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NCLEX Focus - AV Node Block, Sick Sinus, & Bundle Branch Block

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The following are high yield points from the AV Node Block, Sick Sinus Syndrome, & Bundle Branch Block tutorial to help you prepare for the NCLEX.
Review AV Node Block for further summart details.
AV Node Block
ECG Recognition of AV Blocks
First-Degree AV Block:
  • PR interval > 200 milliseconds (long PR)
  • ECG shows prolonged PR with no missed beats
Second-Degree AV Block:
  • Mobitz Type I (Wenckebach): PR interval progressively lengthens until a ventricular beat is dropped
  • Mobitz Type II: PR interval is constant, but occasional QRS complexes are missing
Third-Degree AV Block:
  • Complete AV dissociation: No relationship between P waves and QRS complexes
  • Atria and ventricles contract independently
Symptoms and Clinical Risks by Block Type
First-Degree AV Block:
  • Typically asymptomatic
  • May increase risk of atrial fibrillation
Mobitz Type I:
  • May present with dizziness or fainting
  • Often benign, especially in athletes
Mobitz Type II:
  • Symptoms include chest pain, dyspnea, hypotension, and fatigue
  • Considered pathologic; risk of progression to complete heart block
Third-Degree AV Block:
  • Symptoms: Fatigue, dizziness, fainting, bradycardia
  • Can cause low cardiac output and organ hypoperfusion
Treatment Interventions
First-Degree AV Block:
  • Usually no treatment required
  • Monitor if associated with medications or electrolyte abnormalities
Mobitz Type I:
  • Often no treatment unless symptomatic
  • Investigate for medication-related causes
Mobitz Type II and Third-Degree AV Block:
  • Require pacemaker implantation
  • Type II is a precursor to complete heart block
Sick Sinus Syndrome
    • Defined by sinus bradycardia, sinus pauses or arrest, and junctional escape beats
    • Caused by damage to the SA node, especially due to age-related degeneration
    • May present with mental status changes, dizziness, or syncope
    • Often requires pacemaker for symptom management
Clinical Signs of Poor Perfusion (Due to Bradyarrhythmias)
    • Altered mental status
    • Dizziness
    • Fainting (syncope)
    • Hypotension
    • Fatigue
    • Seen prominently in sick sinus syndrome and advanced AV blocks
Bundle Branch Blocks (ECG + Clinical)
Right Bundle Branch Block (RBBB):
  • May be benign or indicate right heart damage
  • ECG findings:
    • Wide, upwardly deflected QRS in V1
    • rsR' “bunny ear” pattern in V1–V3
    • Slurred S waves in leads I, aVL, V5, V6
Left Bundle Branch Block (LBBB):
  • Suggests left heart disease
  • ECG findings:
    • Wide, downward QRS in V1
    • Broad monophasic R wave and absent Q waves in I, V5, V6
    • ST and T wave displacement opposite QRS direction
Common Causes & Risk Factors
    • First-Degree AV Block:
    • Athletic heart, myocarditis, hypokalemia, hypomagnesemia, digoxin, channel blockers
Mobitz Type II:
  • Cardiac scarring (post-MI), valvular disease, Lyme disease, medications: beta blockers, calcium channel blockers, digoxin, amiodarone
Third-Degree AV Block:
  • Congenital (especially from maternal autoimmune disease)
  • Acquired: surgery, radiation, infections (diphtheria, rheumatic fever), hypertension, cancer, medications (digoxin, CCBs, beta blockers, TCAs, clonidine)
Sick Sinus Syndrome:
  • Age-related degeneration of SA node
  • Associated with tachy-brady syndrome and poor cerebral perfusion.
NCLEX Review Questions
A 70-year-old patient presents with dizziness. ECG reveals a progressively lengthening PR interval followed by a dropped QRS complex. What is the most appropriate initial intervention?
A 75-year-old patient has episodes of bradycardia and tachycardia, and presents with intermittent confusion. ECG shows sinus bradycardia with occasional junctional escape beats. What is the most likely diagnosis?
A patient is diagnosed with third-degree AV block. Which nursing intervention takes priority?

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