OPTIONS IN MANAGING THE PATIENT WITH HIGH DEFIBRILLATION THRESHOLDS

The desired defibrillation threshold (DFT) obtained during intraoperat ive testing of an implantable cardioverter defibrillator (ICD) should be 10 J lower than the maximal energy delivered by the ICD generator. Of the 206 patients undergoing ICD implantation since December 1986, 8 (3.9%) have had initial DFTs with less than the 10-J safety margin us ing the standard large patch-large patch configuration. Patches were i mplanted by left thoracotomy in 6 and sternotomy in 1, and 1 had impla ntation of a transvenous defibrillation lead and subcutaneous patch. O f note, 6 (75%) of the 8 patients with high DFTs had prior open heart operations, half were on a regimen of long-term amiodarone therapy, an d the mean left ventricular mass index was quite large but not signifi cantly greater than that of patients with low DFTs. Multiple technique s were tried to improve the DFTs in this group. Satisfactory DFTs were eventually obtained in 7 (88%); the threshold was lowered from a mean of 41.4 +/- 3.8 J to 26.9 +/- 8.8 J (p = 0.002). The most effective t echniques were addition of a superior vena cava lead attached by a Y c onnector to one of the large patch leads in some patients and conversi on to a biphasic-waveform generator in 2 others. Adding a third epicar dial lead did not lower the DFTs. There were no major postoperative co mplications or deaths attributable to these supplemental procedures. U sing these techniques, satisfactory DFTs were obtained in almost all p atients with an ICD. Consideration should be given to insertion of a s uperior vena cava lead at the initial ICD implantation should an unacc eptably high DFT be obtained with standard patch configurations. Bipha sic-waveform generators and other newer devices may reduce the number of patients who require multiple leads for reliable DFTs.