Rapid exchange infusion catheter

1. An infusion balloon catheter, comprising:

a) an elongated shaft having a proximal end, a distal end, an inflation lumen, an infusion lumen that is disposed therein and that extends distally to a distal port and a guidewire lumen for receiving a guidewire having a diameter, that extends distally from a guidewire proximal port formed in said shaft at a position that is spaced distally from the proximal end of said shaft, wherein said guidewire lumen extends along a length of an inner wall of said infusion lumen distal to said proximal port to merge with said infusion lumen in a substantially parallel configuration at a location proximal to said distal port, wherein said infusion lumen has a restricted passage adjacent to said guidewire lumen, such restricted passage having a transverse dimension that is smaller than said guidewire diameter, wherein said infusion lumen distal to said guidewire lumen is capable of accommodating a guidewire as well as a flow of infusion fluid and wherein said restricted passage prevents a guidewire that is being back-loaded through said distal port from extending through said infusion lumen beyond its merger with said guidewire lumen; and

b) an inflatable balloon on a distal section of the elongated shaft, having an interior in fluid communication with the inflation lumen.

2. The balloon catheter of claim 1 wherein the restricted passage is a crescent-shaped section of the infusion lumen extending along at least a portion of the guidewire lumen.

3. The balloon catheter of claim 2 wherein the infusion lumen has a circular-shaped proximal section located proximal to the crescent-shaped section.

4. The balloon catheter of claim 3 wherein the proximal section of the infusion lumen has an inner diameter which is larger than the transverse dimension of the crescent-shaped section of the infusion lumen.

5. The balloon catheter of claim 3 wherein the crescent-shaped section of the infusion lumen has a proximal end, a distal end and a length extending from the proximal to the distal end thereof, and the length of the crescent-shaped section is substantially equal to the length of the guidewire lumen which extends alongside the infusion lumen.

6. The balloon catheter of claim 1 wherein the restricted passage is a noncircular section of the infusion lumen extending along at least a portion of the guidewire lumen.

7. The balloon catheter of claim 1 wherein the infusion lumen has a circular transverse cross sectional shape along its entire length, such that the restricted passage is a circular-shaped section of the infusion lumen having a smaller inner diameter than sections proximal and distal thereto.

8. The balloon catheter of claim 1 wherein the inflation lumen has an annular proximal section, an annular distal section, and a crescent-shaped section therebetween along the guidewire lumen.

9. The balloon catheter of claim 1 wherein a distal tip of the shaft distal to an inflatable interior of the balloon has a single lumen with a circular transverse cross section with a circular section of the infusion lumen therein.

10. A method of treating a site in a patient's body lumen, comprising:

a) providing an infusion balloon catheter comprising an elongated shaft having a proximal end, a distal end, an inflation lumen, a guidewire lumen which has a proximal section and a common distal section and which extends from a guidewire distal port at the shaft distal end to a guidewire proximal port spaced distally from the proximal end of the shaft, and an infusion lumen which is in fluid communication with the guidewire distal port, wherein said guidewire lumen extends along a length of an inner wall of said infusion lumen distal to said proximal port to merge with said infusion lumen at a location distal to the guidewire proximal port and proximal to a distal end of the inflation lumen, wherein the infusion lumen has a restricted passage adjacent to said guidewire lumen having a smaller transverse dimension than the guidewire lumen so as to prevent the proximal end of a guidewire from slidably extending proximally therethrough into the infusion lumen, and a balloon on a distal section of the elongated shaft having an interior in fluid communication with the inflation lumen;

b) threading a guidewire proximal end into the guidewire distal port, through the guidewire lumen and out the guidewire proximal port;

c) advancing said catheter along said guidewire through the patient's body lumen and positioning the distal end of the shaft at a desired location in the body lumen; and

d) proximally retracting the guidewire relative to the shaft to position a distal section of the guidewire in the proximal section of the guidewire lumen, and delivering a fluid to the patient's body lumen with the guidewire in the proximally retracted position, by infusing the fluid through the infusion lumen to the common distal section of the guidewire lumen and out the guidewire distal port.

11. The method of claim 10 wherein the restricted passageway has a transverse cross section with a crescent-shape which is narrower in a first direction than in a perpendicular second direction, and the guidewire proximal end has a circular transverse cross section with a larger diameter than the narrower first direction of the crescent-shaped restricted passageway such that the guidewire proximal end is prevented from entering the infusion lumen by the restricted passage.

12. The method of claim 10 wherein the guidewire in the proximally retracted position substantially occludes the proximal section of the guidewire lumen to thereby inhibit the fluid from back-flowing proximally out the guidewire proximal port, and including longitudinally displacing the guidewire in the guidewire lumen after c) to slidably dispose the guidewire distal end through the guidewire distal port.

13. The method of claim 10 including inflating the balloon after c) and before d).