Cardiology In Critical Care

Arrhythmia Recognition

Normal Sinus Rhythem


Normal Sinus Rhythm

Impulses originate in the SA node regularly at a rate 60-100 per minute in adults and at faster rates in older children (90-110), small children (100-120) and infants (120-160).  P waves upright in L2 and negative in AVR and of uniform size and contour from beat to beat.  PR interval 0.12-0.20 sec and constant when A-V conduction normal; PR prolonged and/or variable when A-V block present.  Each P followed by QRS with resulting P:QRS ratio 1:1 QRS ratio 1:1.  QRS less than 0.11 sec or QRS wide and bizarre when bundle branch block present.  RR intervals may be slightly irregular especially in the young and elderly.

Rhythm P Wave PR Interval
(in seconds)
(in seconds)
60 - 100 bpm Regular Before each QRS, identical .12 to .20 < .12

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