GB2412069A - Cardiac stimulation system having wireless communication to a stimulator directly attached to the external heart surface. - Google Patents

Abstract

A device for heart pacing comprises a leadless stimulator for direct placement on the heart and a mother device for remote mounting. The stimulator is preferably self-powered by a motion driven generator, e.g. a piezo-electric crystal. The stimulator has interdigitating projections for retention on the heart muscle, such as micro-filaments. The stimulator may have a plurality of individually energizable electrical contact sites, each site comprising one or more electrodes.

Description

24 1 2069 Device for Stimulating the Heart This invention relates to a

device for stimulating contractile muscle, and is particularly concerned with human heart pacing.

Arrhythmia of the human heart is treatable by the use of a so called cardiac pacemaker, which is a device capable of delivering a periodic electric pulse to the heart, and which will cause the heart to beat synchronously. Cardiac pacemakers are well known, are typically implanted subcutaneously. Means to connect the pacemaker to the heart and to an external energy source are required.

Leadless pacemakers have been proposed to eliminate the infection risk consequent on the use of a lead passing through the skin, but thus have the disadvantage that they must be removed for replacement or reprogramming. Furthermore, the energy source of a leadless pacemaker will become exhausted over time and require replacement, by surgery.

Several kinds of pacemaker are required for the treatment of different ailments. The relatively new technique of left ventricular pacing uses electrical leads that pass from the pacemaker to the left ventricular epicardial veins via the coronary sinus. However, for reasons of anatomical variation and disease it is not always possible to use this approach, and in those circumstances the technique of left ventricular epicardial pacing is employed.

This latter technique is used particularly in paediatric practice because the endovascular approach is limited by patient size. Until recently the necessary techniques and equipment have required the patient to undergo major surgery.

Recent advances in endoscopic techniques and minimally invasive surgery have stimulated interest in epicardial lead placement for left ventricular cardiac resynchronization pacing. However, a contiguous electrical connection between a pulse generator and an electrode placed on the epicardial surface is required.

According to the invention there is provided a device for electrical stimulation of contractile heart muscle and comprising a stimulator adapted for direct attachment to the external surface of the heart, and a mother device for remote mounting, wherein the stimulator and mother device are adapted for wireless communication.

Such a device allows the stimulator to be of relatively small size, and thus adapted for direct placement on the epicardial surface of a human heart, using minimally invasive surgical techniques. The mother device consists typically of those components which need not be placed against the muscle surface. In the case of heart pacing, such a mother device would for example be placed close to the stimulator, but in a location not requiring major surgical intervention. Typically the mother device would be mounted subcutaneously, but it could also be worn externally.

Communication between the stimulator and mother device is for example by low power radio frequency signal, but it is envisaged that other wireless techniques may also be suitable. The required communication range is typically less than 100 mm.

The invention is particularly suitable for pacemakers because much of the current drain in conventional devices relates to diagnostics - typically data acquisition, data storage, and analysis of electrogram data - and not to generation of the pacing spike itself. In the present invention the stimulator is in effect an epicardial electrode whose function is in the preferred embodiment restricted to pacing, whilst the mother device comprises the other components and is adapted for access for servicing, updating and so on.

Another advantage of the invention is that the data transmission capabilities need only be very small, being restricted in the preferred embodiment to pacing alone. The invention has the great advantage that the stimulator can be implanted without major trauma, is simple in construction, and thus likely to remain operable indefinitely.

In one embodiment the stimulator is adapted for attachment by the use of a physiologically compatible adhesive, and muscle stimulation is via direct electrical contact between the stimulator and the surface to which it is in use attached.

In a preferred embodiment the stimulator includes projections on the muscle side, which projections are adapted to mechanically engage the muscle surface, or be mechanically engaged by the muscle surface. Such projections can be of any suitable shape and number, and are preferably in a regular array adapted to draw the stimulator into close intimate contact with the muscle surface. It is envisaged for example that a physiologically compatible adhesive may provide temporary retention, and that suitable projections provide a semi-permanent anchor after a few days. This technique allows functionality of the stimulator to be tested in vivo, and allows some freedom for re-positioning of the stimulator.

Projections of this kind assure intimate contact; and thus minimize the possibility for inflammatory material to accumulate or enter between the muscle surface and stimulator. Furthermore the stimulator can be adhered without causing trauma to the muscle surface. The avoidance of inflammatory material is also important in preventing stimulation of such inflammation as may occur.

In a preferred embodiment the projections are electrically conductive, and adapted to pass an electrical stimulus into the muscle surface. The projections may for example comprise an array of micro filaments adapted to interdigitate with the epicardial surface of the human heart. Such conductive projections have the advantage of passing the electrical stimulus directly to the muscle, and thus the risk of attenuation by adhesive or unwanted interstitial material is avoided.

This micro-electrode technology facilitates pacing at very low voltage amplitude charge as compared with conventional pacemakers.

The stimulator is preferably provided with a plurality of individually energizable electrical contact sites, which in the preferred embodiment are individual electrodes, or arrays of electrodes. Such a stimulator is thus adapted to deliver an electrical pulse to the muscle as a single event or as a succession of partial events. The latter technique is especially suitable for causing a muscle to contract in a predetermined manner, for example by propagating a depolarization wavefront through the myocardium of the human heart. For that purpose, the mother device may include a suitable programmable microprocessor.

A typical stimulator will be a disc of around 10 mm in diameter and having a thickness of 3.5 mm. This size is suitable for placement in the epicardial space using endoscopic 1 0 tools.

In order to ensure a wave of electrical stimulus, the stimulator may comprise a flexible strip attachable to the surface of contractile muscle and having a plurality of spaced electrodes along the length thereof.

It will be understood from the foregoing description that the mother device is adapted to telemeter data to the stimulator. However, the stimulator may also be adapted to provide feedback to the mother device, for example to achieve optimisation of a contraction prompted by sequential enegerization of electrodes. The stimulator may also be adapted to sense and transmit information about the contact sites, including for example far field electrical signals, rhythm activity and events, temperature and tissue impedance.

The stimulator may be adapted to provide a contact electrogram, such as an electrocardiogram for the human heart. The stimulator may include a buffer memory to allow such information to be downloaded to the mother device at periodic intervals, or on demand.

In one embodiment the stimulator is energized remotely by the mother device, but in a preferred embodiment it includes a power supply to ensure stand alone operation for a limited period. The power supply may for example be rechargeable by periodic pulses of RF energy from the mother device. However in another preferred embodiment, the stimulator includes a motion driven current generating device, such as a piezo- electric crystal. In the case of the human heart it is envisaged that such a generator could provide the full power requirement of the stimulator also via an energy storage device, such as by trickle charger and a capacitor. Such a stimulator may thus be adapted to be self- contained in the absence of the mother device.

In this embodiment the stimulator is generating only sufficient energy to produce a pacing pulse, which is a small requirement well within the capabilities of an generator driven by heart motion.

Typically a small current drain might occur as a consequence of the leadless communication system, but this is within the capability of an integral motion driven generator and can be minimised by communicating with the mother device periodically, for example 1MS communication every 1OMS operation. The device would thus have a reduced resolution of pacing spike generation whilst not materially affecting efficacy of pacing or timing of pacing. i A suitable generator may comprise a piezo-electric crystal able to flex with heart motion so as to generate a current. Such a generator could be of non-rigid materials.

Claims (14)

1. J

   Claims 1. A device for electrical stimulation of contractile heart muscle and comprising a stimulator adapted for direct attachment to the external surface of the heart, and a mother device for remote mounting, wherein the stimulator and mother device are adapted for wireless communication.
2. 2. A device according to claim 1 wherein communication between the stimulator and mother device is by low power radio frequency signal.
3. 3. A device according to claim 1 or claim 2 wherein the stimulator is adapted for attachment by the use of a physiologically compatible adhesive.
4. 4. A device according to any preceding claim and adapted to stimulate muscle via direct electrical contact between the stimulator and the surface to which it is in use attached.
5. 5. A device according to claim 4 wherein the stimulator includes projections on the muscle side, which projections are adapted to mechanically engage the muscle surface, or to be mechanically engaged by the muscle surface.
6. 6. A device according to claim 5 wherein said projections are adapted to draw the stimulator into close intimate contact with the muscle surface.
7. 7. A device according to claim 5 or claim 6 wherein said projections are electrically conductive, and adapted to pass an electrical stimulus into the muscle surface.
8. 8. A device according to claim 7 wherein said projections comprise an array of micro filaments adapted to interdigitate with the epicardial surface of the human heart.
9. 9. A device according to any preceding claim and provided with a plurality of individually energizable electrical contact sites.
10. 10. A device according to claim 9 wherein each said site comprises one or more electrodes.
11. 11. A device according to claim 9 or claim 10 wherein the stimulator comprises a flexible strip having a plurality of spaced electrodes along the length thereof.
12. 12. A device according to any preceding claim and adapted for two-way communication between stimulator and mother device.
13. 13. A device according to any preceding claim wherein said stimulator is energized remotely by said mother device.
14. 14. A device according to any of claims 1-12 wherein said stimulator includes a motion driven current generating device as energy source.