2355797 TITLE: A GUIDEWIRE OR LIKE DEVICE FOR ARTERIAL ANGIOPLASTY This
invention relates to a guidewire or like device (such as a balloon catheter) primarily, but not exclusively, for percutaneous transluminal coronary angioplasty. Thus the invention is also more generally applicable in related areas i.e. to what is termed peripheral angioplasty as later referred to.
In the case of percutaneous transluminal coronary angioplasty, this is a medical technique for the treatment of coronary heart disease. The object of the technique is to restore to normal the internal lumen of diseased coronary arteries where they have been narrowed or obliterated by accumulation of fatty atheromatous material.
Percutaneous transluminal coronary angioplasty helps to prevent the pain ("angina") caused by coronary heart disease, and may also' prevent future heart attacks and possible death. A large number of percutaneous transluminal coronary angioplasty procedures are performed annually in the USA and Europe.
Conventionally, percutaneous transluminal coronary angioplasty requires a guidewire, a balloon catheter and sometimes a tubular insert or stent. The guidewire is introduced into the diseased coronary artery and is then advanced as far as possible down or along the artery, and acts as a guidepath for the balloon catheter, which is subsequently slid along the guide- wire. Narrowed segments of the artery are then dilated by repeated inflation of the balloon catheter until an appropriate internal diameter has been achieved. Finally, in many cases, the newly widened lumen is reinforced by implantation of a stent, maximising the immediate improvement and helping to preserve the width of the lumen in the longer term. The stent diameter should generally match that of the vessel diameter.
It has been found that ideally the stent length should exceed the length of the diseased artery segment or lesion by 3mm to 4mm so as to overlap the extent of the diseased segment by 1 about 2nim at each end. Both undersizing and oversizing of the stent may increase the complication rate and compromise the effectiveness of the procedure.
Selection of the correct stent length thus depends on accurate measurement of the diseased artery segment length. The measurement of the diseased artery segment is currently based on measurement of the X-ray image (angiogram) of the artery. However, inaccuracies frequently arise due to difficulties in calibration, and due to foreshortening of the image as a result of bends in the artery. Unfortunately, inaccurate measurement is usually not apparent until the stent has been introduced into the artery.
The invention addresses the problem of providing measurement of the length of a diseased artery segment without dependence on angiographic calibration, in particular it enables such measurement to be carried out, which is not affected by angulation or foreshortening of the artery or lesion.
According to the present invention a guidewire or like device (such as a balloon catheter) for arterial angioplasty is calibrated so as to provide marker positions along at least part of its length, the marker positions or the spacing between them being radio- opaque or radio-lucent for radiographic detection and reading.
The calibration may be applied to the guide wire or like device by means of at least one fine strip or filament and the invention includes the provision of such strips or filaments for application to guidewires or similar devices.
Preferably the marker positions are provided at precise intervals and preferably at regular intervals along the length of the guidewire or filament. This allows the length of the diseased artery segment, or lesion, to be measured directly in the manner of holding a tape measure in the artery segment alongside the lesion.
2 Advantages of the invention are that the effects of foreshortening and vessel tortuosity are minimised as the guidewire or like device follows the same course as the artery.
A guidewire or like device according to the present invention has the ability of allowing estimation of lesion lengths to within I mm to 2mm, simply, quickly and consistently.
A finther advantage of the present invention is that existing guide wire or like technology and manufacture can be used and adapted for the present invention and the invention is applicable in principle to all known and probably future types of guidewires or similar devices.
In carrying the invention into practice reference is made by way of example to the accompanying diagrammatic drawings in which:- Figure I is a side elevation on a much enlarged scale of a guidewire having one form of marking or calibration, the leading end being shown in section to reveal construction, and Figures 2 to 4 are enlarged scale side elevations of guidewires, each showing an alternative example of marking or calibration.
Any constructional dimensions or materials referred to below are in accordance with usual practice, but may be varied according to requirements.
Referring generally to the drawings and in a known construction of guide wire I a highly flexible leading end portion or tip usually about 3 to 5cm in length is provided in the form of fine closely coiled wire 2 of stainless steel or related alloys. This coil 2 receives therein a forward reduced diameter part I I (Figure 1) of the major rear part or shaft 10 of the guide wire I which latter is also of stainless steel or the like and of suitable flexibility. Together with the coil 2 the forward part 11 also has a high degree of flexibility for negotiating bends or a tortuous path of an artery.
3 Further in this regard the forward part 11 is connected to a foremost rounded head or nosepiece 12 which facilitates passage along an artery with minimal risk of rupture or other damage to the artery wall. The head 12 also axially locates the coil 2 between it and the major rear part 10 of the guidewire.
The overall length of the guidewire may be of the order of 150 to 300cm and its diameter 0.010 to 0.018inch (0.254 to 0.457nun), the leading end coiled portion 2 being normally of very slightly larger diameter than that of the major rear part 10. For ease of movement (pushability) along an artery the guidewire is entirely or mainly coated with anti-friction material such as Teflon, Microglide, Duraglide or PTFE whilst a lubricant such as silicone may be employed.
The marking or calibration 3 according to this invention along the major part 10 of the guide wire 1, or at least that portion of it likely to be located in use in a coronary artery, is applied or bonded in an integral manner e.g. by a fine strip or filament to the guidewire major part 10. For most purposes the integral length markers 3 so provided are of radio-opaque metal or other material (e.g. gold, tantalum, platinum, iridium or a suitable polymer). The markers 3 are positioned at known intervals (e.g. 5min or 10mm) along a length of say 30cm of the major part 10 of the guidewire from immediately behind the flexible leading end coil 2.
As shown in the drawings the radio-opaque markers 3 may be of various forms and lengths or thickness e.g. as spaced apart dots 31 (Figure 1), rectangles or squares 32 (Figure 2), bars 33 and gaps 333 (Figure 3) or transverse graduations or lines 34 (Figure 4). Such markings correspondingly appear when radiographically read. Other suitable marking may be employed which should be as bold as possible.
In the case of guidewires which are entirely radio-opaque or at least along the operative part thereof, the markers 3 can be in the form of radio-lucent gaps or spaces so that their radiographic reading can also be obtained.
4 Although it is preferably to provide the calibration or markers 3 on the guidewire I in the manner described above, in some circumstances it can be similarly applied along the stem of a balloon catheter e.g. as used in conjunction with a guidewire. Other devices for the same or similar purposes can be calibrated in generally the same way.
In the case of the application of the guidewire or the like to related or peripheral angioplasty such as to renal, iliac, popliteal or carotid arteries as well as the aorta, the guidewire or similar device for such applications may be of similar length to that used in coronary angioplasty, but is usually of larger diameter e.g. up to 0.035 inch (0. 889mm) or even up to 0.060 inch (1.524nun). The construction is usually simpler than that of a coronary guide10 wire, but follows the same principles.
In the above mentioned instances of peripheral angioplasty where larger diameter arteries are usually involved the calibration can be applied to other similar devices in particular to diagnostic and interventional balloon catheters. However, in general, this is less advantageous than providing the calibration or marking on the guidewire.
As well as the important practical advantage of enabling accurate measurement to be readily obtained as regards the diseased extent or lesion of an artery and also the determination of the required length of any stent to be inserted, it will be appreciated that the basic construction, properties and general mode of operation of the guidewire or like device can be retained.