Dr.S.Venkatesan MD

A man  in his 40s presented with an episode of syncope and followed by recurrent episodes of near syncope.

His ECG showed (See image)

• ECG shows absolutely no evidence of sinus activity . That is  sinus arrest.
• He lives by the mercy of his AV node.(“Great  escape” junctional rhythm  ! ) . Please note ,  It  fires at less than its intrinsic rate indicating AV nodal sickness as well.
• The Heart rate is around 18/mt.

SA node is dead(Sinus arrest ) as evidenced by absent p waves. AV node is sick(Depressed) because the junctional rate is less than 20 /mt.

At what  heart rate a person  would develop syncope and near syncope ?

There is no fixed cut off rate for  syncope. It all depends upon the baseline LV function, his exercise capacity, vascular tone etc.

Most will develop some symptoms at  a heart rate less than  40/mt .

Dizziness occur and 30, syncope is sure  when hear rate  dwindles  less than 20 /mt.

A heart rate of 10-15 circulation tends to stall. But still few men are found alive at this rate.

What is the  risk of this patient dying suddenly ?

Contrary to the expectation SCD is not common in  isolated sinus node dysfunction .

It is more common with AV block. The reason being as long as the AV node is fine it will support the rhythm at least at about 30 or s0.

The cause of death in SND is extreme bradycardia induced phase dependent VT /VF.

Will you do a  EP study for him  ?

No. He  does not require it. He is symptomatic ,  and his  ECG shows  tell- tale evidence for SND with AV node depression.

So the there is not even the  necessity to assess  AV nodal status. But .one should  be aware  , there is a battery of tests for SND evaluation (SNRT, cSNRT SACT, etc*) .These are  done only when diagnosis is in doubt or for an academic purpose in teaching hospital.

What pacemaker will you use ?

• DDDR
• AAIR
• VVIR

AAIR can not be used as we have evidence for AV nodal  slowing .

DDDR may be ideal.  In India we still  use VVI mode extensively . Ventricular pacing always safe when you have no EP facilities.  It makes EP study to assess AV nodal function  redundant.

* In all patients with severe bradycardia , a complete workup for systemic diseases like hypothyroidism and other chronic inflammatory pathology must be ruled out. Drug induced bradycardias can exactly mimic pathological  SND. Recognizing these entities could avoid  inappropriate pace maker implantation for  transient reversible bradycardias.

* SNRT – Sinus node recovery time. cSNRT -Corrected sinus node recovery time .SACT-Sino atrial conduction time.