PHYS - Arrhythmias

Question 1

ARRHYTHMIA

Answer 1

• Arrhythmia: any disorder of rate, rhythm, origin, or conduction of impulses in the heart
• Occurrence of arrhythmia as a result of:
  
  • Acute MI = 80-90%
  • General anesthesia = 20-50%
  • Digitalis = 10-20%
    
    • Cardiotonic drug used in heart failure to improve the mechanical performance of the heart
    • But is toxic and difficult to titrate out –> arrhythmia

Question 2

PRECIPITATING FACTORS OF ARRHYTHMIAS

Answer 2

• Ischemia with electrolyte abnormalities
• Excessive myocardial fiber stretch
• Excessive discharge of or sensitivity to NTs
• Exposure to foreign chemicals (ex: digitalis)

Question 3

CONSEQUENCES OF ARRHYTHMIAS

Answer 3

• Compromised mechanical performance
  
  • Tachycardia
  • Extrasystole
  • Bradycardia
  • AV block
  • Fibrillation
• Trigger a more serious arrhythmia
• Thrombi formation

Question 4

MECHANISMS OF ARRHYTHMIA

Answer 4

1. Abnormal Impulse Formation
2. Reentrant Impulse

Question 5

ABNORMAL IMPULSE FORMATION

Answer 5

• Nodes not firing correctly
• No change in pacemaker
  
  • Sinus tachycardia/Sinus bradycardia
• Change in pacemaker: ectopic pacemaker
  
  • AV node or Purkinje fibers become latent pacemakers
  • Oscillations of after-depolarization
• Disorder of impulse conduction
  
  • Slow conduction without reentry
    
    • Ex: AV block, bidirectional block from damaged tissue
  • Slow conduction with reentry
    
    • Ex: unidirectional block from damaged tissue

Question 6

REENTRANT IMPULSE

Answer 6

Block/damage causes impulse to take a new path that circles back and causes node to reexcite self
Requirements for reentry to be possible:

Unidirectional block
Conduction time around alternative pathway must exceed the refractory period of the tissue

Conditions favoring reentry:

Long reentrant pathway
Slow conduction velocity
Short effective refractory period

Question 7

COMMON ARRHYTHMIAS

Answer 7

• Sinus Tachycardia Regular
• Sinus Bradycardia Regular
• Atrial Flutter Regular
• Atrial Fibrillation VERY Irregular
• Paroxysmal Atrial Tachycardia Regular
• AV Tachycardia Regular
• Ventricular Tachycardia Regular or Irregular
• Ventricular Fibrillation No pulse or Irregular

Question 8

DADs and EADs

Answer 8

• These are abnormal impulse formation arrhythmias
• Delayed After-Depolarization
• Ca2+ overload = spontaneous transient depolarization
  
  • Caused by an event that causes abnormal Ca2+ release (into cytoplasm)
  • This is what digitalis toxicity causes (buildup of intercellular Ca2+)
• Early After-Depolarization
  
  • Prolonged plateau favors re-opening of Ca2+ channels –> depolarization
  • Delays repolarization

Question 9

LONG QT SYNDROME

Answer 9

• Inherited/congenital syndrome
  
  • Reduction in expression/loss of function of K+ channels
• Acquired syndrome
  
  • From drug abuse (possible with genetic disposition)
• Longer time needed to repolarize (mediated by K+ efflux, but not enough channels to keep up!) –> Long plateau
• Causes EAD’s
• Leads to Torsades de Pointes (a reentrant impulse)