TITLE
Endoluminal Centring Catheter
This invention relates to an endoluminal centring catheter.
Atherosclerotic cardiovascular disease causes the majority of deaths in North America and Europe, through heart attacks (Ml - myocardial infarction) and strokes (CVA - cerebro-vascular accidents). Furthermore, it causes a very significant morbidity within these populations through angina, non-fatal strokes and peripheral vascular disease, including renal hypertension and renal failure and peripheral vascular disease which includes also intermittent claudication, rest pain, ulceration and gangrene.
Atherosclerotic plaques cause stenosis(es) of the arterial lumen, proceeding towards complete vessel obstruction, often hastened by formation of an occlusive thrombosis. What prompts atherogenesis remains uncertain, although accelerative risk factors include cigarette smoking, diabetes, hypertension, hypercholesterolaemia and a positive family history of the disease.
Therapeutic options for presenting patients include conservative treatments which include increasing exercise and limitation of risk factors, and interventional procedures ranging from balloon dilation (angioplasty) to arterial bypass graft surgery, albeit in the coronary or peripheral circulation. Interventional treatments however, are not without complications which may be of a biological and/or iatrogenic nature. In particular, with both angioplasty and bypass graft surgery, secondary smooth muscle cell neo-intimal hyperplasia
(SMC-NIH) may prompt a re-stenosis of those very vessels recently treated. In many cases, this phenomenon can cause a progressive therapeutic failure such that for example, at two years out from initial femoro-popliteal arterial bypass grafting, greater than 35% of grafts placed have themselves occluded. Earlier, although ongoing, attempts to salvage such situations centred upon re- angioplasty or insertion of metallic stents (uncovered or covered) to mechanically hold open re-stenosing vessels. More recently however, attention has been more focused upon direct prevention of SMC-NIH utilising various approaches, often undertaken as a simultaneous adjunct to the primary interventional procedure being either angioplasty or surgery. Examples include the use of gene therapeutics such as vascular endothelial growth factor - VEGF, direct cell toxins such as Taxol®, or photo-dynamic therapy (PDT using laser light to activate locally, circulating cell toxins. An alternative approach to the direct prevention of SMC-NIH is local radiotherapy - brachytherapy. With brachytherapy, endoluminal irradiation to the inner surface of the recently treated vessel wall, from a gamma or beta source, often from an iridium wire for example, is given immediately following angioplasty to prevent subsequent smooth muscle cell growth. Theoretical and observed complications include in particular, eccentric radiation dosing to the vessel wall causing local, trans-mural cell death, with a potential for arterial wall rupture, later aneurysm formation, or stenosis due to fibrosis. In an attempt to prevent this and to better standardise the exposure of the vessel wall to the irradiation, means to keep the radioactive wire source centred within the vessel lumen, over the entire length of vessel to be treated, have been proposed. Such a measure becomes even more relevant as the diameter of the vessel lumen
decreases, for example in the coronary circulation. Development of these centring catheters is new and of importance also, is the attention that must be paid to the actual means of construction of such a device, so as to minimise potential complications deriving from the use of the device itself, such as further extensive trauma to the intima of the artery that has just been angioplastied, with for example, deflation and withdrawal of the balloon system itself. The following is a brief description of how such a centring catheter would be used. In general, an endoluminal vascular catheter is a flexible tube, of varying diameter and/or length, which can be placed into blood vessels to serve as a conduit for the introduction of extraction of fluids, substances or devices being commonly wires. With and/or without externally attached parts or devices, the catheter allows manipulation of internal parts of the body, without direct surgical exposure.
A balloon catheter is a catheter with a circumferential, inflatable balloon cuff or cuffs attached, which can be expanded forcibly in an area of a blood vessel narrowing, so as to increase the luminal diameter resulting in for instance, an increased blood flow within the vessel. Inflation of the balloon cuff results in the suspension of the internal catheter shaft towards the mid-line of the vessel lumen overall, assuming a symmetrical inflation of the balloon. This effect becomes the primary objective in the production of a centring catheter, whose use would be in delivering local radiotherapy (brachytherapy) to the vessel wall lining in particular, following recent, conventional angioplasty. With brachytherapy, beta or gamma irradiation as example is emitted from a radioactive wire located within the catheter shaft, circumferentially delivering an equal dose to all parts around the circumference of the inner vessel wall. Such
an even dosing can only be achieved if the catheter shaft containing the radiation source is itself positioned centrally within the vessel lumen and over the full length of the vessel to receive treatment. Contact with the vessel wall lining from the irradiation source is potentially very damaging and ideally, should be kept to an absolute minimum.
With known balloon cuffs, which are inflated over a significant length in order to centre the catheter, damage can be caused to the intima of the vessel over a considerable length. In addition these known devices may not retract fully after use and thus leave a shouldered surface and thereby increase contact with and hence, potential damage to the vessel lining on insertion and removal of the whole centring catheter device.
One of the objects of this invention is to reduce the area of contact between the vessel wall and the known inflatable cuff centring means whilst still providing adequate centring. Another object is to achieve an improved degree of by-pass fluid flow, for example blood flow. Yet a further object is to provide for rapid inflation and deflation of the centring means. Yet a further object is to avoid shouldering when the centring means is deflated.
According to this invention there is provided an endoluminal centring catheter consisting of a layer or layers of a bonded elastic silicone having interconnected, unbonded areas, which form extensible protuberances when a pressurised fluid medium is introduced beneath the said bonded silicone layer or layers.
According to this invention there is also provided an endoluminal centring catheter consisting of a layer or layers of a bonded elastic silicone having sub- surface interconnected, unbonded areas between at least two said layers which
form extensible protuberances when a pressurised fluid medium is introduced between the silicone layer or layers in the zone of the unbonded areas.
An endoluminal centring catheter is also provided, according to this invention, wherein the catheter has a core with a central passageway, the wall of the core defining said passageway including a plurality of longitudinally extending ducts, the outer surface of the core being overlaid with an extensible layer bonded thereto, discrete areas each including a bond inhibiting layer located around an aperture in the core wall communication with a duct, the application of pressure fluid to a duct causing distension of the extensible layer where not bonded to the core by means of fluid passing through said aperture thereby producing blistering of the outer layer.
In particular, and according to one preferred form of the present invention, multiple, balloon-like protuberances, preferably part spherical, replace the annular cuffs of the prior art and are formed at zones along a selected length of catheter shaft, by application of a layer or layers of elastic silicone, which is especially hydrophobic and hence particularly slippery and atraumatic within the vessel. This layer is applied to substantially the whole surface of the underlying catheter shaft, leaving a plurality of circumferential areas more particularly discrete zones or areas unbonded. When pressurised gas or fluid is introduced beneath this silicone layer, the silicone blisters-up into a balloon whose size relates to the unbonded area. Several such unbonded areas are connected by a separate channel which runs the length of the catheter shaft, leading ultimately, to a connector near the catheter hub. The catheter shaft itself may or may not have a further entirely separate channel through which a wire may be passed or fluids, introduced or extracted.
Introducing pressurised gas or liquid into this aforementioned channel, results in the simultaneous expansion of the string of blistering balloons distally along the catheter shaft. This is undertaken at the lowest pressure sufficient to prompt centring of the catheter shaft and hence, to minimise the damage to the intima of the vessel. Withdrawal of the pressurised gas or liquid allows the complete elastic retraction of the silicone balloons, which resume their pre- expanded, flat form as part of the silicone layer, leaving no residual material proud of the whole of the smooth outer surface of the centring catheter device. Removal of the catheter will now be as atraumatic as is possible with no shouldering at the interface between the retracted balloon and the catheter shaft, as would be seen with a conventional balloon catheter system. The concept of a long string of blistering silicone balloons allows for more accurate centring of the catheter shaft along the whole length of inner vessel lumen to be treated, with each small, spherical balloon creating less localised inner vessel wall trauma than a single, large balloon.
In another preferred embodiment of the catheter, especially for use in small diameter vessels as for example, in the coronary circulation, there is a desire to preserve blood flow to continue to the end organ whilst the device to centre the brachytherapy-giving catheter is functional. In this case, and according to a preferred embodiment the catheter is designed to allow blood to flow around the outside of the device. Here, the blisters of silicone described previously, would not take on an annular or spherical form but rather, a hemispherical form, placed intermittently at 90 degrees from the previous hemisphere, around the circumference of the catheter shaft. Alternatively, the blisters could take on an elongate fin type appearance or be formed as a
continuous spiral, again placed at intervals around the circumference of the catheter shaft. In each case, the pattern of hemispherical or fin-like blisters would be such that, whilst the shaft of the catheter would still be centred within the lumen of the vessel, blood would remain able to flow around the outside of the catheter in between said blisters and hence, supply the end organ continually. Other patterns of blisters may be possible.
This invention is now further described and illustrated with reference to the drawings showing embodiments by way of examples. In the drawings, which are to be taken in conjunction with the foregoing description: Fig. 1 shows the distal end of a catheter diagrammatically with discrete zones forming extensible protuberances and in a distended condition; Fig. 2 shows the catheter of Fig. 1 in transverse cross-section, on line X-X, with the zones and protuberances in an non- extended condition;
Fig. 3 shows the catheter of Fig. 1 in transverse cross-section, again on line X-X, with the zones in an extended condition forming the protuberances; Fig. 4 shows the catheter of Fig. 2 in longitudinal cross-section on the line Y-Y with the zones and protuberances in an non-extended condition;
Figs. 5 and 6 show a further embodiment, Fig. 6 being an end view
looking in the direction A, with a different configuration of protuberances; and
Figs. 7 and 8 show a further embodiment, Fig. 8 being an end view
looking in the direction B, with a different configuration of
protuberances.
In the drawings and with reference to Figs. 1 to 4, only the end of the
catheter as shown and is referenced generally as 1 . This comprises a semi¬
rigid assembly formed from a plurality of layers of a silicone material. The outer
layer of material 2 is continuous but beneath this layer the material forming the
core of the catheter 3, which may comprises one or more individual inner
layers, includes spaced perforations 5 each of which connects with a duct 6
through which a pressurised fluid may be introduced. The construction shown
here has three ducts 6 and each duct has respective apertures 5 spaced out
along the length.
It will be seen that there are three longitudinally extending lines of
perforations radially spaced at 120 degrees with the perforations 5 of each line
being longitudinally offset. This is seen more clearly in Fig. 1.
The outer layer 2 is bonded to the core 3 at the peripheral interface 4
except at the area around the perforations 5. At this area a thin layer or strip of
easily releasable material 7 is interposed. This layer 7 prevents the layer 2
from bonding to the core 3.
With this arrangement when a pressurised fluid, gas or liquid, is
introduced into ducts 6 there is a localised distension of the outer layer 2 in the zone around the aperture 5 which causes the outer layer to expand in the
manner of a blister to take the form as shown by 8. It will be understood that
the outer layer is bonded to the immediate lower layer except in the discrete
zones immediately surrounding the apertures and as defined by the areas 7.
Fig. 1 shows the three lines of blisters 8 each associated with a duct 3.
In the further Figs. 5 and 6 and Figs. 7 and 8, the general arrangement is the same but the configuration of the unbonded areas of the outer layer 2, where not bonded to the next inner layer core 3, is different. In the further Figures like references identify like parts.
Fig. 1 shows an arrangement of small, near spherical blisters 8. Fig. 5 and Fig. 6 show an arrangement with three or four parallel linear lines of spikes or spines 8a and Fig. 7 and Fig. 8 show a further arrangement with linearly aligned spaced fins 8b. It will be clear that the number of lines of protuberances may be easily varied, three being preferred to achieve centring with greater blood flow area available but four being equally advantages and as shown in the drawings. This invention is not limited to the number or the configuration of the protuberances produced.
A method of producing the discrete zones 7 having the inflatable blisters 8 is disclosed in outline in US 5762 996A and US 5795332A. In these publications inflatable annular cuffs are formed whereas in the method proposed to form a catheter of the present invention silicone material is applied or deposited in the discrete areas of the blisters and which material is unbonded in these areas only. (Reference: "Catheter-based Radiotherapy for Peripheral Vascular Restenosis", Prabhakar Tripuraneni, Vascular Radiotherapy Monitor, Vol. 1, No 3 1999)