Surgery: light – thermal – and electrical application – Light – thermal – and electrical application – Electrical therapeutic systems
Patent
1995-06-15
1997-10-07
Jastrzab, Jeffrey R.
Surgery: light, thermal, and electrical application
Light, thermal, and electrical application
Electrical therapeutic systems
607 36, 607129, 607148, A61N 1368, A61N 1375
Patent
active
056742592
DESCRIPTION:
BRIEF SUMMARY
This application is a continuation-in-part of PCT International Patent Application No. PCT/AU92/00219 having an International Filing Date of 15 May 1992 (15.05.92) and designating the United States (U.S.) among other designated states. PCT International Patent Application No. PCT/AU92/00219 claims the priority of Australian Patent Application No. PK 6207, which has a filing date of 17 May 1991 (17.05.91).
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a heart pacemaker.
2. Description of the Prior Art
An existing cardiac pacemaker consists of a power source and electronic circuitry which together constitute a pulse generator housed within an hermetically sealed metal capsule. The metal capsule is arranged to be inserted within a patients body normally near one of the pectoral muscles. An insulated lead having its proximal end connected into a receiving port of the metal capsule so as to provide a direct connection with the pulse generator, has its distal end connected to one or more bare metal electrodes which are located inside the patients heart. Typically, such transvenous electrodes are positioned in the right ventricle and deliver stimulating impulses to the endocardium. This was first successfully performed by Lagergren et al at the Karolinska Institute in Stockholm Sweden 1962. Prior to this the stimulating electrodes were attached to the epicardium by thoracotomy for both external and implantable pacemakers.
Transvenous electrodes suffer from a number of problems one of which is a loss of synchronous mechanical contraction of the left and right ventricles. This is referred to as pacemaker induced left branch block type conduction disturbance and is recognised by a lengthening of the QRS complex. The resultant reduction in left ventricular chamber performance is indicative of a reduced cardiac output, especially at higher heart rates as with rate responsive physiological pacemakers. The cause of the pacemaker induced left bundle branch block is the positioning of the stimulating electrode on the free wall of the right ventricle. This right ventricular pacing causes an intraventricular delay in the transmission of stimulating impulses to the left ventricle. In a normal healthy heart the ventricles are stimulated to depolarisation by nerves that are found in both the left and the right ventricles, thus ensuring synchronous isovolumic systole occurs in both ventricles in every heart beat. The single transvenous electrode positioned in the right ventricle cannot replicate this process.
Conventional pacemakers using electrodes placed transvenous in the right ventricle of the heart also suffer from a number of other problems. Relatively long conductive leads are used to connect the implanted electrode to the pulse generator housed in the pacemaker body. There is thus a relatively large impedance between the pulse generator and the electrode, requiring the generation of higher voltages and resulting in a large drain on the power source. This shortens the life of the pacemaker.
It is necessary to surgically implant the electrode into the heart. This can be an expensive procedure, which in conventional transvenous electrodes, requires the provision of expensive equipment to perform fluroscopy for positioning of the electrode. The expense of the procedure limits application.
Further, generally only a single electrode is implanted. This single electrode is used both for sensing cardiac activity and providing pacing pulses. In pacing at higher rates, polarisation of the electrode site increases due to the reduced time between succeeding stimulating impulses thereby not permitting dispersion of the voltage of polarisation. Pacing voltage must therefore be increased to overcome the polarisation potential and apparent increase in impedance. This, again, results in an increased drain on the power source.
Further, coupling the sensing and pacing functions in a single electrode results in the possibility of local polarisation interfering with the sensing function.
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