heart block Flashcards
3 types of heart block
first degree
2nd degree
3rd degree (complete)
what are the 2 places that can be blocked
Block in AVN or bundle of His = AV block
Block in lower conduction system = Bundle Branch Block (RBBB or LBBB)
3 causes of heart block
- Coronary artery disease
- Cardiomyopathy
- Fibrosis of conducting tissues (particularly in elderly people)
what is first degree heart block
This is the result of delayed AV conduction (but still makes it to the ventricles) and is reflected by a prolonged PR interval (>0.22s) on the ECG
4 causes of first degree heart block
- LEV’s disease
- IHD – scar tissue from myocyte death blocks conduction pathway
- Myocarditis
- Hypokalaemia
management for first degree heart block
asymptomatic so no treatment required
what is second degree heart block
This occurs when some atrial impulses fail to reach the ventricles
2 forms of second degree heart block
- Mobitz type 1 (Wenckebach)
- Mobitz type II`
what happens in mobitz type 1 heart block
- Generally caused by AV node block and results in progressive PR interval prolongation until a P wave fails to conduct and a QRS is absent after the first P wave (dropped beat)
- Eventually ventricle’s pacemaker cells kick in
- The PR interval then returns to normal and the cycle repeats itself
what does patient with mobitz type 1 heart block experience
light headedness, dizziness and syncope
what happens in mobitz type 2 heart block
- Caused by a block at an intra-nodal level so the QRS is widened and QRS complexes are dropped without PR prolongation
- Fairly random dropped beats – no PR elongation
what does patient with mobitz type 2 heart block experience
chest pain, SOB, syncope and postural hypotension
what is third degree complete heart block
Occurs when there is complete dissociation between atrial and ventricular activity.
E.g. atrial BPM is 60, ventricular is 30 BPM
3 causes of third degree heart block
CHD
Infection
Hypertension
4 symptoms of third degree heart block
Syncope
Dyspnoea
Chest pain
Confusion
what does ECG for third degree heart block show
P waves and QRS complexes occur independent
Ventricular contractions are sustained by spontaneous escape rhythm originating below the site of the block in 2 places
what does ecg show if block is in his bundle
His bundle – gives rise to a narrow QRS complex at a rate of 50-60 BPM and is relatively reliable
what does ecg show if block is in his purkinje system
i.e. distally – gives rise to a broad QRS complex at a rate of <40 BPM, often associated with dizziness and blackouts
treatment for third degree heart block
IV atropine (acute) – increases HR
Permanent pacemaker insertion
what is bundle branch block
Complete block of a bundle branch is associated with a wide QRS complex with an abnormal pattern and is usually symptomatic.
causes of acute bundle branch block
Ischaemia and MI
Myocarditis
causes of chronic bundle branch block
HTN
Cardiomyopathies
2 types of bundle branch block
RBBB
LBBB
what is RBBB bundle branch block
There is sequential spread of an impulse (i.e. LV then RV)
Results in an R wave in V1 and a slurred S wave in V5/6 (
