RT Book, Section
A1 Michaud, Gregory F.
A1 Stevenson, William G.
A2 Jameson, J. Larry
A2 Fauci, Anthony S.
A2 Kasper, Dennis L.
A2 Hauser, Stephen L.
A2 Longo, Dan L.
A2 Loscalzo, Joseph
SR Print(0)
ID 1155973513
T1 Physiologic and Nonphysiologic Sinus Tachycardia
T2 Harrison's Principles of Internal Medicine, 20e
YR 2018
FD 2018
PB McGraw-Hill Education
PP New York, NY
SN 9781259644016
LK accesspharmacy.mhmedical.com/content.aspx?aid=1155973513
RD 2024/04/24
AB The  sinus  node  is  comprised  of  a  group  of  cells  dispersed  within  the  superior  aspect  of  the  thick  ridge  of  muscle  known  as  the  crista  terminalis  where  the  posterior  smooth  atrial  wall  derived  from  the  sinus  venosus  meets  the  trabeculated  anterior  portion  of  the  right  atrium  (Fig.  242-1).  Sinus  p  waves  are  characterized  by  a  frontal  plane  axis  directed  inferiorly  and  leftward,  with  positive  p  waves  in  leads  II,  III,  and  aVF;  a  negative  p  wave  in  aVR;  and  an  initially  positive  biphasic  p  wave  in  V1.  Normal  sinus  rhythm  has  a  range  of  rates  between  60–100  beats/min.  Sinus  tachycardia  (>100  beats/min)  typically  occurs  in  response  to  sympathetic  stimulation  and  vagal  withdrawal,  whereby  the  rate  of  spontaneous  depolarization  of  the  sinus  node  increases  and  the  focus  of  earliest  activation  within  the  node  typically  shifts  more  leftward  and  closer  to  the  superior  septal  aspect  of  the  crista  terminalis,  thus  producing  taller  p  waves  in  the  inferior  limb  leads  when  compared  to  normal  sinus  rhythm.  Sinus  bradycardia  is  defined  as  rates  less  than  60  beats/min;  however,  bradycadia  can  be  normal  during  sleep  and  in  fit  individuals.