Investigation of pacemaker position, lead configuration, and sensitivity setting in pacemakers of 579 deceased patients

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The position of the pacemaker (PM) system (right or left-sided, pectoral, or abdominal), the ventricular lead configuration (unipolar or bipolar), the programmed ventricular sensitivity setting (SS), and the ventricular sensitivity of the pulse generator (PG) against electromagnetic interference (EMI) are decisive parameters with respect to EMI behaviour of PGs. Three of these ventricular parameters were investigated in PM of 579 deceased patients. We investigated PM function provided a regular stimulation pattern in 878 deceased PM patients before cremation. The PG was explanted and then measured in a bench test in the laboratory with respect to the programmed parameters. Further investigations were restricted to 579 patients with PGs implanted between 1998 and 2004. The following parameters were evaluated: (i) position of the PG, (ii) lead configuration, and (iii) programmed SS of the ventricular channel. SS was measured according to the European Pacemaker Standards. Out of 579 patients, 556 PMs were implanted pectorally, with 172 on the left side (30.9%) and 384 on the right side (69.1%). In 23 cases, the implantation site was unknown. Out of 579 PMs, 282 ventricular leads were unipolar (48.7%). Of the 297 bipolar leads (51.3%), 61 (20.5%) had a unipolar sensing function so that a total majority of 343 PM (59.2%) had unipolar sensing. The mean value of SS was 3.24 mV (range: 1.2-8.1 mV) for unipolar leads and 3.55 mV (range: 1.05-10.9 mV) for bipolar ones. The PGs with unipolarized bipolar leads were even more sensitive at 3.0 mV. Of the 579 PM systems, 0.67% possessed a combination of parameters: left side, unipolar and with SS < 2 mV. The results seemed to be paradoxical in that unipolar sensitivity was more sensitive than bipolar sensitivity. Less than 0.67% of patients possessed a worst case PM system with respect to EMI: a unipolar, left-sided PG with a ventricular SS < 2 mV. This implies that ∼2345 PM patients in Germany could be at risk. Out of the 61 PGs with unipolarized bipolar leads, 14 had never been programmed as they still possessed the shipping programming. Unipolar leads can be used with left-side implantation if the SS is 3 mV (median value of all leads in our study) or higher. This would largely improve the immunity of PGs to EMI in the future. This study also demonstrates that there is a need for educational measures.