Precipitous exit block with epicardial steroid-eluting leads

Between January 1990 and October 1992, we implanted 16 steroid-eluting ventricular epicardial pacing leads (Medtronic 10295A and 10295B/4965) in 12 patients. There were 8 males and 4 females ranging in age from 3 months to 49 years (mean 8.7 +/- 13.2, median 6.0 years). Structural cardiac disease was present in 11 of 12 patients. Follow-up ranged from 3-73 months postimplant (mean 35.7 +/- 22.3, median 28.5 months). Lead fracture (10295A) occurred in 1 of 12 patients. Of the remaining 11 patients, 8 of 11 have very low long-term pacing thresholds. Unexpectedly, 3 patients demonstrated precipitous threshold increases from 3 months to 3.5 years postimplant. Although no deaths resulted in these exit block patients, 1 of 3 exit block patients developed marked worsening of congestive heart failure. We reviewed and analyzed the data obtained at 4 weeks postimplant for all of the 10295A and 4965 patients in the entire Medtronic clinical study database. Using the criterion of a 4 week postimplant pacing threshold > or = 0.12 ms (5 V), we found that the long-term risk of eventual exit block was 27.3% for the 10295A lead (P = 0.005) and 7.5% for the 10295B/4965 lead (P = 0.03). We, therefore, recommend that in patients implanted with the 4965 steroid-eluting epicardial lead, ventricular pacing thresholds > or = 0.12 ms (5 V) measured at 4 weeks postimplant should prompt frequent threshold testing to detect late and potentially sudden ventricular pacing threshold increases.