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Core Conditions - Cardiovascular > ECG Interpretation > Flashcards

ECG Interpretation Flashcards

1
Q

What is the order of structures involved in normal impulse conduction?

A
  • sinoatrial node
  • AV node
  • bundle of His
  • bundle branches
  • Purkinje fibres
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2
Q

What is shown by the P wave on an ECG?

A

the P wave shows atrial depolarisation

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3
Q

What is shown by the QRS complex on an ECG?

A

the QRS complex shows ventricular depolarisation

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4
Q

What is shown by the T wave on an ECG?

A

the T wave shows ventricular repolarisation

this is diastole

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5
Q

What is shown by the PR interval on an ECG?

A

this represents atrial depolarisation + delay in AV junction (AV node / bundle of His)

the delay allows time for the atria to finish contracting before the ventricles contract

this extends from the beginning of the P wave (onset of atrial depolarisation) until the beginning of the QRS complex (onset of ventricular depolarisation)

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6
Q
A
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7
Q

What are the 3 pacemakers of the heart?

What are their rates?

A

SA node:

  • dominant pacemaker with an intrinsic rate of 60 - 100 beats/minute

AV node:

  • back-up pacemaker with an intrinsic rate of 40 - 60 beats / minute

Ventricular cells:

  • back-up pacemaker with an intrinsic rate of 20 - 45 beats / minute
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8
Q

What are the small and large boxes on the ECG paper worth?

A

Horizontally:

  • one small box is worth 0.04s
  • one large box is worth 0.20s

Vertically:

  • one large box is 0.5 mV
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9
Q

What vertical marking is present on the ECG paper that is there to help calculate the heart rate?

A

every 3 seconds (15 large boxes) is marked by a vertical line

this helps when calculating the heart rate

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10
Q

What are the 5 steps involved in rhythm analysis?

A
  • step 1 - calculate the rate
  • step 2 - determine regularity
  • step 3 - assess the P waves
  • step 4 - determine the PR interval
  • step 5 - determine the QRS duration
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11
Q

What is a method of calculating rate that involves counting the number of R waves?

A

count the number of R waves in a 6 second rhythm strip and then multiply by 10

e.g. 9 x 10 = 90 bpm

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12
Q

How is it determined whether or not a rhythm strip is regular?

A
  • look at the distances between R waves using a caliper or markings on a pen or paper
  • if they are equidistant apart then it is regular
  • the rhythm may be occasionally irregular, regularly irregular or irregularly irregular
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13
Q

What is a normal heart rate?

A
  • normal heart rate is 60 - 100 bpm
  • tachycardia is > 100 bpm
  • bradycardia is < 60 bpm
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14
Q

What method can be used to calculate the heart rate involving counting the number of large squares?

A
  • count the number of large squares present within one R-R interval
  • divide 300 by this number of calculate the heart rate
  • e.g. 4 large squares in an R-R interval
    • 300 / 4 = 75 beats per minute
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15
Q

What method is used to calculate heart rhythm if the patient’s heart rhythm is irregular?

A
  • the R-R interval differs significantly throughout the ECG
  • count the number of complexes on the rhythm strip
    • each rhythm strip is typically 10 seconds long
  • multiply the number of complexes by 6
    • ​this gives the average number of complexes in 1 minute
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16
Q

What are the 2 different types of irregular heart rhythms?

A
  • regularly irregular has a recurrent pattern of irregularity
  • irregularly irregular is a completely disorganised rhythm
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17
Q
A
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18
Q

What is the cardiac axis?

How is it determined and what is normal?

A

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

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19
Q

What does an ECG look like for a normal cardiac axis?

A
  • lead II has the most positive deflection compared to leads I and III
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20
Q

What are typical ECG findings for right axis deviation?

A
  • lead III has the most positive deflection and lead I should be negative
  • right axis deviation is associated with right ventricular hypertrophy
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21
Q

What are typical ECG findings for left axis deviation?

A
  • lead I has the most positive deflection
  • leads II and III are negative
  • left axis deviation is associated with heart conduction abnormalities
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22
Q

What 4 questions need to be asked when looking at the P waves?

A
  • are P waves present?
  • if so, is each P wave followed by a QRS complex?
  • do the P waves look normal? check duration, direction and shape
  • if P waves are absent, is there any atrial activity?
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23
Q

If P waves are absent, what indications of atrial activity may be present?

A
  • sawtooth baseline is indicative of flutter waves
  • chaotic baseline is indicative of fibrillation waves
  • a flat line suggests no atrial activity at all
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24
Q

What may suggest a diagnosis of atrial fibrillation?

A

if P waves are absent and there is an irregular rhythm

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25
Q

What is a normal PR interval?

What does it suggest if PR interval is prolonged?

A

a normal PR interval should be between 120 - 200 ms

this is equivalent of 3 - 5 small squares

a prolonged PR interval (>0.2 seconds) suggests the presence of atrioventricular delay (AV block)

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26
Q

What is meant by first degree heart block (AV block)?

A

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

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27
Q

What are other names for second-degree heart block (type 1)?

How can this be identified on ECG?

A

Mobitz type 1 AV block or Wenckebach phenomenon

  • there is progressive prolongation of the PR interval until evetually the atrial impulse is not conducted and the QRS complex is dropped
  • AV nodal conduction resumes with the next beat
  • the sequence of progressive PR interval prolongation and the eventual dropping of a QRS complex repeats itself
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28
Q

What is another name for second-degree heart block (type 2)?

What are the typical ECG findings?

A

also known as Mobitz type 2 AV block

  • there is 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 or 4th P wave
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29
Q

What is third-degree heart block (complete heart block)?

What are typical ECG findings?

A
  • this occurs when there is no electrical communication between the atria and the ventricles due to a complete failure of conduction
  • there is the presence of P waves and QRS complexes that have no association with each other
    • this is due to the atria and ventricles functioning independently
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30
Q

Where do narrow-complex and broad-complex escape rhythms originate from in third degree heart block?

A
  • narrow-complex escape rhythms are QRS complexes of <0.12 seconds duration

they originate above the bifurcation of the bundle of His

  • broad-complex escape rhythms are QRS complexes > 0.12 seconds duration

they originate from below the bifurcation of the bundle of His

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31
Q

What is the anatomical location of first-degree AV block?

A
  • this is AV block occurring between the SA node and the AV node (i.e. within the atrium)
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32
Q

What is the anatomical location of second-degree heart block?

A
  • Mobitz I AV block (Wenckebach) occurs IN the AV node
    • this is the only piece of conductive tissue in the heart which exhibits the ability to conduct at different speeds
  • Mobitz II AV block occurs AFTER the AV node in the bundle of His or Purkinje fibres
33
Q

What is the anatomical location of third-degree AV block?

A

this occurs at or after the AV node resulting in a complete blockade of distal conduction

34
Q

What are the 2 possible reasons for a shortened PR interval?

A
  • the P wave is originating from somewhere closer to the AV node so the conduction takes less time
    • the SA node is not in a fixed place and some people’s atria are smaller than others
  • the atrial impulse is getting to the ventricle by a faster shortcut instead of conducting slowly across the atrial wall
    • this is an accessory pathway and can be associated with a delta wave
    • this is a slurred upstroke of the QRS complex associated with Wolff Parkinson White syndrome
35
Q

When assessing the QRS complex, what 3 characteristics need to be assessed?

A
  • width
  • height
  • morphology
36
Q

How can the width of the QRS complex be described?

A
  • it is NARROW when it is < 0.12 seconds
  • it is BROAD when it is > 0.12 seconds
37
Q

Under what circumstances does a narrow QRS complex occur?

A

when the impulse is conducted down the bundle of His and Purkinje fibres to the ventricles

this results in well organised, synchronised ventricular depolarisation

38
Q

Under what circumstances does a broad QRS complex occur?

A

this occurs if there is an abnormal depolarisation sequence

  • e.g. a ventricular ectopic where the impulse spreads slowly across the myocardium from the focus in the ventricle
  • a bundle branch block as the impulse gets to one ventricle rapidly down the intrinsic conduction system and then has to spread slowly across the myocardium to the other ventricle
39
Q

Would an atrial ectopic be described as a narrow or broad QRS complex?

A

it would result in a narrow QRS complex

this is because it would conduct down the normal conduction system of the heart (i.e. bundle of His and Purkinje fibres)

40
Q

In what 2 different ways can the height of the QRS complex be described?

A

the height can be described as either SMALL or TALL

  • small complexes are defined as <5 mm in the limb leads or <10 mm in the chest leads
41
Q

What do tall QRS complexes imply?

A

tall complexes imply ventricular hypertrophy

(although can be due to body habitus e.g. tall, slim people)

there are numerous algorithms for measuring LVH, such as Sokolow-Lyon index or Cornell index

42
Q

How is morphology of the QRS complex assessed?

A

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

  • delta wave
  • Q waves
  • R and S waves
  • J point segment
43
Q

What is the delta wave?

Why might it be present on an ECG?

A
  • it is a sign that the ventricles are being activated earlier than normal from a point distant to the AV node
  • the early activation spreads slowly across the myocardium
  • this causes the slurred upstroke of the QRS complex
44
Q

What is needed to diagnose Wolff-Parkinson-White syndrome?

A
  • the presence of a delta wave alone does NOT diagnose WPW syndrome
  • there must be evidence of tachyarrhythmias AND a delta wave
45
Q

What is a pathological Q wave?

A
  • isolated Q waves can be normal
  • a pathological Q wave is >25% the size of the R wave that follows it
  • OR >2 mm in height and > 40ms in width
46
Q

What can Q waves on ECG be indicative of?

A
  • 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
  • Q waves with T wave inversion are suggestive of previous anterior MI
47
Q

How are R and S waves assessed when assessing the QRS complex?

What can problems with this process indicate on ECG?

A
  • 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 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

it can also occur in very large people due to poor lead position

48
Q

What is the J point?

A

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

49
Q

What is “high take off” related to the J point?

What can it often be confused for?

A
  • the J point can be elevated resulting in the ST segment that follows it also being raised
  • this is “high take off” or benign early repolarisation
  • this is a normal variant that can cause confusion as it LOOKS like ST elevation
50
Q

What are the 4 key points for assessing the J point segment?

A
  • benign early repolarisation occurs mostly under the age of 50
    • over the age of 50, ischaemia is more common and should be suspected first
  • typically, the J point is raised with widespread ST elevation in _multiple territorie_s making ischaemia less likely
  • the T waves are also raised
    • ​in contrast to a STEMI where the T wave remains the same size and the ST segment is raised
  • the ECG abnormalities do not change!
    • ​during a STEMI, the changes will evolve - in benign early repolarisation, they will remain the same
51
Q

Where is the ST segment?

What does it look like in a normal person?

A

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

52
Q

When is ST-elevation significant?

What is it most commonly caused by?

A

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

or >2 mm in 2 or more chest leads

it is most commonly caused by acute full-thickness myocardial infarction

53
Q

What is ST depression and what does it indicate?

A

ST depression >/= 0.5 mm in >/= 2 contigious leads indicates myocardial ischaemia

54
Q

What do T waves represent?

When are T waves considered to be tall?

A

T waves represent repolarisation of the ventricles

T waves are considered tall if they are:

  • > 5mm in the limb leads AND
  • > 10mm in the chest leads
55
Q

What are tall T waves associated with?

A

Tall T waves can be associated with:

  • hyperkalaemia (“tall tented T waves”)
  • hyperacute STEMI
56
Q

When are T waves normally inverted?

A
  • T waves are normally inverted in V1
  • inversion in lead III is a normal variant
57
Q

What can inverted T waves in other leads be a sign of?

A

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

  • ischaemia
  • bundle branch blocks
    • V 4-6 in LBBB and V1-V3 in RBBB
  • pulmonary embolism
  • left ventricular hypertrophy (in the lateral leads)
  • hypertrophic cardiomyopathy
  • general illness
58
Q
A
59
Q

What are biphasic T waves and what conditions are they associated with?

A

biphasic T waves have 2 peaks

they can be indicative of ischaemia and hypokalaemia

60
Q

What are flattened T waves and what do they demonstrate?

A

this is a non-specific sign that may represent ischaemia or electrolyte imbalance

61
Q

What is a U wave?

A

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

U waves are not a common finding

62
Q

Classically, when might U waves be seen?

A
  • these become larger as the bradycardia becomes slower
  • they are seen in various electrolyte imbalances and hypothermia
  • they are also seen secondary to antiarrhythmic therapy, such as digoxin, procainamide or amiodarone
63
Q

What is aetiology of normal sinus rhythm?

A

the electrical impulse is formed in the SA node and conducted normally

this is the normal rhythm of the heart and other rhythms that do not conduct via the typical pathway are called arrhythmias

64
Q

How can arrhythmias form?

A

arrhythmias can arise from problems in the:

  • sinus node
  • atrial cells
  • AV junction
  • ventricular cells
65
Q

What are the 2 possible problems of the SA node?

A

the SA node can:

  • fire too slowly
  • fire too quickly

sinus tachycardia may be an appropriate response to stress

66
Q

What are the possible problems that can occur with atrial cells?

A
  • atrial cells can fire occasionally from a focus
    • this is premature atrial contractions (PCAs)
  • atrial cells can fire continuously due to a looping re-entrant circuit
    • ​this is atrial flutter
  • atrial cells can fire continuously from multiple foci or fire continuosly due to multiple micro re-entrant “wavelets”
    • ​this is atrial fibrillation
67
Q

What is a re-entrant circuit?

A

a re-entrant pathway occurs when an impulse loops and results in self-perpetuating impulse formation

68
Q

What is meant by multiple micro re-entrant “wavelets”?

A

this refers to wandering small areas of activation which generate fine chaotic impulses

colliding wavelets can, in turn generate new foci of activation

69
Q

What is the aetiology of sinus bradycardia?

A

SA node is depolarising slower than normal

the impulse is conducted normally (i.e. normal PR and QRS interval)

70
Q

What is the aetiology of sinus tachycardia?

A

the SA node is depolarising faster than normal

the impulse is conducted normally

this is a response to physical or psychological stress and is not a primary arrhythmia

71
Q

What are the 2 different types of premature beats?

A
  • premature atrial contractions (PACs)
  • premature ventricular contractions (PVCs)
72
Q

What is a premature atrial contraction and how can it be identified on ECG?

A
  • ectopic beats that originate in the atria (but not in the SA node)
  • the contour of the P wave, the PR interval and the timing are different than a normally generated pulse from the SA node
73
Q

What is the aetiology of a premature atrial contraction?

What will the QRS complex look like?

A

excitation of an atrial cell that forms an impulse that is then conducted normally through the AV node and ventricles

when an impulse originates anywhere in the atria (SA node, atrial cells, AV node, bundle of His) and this is conducted normally through the ventricles, the QRS complex will be narrow

74
Q

What is a premature ventricular contraction (PVC)?

When are they uniform or multiform?

A

ectopic beats originate in the ventricles resulting in wide and bizarre QRS complexes

when there is more than 1 premature beat and they look alike, they are called “uniform”

when they look different, they are called “multiform”

75
Q

What is the aetiology of PVCs?

A

one or more ventricular cells are depolarising and the impulses are abnormally conducting through the ventricles

when an impulse originates in a ventricle, conduction through the ventricles will be inefficient and the QRS complex will be wide and bizarre

76
Q

What are the 3 different types of supraventricular arrhythmias?

A
  • atrial fibrillation
  • atrial flutter
  • paroxysmal supraventricular tachycardia
77
Q

What is atrial fibrillation?

How common is it and who does it tend to affect?

A
  • there is no organised atrial depolarisation so no normal P waves (impulses are not originating from the sinus node)
  • atrial activity is chaotic (resulting in an irregularly irregular rate)
  • it is common and affects 2-4% of individuals, 5-10% if >80 years old
78
Q
A

Core Conditions - Cardiovascular (6 decks)

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