EFFECT OF STEROID-ELUTING VERSUS CONVENTIONAL ELECTRODES ON PROPAFENONE INDUCED RISE IN CHRONIC VENTRICULAR PACING THRESHOLD

The aim of this study was to evaluate chronic ventricular pacing thres hold increase after oral propafenone therapy. Eighty-three patients af fected by advanced atrioventricular block and sick sinus syndrome were studied at least 3 months after pacemaker implantation, before and af ter oral propafenone therapy (450-900 mg/day based on body weight). Th e patients were subdivided into three groups according to the type of unipolar electrode that was implanted: group I (41 patients) Medtronic CapSure 4003, group II (30 patients) Medtronic Target Tip 4011, and g roup III (12 patients) Osypka Vy screw-in lead. In all cases a Medtron ic unipolar pacemaker was implanted: 3 0 Minix, 23 Activitrax, 14 Elit e, 12 Legend, and 4 Pasys. Propafenone blood level was measured in 75 patients 3-5 hours after propafenone administration. The pacing autoth reshold was measured at 0.8 V, 1.6 V, and 2.5 V by reducing pulse widt h. At the three different outputs before and after propafenone, thresh old increments were significantly lower in group I in comparison with group II and group III (propafenone ranging from < 0.001 to < 0.05). N o significant difference was found in pacing impedance or in propafeno ne plasma concentration in the three groups. Strength-duration curves were drawn for each group at baseline and after propafenone administra tion. Before propafenone, in group I, the knee was markedly shifted to the left and downward as compared to the classic curve, so that the s teep part was predominant; in group II and group III this shift was pr ogressively less evident. After propafenone we found the curve shifted to the right with the flat part progressively more evident in group I I and group III as compared to group I. We conclude that steroid eluti ng leads cause less threshold increase than conventional and screw-in ones after oral propafenone, thus leading to safer chronic pacing. Chr onic pacing at 2.5-V amplitude and 0.6-msec width was feasible in 97% of group I patients and in 80% of group II patients, but not in group III due to an insufficient safety margin.