Detection of Defibrillation Threshold Using the Upper Limit of Vulnerability Following Defibrillator Implantation

Although the correlation between upper limit of vulnerability (ULV) and defibrillation threshold (DFT) has been well described, there has been no uniform DFT testing protocol taking the advantage of ULV after defibrillator (ICD) implantation. This study was designed to test DFT with the least number of fibrillation inductions using the ULV and to describe the most practical set of ICD during DFT following implantation. A total of 13 patients undergoing a new ICD implantation had a DFT induced with scanned T wave shock. The hypothesis that VF could be defibrillated with 5 J higher than the highest T-wave shock needed to induce VF or with 10 J if the T wave shock needed to induce VF was less than 5 J, was tested. The common features of five patients who did not fulfill the hypothesis were that T wave shock needed to induce VF was either under 5 J (4 patients) or high (1 patient). We propose the first T wave and rescue shock set at 10 J and 15 J, respectively. If any of the scanned T wave shocks could not induce VF, then the T wave and the first rescue shock should be set at 5 J and 10 J, respectively. If the induction of VF has been unsuccessful with T wave shock at 5 J, then a high DFT should be expected.