Atrial Sensing & Undersensing

Report:

Atrial-sensing & pacing ventricular pacemaker rhythm 60/min 3

Atrial premature beats, possibly sinus 3

Blocked or sensed with first degree AV block or not sensed 3

Atrial bigeminy 1

Comment:

All the QRS complexes are paced.

The morphology of the premature P waves is consistent with sinus origin, but not all are clearly demarcated from the associated T waves. The coupling intervals from the paced atrial waves indicate a predicted rate 85-105/min.

The three conducted ones are earlier than the blocked majority; their sensed AV interval is about 0.22 sec. The paced AV interval of the atrially paced dominant rhythm is shorter at 0.18 sec. Atrial pacing only occurs because the preceding atrial activity is not sensed. It keeps the potentially faster native atrial rhythm confined to single P (or P’) waves; we never see two consecutive ones uninterrupted by a paced atrial beat.

What does this all mean? It means that the native impulse formation is OK, but their conduction still leaves much – in fact everything - to be desired. There is no native conduction at all – all the QRS complexes are paced from the ventricle with either atrial pacing or atrial sensing. This resolves the apparent paradox that the early native P waves appear “conducted” and the later ones “blocked” and succeeded by paced atrial beats. They are all blocked, but early ones are sensed while late ones are not.

What should be done, then? Increase the sensitivity. If that fails, increase the atrial pacing rate to produce 100% AV sequential pacing, if higher overall rate is required (current one is about 75/min). If the patient is doing well anyway, do nothing and wait for the native conduction to recover.