The present invention relates to a cardiac pace-maker having a rhythm controlled by regulation signals detected in the nerves, in receivers, or in both simultaneously.
The heart has an impulse conduction system which permits the synchronization of all the fibers of the cardiac muscle. The sinus nodule is the initiator of the heart beat and, therefore, the main natural pace-maker.
In recent years the use of cardiac pace-makers in those patients, whose hearts have lost the capacity of maintaining the rhythm and synchronism necessary between its parts to pump blood efficiently, has been generalized.
A cardiac pace-maker is a device which supplies, rhythmically, electrical impulses to the cardiac muscle, forcing the heart to beat with the rhythm imposed, electronically replacing the natural electric excitation.
There are, at present, three types of pace-makers: asynchronous or fixed rhythm units which give a fixed frequency of beats, synchronous units which adjust the rhythm to that of the auricular contraction when the same is present, and finally units which operate on request and which are inhibited when the presence of natural QRS complex is detected.
The main disadvantage of present-day pace-makers is that they lack the capacity to regulate their rhythm, depending on the biological needs imposed on the patient in each of various activities.
A normal heart regulates its rhythm with the purpose of supplying blood to the tissues, depending on the needs thereof, by means of nerve circuits whose afferent via depart from the nerve receivers, baro receivers, chemoreceivers, etc., and whose efferent via act on the natural cardiac pace-makers, the sinus nodule, the atrio-ventricular nodule, etc.
A conventional cardiac pace-maker is an electronic device comprising a periodic impulse generator which should have a pre-determined shape for its maximum efficiency, fed by a battery and connected to the myocardium by an electrode and its connecting cable. However, this electronic simplicity is counterbalanced by the following disadvantages. Protecting encapsulation of the electronic circuit must be made from a biocompatible material. The environment into which the pace-maker is installed is tremendously aggressive for its components, thus its average life is remarkable reduced. The mercury batteries are affected by the moisture caused by the growth of metal dendrites and, consequently, by short circuits. It has been remarkably improved due to techniques of encapsulation.
The battery is a key element for the average life of the pace-maker. Conventional batteries are of mercury-zinc oxide whose average life is of about 33 months. Use is now being made of lithium batteries, in a solid state, wherein the anode is of lithium and the cathode of iodide, generating electricity by the migration of the lithium ions through the salt. It does not generate gas and can be hermetically encapsulated, which, together with its greater density in energy, assures an average life which is expected to exceed five years.
Another battery presently used employs Plutonium 238 whose radiation is utilized in a thermocell to generate electricity. Its expected average life is more than 10 years, its cost being two or three times that of lithium batteries.
Active research is being undertaken to obtain new sources of energy, especially utilizing electrochemical sources within the human body.
Another disadvantage resides in the stimulation electrode and the connecting cable. The main problems arise from the need of an effective fastening of the electrode which prevents displacements and of the security that the connecting cable does not break due to wear since it is subjected to continuous bending stresses.