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CVS * > S6 Interpreting ECGs > Flashcards

S6 Interpreting ECGs Flashcards

1
Q

What are the 3 types of atrioventricular conduction blocks?

A
  1. First degree heart block
  2. Second degree heart block - Mobitz type 1 and Mobitz type 2
  3. Third degree heart block
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2
Q

What is an atrioventricular conduction block?

A

Delay/failure of conduction of impulses from the atria to the ventricles via the AV node (more than physiological/normal) and Bundle of His

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3
Q

What are the 4 causes of heart blocks?

A
  • degeneration of the electrical conducting system with age (sclerosis and fibrosis)
  • acute myocardial ischaemia
  • medications
  • valvular heart disease
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4
Q

What happens in first degree AV/heart block (describe the rhythm, PR interval and QRS complex)?

A 
Conduction is slowed without skipped beats - all normal P waves are followed By QRS complexes but with a longer PR interval (a partial block)
* Rhythm - regular 
* PR interval - more than 0.2 seconds 
* QRS complex - usually normal 
Usually asymptomatic
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5
Q

What happens in Mobitz type 1/Wenkebach second degree AV/heart block?

A

There are successively longer PR intervals until one QRS is dropped/lost (electrical signal is not conducted through ventricles), then this cycle starts again (an increasing block)

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6
Q

What happens in Mobitz type 2 second degree AV/heart block?

A

The PR intervals don’t lengthen, there is just a sudden drop in QRS complex without any PR changes (the p waves are regular). Ventricular rhythm is irregular

This is symptomatic and has a high risk of progression to a complete heart block

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7
Q

Where can Mobitz type 2 second degree heart/AV block, block?

A
  • level of Bundle of His
  • at bilateral bundle branches
  • at trifascicular bundle branches
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8
Q

What happens in third degree AV/heart block? What does the QRS complex look like? What is required in this type urgently?

A

The atria and ventricles are depolarising independently due to complete failure of AV conduction. So the ventricular pacemaker takes over (at 20-40bpm which is too slow to maintain blood pressure)

Wide

A pacemaker

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9
Q

What is a bundle branch block? What are the P waves, PR intervals and QRS complexes like?

A

Delayed conduction in the bundle branches (left or right bundle branch block)

  • p wave - normal
  • PR interval - normal
  • QRS complex - wide - because ventricle depolarisation takes longer

(V1 - W in S wave, V6 - M in S wave)

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10
Q

Where may abnormal arrhythmias arise from?

A
  1. Atria (supraventricular arrhythmias)
    * sinus node
    * atrium
    * AV node
  2. Ventricles (ventricular arrhythmias)
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11
Q

What are the QRS complexes like in a supreventricular and ventricular arrhythmias?

A

Supraventricular - normal

Ventricular - wide and bizzare

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12
Q

What is atrial fibrillation? What are the impulses like? Describe the P waves, R-R intervals and QRS complex.

A

Supraventricular arrythmia - arises from multiple atrial foci, rapid chaotic impulses

  • P waves - non-existent - just a wavy baseline
  • R-R intervals - irregular
  • QRS complex - normal as ventricles are depolarised normally as not all impulses at AV node are conducted
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13
Q

What are the ECG variations of atrial fibrillation (Afib)?

A
  • slow - ventricular response is less than 60bpm
  • fast - ventricular response is over 100bpm
  • normal rate - 61-99bpm
  • coarse fibrillation - amplitude above 0.5mm
  • fine fibrillation - amplitude below 0.5mm
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14
Q

What happens to atrial and ventricle contractions in atrial fibrillation?

A

The atrial contraction is lost (atria just ‘quiver’), the ventricles contract normally

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15
Q

What happens to the heart rate and pulse in atrial fibrillation?

A

Both are ‘irregularly irregular’

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16
Q

What does the loss of atrial contraction in atrial fibrillation mean for the haemodynamics (of blood in atria)?

A

Increases blood stasis (this is more evident in L atrium) so small clots form in L atrium - this is a risk factor for ischaemic stroke

17
Q

What are premature ventricular ectopic beats/contractions (PVCs)?

A
  • ectopic foci in ventricle muscles provides an extra contraction that doesn’t spread via the His-Purkinje system
  • adds an additional QRS complex in every now and then
  • ventricles have a lower intrinsic heart rate so these extra complexes have a wider QRS
18
Q

What is ventricular tachycardia (VTACH)?

A

A broad complex tachycardia - when you have 3 or more consecutively PVCs (premature ventricular contractions) - this is dangerous and requires urgent treatment and has high risk progression to ventricular fibrillation

19
Q

What is ventricular fibrillation?

A

Abnormal, chaotic and fast ventricular depolarisations due to impulses from numerous ectopic sites in the ventricle - there is no cardiac output as there is no coordinated contraction, the ventricles just ‘quiver’ and if it is sustained, cardiac arrest occurs

20
Q

How can coronary ischamia or infarction occur?

A

Due to narrowing/occlusion of a coronary artery

21
Q

How does ST Segment Elevation Myocardial Infarction (STEMI) occur?

A

Due to complete occlusion of coronary artery (full thickness)

22
Q

What change in ST in STEMI?

A

ST elevation

23
Q

What are the evolving ECG changes in a STEMI?

A
  • acute - ST elevation
  • hours - ST elevation, decreased R wave, Q wave begins
  • day 1 to 2 - inversion of T wave, Q wave deepens
  • days later - ST normalises, the T wave is inverted
  • weeks later - ST and T are normal, Q wave persists
24
Q

Are all Q waves a sign of an old infarct or depolarisation of septum?

A

No - pulmonary embolism may also lead to a Q wave in lead III

25
Q

How can you tell a pathologic Q wave?

A
  • more than 1 small square wide
  • more than 2 small squares deep (except in leads III and aVR where a bigger Q wave could be normal)
  • if depth of Q wave is 1/4 heigh of subsequent R wave
26
Q

What are the ECG changes in non-STEMI and ischaemia?

A
  • ST segment depression

* T wave inversion

27
Q

What are the signs and symptoms of hypokalaemia?

A
  • potassium levels: low - below 3.5mmol/L, moderate - below 3.0mmol/L, severe - below 2.5mmol/L
  • muscle weakness, palpitations, arrythmia, cardiac arrest
28
Q

What does an ECG look like for someone who has hypokalaemia?

A
  • peaked P waves
  • T wave flattened/inverted
  • U waves form
29
Q

What are the signs and symptoms of hyperkalaemia?

A
  • potassium levels: above 5mmol/L

* muscle weakness, palpitations, arrhythmia, cardiac arrest

30
Q

What does an ECG look like for someone with hyperkalaemia?

A
  • tall tented T waves (5.5-6.5)
  • loss of P wave (6.5-7.5)
  • widening QRS (7.5-8.5)
  • widening QRS approaching sine wave (over 8.5)

CVS * (17 decks)

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