ECG 3-Normal Sinus Rhythm (NSR)

•    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