1 2

and 3 to decide whether there's left

axis deviation a normal Axis or right

Axis deviation

from now on in the interpretation we're

assetting individual components of the

ECG complex and it's therefore important

to assess these components in all 12

leads of the ECG to avoid missing any

abnormalities

first off is the P wave which represents

atrial depolarization

the questions we need to ask ourselves

here are are p waves present

and do they look normal

remember we need to be checking this in

all 12 leads

regarding the first question p waves

should precede every QRS complex

the complete absence of p waves with an

irregularly irregular Rhythm leads us to

the diagnosis of atrial fibrillation

this is a very common ECG in medical

school exams and also in clinical

practice so it's good to get familiar

with what this looks like

the second question that a p waste look

normal can lead us to two different

pathologies

peaked p waves also known as P pulmonale

represent right atrial enlargement

this is often seen in pulmonary

hypertension where the right atrium is

having to work hard to overcome the high

pressures in the pulmonary arteries

pulmonary hypertension is usually caused

by COPD which is a lung disease

predominantly though not exclusively

seen in smokers

the other cause of p waves not looking

normal is left atrial enlargements also

known as p mitrali

this is commonly associated with mitral

stenosis since the narrowing of the

mitral valve results in increased

pressure in the left atrium

P mitrali gives broad notched p waves

which look like the letter m

next we need to check the PR interval

this is the time from atrial

depolarization to ventricular

depolarization which essentially

represents atrial ventricular node

conduction

a normal PR interval is 0.12 to 0.2

seconds or 3 to 5 small squares

a prolonged PR interval is anything over

this

ECG shows a prolonged PR interval since

it's over 0.2 seconds or 5 small squares

having a constantly prolonged PR

interval is called first degree heart

block which is caused by the AV node

conducting electricity slower than

normal

this next ECG also has a prolonged Pi

interval but this time each successive

PR interval gets longer until eventually

a QRS complex is dropped

in this case every third QRS is missed

this is known as second-degree heart

block mobitz type 1. sometimes referred

to as wankerback phenomena

there is also second degree heart block

type 2 and 3rd degree heart block

I'll cover these in more detail in the

next video also just be aware the term

heart block is used synonymously with AV

block

after the PR interval we need to assess

the QRS complex

similar to assessing p waves there are

multiple questions we need to ask

firstly is width

is the QRS complex narrow

I.E is at less than 0.12 seconds or

three small squares

or is it broad I.E more than 0.12

seconds

narrow complexes are seen in any rhythm

where the wave of depolarization

originates from above the ventricles for

example normal sinus River

or atrio arrhythmias like atrial flutter

broad complexes originate from the

ventricles which is always abnormal

broad complexes may happen when there's

a bundle branch block

in other words one of the branches that

conducts electricity from the bundle of

hiss is not conducting as it should

a right bundle branch block gives us an

m shape in the V1 QRS complex and W in

V6

this can be remembered using the word

marrow

a left bundle branch block is the

opposite where there's a w in V1 and an

m in V6 this can be remembered using the

word William

next we need to assess height

small complexes are anything less than

five millimeters height in limb leads or

less than 10 millimeters in chest leads

small complexes are normal

large complexes therefore or anything

above this and can be abnormal

often representing left ventricular

hypertrophy

finally morphology I.E does it have a

normal shape

we can see in this ECG there's a slurred

upstroke at the start of the QRS complex

this is called a Delta wave and it's

abnormal

you can see this in Wolf Parkinson White

syndrome

the next ECG shows a pathological Q wave

which is longer and taller than normal

pathological Q waves often represents an

old myocardial infarction

the ST segment comes next

in healthy individuals the St segments

should rest on the isoelectric line

if elevated or depressed it can be a

sign of myocardial infarction

elevation is defined as over one

millimeters in limb leads or two

millimeters in chest leads

and depression is anything over 0.5

millimeters below the isoelectric line

if this is present in two or more

contiguous leads then ischemia is likely

present

for St elevation we refer to this as a

stemi

or St elevation myocardial infarction

this is usually due to ischemia that

affects the full thickness of The

myocardium

an MI without SD elevation is referred

to as an nstemi or non-st elevation

myocardial infarction

an nstemi doesn't necessarily have ST

depression it can also have an ST

segment on the isoelectric line

but with a raised troponin and presence

of chest pain this would lead us to the

diagnosis

an nstemi is usually due to partial

thickness ischemia

another differential to be aware of with

SD elevation is pericarditis which is

inflammation of the pericardium

surrounding the heart often thought to

be associated with viral infections

pericarditis gives saddle-shaped St

elevation which is widespread across

most leads

whereas astemi is often located in one

region

distinguishing between the two is

difficult with an ECG alone and is

slightly above the scope of medical

school exams so don't worry

however just be aware that this could be

a differential diagnosis where there's

St elevation seen on an ECG especially

if it's across many leads

the next step is assessment of T waves

which represents ventricular

repolarization

T waves can be described as tall

normal or inverted

tall T waves are associated with

hyperkalemia or with a stemi

normal T waves are less than five

millimeters in limb leads or 10

millimeters in chest leads

inverted T waves are a normal finding in

leaves 3 AVR and V1

but in other leads they may represent an

old myocardial infarction or a pulmonary

embolus

the final component to assess is the QT

interval which represents ventricular

depolarization and repolarization

together

a normal QT interval is less than 440

milliseconds in men or less than 460

milliseconds in women

it is commonly prolonged due to

medications

for example selective serotonin reuptake

Inhibitors or tricyclic antidepressants

and also antipsychotics but there are

other causes such as hypocalcemia

hypokalemia or incongenital longqt

syndrome

a significantly prolonged QT interval

can increase the risk of a patient

developing torsar's Deport which is a

ventricular arrhythmia that can cause

hemodynamic instability and can lead to

ventricular fibrillation and asystole

QT intervals can appear longer in

bradycardias and shorter and

tachycardias so it's common practice to

calculate the corrected QT interval

which standardizes the QT interval to 60

beats per minute

you don't need to remember any formulas

for doing this just be aware that this

is sometimes done for example using

bezet's formula

so to recap our ECG interpretation we

start by checking patient details and

the calibration of the ECG

we then move on to rate Rhythm and axis

followed by each ECG component in order

thanks for watching and feel free to

watch the third and final video in this

ECG series to learn more about the

common conditions you're going to come

across on ECGs in medical school exams