Can premature beats (Ectopic beats) occur in SA node ? Yes, it can . It’s called sinus premature systole.
Posted Apr 14 2009 11:50pm
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.
Sinus arrhythmia and pause
SA node echo beats (Part of SA node reentry)
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.
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
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.