WO1998036794A1

WO1998036794A1 - A single electrical catheter for sequential cardiac stimulation

Info

Publication number: WO1998036794A1
Application number: PCT/IB1998/000203
Authority: WO
Inventors: Gino Grassi; Luciano Alcidi
Original assignee: Individual
Current assignee: Individual
Priority date: 1997-02-18
Filing date: 1998-02-16
Publication date: 1998-08-27
Anticipated expiration: 1999-08-18
Also published as: ITFI970024A0; ITFI970024A1; IT1291780B1

Abstract

A single electrical catheter for temporary or permanent cardiac stimulation, whether VDD or DDD, includes atrial and ventricular electrodes mounted on the same catheter. The distance between the two electrode groups depends on heart dimensions. The electrodes A, B, C used for atrial sensing and stimulations are located and connected in such a way, that A and C are positioned symmetrically about the central electrode B; A and C are electrically connected to each other and to a terminal of the atrial pacing device, while B is connected to the other terminal. Said electrode configuration allows to decrease the stimulation threshold and to increase the recording sensitivity of the atrial signals.

Description

A single electrical catheter for sequential cardiac stimulation

Technical Field

Sequential pacemakers, known to experts in the field by the abbreviation VDD, have become common instruments of clinical cardiology. Pacemakers of this kind use a single electrical catheter on which both the atrial and the ventricular electrodes are mounted.

Background Art

Detection of electrical atrial activity is normally bipolar using two electrodes which, when the catheter is positioned distally in the ventricle, are situated in the medium or medium- high atrium so as to detect the atrial signals used to synchronize the emission of the ventricular stimulus, after a time delay which simulates the real time delay and which is usually programmable. The fact that it is easier to insert a single catheter through a vein instead of two (one in the atrium and one in the ventricle) has prompted researchers to find a way of using a single catheter also for DDD stimulation. That means the electrodes inserted into the atrium must be used to also stimulate the atrium by appropriately configuring the electrodes themselves or resorting to special circuitry. The results attained so far, however, are not satisfactory.

The use of a normal dipole, like those used until now for VDD stimulation, have several drawbacks if applied to atrial stimulation, namely: a) owing to anatomical shape, it is difficult for the electrodes to remain in contact with the atrial walls and, instead, they practically always float in the blood that is present in the cavity; b) the equipotential lines of the dipole (see Fig. 1A) are shaped in such a way that the zero is located along the axis perpendicular to the dipole itself (Figure IB) so that when the electrodes are no longer in direct contact with the atrial wall, the effectiveness of the stimulus is greatly diminished in the direction perpendicular to the dipole.

For these reasons, the atrial stimulation thresholds that can be obtained with this configuration are very high and unstable precisely because of the mobility of the catheter in the cavity.

Disclosure of the Invention

To overcome the drawbacks mentioned above, the present invention provides an atrial electrode configuration with double symmetrical dipole on the catheter which increases the possibility of stimulation and at the same time achieves more selective recording of the spontaneous atrial signal, with less interference from signals which, like the ventricular signal, come from areas further away.

The essential characteristics of the electric catheter are illustrated in Figures 2A and 2B.

Figure 3A shows the equipotential lines of the electrode disclosed herein. Figure 3B shows the reference values of the atrial electrodes disclosed herein.

Figure 4 shows an example of applying the electrode disclosed herein.

The catheter consists of a single tube on which the atrial and ventricular electrodes are positioned.

The connection to the pacing device may be embodied in the following ways, these being given purely as non-binding examples: in the case of permanent implantation, using two standard IS-1 type bipolar connectors protruding from the proximal end of the catheter body, one of which has the atrial contacts and the other ventricular contacts, as shown in Figure 2b; or using one multiple connector with all the contacts on it; in the case of a catheter for temporary stimulation, using a single or multiple connector, depending on the requirements of quality mark standards (for example, CE, ISO 9001, etc.). The special arrangement of the atrial electrodes A, B and C is the solution which characterizes the electrical catheter forming the subject-matter of the present patent.

At the medial distance from the distal end of the catheter, which the designer of the special system can select and which is usually from 10 to 14 cm, there are three electrodes A, B and C (Figure 2) positioned in such a way that the two outer electrodes A and C are symmetrical about the central electrode B. Electrodes A and C are electrically connected to each other and to one of the terminals (for example the positive terminal) of the pacing device and thus form with B, connected to the other terminal (the negative terminal), two equal and opposite dipoles (Figure 3) .

1/2 1/2 1 V(d,h) = KQ { } + - — }

[d²+ (1-h)²] td²+(l+h)²] ² [d²+h²] ²

By solving the above formula, which represents the electrical field generated by this electrode set-up, one obtains a configuration of the equipotential lines as shown in Figure 3A. In the formula, K is a constant dependent on the ambient medium and Q is the electrical charge applied; the values of d, 1 and h appear in Figure 3B. This solution was proposed for transesophageal pacing in the paper: Marconi P, Grassi G., Decrease of transesophageal pacing threshold and contemporaneous atrial signal recording - 9th Int. Congr . , "The New Frontiers of Arrhythmias", Marilleva (Italy), January 27 - February 3, 1990.

It is immediately evident that, compared to the single dipole shown in Figure IB, a clear directional advantage is obtained.

A stimulation threshold that is around 25 to 30% lower than that which can be obtained with a single dipole is thus possible.

When the electrodes move away from the position where they are in contact with the atrial wall, the distribution of the electrical field created by the symmetrical dipole which remains concentrated in the direction perpendicular to the double dipole is clearly improved. Clinical tests have demonstrated the validity of this solution.

The system can be applied not only to electrical catheters for temporary stimulation but also in those to be implanted with permanent pacemakers .

The distance between electrodes A-B and B-C can be chosen in the range from 5 to 25 mm. The electrodes are the same size as those normally used for endocavitary stimulation, that is, between 5 and 30 mm². The electrodes VI and V2 for ventricular stimulation can be arranged in the same way as in standard catheters. V2 will be present only if bipolar stimulation is required.

The electrodes can be made of the same material as used for electrodes used for the same purpose. The material must be biocompatible and chemically inert (for example, Pt , Ti, stainless steel) .

The surface of the electrodes may or may not be treated using chemical or mechanical or electrical and mechanical methods to improve resistance to polarization or decrease the stimulation threshold (for example TiN) .

The mechanical construction must conform with international standards governing these classes of products (for example, ISO or FDA) .

Preferred solutions will now be described depending on whether stimulation is temporary or permanent.

A) For temporary stimulation, each electrode can be connected to a conductor, preferably made of an inert material (for example, stainless steel) and formed from braided wire strands for flexibility. The symmetrical electrical connection described can be made at the proximal end, in the connector.

B) For implantation in permanent pacemakers, conventional coiled conductors can be used, with insulated coils wound around parallel wires and with each individual electrode connected to its coil . C) Alternatively, a catheter tube with a plurality of lumens

(for example, 3 or 4) can be used, where each coil is fed through a lumen. The connection to the electrodes A and C on the same coil in one of the lumens is mechanically easier.

At least for permanent stimulation, which is deemed to be the most important application, the catheter must allow the insertion of a rigid stylet (for example, a straight steel wire) to provide the necessary stiffness to enable the catheter to be inserted and guided into the blood vessel and heart chambers. This stylet can be inserted into the lumen of the parallel insulated coils, or in the case of multiple lumens, into the lumen that reaches into the ventricle. In the case of temporary electrical catheters, without coiled conductors, the stylet can be inserted through a dedicated plastic tube which reaches as far as the distal end within the catheter.

Naturally, the atrial stimulation threshold will be lower when the catheter that mounts the three atrial electrodes is closer to the atrial wall. The same applies to the spontaneous atrial signal or evoked signal. The closer the catheter is to the atrial wall, the better the signal received.

To make it easier to place the catheter in a suitable position, the part of it that is to be situated in the atrium can be preformed into a C shape so that the electrodes remain close to the atrial wall (Figure 4) . Measured from the distal end, the preformed curved part should start at approximately 5 to 8 cm and end at approximately 16 to 21 cm. The mean curvature radius can be approximately 4 to 9 cm.

During insertion of the catheter into the heart chambers, the curvature is eliminated or attenuated by the straight stylet.

When the stylet is withdrawn, the catheter automatically returns to its original shape which keeps it in the desired position.

Claims

1) A single electrical catheter for temporary or permanent VDD or DDD cardiac stimulation characterized in that the electrodes used for stimulation and sensing in the atrium are located as shown in Figure 3B, that is to say, A and C are positioned symmetrically about the central electrode B; A and C are electrically connected to each other and to a terminal of the atrial pacing device, while B is connected to the other terminal.

2) The single electrical catheter as in the foregoing claim wherein the use of the proposed atrial configuration permits : reception of the spontaneous atrial signals that is more selective than reception by a single dipole, the signals from further away, such as the ventricular signals, being attenuated; the obtainment of a stimulation threshold of the atrium that is acceptable according to the normal criteria for implantable pacemakers . 3) The single electrical catheter as in the foregoing claims wherein the atrial part between approximately 5 to 8 and 16 to 21 cm from the distal end is preformed into a curved shape, with a curvature radius of approximately 4 to 9 cm, which brings the electrodes close to the atrial wall . 4) The single electrical catheter as recited in claim 1 wherein the distance 1 between the electrodes making up the symmetrical dipole can range from 5 to 25 mm according to the preferences of the pacemaker designer.

5) The single electrical catheter as in the foregoing claims wherein the atrial and ventricular electrodes can be made from conventional biocompatible, inert materials, with an electrode surface area ranging from 5 to 30 mm², the distance between the atrial and ventricular electrodes being between 10 and 14 cm.

6) The single electrical catheter as in the foregoing claims wherein the connection to the pacing device can be effected using normalized connectors conforming with international standards (ISO or FDA) both for permanent solutions (IS-1) and temporary solutions .

7) The single electrical catheter as in the foregoing claims wherein the connection between the electrodes and the connectors can be made using separate wires in the case of temporary stimulation, with insulated coils with wires wound in parallel, or using separate coils in a tube with multiple lumens in the case of permanent stimulation. 8) The single electrical catheter as in the foregoing claims which comprises a stylet to be inserted into the catheter to act as a guide and provide stiffness, said stylet being usually inserted up to the distal end, where possible into the lumen of the coiled conductor which reaches into the ventricle or, where there are no coiled conductors, through a dedicated plastic tube inserted into the catheter for this purpose.

AMENDED CLAIMS

[received by the International Bureau on 03 August 1998 (03.08.98); original claims 1-8 replaced by amended claims 1-13 (2 pages)]

1) A single electrical catheter for temporary or permanent VDD or DDD cardiac stimulation electrically connected to a pacing device having two electrical terminals, the catheter comprising: a single tube; aerial electrodes for stimulation and sensing located on the single tube in such a position that the atrial electrodes are in the atrium when the catheter is inserted in the heart; characterized in that the atrial electrodes are three; and in that a first (A) and a third (C) of the atrial electrodes are positioned symmetrically about a second central electrode (B) ; the first (A) and third (C) atrial electrodes being electrically connected to each other and to a terminal of the pacing device, while the second central electrode (B) is connected to another terminal, thus making up a symmetrical dipole which generates an electrical field with the electrical field lines symmetrical disposed and closed around the second central electrode (B) .

2) The catheter as in claim 1, wherein the three atrial electrodes (A, B, C) are so electrically connected to the pacing device and so located in the tube of the catheter that said electrodes (A, B, C) generates an electrical field (V) , considering a point at a distance d from the second central electrode (B) and at a distance from the second central electrode (B) , the distance d being measured in radial direction and the distance h being measured in longitudinal direction in respect to Haid tube of the catheter, according to the formula

1/2 1/2 1 -,

V(d,h) = KQ

(d^!+(l-h)'] [d-'+U+h)⁸] ( '+h²] and wherein K is a constant dependent on the ambient medium, Q is the electrical charge applied, 1 is the distance between each group of two electrodes (A, B) and (B, C) .

3) The catheter as in claims 1 or 2, wherein the atrial pare of the catheter is preformed into a c shape so that the electrodes (A, B, C) remain close to the atrial wall.

4) The catheter as in one of the foregoing claims, wherein the atrial part between approximately 5 to S and 16 to 21 cm from the distal end is preformed into a curved shape, with a curvature radius of approximately 4 to 9 cm, which brings the electrodes (A, B, C⁾ close to the atrial wal .

5) The catheter as in one of the foregoing claims, wherein the distance 1 between each group of two electrodes (A, B) and (B, C) can range from 5 to 25 mm.

6) The catheter as in one of the foregoing claims, wherein the atrial electrodes can be made from conventional biocompatible, inert materials, and the electrodes (A, B, C) have an electrode surface area ranging from 5 to 30 mm².

7) The catheter as in one of the foregoing claims, wherein it comprises two electrodes (VI, V2) located in the ventricular part of the catheter.

8) The catheter as claim 7, wherein the ventricular electrodes can be made from conventional biocompatible, inert materials, and the electrodes (VI, V2) have an electrode surface area ranging from 5 to 30 mm¹.

9) The catheter as in claims 7 or 8, wherein the distance between the atrial and ventricular electrodes being between 10 and 14 cm. 10) The catheter as in one the foregoing claims, wherein the connection to the pacing device can be effected using normalized connectors conforming with international standards (ISO or FDA) both for permanent solutions (IS-l) and temporary solutions.

11) The catheter as in one of the foregoing claims, wherein the connection between the electrodes and the connectors is made using separate wires in the case of temporary stimulation.

12) The catheter as in one of the claims 1 tύ 10, wherein the connection between the electrodes and the connectors is made using insulated coils with wires wound in parallel, or using separate coils in a tube with multiple lumens in the case of permanent stimulation.

13) The catheter as in one of the foregoing claims, wherein it comprises a stylet insertable into the catheter to act as a guide and provide stiffness, said stylet being usually inserted as far as the distal end, where possible into the lumen of the coiled conductor which reaches into the ventricle or, where there are no coiled conductors, through a dedicated plastic tube inserted into th-" -!--jfchRter for this purpose,