Systems and methods for imbedded intramuscular implants

Details Systems and methods for imbedded intramuscular implants Systems and methods for imbedded intramuscular implants

1998-12-15

2004-02-17

Nguyen, Dinh X. (Department: 3626)

Prosthesis (i.e., artificial body members), parts thereof, or ai

Arterial prosthesis

C623S011110, C623S023720

Reexamination Certificate

active

06692520

ABSTRACT:

TECHNICAL FIELD
This invention relates to systems and methods for treating muscle ischemia.
BACKGROUND OF THE INVENTION
To function normally, muscle tissue requires adequate circulatory perfusion. With increases in muscle work, there is an increased demand for blood flow. When arterial inflow is compromised by peripheral vascular disease, this demand cannot be met. The resultant muscle ischemia leads to a syndrome of muscle pain termed claudication. Lower extremities are most commonly affected with peripheral vascular disease and concomitant claudication. Symptoms may abate with sufficient rest, but may then resume with further exertion. Claudication thus can be debilitating. If there is sufficient ongoing muscle ischemia, pain symptoms do not abate with cessation of exertion; the patient then experiences extremity pain at rest. As vascular disease advances, with progressive decrease in arterial inflow, circulation becomes inadequate to support tissue metabolism even at rest. At this point, frank tissue death ensues, including muscle necrosis. Pharmacological treatment offers only minimal palliation of this inexorable process. Surgical intervention through successful arterial revascularization is required before the onset of tissue death if lower extremity amputation is to be avoided.
Acute vascular compromise can also result in tissue necrosis. Embolic phenomena or traumatic injury may occlude major arteries, causing acute ischemia. Emergent surgical intervention is required to prevent catastrophic tissue loss distal to the occlusion. Acute muscle ischemia also occurs following non-vascular trauma. The most common instance of this type of ischemic insult is found in compartment syndromes of the extremities. Compartment syndrome takes place when an injured muscle begins to swell but is restricted in its expansion by some type of local or circumferential compression. Compression may be applied externally, for example by a cylindrical cast or a dressing that is tightly applied, or compression may be applied internally by the fascia covering the muscles within an extremity compartment. The result of a compartment syndrome is some degree of ischemic damage to the muscle, culminating in frank muscle necrosis if the ischemia persists long enough. Treatment of compartment syndromes requires relief of external circumferential compression and release of anatomical compression through surgery. Release of the confining anatomic structures may entail longitudinal incisions in both the skin and the muscular fascia. Even after adequate compartment release, the local ischemia and its sequelae must resolve over time as the compartment pressures and the intravascular perfusion pressures reach a more physiological equilibrium. During this period, further tissue damage may occur, with subsequent functional effects. No specific therapeutic interventions exist to decrease the extent of ischemic damage to muscle tissue following restoration of effective circulation. One example of the outcome of extensive muscle necrosis is Volkmann's ischemic contracture, a condition that results from the death of the forearm flexor wad muscles following a forearm compartment syndrome: a patient afflicted with Volkmann's ischemic contracture positions the wrist and fingers in a permanently flexed position due to the contracture of the damaged muscle mass, and the patient loses the ability either to flex or to extend the wrist or the fingers.
Muscle ischemia, when it occurs in the muscle of the myocardium, leads to similar symptoms of muscle pain and local muscle death and dysfunction. Myocardial ischemia is well-known to lead to angina pectoris and myocardial infarction, disorders that can be debilitating and life-threatening. The American Heart Association estimates that these disorders afflict more than six million people (American Heart Association,
Heart and Stroke Facts,
1994 Statistical Supplement (Dallas: American Heart Association, 1994)). All these conditions entail a mismatch between coronary blood inflow and myocardial oxygen demand. Medical therapies have been developed to alter the demand side of this equation, reducing cardiac preload, afterload, heart rate and contractility. In addition, thrombolytic therapies are available in the setting of acute myocardial infarction to effect restoration of interrupted local blood flow. However, despite the medical interventions that have evolved to treat or palliate the consequences of ischemic heart disease, morbidity and mortality remain substantial.
In cases of life-threatening ischemia, or in cases that have been refractory to medical management, more invasive intervention is required. Available modalities include surgery and percutaneous transluminal coronary angioplasty (PTCA), both designed to improve the supply side of the inflow/demand equation. The predominant surgical procedure, since its introduction by Favaloro in 1967, (R. Favaloro, “Saphenous vein autograft replacement of severe segmental coronary artery occlusion: Operative technique,”
Ann. Thor. Surg.
5:334, 1968) is the coronary artery bypass graft (CABG) operation. Coronary artery bypass grafts, using the patient's native veins or arteries, are conduits that bring blood from vessels proximal to a coronary vascular obstruction to the distal coronary artery. This procedure is long and technically complicated, with a prolonged convalescence and an extensive list of potential complications (S. Mehta and W. Pae, “Complications of cardiac surgery,” pp. 369-402 in
Cardiac Surgery in the Adult,
ed. L E Edmunds (New York: McGraw-Hill, 1997)). The operation usually requires cardiopulmonary bypass, with its own set of risks. Surgical access is through a thoracotomy or, more commonly, a median sternotomy; both access routes are associated with post-operative pain, atelectasis and wound healing problems.
Today, several hundred thousand CABG procedures are performed annually. Survival benefit has been described in patients with higher risk disease, and relief of symptoms occurs in 80-90% of patients for whom medical management had proven inadequate (Yusef et al., “Effect of coronary artery bypass graft surgery on survival: Overview of ten-year results from randomized trials by the Coronary Artery Bypass Graft Surgery Trialist Collaboration,”
Lancet
344:1449, 1994). However, these effects are not permanent. Recurrence of angina following CABG surgery occurs in 3-20% of patients, and 31% will require repeat surgical or interventional cardiologic revascularization by year twelve (Weintraub et al., “Frequency of repeat coronary bypass or coronary angioplasty after coronary artery bypass surgery using saphenous vein grafts,”
Am. J. Cardiol.
73:103, 1994).
Before the CABG operation became accepted, various other methods were attempted to improve arterial inflow. Pedicle grafts of muscle and omentum were employed in the 1930's by Beck and O'Shaughnessy (C. Beck, “The development of a new blood supply to the heart by operation,”
Ann. Surg.
102:801, 1935; L. O'Shaughnessy, “An experimental method of providing a collateral circulation to the heart,”
Br. J. Surg.
23:665, 1935). In the early 1940's, Vineberg developed the technique for implanting a distally ligated internal mammary artery with its side branches not ligated into a bluntly created tunnel in the myocardium (A. Vineberg, “Coronary anastomosis by internal mammary implantation,”
Can. Med. Assoc. J.
78:871, 1958), with clinical application beginning in 1950. Murray et al. used the internal mammary artery experimentally as a pedicled bypass in 1954 (Murray et al., “Anastomosis of a systemic artery to the coronary,”
Can. Med. Assoc. J.
71:594. 1954). By the 1960's, experimenters were working on the techniques that matured into present-day aortocoronary bypass and segmental coronary artery bypass (Johnson et al., “Extended treatment of severe coronary artery disease,”
Ann. Surg.
170:460, 1969).
The technique for percutaneous transluminal angioplasty was introduced in the early 1970's by Gruentzig,

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