Heart block (Complete) Flashcards
What are the main types of heart block?
First degree heart block
Second degree heart block: Type I (AKA Mobitz Type I)
Second degree heart block: Type II (AKA Mobitz Type II)
Third degree heart block
What is first degree heart block?
Type of heart block caused by prolonged conduction along the AV node.
How is first degree heart block identified on ECG?
PR interval >200ms (>5 small squares)
N.B. PR interbval is start of P wave to start of Q wave
N.B. PR segment is end of P wave to start of Q wave
What are the main causes of first degree heart block?
High vagal tone (e.g. athletes)
Acute inferior MI
Electrolyte abnormalities (e.g. hyperkalaemia)
Drugs (e.g. beta-blockers, digoxin, cholinesterase inhibitors)
List examples of drugs which can cause first degree heart block.
Beta-blockers
Digoxin
Cholinesterase inhibitors (e.g. rivastigmine used to treat Alzheimer’s)
Non-DHP CCBs (e.g. fendilline, verapamil)
How is first degree heart block managed?
Is benign condition so no treatment needed.
However, should try to reverse underlying pathological causes (e.g. hyperkalaemia, medications)
What is second degree heart block type I (Mobitz type I)?
Type of heart block caused by reversible conduction block of AV node.
Characterised by PR interval prolongation followed by failure of P wave to conduct a QRS complex.
What are causes of mobitz type I?
MI (mainly inferior)
Drugs such as beta/calcium channel blockers, digoxin
Professional athletes due to high vagal tone
Myocarditis
Cardiac surgery
What is the management plan for Mobitz type I?
Generally assympyomatic and does not require management as risk of complete heart block is low.
If symptoms do arise:
Cardiac monitoring ECG
Medication review to exclude precipitating drugs
Consider atropine if bradycardia (anticholinergic)
What is second degree heart block type II (Mobitz type II)?
Second degree AV block where there are intermittent non-conducted P waves
Unlike Type I, the PR interval isnt increasingly prolonged
N.B. Caused by failure in the bundle of his/purkinje system
What are causes of Mobityz type II?
Infarction: Particularly anterior MI which damages bundle of His
Surgery: Mitral repair or septal ablation (used in treatment of hypertrophic cardiomyopathy).
Inflammatory/autoimmune: Rheumatic heart disease, SLE, Myocarditis, systemic scleorosis.
Idiopathic fibrosis (aka Lenegre’s disease)
Infiltration: Amyloidosis, Sarcoidosis, Haemochromatosis
Medications: Beta-blockers, NDP-CCB, Digoxin, amiodarone
What is the management plan for patients with Mobitz type II?
Permament pacemaker
This is because patients are at high risk of complete heart block and haemodynamic instability
What is complete heart block? (aka third degree)
Type of heart block characterised by:
Severe bradycardia
Desynchronisation between P waves and QRS complex
What are the main signs/symptoms of complete heart block?
Syncope
Cardiac arrest
Bradycardia (30-50bpm)
Wide pulse pressure
JVP canon waves
S1 variable intensity
ECG findings: Severe bradycardia, diassociation of P and QRS complex
What are causes of complete heart block?
Myocardial infarction (especially inferior MI)
Drugs: Beta-blockers, CCB
Idiopathic fibrosis (aka Lenegre’s disease)
