Abstract: A system and method for predicting the defibrillation threshold energy of a defibrillation lead arrangement by determining the upper limit of vulnerability of the heart by shocking the heart at varying times during the T-wave at decreasing test shock energy levels until fibrillation is induced in the heart. The lowest energy level which fails to induce fibrillation is determined to be the upper limit of vulnerability and the defibrillation threshold is predicted to be an energy level incrementally higher in the range of about 5 Joules.

Abstract: An endocardial mapping catheter for locating the ectopic focus of an abnormally functioning heart includes an actuator assembly and an elongated hollow support sheath which extends from the actuator assembly. A plurality of electrical probes are slidingly disposed for independent movement through the sheath, and each probe is attached to the actuator assembly for individual manipulation. A guide is mounted on the end of the sheath opposite the actuator assembly, at the distal end of the sheath, to radially deploy each electrical probe along a separate favorable trajectory as the probe is manipulated to move distally through the sheath. In operation, the probes are initially retracted into the sheath as the guide is positioned inside the left ventricle of the heart. Once the guide is positioned as desired, all of the probes are individually deployed until they have each made contact with the endocardium of the left ventricle.