ECGs

Question 1

How would you approach an ECG?

Answer 1

1) Check Patient ID
2) Rate - Regular = 300/Large Squares; Tachy = 1500/Small Squares; Irregular = R waves x 6
3) Rhythm - P Waves (Check Leads II, V1 & V2)
4) Axis - Upwards/Downwards (Check QRS in Leads I - III; RAD = ↓ In I;LAD = ↓ In II & III)
5) QRS Complexes - Widening = > 3 Small Sqs.
6) ST Segment (Horizontal & Isoelectric; Elevation/Depression/Strain with LVH)
7) Q-T Interval (2 large squares)
8) T Waves (Normal Inversion = V1/V2, aVR & III - not V2 alone; Abnormal Inversion = I, II & V4-V6)

Resources

https: //litfl.com/ecg-rhythm-evaluation/
https: //www.youtube.com/watch?v=ENyBhCJ2llY
https: //learning.bmj.com/learning/course-intro/ecg-skills.html?courseId=10046609&locale=en_GB

Question 2

How is HR calculated?

Answer 2

25 mm/s

Each small square is 0.04s

Each large square is 0.2s - 5 large squares = 1s

6x Number of R waves will give rate or 300/R-R Interval

If more rapid then divide by 1500

< 60 = Bradycardia

> 100 = Tachycardia

Question 3

How is Rhythm Calculated?

Answer 3

Heart Rhythm

Check for electrical activity

Assess P waves: check leads II, V1 & V2 also

Check Sinus Rhythm via PR Interval: PR Interval ~ 3-5 Small Squares

Check Sinus Rhythm - P wave precedes QRS complex; Normal P-R Interval; Constant P-R Interval

Check QRS is regular/irregular or narrow/broad.

Is QRS Regular or irregular?

If irregular is it regularly irregular or irregularly irregular?

Types of Sinus Rhythm

Sinus Tachycardia = > 100 beats/min

Sinus Bradycardia = < 60 beats/min

Sinus Arrhythmia = normal variation in HR with respiration (increase on inspiration)

REGULAR rhythms

Rate = 300 / number of LARGE squares between consecutive R waves

Very FAST rhythms:

Rate = 1500 / number of SMALL squares between consecutive R waves.

SLOW or IRREGULAR rhythms:

Rate = Number of R waves X 6

The number of complexes (count R waves) on the rhythm strip gives the average rate over a ten-second period. This is multiplied by 6 (10 seconds x 6 = 1 minute) to give the average Beats per minute (bpm)

Question 4

Describe P Waves and their Characteristics (including duration)

Answer 4

Represents atrial depolarisation

Assess in Leads II, V1 & V2

P waves should be upright in leads I and II, inverted in aVR

Duration: < 0.12 s (<120ms or 3 small squares wide and 2.5 squares tall)

Atrial abnormalities are most easily seen in the inferior leads (II, III and aVF) and lead V1, as the P waves are most prominent in these leads.

Abnormal = P Pulmonale (Peaked) = Tall, Peaked P Waves (R. Atrial Enlargement)

OR P Mitrale (look like M) = Wide Bifid P Waves (Mitral Stenosis)

https://litfl.com/p-wave-ecg-library/

Question 5

Describe the PR Interval and its characteristics (including duration)

Answer 5

Measured from the start of Atrial depolarisation (P wave) to the start of Ventricular depolarisation (Q wave)

Represents delay at AV node, protects ventricles and allows for ventricular filling

Normal = 120-200ms (3-5 small squares)

Abnormal = >200ms Heart Block (1st Degree, Mobitz 12nd Degree with prolonged PR)

https://litfl.com/pr-interval-ecg-library/

Question 6

Describe the QRS Complex

Answer 6

Normal = <120ms (3 small squares)

Abnormal = Narrow or Broad Complex or Aberrant conduction i.e. LBBB/RBBB

Narrow complexes (QRS < 120 ms/3 small squares) are Supraventricular (above AV node) in origin.

Broad complexes (QRS > 120 ms/3 small squares) may be either ventricular in origin, OR due to aberrant conduction of supraventricular complexes (e.g. due to bundle branch block, hyperkalaemia or sodium-channel blockade).

R wave progression - R waves should increase in amplitude from V1 to V6.

Question 7

Describe the QT Interval

Answer 7

Measured from the start of the QRS until the end of the T wave at Lead II or V5-6.

Represents ventricular repolarisation

Calculated by the Bazett formula: QTC = QT / √ RR

Abnormal = Torsades de Pointes

Question 8

Describe the characteristics of the T wave

Answer 8

Upright in all leads except aVR and V1

Amplitude < 5mm in limb leads, < 10mm in precordial leads (10mm in men, 8mm in women)

Abnormal = Peaked, Hyperacute, Inverted T waves, Biphasic T waves, ‘Camel Hump’ T waves, Flattened T waves.

Question 9

Describe how the Cardiac Axis is Calculated

Answer 9

Assess QRS Complexes in Leads I & avf

Normal = +ve in I and avf

Left Axis Deviation (LAD -30 to 180) = Lead I +ve and Lead avF -ve.

Right Axis Deviation (RAD +90 to +180) = Lead I -ve and Lead avF +ve.

Indeterminate axis = Lead I -ve and avF -ve.

LAD indicative of LVH or MI.

RAD indicative of RVH, PE or MI.

Question 10

List Causes of RAD

Answer 10

Right ventricular hypertrophy

Acute right ventricular strain, e.g. due to pulmonary embolism

Lateral STEMI

Chronic lung disease, e.g. COPD

Hyperkalaemia

Sodium-channel blockade, e.g. TCA poisoning

Wolff-Parkinson-White syndrome

Dextrocardia

Ventricular ectopy

Secundum ASD – rSR’ pattern

Normal paediatric ECG

Left posterior fascicular block – diagnosis of exclusion

Vertically orientated heart – tall, thin patient

Question 11

List causes of LAD

Answer 11

Left ventricular hypertrophy

Left bundle branch block

Inferior MI

Ventricular pacing /ectopy

Wolff-Parkinson-White Syndrome

Primum ASD – rSR’ pattern

Left anterior fascicular block – diagnosis of exclusion

Horizontally orientated heart – short, squat patient

Question 12

What does the following rhythm show?

Answer 12

Sinus Rhythm

Normal ventricular contraction

Atrial contraction initiated by SA node depolarisation

P wave for every QRS complex

AP is propagated through AV node to ventricle after ‘delay’ of <200ms (PR <200ms)

Question 13

What does the following rhythm show and how would you treat?

Answer 13

Sinus Arrhythmia

ECG meets all criteria of sinus rhythm but the rhythm is irregular (R-R interval)

Irregularity caused by physiological changes in the cardiac timing caused by respiration

Considered to be a normal variant

P wave for every QRS complex

No treatment required

Question 14

What does the following rhythm show and describe its treatment?

Answer 14

Atrial Fibrillation

Disorganised electrical activity in the atria (impulses no longer travel from SA to AV node). AV node receives continuing electrical impulses and conducts some of these to the ventricle. Can occur at any ventricular rate (anywhere between 30 - 200 bpm)

Characterised by: Irregularly Irregular. No P Waves, Irregular QRS Complex (R-R intervals) and Ragged Baseline

Treatment:

https://litfl.com/atrial-fibrillation-ecg-library/

Question 15

What does the following rhythm show and describe its treatment?

Answer 15

A regular, usually narrow-complex (QRS <120ms/3 small squares) tachycardia

Caused by a re-entry circuit within the atria, resulting in an atrial rate of 300 bpm.

Characterised by: ‘Saw-Tooth’ Baseline appearance (lead V1 or Lead II, III and aVF), Ventricular Rate is a division of 300 (3F:1 QRS ratio or variable) and F Waves.

Treatment:

https://litfl.com/atrial-flutter-ecg-library/

Question 16

What does the following rhythm show and describe its treatment?

Answer 16

Junctional Rhythm

Originates at the AV junction instead of SA node, therefore electrical impulse travels to atria and ventricles simultaneously. Rate may be normal, bradycardic or tachycardic.

Characteristics: Regular Rhythm. Retrograde (inverted) P waves can be seen in the ST segment (seen as negative deflection) with narrow QRS-Complex unless co-existing LBBB/RBBB.

Treatment:

https://litfl.com/junctional-escape-rhythm-ecg-library/

Question 17

What does the following rhythm show and describe its treatment?

Answer 17

Originates above or involves the AV node. Exclude Sinus, Atrial Fibrillation and Atrial Flutter. Generally involves an accessory pathway i.e. WPW. No obvious flutter waves.

Characteristics: Regular, Narrow-Complex (QRS <120ms/3 small squares) Tachycardia. Often no clear P Waves. Notch on ST-Segment (retrograde p-wave).

Treatment:

https://litfl.com/supraventricular-tachycardia-svt-ecg-library/

Question 18

What does the following rhythm show and describe its treatment?

Answer 18

Supraventricular Ectopics

Sinus rhythm. Differing morphologies of P waves on beats 3, 6 and 9.

Characteristics: Regular, Early P waves on beat 3, 6 and 9, Narrow QRS Complex (<120ms/3 small squares). Varying PR and R-R intervals.

Question 19

Describe the characteristics of Ventricular Rhythms

Answer 19

Originate from ventricles. Always pathological

Always Broad Complex (QRS >120 ms/3 small squares)

Includes: Ventricular Premature Complexes, Ventricular Tachycardia (monomorphic/polymorphic), Ventricular Escape Rhythm, Ventricular Fibrillation.

They need to be differentiated from aberrant rhythms i.e. VF with LBBB.

https://www.aclsmedicaltraining.com/blog/svt-aberrancy-ventricular-tachycardia/

Question 20

What does the following rhythm show and describe its treatment?

Answer 20

Ventricular Premature Complexes (VPCs) - Trigeminy

A premature beat arising from an ectopic focus within the ventricles.

Characteristics: Broad QRS complex (≥ 120 ms) with abnormal morphology. Unifocal — Arising from a single ectopic focus; each PVC is identical or Multifocal — Arising from two or more ectopic foci; multiple abnormal QRS morphologies.

Features:

Broad QRS complex (≥ 120 ms) with abnormal morphology.

Premature — i.e. occurs earlier than would be expected for the next sinus impulse.

Discordant ST segment and T wave changes.

Usually followed by a full compensatory pause.

Retrograde capture of the atria may or may not occur.

Question 21

What does the following rhythm show and describe its treatment?

Answer 21

VPC: Bigeminy - ‘ectopics’, ‘VPB’, ‘PVC’ - may be a normal finding. Characterised by: 1 sinus beat coupled with a VPC.

https://litfl.com/premature-ventricular-complex-pvc-ecg-library/

Question 22

What does the following rhythm show and describe its treatment?

Answer 22

Ventricular Tachycardia

Monomorphic: Most common form. Regular broad-complex tachycardia (QRS >120ms/3 small squares). May be associated with haemodynamic compromise. Always abnormal and must be acted upon.

https://litfl.com/ventricular-tachycardia-monomorphic-ecg-library/

Question 23

What does the following rhythm show and describe its treatment?

Answer 23

Ventricular Tachycardia

Polymorphic: Regular broad-complex tachycardia (QRS >120ms/3 small squares). Looks like Forth Rail Bridge. Torsades de pointes - twisting around the point. May be difficult to distinguish from VF. Often associated with long-QT interval and ‘R’ on ‘T’ phenomenon.

Question 24

What does the following rhythm show and describe its treatment?

Answer 24

Ventricular Fibrillation

Characteristics: Irregular Random baseline. No clear discernable waveforms. Chaotic irregular deflections of varying amplitude. Rate 150 to 500 bpm.

No identifiable P waves, QRS complexes, or T waves. May be subtle.

Always associated with LOC

Treatment: DC Cardioversion

Question 25

What does the following rhythm show and describe its treatment?

Answer 25

**Capture and Fusion Beats** Capture beat occurs when a sinus beat is conducted through the AV node. Early narrow complex beat. Fusion beats are fusion between the sinus beat and next VT beat. Both are proof of independent rhythms in the atria and ventricles. Capture and Fusion beats are almost always diagnostic of VT.

Question 26

Describe the characteristics of 'Aberrancy'

Answer 26

**Aberrancy** Broad QRS Complex (\>120ms/3 small squares) - Hallmark of Ventricular Rhythm. If in doubt, treat as Ventricular Tachycardia. A good predictor of SVT with aberrancy is the pre-existence of LBBB/RBBB. A good predictor of VT is pre-existing Coronary Disease VT should always be confirmed by 12-lead ECG if patient is not in cardiac arrest [https://litfl.com/vt-versus-svt-ecg-library/](https://litfl.com/vt-versus-svt-ecg-library/)

Question 27

Describe the concept of Heart Block

Answer 27

Heart Block (HB) Issue with conduction between atria and ventricles (signal takes longer to reach) Due to AV nodal dysfunction i.e. Drugs, Ischaemia, Age. [https://litfl.com/heart-block-and-conduction-abnormalities/](https://litfl.com/heart-block-and-conduction-abnormalities/)

Question 28

What does the following rhythm show, describe its treatment

Answer 28

**1st Degree HB** **Characteristics:** PR Interval prolonged (\>200ms/1 large square) but constant - no progressive lengthening. Stable rhythm. No haemodynamic disturbance. No specific treatment required **Causes:** Increased vagal tone, Athletic training, Myocarditis, Normal Variant.

Question 29

What does the following rhythm show, describe its treatment

Answer 29

**2nd Degree HB - Mobitz I (Wenckebach Phenomenon)** **Characteristics:** **Progressive PR Interval prolongation (\>200ms/1 large square).** Cyclical. 1st PR Normal. PR then lengthens. Eventually P wave with No QRS Complex i.e. Eventual ‘Missed Beat’ - **‘Drops a beat’.** Due to time taken for the AV node to repolarise in order to ‘accept’ the next impulse. May be a normal variant, especially with high vagal tone (athletes). Not treated unless severe or accompanied with collapse/haemodynamic compromise. **Causes:** Drugs (BBs, CCBs, Digoxin, Amiodarone) **Treatment:** Asymptomatic patients do not require treatment. Symptomatic patients usually respond to atropine. Permanent pacing is rarely required.

Question 30

What does the following rhythm show, describe its treatment

Answer 30

**2nd Degree HB - Mobitz II (Hay)** **Characteristics:** PR Constant. P Wave with No QRS Complex. Subsequent missed beat/QRS. Failure of conduction at the level of the His-Purkinje system (i.e. below the AV node). May deteriorate into CHB/Asystole. **Causes:** Structural damage to the conducting system (e.g. infarction, fibrosis, necrosis). **Treatment:** Immediate admission for cardiac monitoring, backup temporary pacing and ultimately insertion of a permanent pacemaker. [https://litfl.com/av-block-2nd-degree-mobitz-ii-hay-block/](https://litfl.com/av-block-2nd-degree-mobitz-ii-hay-block/)

Question 31

What does the following rhythm show, describe its treatment

Answer 31

**3rd Degree HB (Complete HB/AV Block)** No functioning electrical connection between Atria & Ventricles. Complete absence of AV conduction – none of the supraventricular impulses are conducted to the ventricles. P Waves & QRS Complexes Present. **Characteristics:** No relationship between P wave and QRS complex. Broad QRS Complex (\>120ms/3 small squares) - ventricular escape\* rhythm. Typically the patient will have severe bradycardia with independent atrial and ventricular rates, i.e. AV dissociation. Tip: Mark P Wave Positions, Move along to QRS - P Waves & QRS will be dissociated Treatment: They require urgent admission for cardiac monitoring, backup temporary pacing and usually insertion of a permanent pacemaker. In the event of circulatory collapse with complete HB, IV Atropine and Isoprenaline may be indicated as stabilising measures until trans venous pacing wire insertion can be undertaken. [https://litfl.com/av-block-3rd-degree-complete-heart-block/](https://litfl.com/av-block-3rd-degree-complete-heart-block/%C2%A0) \*Occurs at 30-40bpm and is broad, regular and dissociated from atrial activity. Junctional and ventricular escape rhythms arise when the rate of supraventricular impulses arriving at the AV node or ventricle is less than the intrinsic rate of the ectopic pacemaker. https://litfl.com/junctional-escape-rhythm-ecg-library/

Question 32

Brieftly state the types of Fascicular Block and their features

Answer 32

**Fascicular Blocks** Fascicles refers to AV node, LAHB, LPHB, Rt Bundle Branch [https://litfl.com/ecg-conduction-block-ecg-library/](https://litfl.com/ecg-conduction-block-ecg-library/%C2%A0) **Bifascicular Block - 2 of** PR \> 200ms LAD (LAHB) RBBB [https://litfl.com/bifascicular-block-ecg-library/](https://litfl.com/bifascicular-block-ecg-library/%C2%A0) **Trifascicular Block** PR \>200ms LAD (LAHB) RBBB [https://litfl.com/trifascicular-block-ecg-library/](https://litfl.com/trifascicular-block-ecg-library/%C2%A0) **Trifascicular Block** Alternating RBBB & LBBB

Question 33

What does the following rhythm show, describe its treatment

Answer 33

**Pulseless Electrical Activity** Cardiac Arrest occurring with any rhythm which would usually be associated with a pulse is termed pulseless electrical activity. Treatment: Prompt CPR is indicated and identification of a potential reversible cause. [https://litfl.com/pulseless-electrical-activity/](https://litfl.com/pulseless-electrical-activity/)

Question 34

Describe the ECG Vascular Territories

Answer 34

**Anterior/Anteroseptal** - V1-V4; LAD **Inferior** - II, III & aVF; RCA **Anterolateral** - I, aVL, V4-V6; LAD/LCX **Lateral** - I, aVL +/- V5-V6; LCX **Posterior** - Tall R Waves V1-V2; LCX/RCA

Question 35

State the markers of Ischaemia

Answer 35

**T-Wave Changes** - Tall - Biphasic - Inverted - Flattened **ST Depression** - Subtle - Widespread - Deep - Generally prognostic - Widespread and deep = poor prognostic sign