Surgery – Means for introducing or removing material from body for... – Treating material introduced into or removed from body...
Reexamination Certificate
2001-05-07
2004-03-02
Shaver, Kevin (Department: 3732)
Surgery
Means for introducing or removing material from body for...
Treating material introduced into or removed from body...
Reexamination Certificate
active
06699230
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to medical devices and more particularly to devices and methods for thrombolytic therapy of coronary arteries for patients experiencing an early stage of acute myocardial infarction.
BACKGROUND OF THE INVENTION
Acute myocardial infarction is a major cause of mortality and morbidity in an atherosclerosis-prone contemporary society. Each year approximately 1.5 million Americans suffer a myocardial infarction, and more than 400,000 individuals will likely die from it this year. Few life threatening diseases are as common as acute myocardial infarction. Myocardial infarction is the morphologic manifestation of irreversible cell death in an area of the heart that is caused by a prolonged, and often abrupt, mismatch between the supply of the oxygen and nutrients in the blood and the metabolic needs of the myocardial cells. The most common cause of this condition is the sudden interruption of blood flow in a coronary artery by an occlusive thrombus formed in an area with atherosclerotic disease. A myocardial infarction is an evolving, dynamic event. A coronary occlusion results in ischemia that is initially reversible, but over time becomes irreversible. Necrosis of myocardium, or cardiac muscle, begins 20 to 30 minutes after total occlusion of the vessel. This “wave front of necrosis” proceeds through the ischemic part of the myocardium and is complete within 4-6 hours of occlusion. Later a scar is formed over the necrotic part of the myocardium. The area of myocardium affected by infarction does not contribute any more to the overall pumping function of the heart.
To successfully salvage the myocardium, the blood flow though the occluded artery must be restored before the myocardium cells have been irreversibly destroyed. Restoration of the blood flow, or reperfusion, is more successful at the early stage of evolving infarction. Prompt therapy can make the difference between heart muscle death or salvage.
The most common method of reperfusion heart muscle during a myocardial infarction is the use of medications that dissolve thrombi-thrombolytic agents. Thrombolytic agents, including streptokinase, urokinase, anisteplase, and tissue plasminogen activator (tPA) are extremely efficient in preventing disability and the death among people having heart attacks. About 80 percent of people having a heart attack who receive a thrombolytic agent within 2 hours of the onset of symptoms have reperfusion. Successful reperfusion reduces the size of the myocardial infarction and helps preserve the overall pumping function of the heart.
There are several compelling reasons to start the thrombolytic therapy as early as possible. Probably, the best time for it is approximately 20-30 minutes after onset of symptoms, when no irreversible damage to the myocardium has been done yet. At this time the polymerization of fibrin in thrombus is still in progress and the thrombus is soft and easier to dissolve. This is because at this stage it is more permeable for the thrombolytic agents. The major mechanism of thrombolysis of totally occlusive thrombi is dragging the blood plasma with a thrombolytic agent in it through the body of thrombus by the blood pressure differential before and after the thrombus. Thus, early started thrombolytic therapy allows facilitates the faster dissolution of the thrombus. It is important also that for lysis of a very fresh thrombus that all thrombolytic agents are equally efficient. The tPA agent is about 10 times more expensive than streptokinase, but there is no difference in the time of dissolving of fresh thrombi.
Thus, very early thrombolytic therapy promises a complete salvage of the myocardium with the preservation of the overall pumping function of the heart, and it can be performed with a cost effective choice of thrombolytic drug. Mortality and morbidity of the patients suffering a myocardial infarction can be drastically reduced.
Whether or not thrombolytic treatment is undertaken or successful, additional treatment is usually required. Nitroglycerin is given either under the tongue or by vein to reduce symptoms by decreasing the heart's demand for oxygen and by improving the blood flow through coronary arteries as much as possible. Heart attacks can be very painful, so narcotics such as morphine are given when necessary. Medications such as beta-adrenergic blocking agents may be helpful for reducing pain and enhancing survival. Beta-adrenergic blockers make the heart beat more slowly and less forcefully, so it requires less oxygen. Blood clots can re-form in the coronary artery at the sites where thrombolysis has already dissolved the original blood clot. Thrombolytic drugs dissolve blood clots that already formed; anticoagulants prevent new blood clots from developing. A similar function is performed by antiplatelet medication like aspirin, which can be administered orally or intravenously.
Both thrombolytic therapy and supportive care are available in emergency rooms in hospitals. A lot of effort has been spent to provide the treatment as soon as possible. Nevertheless, the shortest time that passes before the treatment starts is still about two hours. At this time some damage to the myocardium is already done, and the treatment strategy is to minimize it and relieve the symptoms associated with this damage.
In many countries a special emergency mobile care paramedic unit has been introduced for cardiac patients with suspected myocardial infarction. With this “out-of-hospital” approach thrombolytic therapy can be delivered faster than in hospital emergency rooms. It is very promising way of improving cardiac care. The drawback of this approach is that the diagnosis and overall management of the patients by paramedics is not of the quality provided by highly qualified physicians in the emergency rooms in hospitals.
It is desirable that the emergency care be selected, prescribed and managed by the patient's personal cardiologist, who is familiar with the patient's cardiac history and general state of health.
It is desirable also to develop a method to provide a multiple medication therapy for cardiac patients suffering from a heart attack in its earliest stage, in the first 20-30 minutes after the onset of the symptoms. Such an early start would make real a new treatment strategy, the fundamental objective of which is the complete salvage of the myocardium and the preservation of 100% of its pumping function, rather than reducing to minimum the damage made in the first 2 hours.
There have been many known devices and methods for intravenous infusion of drugs, particularly drugs in a dry form, or lyophilized drugs, ready for reconstitution to liquid state before the usage. As an example, U.S. Pat. No. 5,024,657, assigned to Baxter International, and many others in U.S. class 604/85. This device is intended for hospital use by a qualified nurse or physician. It is not automated and can't be used by a person with little or no medical training.
It should be mentioned that a great number of contemporary drugs loose their activity within months of storage at room temperature. It is especially true for the protein based drugs, including thrombolytic agents. The system in accordance with the referred patent does not have a cooler and thus does not warrant the long-term efficiency of the drugs. It can not be held in a stand by state for a long period of time.
Another example of prior art can be U.S. Pat. No. 5,609,572, issued to Volker Lang. In this patent a modular cassette infusion system for multiple infusions and automatic administration of medicaments is described. For infusion control the system utilizes a microprocessor, which has fixed program and manual programming steps and is compatible with the infusion equipment. It substantially reduces the work to be performed by nursing staff. The device described in this patent requires manual reconstitution of dry drugs and does not allow keeping the drug potent and ready for a long time. To operate the system and to make an intravenous (IV) puncture by a st
Chornenky Victor I.
Jaafar Ali
Minnesota Medical Physics LLC
Ramana Anuradha
Shaver Kevin
LandOfFree
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