What is first degree heart block?
Arrythmia with a fixed, prolonged PR interval
What is Mobitz type 1 second degree heart block?
PR intervals slowly increase, before a QRS complex is dropped
What is Mobitz type 2 second degree heart block?
PR intervals remain the same length but QRS complexes are dropped
What is third degree heart block?
P waves and QRS complexes are completely unrelated
What is the anatomical location of the conduction block in first degree heart block?
Between the SA node and the AV node (in the atrium)
Where does the anatomical block to conduction occur in Mobitz type 1 second degree heart block?
In the AV node
Where does the anatomical block to conduction occur in Mobitz type 2 second degree heart block?
Occurs after the AV node in the bundle of His or Purkinje fibres
Where does the anatomical block to conduction occur in third degree heart block?
Anywhere from the AV node down causing complete blockage
What two things could a shortened PR interval on an ECG mean?
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)
An accessory pathway, causing faster conduction to the ventricle than the usual slow route across the atrial wall
When would a broad QRS complex occur?
Abnormalities in the 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, because the impulse gets to one ventricle rapidly down the intrinsic conduction system then has to spread slowly across the myocardium to the other ventricle
What changes on an ECG would an atrial ectopic beat result in?
An atrial ectopic would result in a narrow QRS complex because it would conduct down the normal conduction system of the heart
What do tall QRS complexes on an ECG imply?
Although could just be a tall person
What is a delta wave?
A sign that the ventricles are being activated earlier than normal from a point distant to the AV node e.g. through an accessory pathway
What is the cause of this abnormal ECG?
Hyperkalaemia - see tented T waves (AvR) and ST elevation (all due to hyperkalaemia)
What is the abnormality on this ECG?
Torsade de Pointes
What are the causes for torsade de pointes?
- low blood magnesium, and low blood potassium (commonly seen in malnourished and alcoholics)
- QT prolonging medications such as clarithromycin, levofloxacin, or haloperidol
- taken with fluoxetine
What is a focal tachycardia?
A tachycardia originating from one point in the heart e.g. the SA node
What is an atrial tachycardia and in which patients is this usually seen?
A different focus in the atrium takes over from the sinoatrial node resulting in abnormal P waves preceding QRS complexes
Often seen in patients with chronic lung disease
How is inappropriate (i.e. no underlying cause such as sepsis) sinus tachycardia treated?
Inappropriate sinus tachycardia can be slowed using beta blockers or ivabradine (selective sinus node blocker) but is usually best left alone
How should appropriate (i.e. due to underlying cause such as sepsis or anaemia) sinus tachycardia treated?
Underlying cause treated
How can atrial tachycardias be controlled?
Usually the rate can be controlled with calcium channel blockers or beta blockers
What abnormality is this and what arrythmia is it characteristic of?
Saw tooth baseline
What is atrial flutter?
Atrial flutter is caused by a re-entrant rhythm in either the right or left atrium
This re-entrant circuit around the atrium causes activation of the AV node every time electrical impulses pass through it
Do supraventricular tachycardias give a narrow or broad ECG complex?
Do ventricular tachycardias give a narrow or broad QRS complex?
Is this a supraventricular or ventricular tachycardia?
Ventricular - broad QRS
What is the only SVT that causes wide QRS complexes?
Supraventricular tachycardia with a bundle branch block
What is the abnormality here?
Right bundle branch block - RSR in lead V1 makes an M shape (M for MaRRow)
What is the abnormality here?
Left bundle branch block - RSR' wave in lead V6
What is the most serious ventricular tachycardia?