Failure to Sense

Report:

Atrial fibrillation 1

Ventricular pacemaker 1

Failure to sense 2

R-on-T pacing 2

Fusion beat 2

Incomplete right bundle branch block 1

Nonspecific ST/t changes 1

Comment:

Failure to sense is only intermittent, since the pacemaker discharge is inhibited for much of the tracing. The third spike falls on the T wave of the preceding complex but is too early to cause a depolarisation. The second last spike participates in a ventricular fusion beat.

In failing pacemakers, ability to sense is, as a general rule, lost before the ability to pace.

More of the same is shown below (Fig 51a). A trace 6 month later (not shown) still showed the same problem. I could not see why she needed a pacemaker in the first place. Her coronary arteries were normal, with LV ejection fraction 69%. I was not reassured. I would have waited for better evidence in view of the long-known complications of permanent pacing31.

Fig 51a.

Fig 52. 46 year old man in complete heart block after extensive anterior infarction, treated by an A-V sequential temporary pacemaker. Pulsus alternans was detected on his arterial pressure display and (retrospectively!) on palpation. What is the mechanism of his mechanical alternans?