Heart Block Flashcards
What is the definition of 1st Degree Heart Block?
1st Degree AV Block: prolonged conduction through the AV node
What is the definition of 2nd Degree Heart Block?
2nd Degree AV Block:
- Mobitz Type I (Wenckebach): progressive prolongation of AV node conduction culminating in one atrial impulse failing to be conducted through the AV node. The cycle ten begins again.
- Mobitz Type II: intermittent or regular failure of conduction through the AV node. Also defined by the number of normal conductions per failed or abnormal one (e.g. 2:1 or 3:1)
What is the definition of 3rd Degree Heart block?
3rd Degree (Complete) AV Block: no relationship between atrial and ventricular contraction. Failure of conduction through the AV node leads to ventricular contraction generated by a focus of depolarisation within the ventricle
What is the epidemiology of heart block?
250,000 pacemakers are implanted every year and they are mostly for heart block
What is the aetiology of heart block?
MI or ischaemic heart disease (MOST COMMON)
Infection (e.g. rheumatic fever, infective endocarditis)
Drugs (e.g. digoxin)
Metabolic (e.g. hyperkalaemia)
Infiltration of conducting system (e.g. sarcoidosis)
Degeneration of the conducting system
What are the presenting symptoms of heart block?
1st Degree - asymptomatic
2nd Degree - usually asymptomatic
Mobitz Type II and 3rd Degree - may cause Stokes-Adams Attacks (syncope caused by ventricular asystole) -> May also cause dizziness, palpitations, chest pain and heart failure
What are the signs of heart block upon physical examination?
Often NORMAL
Check for signs of a potential cause of heart block
COMPLETE HEART BLOCK:
- Slow large volume pulse
- JVP may show cannon a waves (Cannon A Waves: waves seen occasionally in the jugular vein of humans with certain cardiac arrhythmias. This occurs when the atria and ventricles contract simultaneously)
Mobitz Type II and 3rd Degree Heart Block = Signs of reduced cardiac output (e.g. hypotension, heart failure)
What are the appropriate investigations for heart block?
ECG - GOLD STANDARD
CXR
- Cardiac enlargement
- Pulmonary oedema
Bloods
- TFTs
- Digoxin level
- Cardiac enzymes
- Troponin
Echocardiogram
- Wall motion abnormalities
- Aortic valve disease
- Vegetations
What is the management plan for heart block?
Chronic Block
- Permanent pacemaker is recommended in:
- > Complete heart block
- > Advanced Mobitz Type II
- > Symptomatic Mobitz Type I
Acute Block
- If associated with clinical deterioration use IV atropine
- Consider temporary (external) pacemaker
What are the possible complications of heart block?
Asystole
Cardiac arrest
Heart failure
Complications of any pacemaker inserted
What is the prognosis for patients with heart block?
Mobitz Type II and 3rd degree block usually indicate serious underlying cardiac disease
What is seen on ECG in 1st Degree Heart block?
First Degree - fixed prolonged PR interval (> 0.2 s)
What is seen on ECG in Mobitz Type I Degree Heart block?
Mobitz Type I (Wenckebach) - progressively prolonged PR interval, culminating in a P wave that is NOT followed by a QRS complex. The pattern then begins again. ‘Going, going, gone’.
What is seen on ECG in Mobitz Type II Degree Heart block?
Mobitz Type II - intermittently a P wave is NOT followed by a QRS. There may be a regular pattern of P waves not followed by QRS (e.g. 2:1 or 3:1)
What is seen on ECG on a complete Heart block?
Complete Heart Block - no relationship between P waves and QRS complexes. If QRS is initiated in the:
- Bundle of His - narrow complex
- More distally - wide complex and slow rate (~ 30 bpm)
