Surgery – Instruments – Light application
Reexamination Certificate
1999-12-08
2004-06-29
Shay, David M. (Department: 3739)
Surgery
Instruments
Light application
C606S007000, C606S010000, C606S013000, C606S046000, C604S020000, C604S022000
Reexamination Certificate
active
06755821
ABSTRACT:
BACKGROUND OF THE INVENTION
Coronary artery disease (“CAD”) is a leading cause of death worldwide. More than 6 million Americans have CAD, of which some 1.5 million suffer heart attacks (myocardial infarction), resulting in 500,000 deaths and nearly 1 million hospitalizations annually in the U.S. CAD is characterized by narrowing of the arteries that feed the heart muscle (“myocardium”); without adequate blood supply, the tissue becomes starved for oxygen (“ischemic”), and the heart does not pump as efficiently. A heart attack (which usually indicates a complete blockage of a coronary artery) can result in a portion of the heart muscle being ischemic for a prolonged time and then dying, which can permanently reduce the patient's ability to perform exercise, such as walking. The treatment of CAD includes preventive measures (modification of diet and/or exercise, reduction in hypercholesterolemia through various drugs, etc.), minimally invasive clearing of arteries (angioplasty, atherectomy, intravascular stenting), and surgical bypass of the diseased artery(ies) (coronary artery bypass surgery, “CABG”). While preventive measures have helped to reduce the number of CAD patients, CAD remains one of the greatest health problems in the world today.
Angioplasty and related catheter-based procedures can unblock some arteries, but the blockages, or “stenoses”, typically return, a condition known as “restenosis,” within 6-18 months due to intimal hyperplasia, which is creation of scar tissue from the traumatic vessel wall damage during the angioplasty procedure. The use of stents (metal or polymer tubes or coils which hold the artery open) has decreased the restenosis rate by about one half. Radioactive devices (catheters and stents) are being developed to further reduce the restenosis rate. However, angioplasty has fundamental limitations, which are unlikely to ever be solved completely. These include inability to reach smaller vessels, morbidity associated with failed angioplasty procedures, poor success rate in certain vessels, e.g., saphenous vein grafts, and general inability to completely revascularize the heart muscle (myocardium). Approximately 800,000 coronary angioplasty procedures are performed annually in the U.S.
Coronary artery bypass procedures are performed on approximately 400,000 people in the U.S. annually, and nearly 800,000 people worldwide.
Although the primary result of CABG is generally satisfactory, the saphenous veins used in most patients become blocked 10-15 years after surgery. Also, CABG procedures are very traumatic, and carry a risk of mortality around 1-3%. Although “heart port”, “off-pump”, and other minimally invasive types of CABG procedures are being developed, they are all quite invasive and/or utilize a pump and oxygenator (“heart-lung machine”), which introduces additional trauma to the patient.
Transmyocardial revascularization (TMR) using a laser (sometimes referred to as TMLR, LTMR, PMR, PTMR, or DMR) has been developed over the past decade, initially by a company called PLC Systems, Inc., of Franklin, Mass. PLC's system utilizes a high power (800-1000 W) carbon dioxide (CO
2
) laser which drills small channels in the outside (epicardial) surface of the myocardium in a surgical procedure. The holes communicate with the left ventricle, which delivers blood directly to the heart muscle, mimicking the reptilian heart. Many other companies are developing laser TMR systems, most introducing the laser light via optical fibers through a flexible catheter, making the procedure less-invasive. These companies include Eclipse Surgical Technologies, Inc., of Sunnyvale, Calif., and Helionetics, Inc., of Van Nuys, Calif. The Eclipse TMR system uses a Ho:YAG laser with a catheter-delivered fiber optic probe for contact delivery to the myocardium. The Helionetics system is based on an excimer laser. In addition to the holmium:YAG and excimer lasers, and other types of lasers have been proposed for TMR.
While the channels created during TMR are known to close within 2-4 weeks, most patients tend to improve clinically over a period of 2-6 months.
Such clinical improvement may be demonstrated by reduction in chest pain (“angina”), and a dramatic increase in exercise tolerance (“ETT”, or treadmill test). The mechanism of laser TMR is not fully understood, but it is postulated that the laser causes near-term relief of angina through denervation or patent channels, with subsequent long-term clinical improvement due to angiogenesis, i.e., growth of new blood vessels, mainly capillaries, which perfuse the heart muscle. These new “collateral” vessels enable blood to reach downstream (“distal”) ischemic tissues, despite blockages in the coronary arteries. Some of the possible mechanisms by which the laser induces angiogenesis could include activation of growth factors by light, thermal, mechanical, cavitational or shockwave means. In fact, all lasers which have been successfully used for TMR are pulsed systems, and are known to create shock waves in tissue, and resulting cavitation effects.
Cavitation can be induced in a liquid-rich environment like tissue. An opening or cavity can be created in a fluid by thermal vaporization or an rapid movement of a solid through the liquid (such as explosive expansion of a gas bubble formed in the tissue). When energy is focused into a small area of a liquid in a short time, e.g., <1 ms, the temperature can rapidly rise above boiling temperature and vapor is formed. Typically, the vapor volume is over 1000 times the original liquid volume. The vapor is formed at very high pressure and an explosive vapor bubble will be created, rapidly expanding to equalize the internal bubble pressure to ambient pressures. This bubble creates an opening in the liquid (or tissue) environment. While the bubble is expanding, the temperature inside will decrease and drop below the boiling point. The vapor then turn backs into liquid. Due to the momentum of expansion however, the bubble expands, further creating a semi-vacuum. At some point, the negative pressure overcomes the momentum of expansion, and the process becomes an implosion. Like the expansion, the implosion can be very fast, inducing a high momentum in the surrounding liquid. The motion of the liquid during implosion will be spherically symmetric, concentrated in the middle of the imploding bubble. The collision at the moment of total implosion is very forceful and is capable of creating supersonic density waves in the liquid, or “shock-waves.” If the energy release at the start of bubble formation is also very concentrated, a shock-wave can also be generated at the very start of the bubble.
Cavitation bubbles can also be formed by focusing shock waves into the liquid/tissue from an external shock wave generator. Shock-wave generators create locally very high temperatures inducing plasmas in liquids. The heat transfer to the environment subsequently creates a vapor bubble inducing the process as described above.
Another method to induce cavitation effects in liquid is by displacing the liquid at high speed by moving a solid object through the liquid. Because a delay occurs before the liquid can fill in the gap behind the object moving through the liquid, a vacuum will briefly form. The liquid filling this vacuum will be accelerated to very high speeds. At the instant the gap is filled, the liquid collides within the center of the gap, forming a shock-wave. In tissue environment, cells are sucked from their matrix by the rapidly moving liquid causing the tissue itself to effectively become liquefied.
Catheters have been previously developed which can deliver high intensity ultrasound energy to the coronary arteries for the purpose of removing thrombus (blood clots) and/or atherosclerotic plaque (see, e.g., U.S. Pat. No. 5,524,620 of Rosenschein) [note that these catheters are quite different from the intravascular imaging devices that use low intensity ultrasonic signals to probe and image arterial cross-sections]. These catheters could be modified to deliver ultrasou
Cardiocavitational Systems, Inc.
Gordon & Rees LLP
Shay David M.
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