Heart disorders are a common cause of death in developed countries. They also impair the quality of life of millions of people and restrict activity by causing pain, breathlessness, fatigue, fainting spells and anxiety. The major cause of heart disease in developed countries is impaired or inadequate blood supply. The coronary arteries may become narrowed due to arteriosclerosis and part of the heart muscle is deprived of oxygen and other nutrients. The resulting ischemia or blockage can lead to angina pectoris, a pain in the chest, arms or jaw due to lack of oxygen to the heart's myocardium, infarction or tissue necrosis in myocardial tissue. Alternatively, and particularly with age, the extent of vascularization of the heart may diminish, leaving the heart undersupplied with oxygen even in the absence of significant arteriosclerosis.
Coronary-artery blockage can be relieved in a number of ways. Drug therapy, including nitrates, beta-blockers, and peripheral vasodilator drugs (to dilate the arteries) or thrombolytic drugs (to dissolve clots) can be very effective. If drug treatment fails, transluminal angioplasty is often indicated—the narrowed part of the artery, clogged with atherosclerotic plaque or other deposits, can be stretched apart by passing a balloon to the site and gently inflating it a certain degree. In the event drug therapy is ineffective or angioplasty is too risky (introduction of a balloon in an occluded artery can cause portions of the arteriosclerotic material to become dislodged which may cause a total blockage—at a point downstream of the subject occlusion, thereby requiring emergency procedures), the procedure known as coronary artery bypass grafting (CABG) is the most common and successful major heart operation performed, with over 500,000 procedures done annually in America alone. A length of vein is removed from another part of the body. The section of vein is first sewn to the aorta and then sewn onto a coronary artery at a place such that oxygenated blood can flow directly into the heart. CABG typically is performed in an open chest surgical procedure, although recent advances suggest minimally invasive surgery (MIS) techniques may also be used.
Another method of improving myocardial blood supply is called transmyocardial revascularization (TMR), the creation of channels from the epicardial to the endocardial portions of the heart. Initially, the procedure used needles to perform “myocardial acupuncture,” and has been experimented with at least as early as the 1930s and used clinically since the 1960s, see Deckelbaum. L. I., Cardiovascular Applications of Laser Technology, Lasers in Surgery and Medicine 15:315-341 (1994). This procedure has been likened to transforming the human heart into one resembling that of a reptile. In the reptile heart, perfusion occurs via communicating channels between the left ventricle and the coronary arteries. Frazier, O. H., Myocardial Revascularization with Laser—Preliminary Findings, Circulation, 1995; 92 [suppl 11:11-58-11-65]. There is evidence of these communicating channels in the developing human embryo. In the human heart, myocardial microanatomy involves the presence of myocardial sinusoids. These sinusoidal communications vary in size and structure, but represent a network of direct arterial-luminal, arterial-arterial, arterial-venous, and venous-luminal connections. The needle technique was not continued because the channels did not remain open, replaced by the use of laser energy to accomplish TMR.
Drug therapies with angiogenic growth factors may expedite and/or augment collateral artery development. To accomplish these needs, drug transfer devices for delivering precise amounts of these drugs can enhance this healing process. Surgeons who deal with minimally invasive surgical techniques and interventional cardiologists who deal with percutaneous approaches, need devices for drug delivery procedures. The drugs used in modern medical technology are often quite expensive, potentially mixing and/or handling sensitive, and it is a new challenge to make these drugs or other compounds readily available for precise, predetermined delivery during these advanced or other procedures.
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