questions 6

Heart Block

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Topic updated on 12/22/16 4:08pm

Snapshot
  • A 74-year-old male with a history of a prior MI comes to your office for palpitations and lightheadedness. On exam, he has a wide pulse pressure and pronounced a waves in his internal jugular vein. An EKG is ordered.
First Degree Heart Block (AV Block)
  •  Introduction
    • conduction defect notable for increased PR interval (>0.2 seconds)
      • all atrial impulses are conducted
    • epidemiology
      • mostly occurs in normal, healthy individuals
    • causes include
      • increased vagal tone
        • such as in highly conditioned athletes
      • medications
        • slow AVN conduction
  • Presentation
    • Symptoms
      • asymptomatic
    • physical exam
      • decreased intensity of S1 on auscultation
    • EKG
      • increased PR interval ( > 0.2 seconds)
      • usually an incidental finding
  • Treatment
    • no intervention required
Second Degree Heart Block (Mobitz Type I - Wenckebach)
  •  Introduction
    • PR interval progressively increases until beat is dropped
      • conduction then returns to baseline and the cycle repeats
    • epidemiology
      • may occur in 
        • normal, otherwise healthy individuals
        • well-conditioned athletes
        • individuals without structural heart defects
    • causes include
      • increased vagal tone
      • medications 
        • may occur in people taking beta-blockers, digoxin, and calcium channel blockers
  • Presentation
    • symptoms
      • asymptomatic in most cases
      • may show signs of decreased cardiac output
      • chest pain
        • only in setting of myocarditis
    • EKG 
      • shows progressively increasing PR intervals  
      • predictable, interval drop of QRS complexes
  • Treatment
    • stop offending medication
Second Degree Heart Block (Mobitz Type II)
  • Introduction 
    • characterized by sudden, fixed dropped beat without preceding PR prolongation
      • PR interval fixed at > 0.2 seconds
    • causes include 
      • primary fibrotic disease
        • usually defect in the His-Purkinje system distal to AV node
      • scar formation
        • prior infarction
  • Presentation
    • symptoms
      • decreased cardiac output
      • rarely asymptomatic
    • physical exam
      • regularly irregular pulse
      • bradycardia
      • hypotension
      • signs of hyperperfusion
    • EKG
      • sudden loss of QRS complex with stable PR intervals 
  • Treatment
    • ventricular pacemaker
      • even in asymptomatic patients
  • Prognosis, prevention, and complications
    • prognosis is poor
      • increased chance of progressing to tertiary heart block
Third Degree Heart Block (Complete AV Heart Block)
  • Introduction  
    • no conduction through the atrioventicular node (aka, complete heart block)
      • escape rhythm can occur anywhere between AVN and His-Purkinje system
      • produces a fixed heart rate
        • unable to compensate for exertion
    • causes include
      • congenital
        • usually occurs at level of AVN
        • often associated with SS-A (Ro) and SS-B (La)
          • note: SS = Sjogren's syndrome
      • acquired
        • medications
          • antiarrhythmics
          • digoxin
        • Lyme disease
        • rheumatic diseases
        • infiltrative processes
        • neuromuscular disorders
        • ischemia/infarct
        • metabolic causes
        • toxins
  • Presentation
    • symptoms
      • most often profoundly symptomatic
      • dramatically reduced cardiac output
      • may cause sudden death
    • physical exam
      • irregular, weak pulse
      • wide pulse pressure
      • signs of CHF
      • tachypnea
      • pale complexion
    • EKG
      • no relationship between P-P interval and QRS interval 
  • Treatment
    • permanent ventricular pacemaker
      • frequent follow-up required
  • Prognosis, prevention, and complications
    • prognosis
      • poor if left untreated
      • excellent with permanent pacing


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(M1.CV.8) A 29-year-old computer programmer presents to the general medicine clinic complaining of dizziness, fatigue, and shortness of breath. One month ago, the patient went on a camping trip in northern Connecticut. On assessment, vital signs are temperature 36.9°C, blood pressure 100/65, heart rate 41, and respiratory rate 16 with an oxygen saturation of 99%. A print of the EKG strip is shown below. What is the most likely diagnosis? Topic Review Topic
FIGURES: A          

1. Wolff-Parkinson-White syndrome
2. Second degree Mobitz type I AV block
3. Second degree Mobitz type II AV block
4. First degree AV block
5. Third degree (complete) AV block

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