WO1988003822A1

WO1988003822A1 - Apparatus for transoesophageal cardiac stimulation implemented with a minimized energy threshold, and a relative method of stimulation

Info

Publication number: WO1988003822A1
Application number: PCT/IT1987/000098
Authority: WO
Inventors: Gino Grassi; Paolo Marconi
Original assignee: C.B. Bioelettronica S.R.L.
Priority date: 1986-11-20
Filing date: 1987-11-19
Publication date: 1988-06-02
Also published as: IT8603581A0; IT1216198B

Abstract

The apparatus is designed to generate a stimulation pulse (1) of sine wave or triangular wave shape that rises above the cardiac stimulus threshold, and a compensating pulse (2) of inverse polarity which is equivalent in terms of energy but remains below the the threshold value; use is made of an oesophageal probe with at least three electrodes, the endmost of which (4, 6) are wired up to a pulse generator (11), and the middle (5), however many, to a pulse recorder (12).

Description

Apparatus for t ransoesophagea L cardiac stimulation implemented with a minimized energy threshold, and a relative method of stimulation.

The invention disclosed relates to an apparatus for transoesophagea I cardiac stimulation that, features minimization of the cardiac stimulus threshold, and to a relative method of stimulation. One of the problems connected with transoesophageal cardiac stimulation is the discomfort caused to the patient, a factor due to the relatively high levels of energy that are required conventionally for an efficient stimulation. This situation arises from the fact that the electrical stimulus transmitted by the probe must be geared to somewhat high thresholds in order to compensate for the indirect nature of the contact created between the cardiac muscle and the electrode, which occurs via adipose tissue and muscular bundles; such intervening layers in fact produce a high dielectric rigidity in the capacitive medium thus created.

An additional problem is that of the need to effect a recording of the cardiac signal immediately after stimulation ceases, in order to monitor the response of the patient's heart.

Transoesophageal stimulation is currently effected utilizing apparatus capable of generating a square wave pulse of strength greater than the stimulus threshold, much in the same way as is effected with external electrodes (applied to the chest⁾ or with pacemakers implanted directly in the cardiac muscle. Given the particular type of use and the positioning of these two expedients, however, the aforementioned problems are not encountered; external stimulation of the heart is effected in emergencies for the most part, where no monitoring requirement exists, whilst the output generated by a conventional pacemaker is extremely low. -*

In transoesophageal cardiac stimulation, however, both problems exist at one and the same moment. Each burst of stimulation involves the delivery of a high amount of energy, which occasions discomfort to the patient; more exactly, the energy put out at the moment of stimulation, i.e. at the moment the pulse is generated, produces a capacitive effect through the living tissues, polarizing the oesophagus wall. With the current adoption of this polarizing type of stimulation, which implies using signals generally of between 300 and 500mV and >300msec duration, it becomes impossible to effect a recording of cardiac response, as the return signals are of extremely low strength, around 1mV.

Accordingly, the object of the invention is that of overcoming the drawbacks described above by limiting the amount of energy generated in transoesophageal stimulation, and attenuating its polarizing effects. The stated Object is achieved with an apparatus for transoesophageal stimulation as characterized in the appended claims. According to the invention, the problems outlined above are defeated by adopting an apparatus capable of generating stimulation pulses of sinusoidal, or triangular, or similar waveform, in combination with compensating pulses of opposite polarity, which are equivalent in terms of energy output while remaining below the cardiac stimulus threshold Level. A first advantage provided by the invention consists essentially in the fact that the physical discomfort experienced with cardiac stimulation is lessened, thanks to a considerable limitation of the amount of energy transmitted. Assuming peak stimulation output as par, sine wave and triangular pulses generate energy levels one half and one third, respectively, of that delivered by a pulse of square waveform. Practical research has in fact shown that it is the peak amplitude of a cardiac stimulation pulse that is important, not the energy output. Another advantage of the invention is the facility it provides of effecting a more immediate recording of cardiac response, since the polarizing effect of stimulation is minimized. The compensating pulse produces no stimulation of the cardiac cells, but serves simply to obtain an inverse polarity such as will cancel out, or at least drastically reduce, the polarizing effects of stimulation.

A further problem encountered in cardiac stimulation and recording of cardiac response is attributable to the gastronasal type of probe currently employed in effecting transoesophageal stimulation. Such probes are frequently a cause of discomfort to patients, as they must be inserted through the nasal choanae and the pharynx.

What is more, the dimensions of tri- and quadripole electrodes will almost invariably be such as to cause discomfort during and following ingestion. A further object of the invention is thus to embody a probe for use in conjunction with the apparatus disclosed, that will render transoesophageal card ac stimulation and recording a much less uncomfortable process than with the probes currently utilized. This additional object is amply realized with an oesophageal probe as characterized in the appended claims, which incorporates at least three electrodes that are substantially spherical, or at all events, devoid of sharp edges or surface roughness, so that no spiking effect will occur when the stimulation pulse is discharged; moreover, the electrodes are enveloped in a capsule fashioned from gastrically soluble material, and can be ingested orally. A further advantage of the invention is the minimum discomfort to which individuals are subjected during stimulation, a factor which reduces the likelihood of emotional disturbance triggered by its effects in those patients for whom a calm state is essential. Yet another advantage of the invention is that of the optimum contact achieved between the probe and- the wall of the oesophagus, which shrinks naturally around the single electrodes, engulfing them almost entirely. The invention will now be described in detail, by way of example, with the aid of the accompanying drawings, in which: fig 1 is a graph illustrating the waveform of three pulses, one conventional and two according to the invention, which are superimposed to allow a more immediate comparison; fig 2 is a block diagram illustrating an example of the circuit in apparatus according to the invention; fig 3 illustrates the arrangement of the electrodes in an oesophageal probe as disclosed, viewed in plan, packaged for ingestion by the patient; fig 4 is the section through a probe as disclosed, viewed following ingestion, positioned in readiness both to transmit stimulation pulses, and to receive signals reflecting cardiac response.

The method of transoesop ageal cardiac stimulation disclosed, and the apparatus for its implementation, provide for the generation of stimulation pulses 1 exhibiting sine wave or triangular wave shape, as i I lust rated in fig 1.

It will be seen from fig 1 that the pulse with the square waveform as adopted hitherto, denoted 1q, and those according to the invention, i.e. the sine wave denoted 1s and the triangular denoted 1t, all reach the same peak amplitude, rising above the stimulus threshold denoted Vs.

In order to highlight the features of the invention, the different stimulation pulses 1q, 1s and 1t, are illustrated in superimposed format; it will be seen immediately that the energy generated in each case, i.e. the area subtended by each waveform, differs in considerable measure.

According to the invention, the apparatus generates not only a stimulation pulse 1, but a compensating pulse 2 besides; the peak value of this additional pulse remains below the cardiac stimulus threshold in absolute terms, and its polarity is inverted in relation to the stimulation pulse 1. The width of the inversely polarized compensating pulse 2 is adjusted in such a way that its energy output substantially matches that of the stimulation pulse 1; accordingly, the polarizing effect of the stimulation pulse 1 can be drastically reduced, if not eliminated altogether.

The compensating pulse 2 is indicated in fig 1 as preceding the stimulation pulse 1; whilst this would be the preferred sequence, its inversion will alter nothing in practice.

A possible embodiment of the apparatus is shown in the block diagram of fig 2, where the probe 13 is connected to a pulse generator 11 and to a pulse recorder 12, e.g. an electrocardiograph. 3 denotes a. blanking module operated by the pulse generator 11, and 14 a filter; these two stages are connected in series between the pulse generator and recorder. More exactly, the blanking module 3 is embodied as. a switch interlocked to the pulse generator 11, and will be activated to break the circuit into which it is wired, for the duration of the stimulation and compensating pulses 1 and 2.

To reiterate, generation of a compensating pulse 2 renders it possible, if not to eliminate entirely, then at least to ensure a drastic reduction in the polarizing effect of the stimulation pulse 1. Put in other words, the signal returned by the probe 13, whi ch_^ ref lects cardiac activity and is much weaker than that attributable to the polarizing effects of the stimulation pulse 1, will be discernable by the recorder 12 only when stimulation ceases, hence in real time. Any residual interference will be taken out by the filter 14.

The oesophageal probe 13 according to the invention, illustrated in fig 3, incorporates at least three electrodes denoted 4, 5 and 6; each is substantially spherical in shape, and at all events, free of sharp edges and roughness.

The endmost electrodes 4 and 6 are connected firmly to respective leads 8 and 10 returned to the pulse generator 11. The middle electrode ^'5, on the other hand, is connected to the recorder 12, via a further lead denoted 9. In practice, there might be four or even more electrodes, in which case at least one of those located in the middle must be connected to the recorder 12.

Packaged ready for ingestion by the patient, the electrodes 4, 5 and 6 are contained in a capsule 7, of gastrically soluble material; the dimensions of the electrodes 4, 5 and 6 and the capsule 7 will be such that the probe is easily swallowed, and good contact established between the electrodes and the oesophagus wall 15 (fig 4). The size of a suitable capsule for general use might be, say, 6 x 18mm. The middle electrode/s 5, that is, connected to the recorder 12, might be embodied smaller than the end electrodes 4 and 6 connected to the pulse generator 11, as the wall 15 of the oesophagus will generally shrink around the electrode regardless, enveloping it almost entirely Cfig 4

The length of the leads 8, 9 and 10 is dissimilar, so that with the capsule 7 swallowed and dissolved, the electrodes 4, 5 and 6 will simply gravitate to the required level, extending the leads 8, 9 and 10 as in fig 4. Contact with the oesophagus wall 15 is enhanced by providing the electrodes 4, 5 and 6 with an axial bore; the leads 8 and 9 of the two farthest electrodes 4 and 5 thus pass through the nearest 5 and 6, which remain uppermost following destruction of the capsule 7. The two leads 8 and 9 might pass loosely through the two electrodes 5 and 6, as in fig 3, which illustrates the leads gathered into the capsule 7, or might be attached to them firmly. The length of each lead 8, 9 and 10 will be selected in such a way that with the capsule 7 dissolved, the distance between the stimulation electrodes 4 and 6, i.e. those located endmost and wired up to the pulse generator 11, will be optimum -viz, 30mm approx. In ultimate embodiment, the electrodes 4, 5 and 6 might exhibit a shape other than spherical, as shown in figs 3 and 4, provided that the probe 13 retains its dynamic configuration, combining the advantage of oral ingestion with that of small dimensions of the electrodes 4, 5 and 6, and with that of a low cardiac stimulus threshold, this ensured by optimum distancing of the electrodes at approx 30mm apart, as aforementioned.

In a preferred embodiment, however, the electrodes 4, 5 and 6 wilt be spherical, to facilitate their extraction, and the leads 8, 9 and 10 will be thin, ultra-flexible and well-insulated wires made fast mechanically to the electrodes as in figs 3 and 4.

Claims

1) Apparatus for transoesophageal cardiac stimulation, characterized in that it comprises:

-a pulse generator (11), the pulse train from which consists in a combination of stimulation pulses ⁽1⁾ exhibiting sinusoidal or triangular or similar wave shape, the peak amplitude of which rises above the cardiac stimulus threshold, together with inversely polarized compensating pulses (2) the peak amplitude of which remains below the stimulus threshold; -an oesophageal probe (13), connected to the output of the pulse generator (11), incorporating at least one stimulation electrode (4, 6), and at least one electrode (5) in receipt of the signal reflecting cardiac response;

-a blanking module (3) in receipt of the signal from the response electrode (5), which is cascaded by way of a filter (14) into a pulse recorder (12), and connected additionally to the pulse generator (11) in such a way as to permit deactivation at least for the period of time during which the stimulation and compensating pulses (1, 2) are transmitted.

2) Apparatus as in claim 1, comprising an oesophageal probe ⁽13⁾ with at least three electrodes (4, 5, 6) of substantially spherical shape, or at all events devoid of sharp edges or roughness, contained prior to ingestion in a capsule (7) of gastrically soluble material, wherein the endmost electrodes (4, 6) are connected via respective leads (8, 10) to the pulse generator (11), and the middle electrode/s (5) via a respective lead or leads (9) to the pulse recorder (12), and the distance separating the electrodes (4, 5, 6) following oral ingestion is determined by the length of the leads (8, 9, 10) when fully extended.

3) Apparatus as in claim 2, wherein the dimensions of the middle electrode or electrodes (5) are smaller than those of the endmost electrodes (4, 6).

4) Apparatus as in claim 2, wherein the leads (8, 9) connected to the electrodes (4, 5) that gravitate following destruction of the capsule (7) are routed through the electrodes (5, 6) lying in their path.

5) Apparatus as in claim 4, wherein the leads (8, 9) connected to the electrodes (4, 5) that gravitate following destruction of the capsule (7) are routed loosely through the electrodes (5, 6) lying in their pat .

6) A method of transoesophageal cardiac stimulation as in claim 1, characterized in that stimulation is effected with a pulse (1) of sinusoidal, triangular or similar waveform, peak amplitude of which rises above the cardiac stimulus threshold, compensated by an inversely polarized pulse (2) with substantially the same energy output, the peak amplitude of which remains below the stimulus threshold.

7) Method as in claim 6, wherein the compensating pulse (2) precedes the stimulation pulse (1).

8) Method as in claim 6, wherein the compensating pulse (2) follows the stimulation pulse (1).