Heart blocks (AV, RBBB, LBBB)

Question 1

Heart blocks (AV, RBBB, LBBB): Definition

Answer 1

• AV: cardiac electrical disorder defined as impaired (delayed or absent) conduction from the atria to the ventricles
  
  • 1st degree: dalay in AV node conduction
  • 2nd degree (type I&II): not every atrial depolarisation is conducted to the ventricles
  • 3rd degree: no atrial impulses at all make it through to the ventricles; ventricles respond by generating their own ‘escape rhythm’ and so the A and V contract at their own, seperate, intrinsic rate
• LBBB: activation of LV is delayed so LV contracts later than RV
• RBBB: activation of RV is delayed and caused by spread of LV myocardium rather than normal septal branch conduciton system

Question 2

Heart blocks (AV, RBBB, LBBB): Aetiology

Answer 2

• AV
  
  • fibrosis and calcification of the conduction system
  • CAD
  • medication such as AV blocking agents (BBs, CCBs, adenosine)
  • antiarrhythmic medications (Na++ CB)
  • congenetal/ surgical cause/ idiopathic defects of heart
• LBBB
  
  • often associated with extensive LV disease such as aortic stenosis and HTN
• RBBB
  
  • isolated congenital anomaly
  • or associated with cardiac or pulmonary conditions

Question 3

Heart blocks (AV, RBBB, LBBB): Risk Factors

Answer 3

• AV block
  
  • Patients tend to be older males with underlying cardiovascular disease
• L+R BBB
  
  • HTN
  • Older age

Question 4

Heart blocks (AV, RBBB, LBBB): Pathophysiology

Answer 4

AV

• 1st degree: dalay in AV node conduction
  
  • caused by
    
    • • 2nd degree (type I&II): not every atrial depolarisation is conducted to the ventricles
• 3rd degree: no atrial impulses at all make it through to the ventricles; ventricles respond by generating their own ‘escape rhythm’ and so the A and V contract at their own, seperate, intrinsic rate
• LBBB: activation of LV is delayed so LV contracts later than RV
  
  • caused by
    
    • • RBBB: activation of RV is delayed and caused by spread of LV myocardium rather than normal septal branch conduciton system
  • caused by
    *

Question 5

Heart blocks (AV, RBBB, LBBB): Cinical manifestations: key presentations, other symptoms and signs

Answer 5

• AV
  
  • Often asymptomatic
  • Markedly prolonged PR interval may cause excersize tollerance in some patients
  • Syncope may result from transient high-degree AV block
  • Patients may have a history of past heart disease, including myocarditis/ MI
  • Patients may be highly conditioned athletes with a high degree of vagal tone
  • may be on medications that slow conduction through the AV node
• R/LBBB
  
  • often asymptomatic
  • RBBB causes wide but physiological splitting of the second heart sound
  • LBBB may cause reverse splitting of the second sound
  • BBB patients may complain of syncope

Question 6

Heart blocks (AV, RBBB, LBBB): Investigations (diagnosis): 1st line, gold standard & other

Answer 6

• AV - ECG
  
  • First degree: showing fixed prolonged of the PR interval (PR interval > 0.2s)
  • Second degree type I: showing progressive prolongation of the PR interval and dropped QRS complexes
  • Second degree type 2: fixed, unchanging PR intervals and dropped QRS complexes
  • Third degree: is complete, persistent loss of conduction from the atria to ventricles (aka complete heart block)
    
    • third-degree shows no consistent PR relationship
    • QRS are usually wide and bizarre shape.
• BBB - ECG
  
  • general: Widened QRS (>0.12s) the shape of the QRS depends on if its LBBB or RBBB
  • LBBB
    
    • broad QRS with V1 showing ‘W’ appearance and V6 showing ‘M’ appearance R wave. Remember WiLLiaM. May have ST depression in (leads I, AVL and V6, all of these are lateral leads)
    • Diagnostic criteria:
      • QRS > 120ms
      • Dominant S wave in V1
      • Broad monophasic R wave in lateral leads (I, aVL, V5-6)
      • Absence of Q waves in lateral leads
      • Prolonged R wave peak time
  • RBBB
    
    • classic is ‘M’ shape seen in V1 and ‘W’ shape in V6. Remember ‘MaRRoW’
    • Broad QRS
    • RSR’ pattern in V1-3 (‘M-shaped’ QRS complex)
    • Wide, slurred S wave in lateral leads (I, aVL, V5-6)

Question 7

Heart blocks (AV, RBBB, LBBB): Cinical manifestations: key presentations, other symptoms and signs: DDx

Answer 7

• other kinds of arrythmias

Question 8

Heart blocks (AV, RBBB, LBBB): Management

Answer 8

• AV:
  
  • 1st degree/ 2nd degree type I
    
    • If asymptomatic, only monitoring is needed
    • If symptomatic, review meds to treat underlying cause, rarely a pacemaker is used
  • 2nd degree type II
    
    • Discontinuation of AV node-blocking drugs
    • Treating underlying cause, often HD such as ACS
    • Pacemaker if symptomatic
• BBB
  
  • Don’t always require treatment - may just need monitoring
  • Possibly a pacemaker
  • Treating underlying cause may improve condition considerably