Tachycardia – Bradycardia syndrome is the hall mark of sinus node dysfunction.
- The commonest tachycardia in sinus node dysfunction is Atrial fibrillation . Followed very closely by sinus tachycardia . In fact alteration between sinus tachycardia and sinus bradycardia without other pathological arrhythmia is rare . (Of course , we have a name for such an entity as inappropriate sinus tachycardia / bradycardia )
- Atrial tachycardia occurs a distant 3rd
- Ventricular tachycardia may be an exception (Please note , extreme bradycardias which lead to pause dependent VT is not directly related to sinus node disease )
The commonest bradycardia in SND is
- Sinus bradycardia (This fact is undisputed unlike the tachycardia component of SND !)
- Followed be sinus pause , SA blocks and sinus arrest .
- AF with slow ventricular response ( Bradycardic AF) We are not sure about the rhythm here (Is it truly junctional /or conducted atrial ? )
- Associated AV block can occur up to 20 % of patients .If AV block is present the true nature of SA node disease is masked and it’s function becomes almost irrelevant .
Dr.S.Venkatesan MD 
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