PMR catheter

Details PMR catheter PMR catheter

1999-02-24

2001-04-17

Cohen, Lee (Department: 3739)

Surgery

Instruments

Electrical application

C606S049000, C606S050000, C607S099000, C607S105000, C607S113000, C604S022000

Reexamination Certificate

active

06217575

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates generally to devices and methods for promoting blood circulation to the heart muscle. More particularly, the present invention relates to devices and methods for forming holes or channels in the walls of a heart chamber such as those created during a percutaneous myocardial revascularization (PMR) procedure.
BACKGROUND OF THE INVENTION
Assuring that the heart muscle is adequately supplied with oxygen is critical to sustaining the life of a patient. To receive an adequate supply of oxygen, the heart muscle must be well perfused with blood. In a healthy heart, blood perfusion is accomplished with a system of blood vessels and capillaries. However, it is common for the blood vessels to become occluded (blocked) or stenotic (narrowed). A stenosis may be formed by an atheroma which is typically a harder, calcified substance which forms on the walls of a blood vessel.
Historically, individual stenotic lesions have been treated with a number of medical procedures including coronary bypass surgery, angioplasty, and atherectomy. Coronary bypass surgery typically involves utilizing vascular tissue from another part of the patient's body to construct a shunt around the obstructed vessel. Angioplasty techniques such as percutaneous transluminal angioplasty (PTA) and percutaneous transluminal coronary angioplasty (PTCA) are relatively non-invasive methods of treating a stenotic lesion. These angioplasty techniques typically involve the use of a guidewire and a balloon catheter. In these procedures, a balloon catheter is advanced over a guidewire such that the balloon is positioned proximate a restriction in a diseased vessel. The balloon is then inflated and the restriction in the vessel is opened. A third technique which may be used to treat a stenotic lesion is atherectomy. During an atherectomy procedure, the stenotic lesion is mechanically cut or abraded away from the blood vessel wall.
Coronary bypass, angioplasty, and atherectomy procedures have all been found effective in treating individual stenotic lesions in relatively large blood vessels. However, the heart muscle is perfused with blood through a network of small vessels and capillaries. In some cases, a large number of stenotic lesions may occur in a large number of locations throughout this network of small blood vessels and capillaries. The torturous path and small diameter of these blood vessels limit access to the stenotic lesions. The sheer number and small size of these stenotic lesions make techniques such as cardiovascular bypass surgery, angioplasty, and atherectomy impractical
When techniques which treat individual lesions are not practical a technique know as percutaneous myocardial revascularization (PMR) may be used to improve the oxygenation of the myocardial tissue. A PMR procedure generally involves the creation of holes, craters or channels directly into the myocardium of the heart. PMR was inspired in part by observations that reptilian heart muscles are supplied with oxygen primarily by blood perfusing directly from within heart chambers to the heart muscle. This contrasts with the human heart, which is supplied by coronary vessels receiving blood from the aorta. Positive clinical results have been demonstrated in human patients receiving PMR treatments. These results are believed to be caused in part by blood flowing within a heart chamber through channels in myocardial tissue formed by PMR. Increased blood flow to the myocardium is also believed to be caused in part by the healing response to wound formation. Specifically, the formation of new blood vessels is believed to occur in response to the newly created wound. This response is sometimes referred to as angiogenisis. In addition to promoting increased blood flow, it is also believed that PMR improves a patient's condition through denervation. Denervation is the elimination of nerves endings. Specifically, the creation of wounds during a PMR procedure results in the elimination of nerve endings which were previously sending pain signals to the brain as a result of hibernating tissue.
SUMMARY OF THE INVENTION
The present invention pertains to devices and methods for performing percutaneous myocardial revascularization (PMR). A device in accordance with the present invention may be used to form wounds in the myocardium of a patient's heart. Several general types of wounds may be created with this device. For example, this device may be used to form a channel wound (e.g., a wound with a depth greater than its width). By way of a second example, this device may be used to form a crater wound (e.g., a wound with a width greater than its depth).
In a preferred embodiment, a catheter in accordance with the present invention includes an elongate shaft having a proximal end and a distal end. The elongate shaft defines a lumen which extends substantially through the elongate shaft. An insulator is fixably attached to the elongate shaft at its distal end. The insulator includes at least two holes. The catheter also includes a conductor having a bent portion, a first leg portion and a second leg portion. The first and second leg portions of the conductor pass through the holes of the insulator and are disposed in the lumen of the catheter. The bent portion of the conductor substantially forms an electrode protruding from the distal end of the catheter.
The distance which the electrode protrudes from the insulator is carefully controlled during the manufacture of the catheter. This helps to control the depth of the wounds which will be created with the catheter during a PMR procedure. In a presently preferred embodiment of the present invention, the electrode proceeds to penetrate the heart until the insulator contacts the heart tissue.
The insulator includes two landing zones which extend away from the electrode. The width of the landing zones is generally larger than the width of the electrode. The relatively large area of the landing zones assures that the travel of the electrode into the heart will stop when the landing zones contact the heart tissue.
It is a desirable feature of this invention that the landing zones extend beyond the wound created in the heart tissue during a PMR procedure. This is because the wounded tissue is substantially softened, and it is possible for a PMR catheter to be pushed through soft, injured tissue.
The distance which the electrode protrudes from the landing zone and the relative surface areas of these elements are carefully selected to create a therapeutically effective wound while reducing the likelihood of unintentionally perforating the myocardium. Preferably, a therapeutically effective wound will, at a minimum, perforate through the endocardium and damage blood vessels and capillaries in the myocardium. The likelihood of unintentionally perforating through the myocardium to the epicardium is reduced when the depth of the wound created is only enough to penetrate the endocardium adjacent the myocardium.
In one embodiment of a device in accordance with the present invention, the conductor defines a conductor lumen and at least one hole in fluid communication with the conductor lumen. The conductor lumen may be used during a PMR procedure to deliver fluid to the distal end of the catheter. The fluid delivered during the PMR procedure may include contrast, saline, therapeutic agents, etc. The fluid may be used for a number of tasks, including mapping a heart, marking an injury site or promoting angiogenic effects.
In a presently preferred method in accordance with the present invention, pressurized fluid may be delivered to the wound site during or after wound formation. The formation of the wound may be enhanced by collateral damage to the myocardium induced by directing this pressurized fluid into the wound site. The impact of pressurized fluid causes vessels, capillaries and sinuses to rupture. By creating this collateral damage, the number of wounds which need be made during a PMR procedure may be substantially reduced. A second benefit of this collateral

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