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Pacer catheter for an A-V stimulator comprising a catheter assembly which
may be passed through a single channel to the heart which assembly will
carry both atrial and ventricular stimulation. The catheter provides at
least two mutually insulated spatially adjustable electrical conductors,
one for stimulating the atrium and an additional one for stimulating the
Bures; Alan R. (Irvine, CA)
The Regents of the University of California
Rogel et al., "Journal of Thoracic & Cardiovascular Surgery," Vol. 61, No. 3, March, 1971, pgs. 466-471.
. Dorstmann et al., "American Journal of Cardiology," Vol. 30, July 11, 1972, pgs. 74 & 75,
. Castillo et al., "Chest," Vol. 59, No. 4, April, 1971, pgs. 360-364..
Primary Examiner: Kamm; William E.
Attorney, Agent or Firm:Nealon; William C.
Berkenstock, Jr.; H. R.
1. An elongate pacing electrode catheter system capable of pacing both the atrium and the ventricle comprising:
an elongate flexible electrode extending the length of the catheter system for stimulating the ventricle and comprising a ventricle electrode system, said ventricle electrode system terminating in a distal tip arranged to be moved axially of the
catheter system into stimulating contact with the wall of a ventricle,
an elongate atrial electrode system extending the length of the catheter system and comprising an atrial electrode system, said atrial electrode system comprised of at least two energy conducting elements reciprocally movably mounted in opposed
positions about a central portion of the ventricle electrode system rearward of the distal tip thereof, said elements including stimulation distal tips,
there being means arranged to reciprocally move said atrial electrode system stimulating distal tips from a collapsed to an extended operative position,
means allowing said ventricle electrode system to be moved relative to the atrial electrode stimulating tips when said tips are in an extended position for atrial stimulation.
2. The electrode system of claim 1 in which:
said elongate flexible ventricle electrode for stimulating the ventricle is substantially along a central axis of the system,
and the elongated atrial electrode system is mounted concentric to the ventricle electrode.
3. The system of claim 2 in which the means arranged to reciprocally move said atrial electrode system is a catheter through the center of which passes the ventricle electrode.
4. The system of claim 3 in which the atrial electrode system is comprised of at least two electrode wires mounted in association with said catheter.
5. The system of claim 4 in which a second catheterlike member is mounted for reciprocal movement over said electrode wires.
6. An elongate pacing electrode catheter system according to claim 1 in which a catheter covering is movably mounted about a major portion of the ventricle electrode system and in which the ventricle electrode system has mounted thereabout
portions of the atrial electrode system terminating in resilient deformable normally S-shaped stimulating tips.
7. An elongate pacing electrode catheter system capable of pacing both the atrium and the ventricle comprising:
an elongate flexible electrode extending the length of the catheter system for stimulating the ventricle, said electrode for stimulating the ventricle including a distal tip arranged to be moved into stimulating contact with the wall of a
an elongate atrial electrode system, said atrial electrode system comprised of at least one energy conducting element mounted about a central portion of the ventricle electrode rearward of the distal tip thereof, said elements including
stimulation distal tip means,
there being means arranged to reciprocally move said atrial electrode system stimulating distal tip means from a first substantially coaxial position to an extended operative position.
FIELD OF THE INVENTION
This invention relates to heart stimulation devices of the catheter type normally used to inter-connect a remotely situated pacer and a source of stimulating energy with the heart of a patient.
OF THE PRIOR ART
In the electro-medical field today therapeutic heart stimulating devices are well known. Some of these devices are called heart pacers and they provide stimulation to the heart when its natural stimulating system is inoperative or diseased.
Artificial stimulation is controlled to cause heartbeat at a substantially normal rate.
The more conventional pacer provides stimulation only to the ventricle, bypassing the atrium. A new type of pacer, now coming into use, provides sequential stimulation of first the atrium and then the ventricle to cause the heart to beat in a
more natural and thus efficient manner. When functioning naturally, the sinus node causes the atrium to contract first and then send electrical stimulus through fibers in heart walls to the ventricle causing its contraction. Such a pacer is one
according to U.S. Pat. No. 3,595,242 entitled "Atrial and Ventricular Demand Pacer" which is capable of supplying this sequential atrium-ventricle stimulation. Background material disclosed in this patent is incorporated herein by reference.
In earlier research work utilizing the sequential type pacemaker, it was found necessary to use two separate catheters, one each for the atrium and the ventricle. Either or both of the catheters was subject to dislodgement. Implantation
required two veins (or one very large one). It was apparently often the case that insertion of one catheter might dislodge one previously placed. Another suggested catheter procedure included use of a J-shaped electrode system which rests its tip in
the right atrium appendage. This structure also apparently could be dislodged. In addition, it has been discovered that either of these systems apparently does not offer the capability of A-V pacing should A-V block develop subsequent to the S.A.
nodal disease as often occurs. With current atrial pacing techniques, a second catheter has to be implanted in order to take advantage of the increased cardiac output that sequential A-V pacing provides. Thus, the present invention seeks to provide a
single catheter construction which includes electrodes for separately stimulating both the atrium and the ventricle while simultaneously assuring good contact with the atrium.
SUMMARY OF THE INVENTION
According to this invention, there is provided a catheter construction capable of stimulating both the atrium and the ventricle. With the proper type of pacer, the system is likewise capable of pacing either or both the atrial and the ventricles
whether or not the need of such a capability was manifest at the time of initial pacer electrode implantation.
At present, the most common reason for long term cardiac pacing is the Stokes-Adams Syndrome. In certain instances, (as in other heart block syndromes) sequential A-V pacing has proven useful. For example, by synchronizing atrial with ventricle
contractions, cardiac output has been increased by as much as 24 percent according to published literature. This system is also applicable to a large number of patients with the variety of other arrhythmias that require cardiac pacing. Many of these
patients are now of necessity paced by way of the right ventricle with unavoidable A-V dissociation.
For example, those patients with myocardial infarction are not good candidates for even the limited thoracotomy which certain new procedures require. Nevertheless, myocardial infarction patients with A-V block should benefit from A-V pacing in
several ways. First, as noted, A-V synchronization should be expected to increase cardiac output. Second, mean left atrial pressure would be anticipated to be lower in A-V pacing than in A-V dissociation given any constant left ventricular end
diastolic pressure. This being true, I would anticipate mean pulmonary artery capillary pressure to be reduced, decreasing any tendency towards transudation, pulmonary edema, hypoxia, and other ventilatory and perfusion abnormalities. The co-axial
catheter system of this invention has the advantage of using the transvenous technique of insertion (no major surgery is required), with a low associated morbidity and is stable and reliable for long term pacing.
It is thus among the objects of this invention to provide a transvenous pacemaker cathode electrode system which can be easily placed in both the atrium and ventricle and is reliable and stable in these positions. It is a further object of the
invention to provide a pacer catheter electrode system capable of implantation by the transvenous technique, which is easy to implant, and is capable of long term pacing characterized by stability and reliability in place.
Briefly, a catheter electrode system according to this invention is comprised of a series of concentric elements including a substantially centrally located, reciprocally movable ventricular electrode encapsulated within a hollow catheter cover.
Movably associated with the catheter cover is a pair of atrial leads. Preferrably the leads are mounted 180.degree. from each other on the outer surface of said catheter. The distal end of the atrial leads are deformed. The deformation is such that
an outer sheet or catheter mounted about the inner catheter compresses the deformed atrial leads into close association with the inner catheter. Upon insertion of the electrode system into the heart, the outer sheath is pulled back allowing the deformed
ends of the atrial leads to spring open and nest against ("snug" up against) adjacent walls of the atrium.
Other objects, advantages and details of the present invention will become readily apparent to those skilled in the art by referring to the
detailed description which follows with reference to the appended drawings.
In these drawings:
FIG. 1 is a schematic representation of an illustrative embodiment of the present invention placed within the heart;
FIG. 2 is a schematic elevation in partial section of a catheter electrode system according to this invention;
FIG. 3 is an end view of a system according to this invention showing the atrial leads extended as in their atrial wall-contacting configuration;
FIG. 4 is an alternative embodiment of the invention; and
FIGS. 5 and 6 are yet another alternative embodiment.
DESCRIPTION OF THE PREFERRED EMBODIMENT OF THE INVENTION
In FIG. 1, I have shown a schematic view of a heart 10. The heart includes a right ventricle 11 and an associated atrium 12. Entering through the superior vena cava 13 is a catheter construction 15 according to my invention. The construction
includes a ventricular lead 16, a number 9 French (or other) catheter 17 concentrically positioned about the lead 16 and having secured to opposed outer surface positions thereof a pair of atrial leads 18 and 19. When I mention "opposed" positions in
the preferred embodiment, I am describing positions 180.degree. relative to each other. Concentric the inner catheter 17 is an outer catheter or sheath 20. Referring, for the moment, to FIG. 2, the bipolar ventricular lead 16 is shown to be comprised
of a pair of electrodes 25 and 26. The electrodes 25 and 26 are encapsulated in suitable electrical insulating material and from the plug 16 to the opposite end are concentric to each other. At the internal end, the leads 25 and 26 are exposed for
contact with a ventricle wall. This is a typical bipolar pacing catheter in common use. The instant embodiment would work equally as well in a unipolar requiring only electrode 26. The other pole then becomes the pulse generator itself or other remote
or distant pole. Mounted about the concentric ventricle leads q5 and 26 is the sheath 17 which in the embodiment I am describing herein was a number 9 French catheter (or similar/equivalent).
The internal ends of the atrial leads 18 and 19 have been described as "deformed". Reference to FIG. 3 presents one with a better idea of the configuration being described. Each of the leads 18 and 19, for a substantial portion of their
respective lengths, is mounted 180.degree. relative to each other on the outer surface of the French catheter 17 by attaching with epoxy resin. They extend substantially parallel to each other and are parallel to the central axis of the catheter.
Substantially adjacent the distal end of each lead 18 and 19 is a bend or deformation in opposite directions. Preferrably, the planes in which the respective deformed portions reside are parallel to each other and spaced apart a length equal to the
outer diameter of the catheter 17.
Thus, in operation, when the sheath 20 is moved forwardly towards the stimulating end of the atrial leads, the deformed ends 18 and 19 are urged towards a configuration or position which is substantially parallel to the central axis of the
catheter 17. Upon rearward movement of the sheath or cover 20, the deformed ends 18 and 19 spring outwardly to deformed position to thereby contact or "snug" against the adjacent wall of the atrium.
In initially undertaking the experimental work which resulted in this invention, it was considered necessary, or at least desirable, to determine those sites in the atrium which were the best for stimulation. The ventricular site had been
decided by experimental and clinical practice to be beneath the trabeculae just medial to the right ventricular apex. The best atrial site required further evaluation. Prior knowledge suggested that the region of the S.A. node would be advantageous
for many reasons. For example, atrial systole would proceed in a normal direction (cephalad to caudad direction) and the specialized atrial conducting tracts might be utilized to simulate normal ventricle systole.
Also, the possibility was investigated that the atrial conducting system might make one point on the endocardial atrial surface more advantageous to pace than another one due to lower threshold to electrical stimulation. Of course, I realized
that electrophysiologic grounds were not the only criteria to influence the choice of position for optimal atrial pacing. The selected position should also be as mechanically immobile as possible. This was viewed as necessary or desirable to reduce the
tendency of the pacer electrode to dislodge. In addition, it would reduce the tendency for inflammatory fibrous tissue to form about the electrode because of relative movement. The formation of such fibrous tissue can cause electrical threshold to
increase. When I mention "threshold" herein, I refer to that minimum level of energy which is necessary to stimulate the heart muscle.
In a first series of laboratory experiments, 5 mongrel dogs, ranging from 14 to 27 kilograms were obtained. Each animal was anesthetized with sodium pentobarbital (25 to 30 millograms per killogram of body weight). The trachea was intubated and
the animal placed on a positive pressure respirator at 12 to 20 breaths per minute, breathing oxygen at a pressure of 10 to 15 centimeters of water. This previously had been shown to produce acceptable pH and pCO.sub.2 values while maintaining
oxygenation and acceptable hemodynamics. The chest was then opened by a careful midline dissection with extreme care to minimize blood loss. In each of the five successful attempts reported here, blood loss was held to less than 125 cubic centimeters
for the duration of the experiment. Any lost fluid volume was promptly replaced with physiological saline solution. After the chest was opened, the pericardium was opened by a midline incision. Each side of the pericardium was clamped to the adjacent
chest wall at the level of the original incision in the chest making a loose sling of the pericardium. The myocardium was kept wet with saline.
The external jugular vein was isolated and cannulated. A standard pacer and electrode were attached and set at a rate of 150 per minute, 9 to 12 volts, with the current varying for test conditions. The sinoatrial node was identified and
destroyed by crushing and direct perfusion with 99 percent isopropyl alcohol. Destruction of the tissues surrounding the node was kept to an absolute minimum. This caused the heart rate to slow so that it could be captured with the pacer. The rate
drop was from between 150 and 200 to one between 85 and 125 beats per minute. Due to the dog's effective atrial escape mechanism, the heart did not stop, nor, did P waves or the QRS complex. The P wave configuration, however, changed visibly.
Electrical thresholds to stimulation at various points in the right atrium of the five dogs was determined and reported. For each of the experimental animals, three measurements were made of the threshold for electrical stimulation. The data
for all the animals was averaged rounded off to one significant figure and summarized. On two of the dogs, initial measurements were made 1 and 2 centimeters above the atrium in the superior vena cava.
The above experimental work indicated that any point in the right atrium is as good for pacing as any other from a threshold standpoint. Pacing can even be achieved at some slight distance from the atrial tissue. While no point within the
atrium seemed particularly advantageous from a threshold standpoint anatomical considerations yielded a different result. Observations demonstrated that the area directly adjacent the junction of the vena cava to the atrium is well anchored by fascia to
surrounding structures of the mediastinum. Proceeding from this position outward into the atrium produced increased movement of the electrode. In contrast, in areas close to the vena cave, movement was definitely limited. Based on these observations
and the threshold data, the coaxial electrode system referred to above was designed. When implanted and placed as schematically shown in FIG. 1, there is assurance of proper positioning of the atrial leads adjacent the area of the atrium close to the
vena cava. When implanted, upon rearward tension or movement of the coaxial system, tension is applied to the catheter drawing the atrial leads against the atrium walls maintaining good electrical contact without exerting any substantial force. The
stability and relative immobility of this system allowed successful pacing without dislodgement.
The best mode now known for the practice of the invention was that structure fabricated after the above tests to determine threshold and maximum atrium stimulation points had been completed and was as follows:
A standard bipolar transvenous cardiac pacer electrode (one manufactured by the Cordis Corporation of Miami, Fla. and identified Cordis 370-110) was inserted in size 9 French cardiac catheter. To the outside of the catheter, two steel wire
electrodes were glued with epoxy resin. The wires were parallel to the catheter and 180.degree. from each other on opposite sides of the catheter surface. The pacing or atrial ends were bent in the form of an S (see FIG. 3). When permitted to assume
their preshaped form in the atrium, these bent ends unfolded outward as shown in FIG. 1 or FIG. 3. Endocardial contact occurred when the structure was drawn adjacent the superior vena cava-atrial junction. The portions of the leads 18 and 19 making
contact with the endocardium were curved and the tips blunted as shown generally at 30 in FIG. 2 and 3. Over the previously described assembly, a thin outer catheter was placed. When this was advanced over the atrial electrode wires, a small compact
package was formed that was placed readily in a vein and advanced centrally thereof. When the outer catheter was withdrawn or moved rearwardly, the atrial leads unfolded to position the atrial electrodes in the position described above. The central
electrode was then advanced through the number 9 French catheter into the ventricle and manipulated into position for good electrode contact.
To prevent blood from refluxing between the inner and outer catheters or covers by capillary action, this space was filled with sterile saline (Area 31 in FIG. 2. Suitable seals were provided at 32 and 33 as shown in FIG. 2 to prevent escape of
the saline). It should be noted that the two electrodes which comprised the atrial leads were so constructed that they would not snag each other when folded or urged into position substantially parallel to the central axis of the ventricular lead 16.
Also, as noted above, since the atrial leads are in two different parallel planes, lateral movement of the atrial electrode ends is always in a direction parallel to but separate from the other electrode. This not only facilitates implantation but
allows removal of the electrode system if that becomes desirable at a later date.
With a coaxial pacer electrode constructed as described above, 4 mongrel dogs weighing 9 to 27 kilograms were paced for short periods (from 20 minutes to 1 hour). The chest was opened as before and the right external jugular vein cannulated
using the coaxial system described. When the right atrium was reached, the outer catheter was withdrawn allowing the atrial leads to unfold. The catheter to which they were attached was withdrawn until the electrodes contacted the antrial-superior vena
cava border. The center ventricular lead was then advanced into the ventricle and manipulated to assure good pacing contact. One atrial lead was attached to a fixed rate pacer at 150 beats per minute, 9 to 12 volts, 0.5 millograms (in my experimental
work I utilized a pacer of the Medtronic Company of Minneapolis, Minn., designated No. 5840). The other atrial lead was attached to the sensing pole of a paired pulse generator, (a pacer of the Cordis Company of Miami, Fla., designated the Cordis
Synchrocor) which was thus changed to an external P-wave synchronized pacemaker. The ventricular pacing catheter was attached to the pacing output of this unit. Of course, utilizing a unitary A-V pacing unit such as that disclosed and claimed in U.S.
Pat. No. 3,595,242 discussed above, the use of two pacemakers would not be required.
In any event, using the arrangement described above, including two different pacemakers, the S. A. node of each dog was destroyed as noted before or the total electrical activity of the heart was stopped with carbonyl choline, 0.25 millograms
given rapidly intravenously. The pacers were switched on with the ventricular pacer set at 0.5 milliamps current flow, 9 to 12 volts, with a sensitivity (for the P wave) of 0.1 millivolts and a refractory period of 300 milliseconds. The A-V delay was
set at 100 milliseconds. The A-V delay under these conditions was less than the usual physiological delay of 160 milliseconds. This shorter setting permitted the demonstration of ventricular capture despite the presence of an intact A-V conducting
system. Artificially shortening the A-V conduction time obviated the difficult problem of sectioning the His bundle to produce A-V block. Nevertheless, under the influence of carbonyl choline used in the last animal to generate total asystole,
sequential atrioventricular pacing was achieved as in the other animals. In all animals on which the experiment was carried out, capture was proven by recording sequential paced beats on a surface electrocardiogram.
As mentioned, the relationship between the ventricular lead and the atrial leads as well as the tension which is applied when the catheter is drawn up against the high right atrium, maintains good electrical contact without exerting great force.
The stability and relative immobility was proven in that successful pacing was accomplished without dislodgement.
With the S. A. node destroyed, the heart rate dropped abruptly to an average of 110 beats per minute until the atrial pacer was switched on at a rate of 150 beats per minute. The ECG showed atrial capture followed by normal QRS complexes. With
both atrial and ventricular units operating, the ECG clearly showed that the ventricles as well as the atrial were captured.
With the latter four dogs, in the initial three experiments, wherein the sinus node was destroyed, identical results were obtained. Furthermore, during the time the animals were paced (at least 30 minutes each) no complications were encountered. Other than occassional permature beats at the time of placement, no arrhythmiaswere incuded. No atrial or ventricular clotting was found. The sealing system prevented blood reflux between the two catheters and the use of a standard flexible ventricular
pacing catheter aided maintenance of electrical contact with the endocardium without perforation. In the fourth animal, wherein the inntravenous carbonyl choline was used to suppress all electrical activity of the heart instead of local destruction of
tissue, the same results were obtained.
In addition to its potential capability for long-term pacing, my work suggest that the coaxial electrode system offers usefulness on a short term basis. For example, this pacing catheter may be applicable to patients in cornary care units with
A-V block and compromised cardiac function with low cardiac output wherein atrial stimulation would be an advantage. In this circumstance, the atrial electrode could act as a sensor of the patient's own T-waves providing a trigger for a synchronized
ventricular pacing pulse.
In the embodiment discussed above, the atrial electrode wires were fastened about the catheter encapsulating the ventricular electrode. The atrial electrode leads can also be built or encapsulated within the wall of this catheter. In addition,
while in the embodiment discussed above, the atrial electrode wires were round, it would be desirable that they be flat, or rectangular in cross-section, to assist in preventing tendency towards atrial perforation, to assure better surface to surface
contact with the atrium and to reduce required inner catheter space. In the construction discussed above, I described use of saline with an oil seal. In a more refined embodiment, it is suggested the use of plastic material having inherent "slippery"
characteristics, such as teflon, would eliminate the necessity of the liquid.
The materials used in the preferred catheter construction were simple stainless steel catheter tip occluders (Breckenbrough Curved Tip Occluder) manufactured by United States Catheter Instrument Corporation, Catalog No. 9639 (p. 19). Next, the
epoxy cement used was Duro Epoxe (manufactured by Woodhill Chemicals, Cleveland, Ohio 44128, stock number EXP-1).
Alternative catheter constructions are possible using many of the inventive features herein disclosed. For example, the construction shown in FIG. 4 in which the leads 18' and 19' are flat or rectangular in cross-section and fixed along the
opposite sides (180.degree. from each other preferably) of the sheath. These leads are spatially movable or adjustable relative to leads 25' and 26' thereby allowing adjustment of distance between atrium and ventricle stimulation -- a most beneficial
feature of my invention since all hearts are not the same size. The parts of FIG. 4 bear numerals similar to FIGS. 1-3 except for the addition of prime signs since similar part designations and functions exist. The same is true of FIGS. 5 and 6 except
double prime designations are used.
Referring to FIGS. 5 and 6, a further unique feature of pacer electrode construction according to my invention will become evident. In FIGS. 5 and 6, the atrial electrode 18" - 19" is ring shaped.
The arrangements of FIGS. 4, 5 and 6 may be more desirable for long term implantation since critics have suggested the electrodes 18 and 19 may become quite adherent to the atrial wall and perforation might be possible.
In the preferred construction discussed above, I have shown two atrial electrodes. It is, of course, recognized that more or less than two electrodes could be used. For example, three or more electrode leads spaced approximately equally about
the ventricle electrode.
Having thus described a preferred embodiment and the best mode now known for the practice of my invention what is desired to have protected by letters patent is set forth in the following claim.