S Muccione | PubMed Health

PubMed1981

Inhibition of programmable demand pacemaker by pacemaker-induced myopotentials.

Pacemaker-induced myopotentials caused inhibition of a demand pacemaker in two cases in which the unipolar partially encapsulated pacemaker flipped over in its pocket and directly stimulated the muscles of the chest wall. This pacemaker-induced muscular stimulation, possibly combined with afterpotential sensing or T-wave sensing (or both), caused the rate of the demand pacemaker to fall when the output of the programmable pacemaker was set to deliver high energy charges. By programming the unit to deliver a lower charge (shorter width of pulse), the rate rose appropriately to the programmed rate. Likewise, manual rotation of the unipolar pacemaker into proper orientation with the active uninsulated surface directed towards the skin also solved the problem temporarily.

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PubMed1979

Pitfalls in measuring R waves in pacemaker-dependent patients.

Determination of adequate R wave sensing is an important step in pacemaker electrode implantation and pacemaker replacement operations. In patients who are completely pacemaker dependent, these operations are usually performed with a functional temporary pacemaker in place throughout the testing period. In such patients, there is the special problem of determining whether the test system is sensing the temporary pacemaker spike rather than the resultant QRS voltage. Patients were studied and a laboratory model was created to evaluate the response characteristics of a standard R wave test device. Patients showed two general types of curves as R waves were measured at various output voltages of the temporary pacemaker. Type A responses showed direct correlation between output voltage and measured R waves. Type B responses showed an initial high plateau of R waves followed by an abrupt fall below acceptable values, and then a direct correlation between R waves and output voltage. Laboratory testing revealed that the temporary pacemaker spike, and not the R wave, was being "sensed" in Type A curves, and that the R wave was sensed only in the initial plateau of the Type B curves. This pitfall can lead to acceptance of an unsatisfactory electode position in some patients and to futile electrode repositioning in others.

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