Rosen & Barkin's 5-Minute Emergency Medicine Consult (117 page)

• Blockage of intraventricular electrical impulses through the right and left bundles
  
• Complete bundle branch block:
  
  • Absence or delay of conduction down one bundle, with normal conduction down the other bundle
    
  • Affected ventricle depolarizes from muscle to muscle in a slower and more disorganized fashion.
    
  • Quasi-random signal (QRS) complex at 120 msec or longer
    
• Incomplete bundle branch block:
  
  • Delayed depolarization, but less than complete bundle branch block
    
  • QRS complex duration 100–120 msec
    
• Right bundle branch block (RBBB):
  
  • Delayed depolarization of the right ventricle
    
• Left bundle branch block (LBBB):
  
  • Delayed depolarization of the left ventricle
    
  • LBBB can be caused by delay of conduction in main left bundle or delay in both fascicles of the left bundle.
    
  • Causes early activation of the right side of the septum and the right ventricular myocardium (so explaining loss of “septal Q” on ECG)
    
  • Left bundle branches into 2 fascicles:
    
    • Left anterior fascicle: Initial septal activation proceeds inferiorly, anteriorly, and to the right.
      
    • Left posterior fascicle: Isolated blockage rare; activation begins in the midseptum and finishes in inferior and posterior walls.
      
• Bifascicular block:
  
  • RBBB with concomitant block of the left anterior or left posterior fascicle
    

• Myocardial infarction
  
• Cardiomyopathy
  
• Hypertension
  
• Age-related fibrosis of Purkinje fibers
  
• Valvular disease
  
• Exercise induced
  
• Congenital/atrial septal defect
  
• Brugada syndrome (RBBB): Cause of sudden cardiac death in otherwise healthy patients.
  
• Chagas disease (especially Central/South America)
  
• Postoperative, following cardiac surgery
  
• Drugs:
  
  • β-Blockers
    
  • Calcium blockers
    
  • Tricyclic antidepressants
    
  • Type Ia and Ic antiarrhythmics
    
  • Digitalis
    

DIAGNOSIS

• Asymptomatic
  
• RBBB: Split S
  ₂
  that persists with expiration
  
• LBBB: Reversed/paradoxical split S
  ₂
  
• Syncope
  
• Chest pain
  

ECG:

• RBBB:
  
  • Complete: QRS complex ≥0.12 sec
    
  • Incomplete: QRS complex duration 0.10–0.12 sec
    
  • rsrʹ, rsRʹ, rSRʹ in V
    ₁
    or V
    ₂
    (
    M
    shape)
    
  • Wide and deep S-wave in V
    ₅
    –V
    ₆
    
  • Brugada syndrome: RBBB and ST-segment elevation in V
    ₁
    –V
    ₃
    
• LBBB:
  
  • Broad slurred R-waves in leads V
    ₅
    –V
    ₆
    , aVL, and I
    
  • Small/absent R-wave in V
    ₁
    –V
    ₂
    and deep S-waves
    
  • Absence of normal Q-waves in leads V5–V6 and I
    
• Left anterior fascicular block:
  
  • QRS complex <120 msec, axis 45°–90°
    
  • Deep S-wave in leads II, III, aVF, qR in leads aVL and I
    
• Left posterior fascicular block:
  
  • QRS <120 msec, axis ≥120°
    
  • RS-waves in leads I and aVL, qR in leads II, III, and aVF
    
  • Exclusion of other things causing right axis deviation (right ventricle overload, right ventricular hypertrophy, lateral infarction)
    

• Electrolytes if hyperkalemia, hypercalcemia are suspected
  
• Cardiac enzymes if ischemia is suspected
  

• CXR:
  
  • May reveal cardiac enlargement or CHF
    
• Electrophysiologic testing:
  
  • Especially for unexplained syncope in patient with structural heart disease, as part of inpatient workup
    

• Ventricular tachycardia
  
• MI:
  
  • Criteria for diagnosing MI with LBBB (Sgarbossa criteria) include any of the following:
    
    • ST-segment elevation ≥1 mm concordant with QRS
      
    • ST-segment elevation ≥5 mm discordant with QRS
      
    • ST-segment depression ≥1 mm in leads V
      ₁
      –V
      ₃
      
• Hyperkalemia
  
• Ventricular hypertrophy
  
• Drug effects (see “Etiology” section)
  

TREATMENT

Cautions:

• Monitor: Difficult to diagnose from single lead
  
• Avoid confusing with ventricular tachycardia or ischemia, use.
  
• Treat patient; bundle branch block requires no specific therapy.
  

• Standard treatment for symptoms of ischemia, dyspnea, and syncope
  
• Symptomatic bifascicular block and high-degree atrioventricular block:
  
  • Apply transcutaneous pacing pads to back and chest.
    
  • IV sedation and analgesia
    
  • Gradually increase current until capture is achieved.
    

• Asymptomatic: None
  
• Thrombolysis or cardiac catheterization for symptoms suggestive of myocardial infarction and new bundle branch block
  
• Transvenous pacemaker indications:
  
  • Bifascicular block and type II 2nd- or 3rd-degree atrioventricular block
    
  • Alternating LBBB and RBBB
    

FOLLOW-UP

• Suspected myocardial ischemia
  
• Syncope
  
• Dysrhythmias
  
• Bundle branch block with high-degree atrioventricular block
  

Asymptomatic or incidental finding of bundle branch block

At discharge, patient should be referred to cardiologist for evaluation of underlying disease.

• Reassure patients that usually no treatment is needed.
  
• Instruct patient to return or call for help if:
  
  • Dizziness
    
  • Fainting
    
  • Palpitations
    

• Myocardial ischemia should be considered in all patients who develop new conduction abnormalities.
  
• Specific criteria can be used to diagnose cardiac ischemia in patients with a bundle branch block.
  

• Brugada J, Brugada R, Brugada P. Right bundle-branch block and ST-segment elevation in leads V1 through V3: A marker for sudden death in patients without demonstrable structural heart disease.
  Circulation.
  1998;97:457–460.
  
• Chevallier S, Forclaz A, Tenkorang A, et al. New electrocardiographic criteria for discriminating between Brugada types 2 and 3 patterns and incomplete right bundle branch blocks.
  J Am Coll Cardiol.
  2011;58:2290–2298.
  
• Neeland IJ, Kontos MC, de Lemos JA. Evolving considerations in the management of patients with left bundle branch block and suspected myocardial infarction.
  J Am Coll Cardiol
  . 2012;60(2):96–105.
  
• Prineas RJ, Le A, Soliman EZ, et al. United States national prevalence of electrocardiographic abnormalities in black and white middle-age (45- to 64-year) and older(≥65-year) adults (from the Reasons for Geographic and Racial Differences in Stroke Study).
  Am J Cardiol
  . 2012;109(8):1223–1228.
  
• Zhang ZM, Rautaharju PM, Soliman EZ, et al. Mortality risk associated with bundle branch blocks and related repolarization abnormalities (from the Women’s Health Initiative [WHI]).
  Am J Cardiol.
  2012;110:1489–1495.
  

CODES

• 426.3 Other left bundle branch block
  
• 426.4 Right bundle branch block
  
• 426.50 Bundle branch block, unspecified
  

BASICS