TY  - CHAP
M1  - Book, Section
TI  - Sinus Rhythms
A1  - Zimmerman, Franklin H.
Y1  - 2023
N1  - 
T2  - ECG Core Curriculum
AB  - Let’s  start  our  discussion  of  the  cardiac  rhythms  at  the  very  beginning  by  learning  about  normal  sinus  rhythm  and  its  abnormalities.  Sinus  rhythms  originate  in  the  sinoatrial  (SA)  node,  located  within  the  wall  of  the  high  right  atrium  near  the  inlet  of  the  superior  vena  cava  (Figure  14-1).  From  this  anatomical  location,  the  SA  node  first  depolarizes  the  right  atrium  in  a  leftward,  inferior,  and  anterior  direction,  followed  by  the  left  atrium  in  a  leftward,  inferior,  and  posterior  direction  (Figure  14-2).  The  mean  axis  of  the  normal  P  wave  in  the  frontal  plane  is  between  0  and  +75  degrees.  Accordingly,  we  see  normal  sinus  P  waves  that  are  positive  in  leads  I,  II,  and  aVF  with  a  negative  P  wave  in  lead  aVR.  Remember  that  the  SA  nodal  depolarization  is  too  small  to  be  seen  on  the  surface  ECG  so  our  first  evidence  of  this  discharge  is  the  appearance  of  a  normal  P  wave,  indicating  successful  depolarization  of  the  atria.  By  convention,  the  normal  sinus  rate  is  defined  as  60  to  100  bpm.  The  term  normal  sinus  rhythm  implies  depolarization  by  the  SA  node  at  a  standard  rate  with  normal  atrial  depolarization,  followed  by  transmission  through  the  AV  node  and  His-Purkinje  system  to  the  ventricles  (Figure  14-3).  This  results  in  a  normal  P  wave  that  is  accompanied  by  a  normal  PR  interval  (0.12-0.20  sec).  The  P-P  interval  between  complexes  is  regular,  with  any  variation  between  the  longest  and  shortest  cycle  lengths  no  more  than  0.12  seconds  or  10%  (Figure  14-4).  
SN  - 
PB  - McGraw Hill Education
CY  - New York, NY
Y2  - 2024/04/20
UR  - accesscardiology.mhmedical.com/content.aspx?aid=1200100617
ER  -