• Etiology: the electrical impulse is formed in the SA node and conducted normally.
• This is the normal rhythm of the heart; other rhythms that do not conduct via the typical pathway are called arrhythmias.
NSR Parameters
• Rate 60 - 100 bpm
• Regularity regular
• P waves normal
• PR interval 0.12 - 0.20 s
• QRS duration 0.04 - 0.12 s
Any deviation from above is sinus tachycardia, sinus bradycardia or an arrhythmia
Arrhythmia Formation
Arrhythmias can arise from problems in the:
• Sinus node
• Atrial cells
• AV junction
• Ventricular cells
SA Node Problems
The SA Node can:
fire too slow--- Sinus Bradycardia
fire too fast--- Sinus Tachycardia
Atrial Cell Problems
Atrial cells can:
• fire occasionally from a focus ---Premature Atrial Contractions (PACs)
• fire continuously due to a looping re-entrant circuit ----Atrial Flutter
Atrial Cell Problems
Atrial cells can also:
• fire continuously from multiple foci Atrial Fibrillation
or
fire continuously due to multiple micro re-entrant “wavelets” Atrial Fibrillation
AV Junctional Problems
The AV junction can:
• fire continuously due to a looping re-entrant circuit--Paroxysmal Supraventricular Tachycardia
• block impulses coming from the SA Node--AV Junctional Blocks
Ventricular Cell Problems
Ventricular cells can:
• fire occasionally from 1 or more foci --Premature Ventricular Contractions (PVCs)
• fire continuously from multiple foci--Ventricular Fibrillation
• fire continuously due to a looping re-entrant circuit--Ventricular Tachycardia
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