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
2
Q
What is shown by the P wave on an ECG?
A
the P wave shows atrial depolarisation
3
Q
What is shown by the QRS complex on an ECG?
A
the QRS complex shows ventricular depolarisation
4
Q
What is shown by the T wave on an ECG?
A
the T wave shows ventricular repolarisation
this is diastole
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)
6
Q
A
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
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
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
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
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
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
13
Q
What is a normal heart rate?
A
- normal heart rate is 60 - 100 bpm
- tachycardia is > 100 bpm
- bradycardia is < 60 bpm
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
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
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
17
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A
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
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
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
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
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?
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
24
Q
What may suggest a diagnosis of atrial fibrillation?
A
if P waves are absent and there is an irregular rhythm
25
What is a normal PR interval?
What does it suggest if PR interval is prolonged?
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)**
26
What is meant by first degree heart block (AV block)?
first-degree heart block involves a **_fixed prolonged PR interval_** (**\>200 ms**)
27
What are other names for second-degree heart block (type 1)?
How can this be identified on ECG?
**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**
28
What is another name for second-degree heart block (type 2)?
What are the typical ECG findings?
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_**
29
What is third-degree heart block (complete heart block)?
What are typical ECG findings?
* 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
30
Where do narrow-complex and broad-complex escape rhythms originate from in third degree heart block?
* **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**
31
What is the anatomical location of first-degree AV block?
* this is AV block occurring **_between the SA node_** and the **_AV node_** (i.e. within the atrium)
32
What is the anatomical location of second-degree heart block?
* 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
What is the anatomical location of third-degree AV block?
this occurs **_at or after the AV node_** resulting in a complete blockade of distal conduction
34
What are the 2 possible reasons for a shortened PR interval?
* 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
When assessing the QRS complex, what 3 characteristics need to be assessed?
* width
* height
* morphology
36
How can the width of the QRS complex be described?
* it is **_NARROW_** when it is **_\< 0.12 seconds_**
* it is **_BROAD_** when it is **_\> 0.12 seconds_**
37
Under what circumstances does a narrow QRS complex occur?
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
Under what circumstances does a broad QRS complex occur?
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
Would an atrial ectopic be described as a narrow or broad QRS complex?
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
In what 2 different ways can the height of the QRS complex be described?
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
What do tall QRS complexes imply?
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
How is morphology of the QRS complex assessed?
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
What is the delta wave?
Why might it be present on an ECG?
* 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
What is needed to diagnose Wolff-Parkinson-White syndrome?
* the presence of a delta wave alone does NOT diagnose WPW syndrome
* there must be evidence of **_tachyarrhythmias AND a delta wave_**
45
What is a pathological Q wave?
* **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
What can Q waves on ECG be indicative of?
* 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
How are R and S waves assessed when assessing the QRS complex?
What can problems with this process indicate on ECG?
* 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
What is the J point?
the J point is where the **_S wave joins the ST segment_**
49
What is "high take off" related to the J point?
What can it often be confused for?
* 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
What are the 4 key points for assessing the J point segment?
* 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
Where is the ST segment?
What does it look like in a normal person?
the ST segment is the part of the ECG between the **_end of the S wave_** and the **_start of the T wave_**
52
When is ST-elevation significant?
What is it most commonly caused by?
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
What is ST depression and what does it indicate?
ST depression **\>/= 0.5 mm** in **\>/= 2 contigious leads** indicates **_myocardial ischaemia_**
54
What do T waves represent?
When are T waves considered to be tall?
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
What are tall T waves associated with?
Tall T waves can be associated with:
* **_hyperkalaemia_** ("tall tented T waves")
* **_hyperacute STEMI_**
56
When are T waves normally inverted?
* T waves are normally inverted in **V1**
* inversion in **lead III** is a normal variant
57
What can inverted T waves in other leads be a sign of?
**_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
59
What are biphasic T waves and what conditions are they associated with?
biphasic T waves have **_2 peaks_**
they can be indicative of **_ischaemia_** and **_hypokalaemia_**
60
What are flattened T waves and what do they demonstrate?
this is a **non-specific sign** that may represent **_ischaemia_** or **_electrolyte imbalance_**
61
What is a U wave?
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
Classically, when might U waves be seen?
* 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
What is aetiology of normal sinus rhythm?
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
How can arrhythmias form?
arrhythmias can arise from problems in the:
* sinus node
* atrial cells
* AV junction
* ventricular cells
65
What are the 2 possible problems of the SA node?
the SA node can:
* fire too slowly
* fire too quickly
sinus tachycardia may be an appropriate response to stress
66
What are the possible problems that can occur with atrial cells?
* 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
What is a re-entrant circuit?
a re-entrant pathway occurs when an impulse **loops** and results in **self-perpetuating impulse formation**
68
What is meant by multiple micro re-entrant "wavelets"?
this refers to wandering small areas of activation which generate fine chaotic impulses
colliding wavelets can, in turn generate new foci of activation
69
What is the aetiology of sinus bradycardia?
SA node is depolarising **slower than normal**
the impulse is conducted **normally** (i.e. normal PR and QRS interval)
70
What is the aetiology of sinus tachycardia?
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
What are the 2 different types of premature beats?
* premature atrial contractions (PACs)
* premature ventricular contractions (PVCs)
72
What is a premature atrial contraction and how can it be identified on ECG?
* **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
What is the aetiology of a premature atrial contraction?
What will the QRS complex look like?
**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
What is a premature ventricular contraction (PVC)?
When are they uniform or multiform?
**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
What is the aetiology of PVCs?
**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
What are the 3 different types of supraventricular arrhythmias?
* atrial fibrillation
* atrial flutter
* paroxysmal supraventricular tachycardia
77
What is atrial fibrillation?
How common is it and who does it tend to affect?
* 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
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