1. Field of the Invention
The present invention relates to a stent for blood vessels, and more particularly, to a stent for protecting a branch blood vessel at a branch-point lesion, in which radiopaque markers are formed between cells of the stent inside a main blood vessel so as to more safely protect the branch blood vessel and to insert an instrument such as a guide wire in the direction of the branch blood vessel in a more accurate and easy manner simultaneously, thereby allowing the stent to be guided to the location of an opening of the branch blood vessel.
2. Discussion of Related Art
In general, among a variety of diseases that attack the human body, when a disease narrows lumens in the human body to reduce their original function, or narrows blood vessels to restrict blood circulation, a medical instrument called a stent is inserted into and expands lumens or blood vessels.
Fat components are deposited on vessel walls of coronary arteries, and the resultant inflammation reaction gradually narrows lumens of the coronary arteries. The narrowed lumens of the coronary arteries obstruct sufficient supply of blood to the heart muscle (myocardium), which causes coronary artery disease or ischemic heart disease.
When blood is not sufficiently supplied to the myocardium, cardialgia, dyspnea, and other symptoms occur according to the extent of the deficiency in the supply. This coronary artery disease develops into a clinical manifestation such as angina pectoris, acute myocardial infarction, or sudden cardiac death.
Percutaneous coronary intervention (PCI) is a therapeutic method that physically expands the lumens of coronary arteries which are narrowed by the deposits of cholesterol on walls of blood vessels using a balloon catheter or a stent. However, the percutaneous transluminal coronary angioplasty using the balloon catheter may cause typical complication such as acute coronary occlusion or artery dissection.
In contrast, the therapeutic method using the stent can prevent the acute coronary occlusion and the artery dissection that may be caused by the therapeutic method using the balloon catheter. In the case of coronary artery branch-point lesions, this stent intervention fails to contribute to reduction in restenosis of blood vessels.
FIG. 1 is a conceptual diagram showing a coronary artery branch-point lesion B in which stenosis occurs at proximal and distal sections 1a and 1b of a main blood vessel 1 and a boundary of a branch blood vessel 2. The branch blood vessel 2 is inclined on one side of the main blood vessel 1 in spatial connection with the main blood vessel 1. An open boundary between the main blood vessel 1 and the branch blood vessel 2 is referred to as an opening H of the branch blood vessel 2.
When severe stenosis is found to occur at the main blood vessel 1 in the coronary artery branch-point lesion, a stent 3 is inserted into the main blood vessel 1. The stent 3 is contracted when inserted, and then is expanded by a balloon catheter 6. Thereby, the stent 3 remarkably reduces the severe stenosis of the main blood vessel 1 and is supported on an inner wall of the main blood vessel 1. The stent 3 is made up of a plurality of cells 4. The cells 4 may generally include a single open cell and a plurality of closed cells, either of which has a rhombic cross section and a root and a crest.
The stent 3 inserted in this way is disposed across the opening H of the branch blood vessel 2, as shown in FIG. 1.
Here, the stent 3 runs across the opening H of the branch blood vessel 2. Thus, depending on how many cell wires of the stent 3 are located at the opening, it determines whether the flow of blood between the main blood vessel 1 and the branch blood vessel 2 is obstructed. If the cell wires of the stent are densely located at the opening H of the branch blood vessel, this presents an obstacle to the flow of blood to the branch blood vessel. This results in a poor clinical outcome.
Thus, when this situation occurs, it is necessary to insert the balloon catheter into the stent 3 that has been inserted into the main blood vessel 1, to expand the inserted balloon catheter to widen the cells 4 of the stent 3. That is, since an interval between the cells 4 of the stent 3, which is located at the opening H, are expanded to secure a wider passage towards the branch blood vessel 2. Thereby, the flow of blood towards the branch blood vessel is made smoother.
In FIG. 2, it is shown that the stent 3 is inserted into the main blood vessel 2. Here, C1 indicates a single open cell, and C2 indicates a plurality of closed cells. As can be seen from FIG. 2, the single open cell C1 is larger than each of the plurality of closed cells C2.
In this case, the balloon catheter 6 inserted into the stent 3 should be positioned and expanded in the open cell C1 or between the closed cells C2 so as to widen the interval between the cells. Preferably, an area between the cells expanded in this way should be larger than that of the opening H. Thereby, the flow of blood towards the branch blood vessel can be kept smooth. Further, another stent, a guide wire, related tools, and a catheter can be inserted into the branch blood vessel 2 via the main blood vessel 1 in an accurate and easy manner.
However, this related art has the following problems.
When the stent 3 is inserted into the main blood vessel 1, the major cause of obstruction of the smooth flow of blood towards the branch blood vessel 2 is derived from the many cell wires that are distributed around the opening H of the branch blood vessel 2 in a undesired pattern against the smooth flow of blood. When the stent 3 is inserted into the main blood vessel 1 using a typical method, it is impossible to ascertain how the cell wires of the stent 3 are disposed at the opening H of the branch blood vessel 2.
First, just before the stent 3 is inserted into and expanded in the main blood vessel 1, efforts should be made to prevent the cell wires of the stent 3 from being disposed at the opening H of the branch blood vessel 2 or to dispose the cell wires of the stent 3 at the opening H of the branch blood vessel 2 as little as possible. Nevertheless, when the stent 3 is inserted by typical intervention, it is impossible to ascertain a positional relation between the cell wire and the opening of the branch blood vessel.
Second, to enable the blood to smoothly flow towards the branch blood vessel 2, the guide wire passes through the single open cell C1, if possible, after the stent 3 is inserted into the main blood vessel 1, and the balloon expansion occurs at the single open cell. Thereby, a wider passage by which the opening H of the branch blood vessel 2 is not restricted is secured to provide a desired flow of blood towards the branch blood vessel 2.
However, in the typical intervention using the conventional stent 3, when the guide wire is inserted towards the branch blood vessel 2 after the stent is inserted into the main blood vessel 1, it is impossible to ascertain through which one of the single open cell C1 and the plurality of closed cells C2 the guide wire passes. As one example, the balloon catheter 6 is generally inserted at a position corresponding to the opening H of the branch blood vessel 2, and then it is positioned and expanded between the cells. If the balloon catheter 6 is expanded when the closed cells C2 having a relatively small size are located at the opening H, there is a limit to widening the interval between the cells, as shown in FIGS. 3 and 4. Thus, even after the balloon catheter 6 is expanded, the flow of blood introduced into the branch blood vessel 2 may be obstructed because the area of each closed cell C2 is smaller than that of the opening H of the branch blood vessel 2. Further, when another surgical instrument such as another stent is inserted later, the instrument may get caught on one of the closed cells C2.