[Sensing anomalies with the VVI pacemaker. Clinical study by Holter]

Defective sensing incidence is controversial. It has rarely been assessed by Holter in series of consecutive patients. Holter was used in 59 cases (84% of implants over 9 months) with a follow-up of between 7 and 19 months. The generators came from 2 manufacturers, 44 unipolar and 15 bipolar, with standard sensitivity level and in VVI with rates covering up the patient's own rythm. Results. Unipolar: all asymptomatic registration and two symptomatic in the follow-up. There were myopotential inhibitions in 31 (70%), but only in 6% lasted over 2,000 msec, there were less than 16 episodes in 94% of cases distributed along the day with an increase between 6 am and 3 pm, and absent from 4 to 6 am. In six (14%) there were inhibitions and reversion to asynchronous.+ pacing with the R on T phenomenon and non conducted artifacts in four; in one case the asynchronous stimulation occurred over sinus rhythm. Undersensing was confirmed in four (9%) but in three was caused by PVC. Bipolar: all were asymptomatic and without sensing anomalies. Conclusions. The high incidence of asymptomatic oversensing in unipolar generators limits Holter's value in the diagnosis of symptomatic cases by myopotential interference. Its routine use for detecting anomalies in sensing seems inadvisable. The reversion to asynchronic functioning is not unusual and could be a potentially provocative mechanism of ventricular arrhythmias.