When implantable cardiac defibrillators are implanted (ICDs), the defibrillation threshold (DFT), of the amount of energy required to effectively terminate life-threatening arrhythmias is determined. The device is then programmed to discharge a larger amount of energy in order to provide a safety margin. In some patients, the DFT is so high, that an adequate safety margin is not programmable. Placement of a defibrillation lead in the azygos vein has been found to be helpful in these patients. This goal of this trial is to attempt to quantify the average reduction in the DFT (if any) that results from the addition of the azygos lead.

Patients undergoing placement of an ICD for the primary or secondary prevention of sudden cardiac death will be asked to participate. Patients will undergo implantation of a standard right ventricular ICD lead at the time of ICD implantation. In addition, patient will receive another high voltage ICD lead placed in the azygos vein as has been previously described in the literature (1). After sedating the patient, the DFT will be determined using a binary search algorithm. This consists of testing the device at a given output for the first shock after inducing ventricular fibrillation (VF). Should the shock fail, external defibrillation will be attempted, as is the standard method for performing DFT testing. As per the standard method of DFT testing, VF will be induced a second time, with the shock strength dependent on the success of the first shock. If the first shock was unsuccessful, the second will be at a higher output. If the first shock was successful, the second will be at a lower output. A third shock will then be delivered, based on the success or failure of the preceding shock to define the DFT. Of note, as the device can be programmed to give multiple shocks for one episode, VF will not necessarily need to be induced each time. For example, VF could be induced, and the device programmed to give a 20 Joule (J) shock followed by a 23J shock if not successful, thus limiting the number of VF inductions required. DFT testing will be done using both the standard configuration of high voltage leads as well as using the azygos lead. We hypothesize that using the azygos lead will result in a lower DFT.

Inclusion Criteria:

• Any patient undergoing elective placement of an ICD for the primary or secondary prevention of sudden cardiac death is eligible. Exclusion criteria include any contraindication to endovascular ICD implantation which includes but is not limited to; active infection, occluded venous access, or inability to perform DFT testing secondary to the inability to sedate the patient or hemodynamic compromise.

Exclusion Criteria:

• Any contraindication to ICD or the inability to place an azygos vein coil.

32 patients were enrolled. There was inability to place an and azygos coil in 6. 1 could not be sedated for defibrillation testing. 25 patients were analyzed.

24 hours

Definitions are as the clinicaltrials.gov definitions.

Patients were follow for clinically for 24 hours after their implant and defibrillation testing procedure.