Source: {"pile_set_name": "USPTO Backgrounds"}

1. Field of the Invention
The present invention is directed to an implantable arrangement for defibrillation or cardioversion of a heart.
2. Related Application
The subject matter of the present application is related to that of application Ser. No. 07/895,810, filed simultaneously herewith, of the same inventors and assigned to the same Assignee as the present application.
3. Description of the Prior Art
An implantable system for in vivo defibrillation or cardioversion of a heart is disclosed in U.S. Pat. No. 4,662,377. This known system includes two intravascular electrodes, which are both carried on a catheter which is introduced into the right half of the heart. The intravascular electrodes are spaced from each other along the cathode so that when the cathode is properly in place within the heart, one electrode is disposed in the right ventricle of the heart and the other electrode is disposed in the superior vena cava. A planar electrode is disposed outside of the heart, opposite the left ventricle and is subcutaneously implanted at that location. The planar electrode is connected to the electrode in the superior vena cava and is connected to an output terminal of an implantable defibrillation pulse generator. The other output terminal of the pulse generator is connected to the electrode disposed in the ventricle so that, when defibrillating the heart, the current surge is divided into a first sub-current between the electrode in the ventricle and the electrode in the superior vena cava, and a second sub-current between the electrode in the ventricle and the planar electrode.
Another arrangement for defibrillation or cardioversion of a heart is disclosed in U.S. Pat. No. 4,708,145 which also uses a catheter having an electrode disposed in the right ventricle and another electrode in the superior vena cava, and a planar electrode which can be either subcutaneously disposed or epicardially disposed in the proximity of the diaphragm. Defibrillation pulses are supplied sequentially between the electrode and the superior vena cava and the electrode in the ventricle, and the planar electrode and the electrode in the ventricle. Thus, only two electrodes simultaneously participate in the delivery of pulses, and a true distribution of the current density into different zones of the heart muscle therefore does not occur. As an alternative to the aforementioned electrode placement, the electrode in the superior vena cava may be disposed in the inferior vena cava. Another electrode arrangement is disclosed in this patent wherein only planar electrodes are arranged on the heart.
A defibrillation arrangement is disclosed in European Application 0 373 953 wherein, when employing three electrodes, one electrode is arranged in the right ventricle via a catheter, another electrode is arranged in the vena cordis magna (great coronary vein) via a further catheter, and a third planar electrode is subcutaneously arranged disposed opposite the left ventricle. Defibrillation pulses are supplied either between one of these electrodes and the two other electrodes, which are connected to each other to achieve this purpose, or alternatively the electrodes may be successively charged with a defibrillation pulse in pairs.
Lastly, German OS 39 19 498 discloses an implantable arrangement for defibrillation or cardioversion of a heart, wherein one of a plurality of electrodes is disposed in the right ventricle, and the other electrodes, which are planar electrodes, are placed outside the heart or implanted subcutaneously. Defibrillation pulses are supplied between the electrode in the ventricle and the outer electrodes, which are connected to each other, so that the electrical current density is divided according to the spatial arrangement of the electrodes, and thus tends to penetrate the thickest zones of the heart muscle. If the defibrillation energy is to be optimally exploited, it is then necessary that the outer electrodes be applied directly to the epicardium. This requires, however, surgical opening of the thorax.