Total or near-total occlusions in arteries can prevent all or nearly all of the blood flow through the affected arteries. It has been estimated that 5% to 15% of patients on whom percutaneous coronary angioplasty (PTCA) is attempted are found to have chronic total occlusions (CTO's) of at least one coronary artery. Chevalier, B. et al., Chronic Total Occlusion, The Paris Course on Revascularization, Pages 131–148 (May 2000) In patients who suffer from coronary CTO's, the successful performance of a PTCA is a technical challenge. The factor that is most determinative of whether the interventionalist can successfully perform PTCA on patient who presents with a coronary CTO is the interventionalist's ability (or inability) to advance a suitable guidewire from a position within the lumen of the artery upstream of the lesion, across the lesion (i.e., either through the lesion or around it), and then back into the artery lumen at a location downstream of the lesion.
In some instances, such as where the occlusive matter is soft or where the occlusion is less than total, the guidewire can simply be pushed through the occlusive matter itself, thereby allowing the guidewire to remain within the artery lumen. However, in other cases, such as where the artery is totally occluded by hard, calcified atherosclerotic plaque, the guidewire may tend to deviate to one side and penetrate through the intima of the artery, thereby creating a neo-lumen through the sub-intimal space (i.e., within the wall of the artery between the intima and adventitia). In these cases, after the distal end of the guidewire has been advanced to a position distal to the lesion, it is then necessary to divert or steer the guidewire from the sub-intimal space back into the lumen of the artery at a location downstream of the lesion. This process of causing the guidewire to reenter the artery lumen is often difficult and others have proposed various means for dealing with such problem. For example, PCT International Publication No. WO 00/18323 describe techniques where a catheter that has a through lumen terminating distally in a laterally directed outlet port is advanced into the sub-intimal space past the lesion and a penetrator or guidewire is then advanced through the catheter, out of the laterally directed outlet port, and back into the lumen of the artery. WO 00/18323 further states that optionally a wire may be passed through a lumen of the catheter and that such wire may further comprise an imaging apparatus such as an ultrasonic imaging means. Also, WO 00/18323 states that the catheter may include a marker near its distal end that is visible on fluoroscopy and that such marker may be configured to permit visual determination of the rotational orientation of the distal end of the catheter when viewed as a two-dimensional fluoroscopic image. However WO 00/18323 does not describe any means for correlating the rotational orientation of the catheter to the trajectory on which the penetrator or guidewire will subsequently advance. A number of variable can affect the trajectory on which the penetrator or guidewire will advance, including the location of the outlet aperture from which the penetrator or guidewire exits the catheter body, the density and resistance of the tissue through which the penetrator or guidewire advances and any bias, shape or curvature that the penetrator or guidewire will assume after it is no longer constrained by the catheter.
Another approach to bypassing a CTO, as described in U.S. Pat. No. 6,068,638 (Makower), U.S. Pat. No. 5,830,222 (Makower) and U.S. Pat. No. 6,190,353B1 (Makower, et al.) utilizes a tissue penetrating catheter device that has an on board guidance element that allows a tubular penetrator cannula to penetrate outwardly through the intima of the artery wall upstream of the lesion after which a member is advanced trough the cannula and bores through tissue located outside of the vessel's intima, to a position distal to the obstructive lesion, and then reenters the lumen of the artery at a location downstream of the lesion. Tissue penetrating catheters of this type, having on-board guidance and/or orientation capabilities and penetrator cannulas that are advanceable laterally from the catheter body, have previously been devised. (Transaccess® catheters by Transvascular,® Inc., Menlo Park, Calif.)
There exists a need in the art for the development of new and better techniques for catheter-based treatment of CTO and other total or near-total obstruction of arteries or other anatomical conduits, especially with respect to improving the available techniques for causing a guidewire to reenter the lumen of an artery from a location within the sub-intimal space or even outside of the artery wall and for facilitating verification of the intended re-entry into the artery lumen and prompt delivery of arterial blood or some other oxygenated perfusate to tissues that would normally receive arterial blood flow from the obstructed artery.