Posts Tagged ‘sinus premature systole’

This is an  ECG which  I reported  yesterday in my clinic . I thought it was a  near perfect example for sinus node premature beat .

sinus premature beat spb 2

(Of course I need to explain  why the  P morphology  slightly  differs )

A  sudden unexpected  QRS  complex is often called as  ectopic beat . If it occurs prematurely (ie earlier than anticipated )  it is called as premature beat. If it occurs late it is refereed  to as escape beat .Please note the difference is not absolute .

Sinus node is a dramatic bundle of energy with divine powers that  drives rhythm of life !

The pacemaker cells are arranged in a compact fashion with  differential properties from cranial cells firing fast and caudal cells little slower. The neural control is under constant Neuro/electro/humoral  servo control mechanism.It is well known the pacemaker shifts it’s firing location within the SA node in fairly regular fashion .The entire SA node has rich adrenergic and  cholinergic  innervation , with  a dominant control by the later . (This is  why the intrinsic heart rate is  in the tachycardia  range (around 116 )  when SA node is denerved  pharmacologically )


sinus premature systole spd sinus node ectopics002

SA node ,  being  a complex structure ,  it is not surprising to note  few beats to fire  slightly late  or  prematurely.If it occurs late it is called sinus pause ,  if it occurs early it is sinus premature beat , if  both occurs  interchangeably  we refer it as  sinus arhhytmia. (Read  about sinus pause here)

What is the clinical significance  of   SPD ? (Sinus premature depolarisation )

It is a  very benign entity that it is  merely an  academic fascination . By  stretching my  imagination  I  can  correlate  it  with few possible  clinical issues.

  • May be it has potenital to trigger a  SA nodal reentry tachycardia  or In appropriate sinus tachycardia/bradycardia.
  • It may be imporatnt in sinus node modification process.
  • However ,the main issue is  thee  cardiac physicians  in their enthusiasm should not mistake it for some serious  cardiac arrhythmia !

Related article


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Ectopic beats or premature depolarisations are the commonest  cardiac arrhythmia encountered . Human heart , is a  non stop  electro mechanical organ ,  and it is not surprising   ectopic beats are so common  and can literally originate  from every cell of heart. But , generally it   emanates  primarily from  the special conducting cells . At times  ,  even  other cells (Myocytes, interstitial cells )  can generate abnormal electrical potential.These ectopic electrical potentials  can be compared  to  electrical load shedding when there is excess electrical strain .

Vast  majority of ectopic are benign  in human population. When this occurs ,  in the milieu of underlying heart disease or during ischemic  episodes they become clinically important and initiate a sustained arrhythmia.

Classically and traditionally ectopic beats are described in the

A.Ventricle :      Ventricular premature beats, (VPD)

B.Atrium:             Atrial premature beats(APD)

C.AV junction : Junctional premature beats.(JPD)

If you note , one important structure is missing from the list.

Yes , it is  SA node.  Can it result in premature depolarisation ?

When do you suspect a SPD(Sinus premature depolarisation)

  • It manifests a  an sudden unexpected , sinus beat exactly as the previous sinus beat. Followed by a pause.
  • The P wave morphology exactly is similar to prior p wave.
  • Many times we miss this entity as we tend to over  diagnose APD than SPD.
  • SPDs tend to occur in bigeminy rhythm.

Differential diagnosis

  • Sinus arrhythmia and pause
  • APD
  • SA node echo beats (Part of SA node reentry)
  • SA blocks

How do differentiate  a sinus arrhythmia from sinus premature depolarisation (SPD ) ?

Sinus arrhythmia occurs in a baseline bradycardia environment.

It does not not come as   “on -off ” pattern . It has a gradual onset offset dynamics.

Clinical significance

This is a clinically unimportant arrhythmia* .This  is probably the reason , it is not a popular concept .

*But it can confound in the diagnosis of  , other important rhythm  disorders.it could be a expression of  sinus node dysfunction and a precursor of  inappropriate  sinus tachycardia The significance could be substantial in atrial triggered  based  pace maker rhythm

Final message

When you confront an unexpected , early , sinus beat not accountable to sinus  arrhythmia  or APD

suspect SPD.It is  not rare , it is a  grossly under diagnosed entity.


Sinus premature systole  http://www.chestjournal.org/content/64/1/111.full.pdf?ck=nck

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