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Heart Block (Bundle Branch Block (Complete block of a bundle branch (Right…

- - - - Produces the late activation of the right ventricle
      - Seen as deep S wave in leads I & V6 and as a tall late R wave in lead V1
      - Right bundle no longer conducts, meaning that the two ventricles do not get impulses at the same time, and instead spread from left to right
      - Causes wide physiological splitting of the SECOND HEART SOUND
      - Causes: PE, ischaemic heart disease & atrial/ventricular septal defect
      - On ECG
        
        Looks like maRRow
        
        maRROW - Right bundle branch block
        
        MarroW
        
        M - QRS looks like a M in lead V1
        
        W - QRS looks like W in V5 & V6
    - - Seen as deep S wave in lead V1 and a tall late R wave in leads I & V6
      - Since the left bundle branch conduction is normally responsible for the initial ventricular activation, left bundle branch block also produce abnormal Q waves
      - Produces the late activation of the left ventricle
      - Causes reverse splitting of the SECOND HEART SOUND
      - Causes: ischaemic heart disease and aortic valve disease
      - On ECG
        
        Looks like wiLLiam
        
        wiLLiam - Left bundle branch block
        
        WilliaM
        
        W - QRS looks like a W in leads V1 & V2
        
        M - QRS looks like an M in leads V4-V6
- - - - Hypokalaemia
      - Myocarditis
      - Inferior MI
      - AVN blocking drugs e.g. beta blockers, calcium channel blockers and Digoxin
  - - - Also known as the Wenckebach block phenomenon
      - A progressive PR interval prolongation until beat is 'dropped' and P wave fails to conduct i.e. excitation completely fails to pass through the AVN/bundle of His
      - The PR interval before the blocker P wave is much longer than the PR interval after the blocked P wave
      - Causes
        
        AVN blocking drugs e.g. beta blockers, calcium channel blockers and Digoxin
        
        Inferior MI
      - Results in light headedness, dizziness and syncope
      - Does not require a pacemaker unless its poorly differentiated
    - - PR interval is constant and QRS interval dropped
      - Failure of conduction through the His-Purkinje system
      - Causes
        
        Anterior MI
        
        Mitral valve surgery
        
        SLE and Lyme disease
        
        Rheumatic fever
      - Results in shortness of breath, postural hypotension and chest pain
      - High risk of developing sudden complete AV block and a pacemaker should be inserted
  - - - Structural heart disease
      - Ischaemic heart disease
      - Hypertension
      - Endocarditis/Lyme disease
    - - Implies block originates in Bundle of His and thus the region of block lies more proximally in the AVN
      - Recent-onset, narrow-complex AV block that has transient causes may respond to IV atropine
      - QRS complex less than 0.12 seconds
      - Chronic narrow-complex AV block requires permanent pacemaker if it is symptomatic
    - - Implies block originates BELOW the bundle of His and thus the region of block lies more distally in the His-Purkinje system
      - Dizziness and blackouts often occur
      - QRS complex is greater than 0.12 seconds
      - Permanent pacemaker implantation is recommended
    - - Depends of aetiology
      - One option is permanent pacemaker
      - IV atropine