High defibrillation energy requirements are encountered rarely with modern dual-chamber implantable cardioverter-defibrillator systems.

Aims: Defibrillation conversion testing to assure a 10 J safety margin is a standard practice during implantable cardioverter-defibrillator (ICD) implantation. Little data are available on the number of patients who do not have a 10 J margin initially and therefore require system revisions, further testing, or a higher energy output device.

Methods And Results: The INTRINSIC RV study enrolled 1530 new ICD recipients who were not in permanent atrial fibrillation who received a VITALITY AVT (Guidant, St Paul, MN, USA) standard energy (31 J maximum) ICD and underwent defibrillation conversion testing at the time of implantation from 108 centres. Among enrolled patients, 59 (3.9%) did not initially meet the 10 J safety margin criterion. In these 59 patients, a 10 J safety margin was achieved by making at least one system revision: reversing shocking polarity (n = 33, 56%), right ventricular lead repositioning (n = 19, 32%), repeat testing at a later date (n = 1, 2%), adding a subcutaneous array (n = 1, 2%), or other means (n = 10, 17%). Only New York Heart Association class (P = 0.001) and no previous myocardial infarction (P = 0.044) predicted a failed initial conversion test. There were no reported complications from ICD shock testing.

Conclusion: Successful defibrillation conversion criteria with the first configuration tested with a standard energy device is almost always met with modern dual-chamber ICD systems. The need for revising the initial ICD shock configuration to achieve a 10 J safety margin appears extremely low and of low risk.