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 >0.20s [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
PR interval = number of small squares x 0.04s
What are the main causes of first degree heart block?
High vagal tone (e.g. young healthy individuals/athletes)
Drugs (especially in elderly patients)
* Beta-blockers/CCB
* Cholinesterase inhibitors
* Digoxin
Acute inferior MI (RCA supplies AV node)
Electrolyte abnormalities (e.g. hyperkalaemia)
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?
Inferior MI (most common cause)
Drugs such as beta/calcium channel blockers, digoxin
Professional athletes due to high vagal tone
Myocarditis
Cardiac surgery (e.g. CHD repair)
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?
Idiopathic fibrosis (Lenegre’s disease)
* Most common, especially in older adults
Anterior MI (Damages bundle of His)
Medications
Inflammatory/autoimmune disease
* Rheumatic heart disease
* SLE
* Myocarditis
* Systemic sclerosis
Infiltration
* Amyloidosis
* Sarcoidosis
* Haemochromatosis
Surgery: Mitral repair or septal ablation (used in treatment of hypertrophic cardiomyopathy).
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)
What is the management plan for patients with complete heart block?
Acute management:
IV atropine 500 micrograms (up to 3mg/6 doses)
Long-term management:
Permament pacemaker
This is due to high risk of sudden cardiac death
Why does inferior MIs tend to cause heart blocks?
AV nodal artery branches off right coronary artery
Why can 2nd degree heart block be caused by anterior MI?
Bundle of his located in septum which is supplied by left anterior descending
When would you start with 3 shocks followed by compressions during cardiac arrest?
Monitored, immediately witnessed cardiac arrest in following areas if a defibrillator is immediately available:
Cath lab
Critical care area
Coronary care unit
After cardiac surgery
In normal cases its 1 shock followed by compressions
