fig1 illustrates the typical configuration of a conventional left coronary guiding catheter in the aorta when engaged within the left main coronary artery during the performance of a left coronary artery 18 ptca . ( the guiding catheter has been drawn with a relatively large caliber for the purpose of clarity .) the aorta 10 includes an ascending portion 12 and a descending portion 14 . the angioplasty dilation balloon 28 and intracoronary guide wire 25 have been included in fig1 for the purpose of orientation . although a left judkin &# 39 ; s configuration guiding catheter was selected for this , and subsequent illustrations , this discussion is not meant to be confined to this configuration alone . the concept of a variably compliant guiding catheter may be applied to all configurations of guiding catheters including the judkin &# 39 ; s , sone &# 39 ; s , stertzer and amplatz configurations . for the performance of an angioplasty of the right coronary artery 16 , a guiding catheter with a different configuration must be employed . the concept of a variably flexible guiding catheter applies to these configurations as well . as described above , the performance of an angioplasty initially requires the introduction of a guiding catheter within a peripheral artery . by virtue of a guidewire ( not shown ) and the preshaped nature of guiding catheter 20 at its distal end 32 , the catheter is manipulated up the descending aorta 14 and down the ascending aorta 12 to place the end 32 of the guiding catheter 20 within the coronary ostium thus permitting subsequent advancement of the angioplasty guidewire 25 and balloon catheter 28 within the diseased vessel . fig2 illustrates a disadvantage of a guiding catheter of the prior art . the components depicted in fig2 have been labeled with reference numerals corresponding to the components in fig1 . in fig2 the dilation balloon 28 has been advanced to the region of stenosis 19 . because the resistance imparted by the lesion exceeded the compliance characteristics of the guiding catheter , however , further attempts to advance the balloon catheter resulted in disengagement of the guiding catheter 22 and prolapse of the balloon catheter . in this condition attempting to advance the balloon 28 only causes the guiding catheter to back out further , and the guidewire and inflation channel to prolapse within the ascending aorta , as shown generally by reference numeral 33 . disengagement of the guiding catheter from the coronary ostium just as the operator attempts to advance the angioplasty dilation balloon 28 across the stenosis represents one of the principal causes for failure during the course of an angioplasty procedure . the instability of the guiding catheter is believed to result from several causes . first , the catheter has intrinsic flexibility to accommodate introduction . secondly , the material from which the catheter itself is manufactured ( multiple layers of dacron webbing coated with plastic polymer ) becomes more flexible as it warms to body temperature . thirdly , the configuration of the catheter provides little or no resistance to the forces which cause it to back out . for example , as shown in fig3 the application of pressure on the dilation balloon 28 for the purpose of advancing the dilation balloon across the region of stenosis increases the torque on bend 35 in guiding catheter 20 , causing the angioplasty balloon catheter to prolapse in the ascending aorta precluding any further progress . fig4 illustrates one embodiment of the guiding catheter 40 of my invention . in contrast to prior art devices , the guiding catheter includes means for varying the flexibility of the catheter in a manner selected by the operator . for the embodiment shown in fig4 the variable flexibility is provided by a balloon 50 which extends along the exterior surface of housing 42 . balloon 50 is inflatable and deflatable as desired by the operator , for example , by use of a syringe connected to a communicating channel 52 ( see fig6 ) extending through or along the catheter from exterior of the patient to the balloon 50 . as also shown in fig4 balloon 50 , when inflated to high pressure , adds substantially to the rigidity of the distal end of catheter 40 . this enables the use of additional force to advance the dilation balloon 28 through the region of stenosis . once the dilation balloon 28 has been advanced through the region of stenosis , the balloon 50 affixed to the guiding catheter is deflated , rendering the guiding catheter 40 substantially more flexible , and hence less likely to induce any intimal vascular damage . a pressure source is then applied to inflate the balloon 28 and thereby ablate the stenosis . my invention offers several advantages over conventional guiding catheters used in the performance of an angioplasty procedure . present catheters , in an effort to reach a compromise between flexibility and rigidity , are generally stiff , and therefore substantially more difficult to engage within the ostium . the use of my guiding catheter with variable flexibility in its most flexible condition at the outset permits easier engagement within the coronary ostium . once engaged , the relative inflexibility of my catheter enables it to remain engaged within the ostium in a more stable manner than conventional catheters . this stability precludes the need for multiple angioplasty catheters and exchange wires , with their associated disadvantages described above . furthermore , the relatively inflexible catheter minimizes traumatic injury to the coronary ostium by minimizing the use of force . disruption of the intima of the coronary ostium by conventional guiding catheters represents a well known complication of angioplasty procedures . this complication can result in a coronary occlusion , and hence , myocardial infarction . finally , the compliance characteristics of this guiding catheter are not affected by &# 34 ; warming up &# 34 ; to body temperature . in the embodiment depicted in fig4 the balloon 50 may be filled by means of a syringe at the extracorporeal end of the catheter . typically , the balloon will be designed to tolerate pressure on the order of 10 atmospheres . because the catheter itself need not be as rigid as conventional catheters , the walls of the housing 42 need not be as thick . accordingly , the caliber of the catheter with balloon 50 deflated may be less than the caliber of conventional guiding catheters . this feature will permit insertion of the catheter within a smaller arteriotomy . furthermore , by fabricating the channel 52 connecting the exterior balloon 50 to the syringe of relatively large caliber , changes in balloon tension may be accomplished rapidly . a further advantage of the catheter depicted in fig4 is that the use of the catheter may preclude the normal requirement for two physicians . in the prior art two physicians were typically necessary , one to monitor the engagement of the guiding catheter , and one to advance the guidewire and balloon catheter . with the catheter of the depicted embodiment , a physician may advance the catheter with one hand while inflating and deflating the balloon 50 with the syringe in the other hand , thus increasing and decreasing the rigidity of the catheter as necessary to advance it . fig5 illustrates the means by which the preferred embodiment of the catheter of my invention provides additional &# 34 ; back pressure &# 34 ; to oppose the pressures described in fig3 . the balloon is preshaped to conform to the configuration of the guiding catheter when engaged in the coronary artery . as indicated , the arc 55 of the balloon 50 , when inflated , is more acute than the corresponding arc of the distal aspect of the guiding catheter 42 . as the balloon 50 is inflated , the catheter will begin to assume the configuration of the preshaped balloon 50 . this will result in enhanced &# 34 ; back pressure &# 34 ; and thus enhanced stability of the guiding catheter during advancement of the angioplasty dilation balloon catheter 30 . fig6 is an expanded view of the distal end of the catheter showing housing 42 and balloon 50 in further detail . a cross section of the catheter is also depicted . communicating channel 52 , also contained within the catheter , connects to balloon 50 through lumen 51 to allow pressurization . fig7 is a cross section of the distal end of the catheter showing balloon 50 . fig6 also illustrates an optional feature of my catheter . in this embodiment a second external balloon 46 is provided which is coupled to communicating channel 44 by lumen 48 . in the same manner as balloon 50 , balloon 46 may be inflated from outside the patient . secondary balloon 46 enables selective deflection of the distal end of catheter 40 to assist in positioning the catheter within the coronary artery . by placing the secondary balloon on catheter 40 at 90 ° rotation from the preshaped curve 49 ( and from the orientation of balloon 50 ), the distal end of the catheter may be deflected anteriorly or posteriorly to aid subselective cannulization of the lad and circumflex branches of the left coronary system . fig8 illustrates another approach to bonding the balloon 50 to the catheter housing 42 . in this embodiment , the balloon is composed of an elastic material that permits elongation of the balloon with inflation to high pressures . in this embodiment , the preshaped configuration of the balloon is less important than in the embodiment described in fig5 . since the balloon is attached to the circumferential aspect of the distal end of the guiding catheter , and since the balloon elongates with progressive inflation , the application of enhanced inflation pressure will change the configuration of the guiding catheter , providing enhanced &# 34 ; back pressure .&# 34 ; fig9 illustrates another embodiment of my invention in which the stiffness of the catheter is imparted by the introduction of iced saline solution or other coolant . in this embodiment an additional tube 53 surrounds the interior channel 47 ( through which the angioplasty dilation catheter is passed ) to provide two or more openings 54 , 56 between housing 42 and tube 53 . inner channel 53 is coupled to outer housing 42 at least at two locations 55 to thereby provide a first chamber 54 and a second chamber 56 . by circulating iced saline into one of the chambers 54 and 56 and out the other , and / or by manufacturing housing 42 from material which is temperature sensitive , the rigidity of the catheter may be substantially increased as necessary . in another embodiment of my invention , the rigidity of the catheter can be enhanced by the insertion of relatively stiff wires through channels along the periphery of the catheter . this embodiment is shown in fig1 . as shown , the housing 42 includes several integral channels 43 to permit insertion of one or more relatively stiff wires 58 along the periphery of the catheter . by bending the wires into the desired configuration and then inserting them after the catheter has been properly positioned , the wires 58 will add to the stiffness of the catheter . as before , the chamber 47 for the dilation balloon catheter is disposed within housing 42 . in a further embodiment of my invention , instead of using stiff wires , relatively flexible wires are positioned around the periphery of the housing 42 and then tension applied to them after the catheter is properly positioned to increase the rigidity of the catheter . in such an embodiment , wires 58 are affixed to the distal end of the catheter . of course , it is not essential that individual pockets for the wires 58 be employed , rather a conventional housing may be chosen and the wires simply inserted within chamber 47 . in other embodiments of my invention , other means for stiffening the catheter may also be employed . for example , wires 58 may be fabricated from memory alloys or bimetal thermocouples which are then heated or cooled to the desired temperature by circulation of fluid through the catheter . in such an embodiment , the wires will be relatively flexible at body temperature , and then caused to assume a desired shape by either being cooled to a lower temperature , or heated to a higher temperature . in still further embodiments of my catheter , the guiding catheter is fabricated from material having properties which change when subjected to light , ultrasound , radio frequency , magnetic fields or other penetrating forces such as electric current . a laser , ultrasound source , etc ., is then employed once the catheter is properly positioned to increase its rigidity . the foregoing has been a description of the preferred embodiments of the invention . although many specific details have been described , it should be understood that the description is only for the purposes of explaining the invention , and not limiting it . it should be further understood that the configuration of the catheter proposed herein is not limited to the left jodkin &# 39 ; s configuration alone . this configuration was selected for the purpose of illustration only . the scope of the invention may be ascertained from the appended claims .
a guiding catheter 40 of variable , operator - controlled flexibility to be used in the performance of a percutaneous translumenal coronary angioplasty procedure is described which includes an elongate housing 42 suitable for insertion into an artery , as well as an operator - controlled variable stiffener coupled to the distal aspect of the catheter to permit the operator performing the angioplasty procedure to increase the rigidity of the catheter . in a preferred embodiment the stiffening apparatus consists of a balloon 50 extending longitudinally along the distal end of the catheter to allow increases in rigidity of the distal end as desired by the operator . increasing the rigidity of the guiding catheter , once installed within the coronary ostium , precludes disengagement of the guiding catheter , thus expediting the performance and enhancing the safety of the procedure .