Heart block Flashcards
What is heart block?
Refers to an obstruction in the electrical conduction system of the heart.
This obstruction can occur at various points in the conduction system, including the SA node, AVN node, Bundle of His, or bundle branches.
What is First Degree Heart Block? ECG findings?
Consistent prolongation of the PR interval (defined as >0.20 seconds) due to delayed conduction via the atrioventricular node.
Regular rhythm
Every P wave is followed by a QRS complex.
PR interval: prolonged >0.2 seconds (5 small squares)
Causes of First Degree Heart Block?
High vagal tone: e.g. athletes
Acute inferior MI
Lyme disease
Systemic lupus erythematosus
Thyroid dysfunction
Electrolyte abnormalities: e.g. hyperkalaemia
Drugs: e.g. NHP-CCBs, BB, digoxin, cholinesterase inhibitors
Management of First Degree Heart Block?
Any AV blocking drugs should be stopped.
No intervention is usually required if the patient is asymptomatic.
If the pt is symptomatic, a pacemaker may be considered.
Types of Second Degree Heart Block?
Mobitz Type I (Wenckebach phenomenon)
Mobitz Type II
What is Mobitz Type I (Wenckebach phenomenon)? ECG findings?
Occurs due to reversible conduction block at the AV node.
Progressive prolongation of the PR interval until eventually the atrial impulse is not conducted and the QRS complex is dropped.
AV nodal conduction resumes with the next beat and the sequence of progressive PR interval prolongation and the eventual dropping of a QRS complex repeats itself.
Rhythm: irregular
P wave: every P wave is present, but not all are followed by a QRS complex
PR interval: progressively lengthens before a QRS complex is dropped
Causes of Mobitz Type I (Wenckebach phenomenon)?
Professional athletes due to high vagal tone
Myocarditis
Cardiac surgery
MI (mainly inferior)
Drugs such as BB, CCB, digoxin, amiodarone.
Management of Mobitz Type I (Wenckebach phenomenon)?
AV blocking drugs should be stopped.
Usually, no intervention is required if the patient is asymptomatic.
If the patient is symptomatic a pacemaker may be considered.
Bradycardic with adverse features = atropine
What is Mobitz type II block? ECG findings?
Consistent PR interval duration with intermittently dropped QRS complexes due to a failure of conduction, especially at the His-Purkinje system.
The intermittent dropping of the QRS complexes typically follows a repeating cycle of every 3rd (3:1 block) or 4th (4:1 block) P wave.
Rhythm: irregular (may be regularly irregular in 3:1 or 4:1 block)
P wave: present but there are more P waves than QRS complexes
PR interval: consistent normal PR interval duration with intermittently dropped QRS complexes
QRS complex: normal (<0.12 seconds) or broad (>0.12 seconds)
Causes of Mobitz type II block?
MI
Surgery: mitral valve repair or septal ablation
Inflammatory/autoimmune: rheumatic heart disease, SLE, systemic sclerosis, myocarditis
Infiltrative myocardial disease (amyloidosis, haemochromatosis, sarcoidosis)
Hyperkalaemia
Drugs such as BB, CCB, digoxin, amiodarone.
Symptoms/signs of Mobitz type II block?
Palpitations
Pre-syncope
Syncope
Regularly irregular pulse
Management of Mobitz type II block?
Permanent pacemaker (due to risk of complete heart block and becoming haemodynamically unstable)
What is Complete (Third degree) Heart Block? ECG findings?
No electrical communication between the atria and ventricles due to a complete failure of conduction.
Rhythm: variable, severe bradycardia
P wave: present but not associated with QRS complexes
PR interval: absent (as there is atrioventricular dissociation)
QRS complex: narrow (<0.12 seconds) or broad (>0.12 seconds) depending on the site of the escape rhythm
Causes of Complete (Third degree) Heart Block?
MI
Infections: endocarditis, Lyme disease, Chagas disease
Non-ischaemic heart disease: calcific aortic stenosis, idiopathic dilated cardiomyopathy, infiltrative disease (e.g. sarcoidosis, amyloidosis)
Iatrogenic: post-ablative therapies and pacemaker implantation, post-cardiac surgery
Autoimmune conditions: SLE, rheumatoid arthritis
Thyroid dysfunction
Drugs such as BB, CCB, digoxin, amiodarone.
Symptoms/signs of Complete (Third degree) Heart Block?
Palpitations
Pre-syncope/syncope
Confusion
Shortness of breath (due to heart failure)
Chest pain
Sudden cardiac death
Irregular pulse
Profound bradycardia
Haemodynamic compromise (e.g. prolonged capillary refill time and hypotension)
