Trigeminy

Report:

Demand pacemaker rhythm 65/min 2

Hysteresis rate 60/min 3

Intermittent retrograde conduction 2

Sinus capture beats 2

Trigeminy 1

Probable sick sinus syndrome 0

Comment:

To comment on the appropriateness of the pacing rate one has to know the programmed pacemaker parameters. Most likely the rate of 65/min is deliberately set to allow the patient more time in sinus rhythm. The pacemaker paces at 65/min, but captures the ventricles at an interval corresponding to 60/min; this is its rate hysteresis (delay) feature, again designed to allow more time in supraventricular (in this case, sinus) rhythm.

The paced beats preceding sinus captures show no evidence of retrograde conduction, but the ones before them show either retrograde P waves (the last two groups) or an atrial deflection consistent with either a blocked sinus P wave, a retrograde wave or an atrial fusion distorted by lead transition artefact (third QRS in the strip). This recurrent failure of retrograde conduction of the paced beats allows sinus captures to occur. They occur, however, 1.36” after the retrograde P waves, indicating a prolonged sinoatrial recovery time – a sick sinus (another hysteresis of sorts: undisturbed sinus rhythm would almost certainly be faster). This is now the commonest indication for permanent pacemaker implantation in the USA and, ipso facto, Australia.

The trigeminy produced here is the reverse of the usual pattern, where two sinus beats are followed by a ventricular premature one or a single sinus beats is followed by two VEBs. Here two escape beats (that’s what pacemakers are for) are followed by a sinus beat. Were it not for the retrograde conduction of the paced beats, I would call this escape-capture trigeminy!

Can she be reassured concerning her palpitation? Defensive medicine says no; common sense and sympathy say yes! There’s also a third way, a compromise: a few more tests. It’s an ideal phrase for fobbing off patients and relatives.