One turn more: threshold superiority of 3-turn versus 2-turn screw-in myocardial electrodes

Epicardial electrodes are an alternative for patients in whom the transvenous approach presents technical difficulties. We have had clinical experience with two types of myocardial sutureless electrodes inserted in the anterior left ventricular wall: the 3-turn screw-in electrode (Medtronic 6917) was used in 209 patients from 1974 to 1977 and the 2-turn screw-in lead (Medtronic 6917 A) was used in 61 patients from 1978 to 1981. The initial threshold was equal and acceptable with both types of electrodes. During a follow-up period (up to 48 months), critical elevation of the pacing threshold resulting in exit block was found in 12% (25) of the patients with the 3-turn screw-in electrode and in 20% (12) of the patients with the 2-turn electrode (p less than 0.05). Elevation of the pacing threshold developed fairly early, usually within 6 months, with the 2-turn screw-in electrode, but much later, within 2-4 years, with the 3-turn electrode. During a longer follow-up time of up to 96 months the frequency of exit block increased up to 16% with the 3-turn electrode. Our results indicate that late critical elevation of the pacing threshold is surprisingly frequent with screw-in electrodes inserted into the left ventricular myocardium, and it is especially common with the 2-turn screw-in electrode.