Abnormalities in ECG traces

Question 1

How will atrial fibrillation affect the heart beat?

Answer 1

there will still be a regular pulse + HR, just chaotic atrial depolarisation

Question 2

Roughly what is the HR of atrial fibrillation and QRS complex period?

Answer 2

100-160bmp

Question 3

What happens in ventricular fibrillation?

Answer 3

not coordinated ventricular contraction due to multiple impulses arising from many ectopic sites within ventricles (varying amplitude, chaotic, accelerated rhythm)
can lead to cardiac arrest
looks like squiggles (Torsades de Pointes is a type of VF which looks like the cover of arctic monkey’s AM album)

Question 4

What happens in ventricular ectopic beats? What can it lead to?

Answer 4

Depolarisation spreads through ventricular muscle instead of Purkinje fibres, so depolarisation takes a lot longer, leading to WIDE QRS complex
can lead to ‘ventricular tachycardia’ which is a run of 3 OR MORE ventricular ectopic beats (abnormal + prolonged QRS)

Question 5

What is ectopic foci?

Answer 5

abnormal pacemaker sites within the heart which isn’t SAN or AVN
normally suppressed by the higher rate of regular SAN (overdrive suppression)
can be atrial or ventricle

Question 6

What is a 1st degree heart block?

Answer 6

normal P wave and normal QRS complex, BUT prolonged time interval between the 2
normally because there is a lack of blood supply leading to lack of O2 or degenerative changes
PR interval > 5 small squares (0.2ms)

Question 7

What is 2nd degree heart block? (Mobitz 1B / Wenkebach phenomenon)

Answer 7

Progressive lengthening of PR interval until a P wave isn’t conducted - allows time for AVN to recover
from malfunctioning AV node cells - progressively fatigue until they fail to conduct an impulse

caused by B-blockers, Ca2+ channel blockers, tetralogy of Fallot repair, mitral valve repair

Question 8

What is type 2 second degree heart block? (Mobitz I)

Answer 8

PR interval normal but missing QRS complex every so often, requires pacemaker as can lead to complete HB
due to cells of His-Purkinje system fail suddenly and unexpectedly

Cause: B-blockers, Ca2+ channel blockers, after cardiac surgery (tetralogy of Fallot + mitral valve repair)

Question 9

What is complete AV block? (3rd degree heart block)

Answer 9

1. P waves normal but not conducting to the ventricles - very slow HR (30-40bpm)
2. so ventricular pacemaker takes over, rhythm out of synch with P waves
3. wide QRS complex as it takes a long time for the ventricles to complete course of depolarisation
4. URGENT pacemaker required, HR too slow to maintain perfusion

Question 10

How does atrial fibrillation appear? Why?

Answer 10

1. No P waves (atrial depolarisation): AP not fired regularly in SAN (atrium), no constant pulses towards AVN (atrium ‘quivering’)
2. QRS irregularly irregular: should an AP be fired from SAN to AVN, it sends AVN into refractory period
3. Irregular impulse to ventricles - irregular PR interval (atrial to ventricle depolarisation)

Question 11

How will a patient with type 3 heart block present?

Answer 11

severe bradycardia with independent atrial and ventricular rates (AV dissociation)
Atrial rate is more regular and quicker than ventricular

From end point of either Mobitz 1 (progressive fatigue of AVN) or Mobitz II (failure of His-Purkinje system)
Treat with atropine / isoprenaline