Atherosclerosis is a generalized disorder of the arterial tree, manifested by plaque formation along the inner surface of arteries. The formation of plaque involves a dynamic process of biologically active endothelial cells (cells lining the inner surface of arteries) interacting with various hemodynamic, mechanical, metabolic, and chemical forces and substances. Normally, endothelial cells serve to maintain the integrity of the arterial wall, adapting to stress and injury by increasing wall thickness or altering the diameter to the lumen (channel cavity) of the vessel, increasing (vasodilatation) or decreasing (vasoconstriction) its size.
In atherosclerosis, the usual endothelial response to stress and injury becomes maladaptive. Dead cells, tissue debris, cholesterol, calcium, and other products are deposited beneath a layer of over-exuberant healing (hyperproliferative) endothelial cells to form a plaque. As the plaque continues to mature, its core becomes necrotic and a fibrous cap forms over the surface. Over several years, this narrowing ultimately reduces blood flow to the heart and the extremities to the point where it becomes insufficient to meet its aerobic and metabolic demands. In some cases, the fibrous cap that forms on top of the plaque can rupture, thus exposing the previously contained debris to the coagulation factors of the bloodstream, leading to an acute thrombosis (blood clot) that may completely occlude the vessel lumen, often with catastrophic consequences.
Large-vessel atherosclerosis. Large-vessel atherosclerosis refers to disease in the aorta and its major branches above the level of the chest. Some arterial thickening and changes in the size of arterial walls appear to be, in part, due to the aging process. While there does not appear to be any one single identifiable etiologic cause, several risk factors have been associated with the genesis of atherosclerosis. Nonmodifiable factors include gender, age, and genetics. Males are more prone than females. Incidence increases with age, reaching approximately 10 percent in adults over the age of seventy. There also appears to be an increased incidence of significant atherosclerosis in those having a first degree relative who has experienced atherosclerosis. Additionally, people with a family history of atherosclerosis, high blood pressure, or heart disease are at greater risk than the rest of the population.
Modifiable risk factors include smoking, hyperlipidemia, hypertension, and diabetes. The disease appears to be exacerbated in those who have a sedentary lifestyle, who are obese, and who have high levels of emotional stress. Elderly persons carry the additional complication of being prone to multi-system disease (disease that affects more than one organ).
The lower legs and feet, being farthest ‘‘down the pipe’’ of the arterial circulation, are often the first areas of the body to show the effects of this disease. Alternatively, other patients may manifest their initial symptoms as a transient ischemic attack (TIA, or mini-stroke) or significant permanent stroke from plaque formation in the carotid arteries in the neck. This arterial disease can occur anywhere along the vascular tree, but occurs more commonly at branch points, where blood vessels bifurcate.
Symptoms vary, depending on the degree of restriction of blood flow caused by the atherosclerotic stenosis (narrowing of the vessel lumen). Initially, patients may experience intermittent claudication which is an exercise-induced, crampy, heavy feeling in the muscles of the calf, and thigh, or disease in the arterial tree. With disease progression, ischemic symptomology is elicited with less and less activity, eventually occurring at rest. Patients may also experience cyanosis (a blue or pale discoloration) and decreased sensation or parathesias (a pins and needles feeling) in toes or feet. Additionally, patients with this disease may experience decreased hair growth; nail bed changes (onycogryphosis, or the thickening of the toenails); persistent, nonhealing ulcers or infections, and gangrenous (dead tissue) changes in the lower extremities. This is referred to as critical ischemia and occurs in about twenty percent of patients with large-vessel atherosclerosis.
Diagnosis. Diagnosis of chronic occlusion atheromatous disease consists of a thorough clinical exam, including both noninvasive and invasive testing. A Doppler ultrasound is used to determine flow patterns in the legs and ascertain the level and severity of disease. The information gathered will establish the appropriate course of treatment. If the findings indicate that surgery is required, a catheter-based dye test (angiogram) is performed to develop a ‘‘road-map’’ of the diseased arteries and determine the appropriate operative strategy.
Treatment. The initial treatment for limb ischemia should be conservative, consisting of a daily walking and biking regimen in an attempt to stimulate collateral vessel growth (vessels that naturally ‘‘bypass’’ the blockage in the artery). Often, in a diligent patient, this may be the only treatment necessary. Other medical therapy consists of agents that dilate vessels or decrease blood viscosity. However, both of these approaches may not be suitable for elderly patients due to concurrent comorbidities (i.e., osteoarthritis) and possible polypharmaceutical interactions.
The goal of surgical treatment is to reestablish flow to (revascularize) the ischemic tissue. This can be done percutaneously with angioplasty and stenting, or (more invasively) by using an alternate conduit to bypass the blockages in the diseased artery. For the a peripheral artery bypass a vein graft synthetic material (e.g., Gortex) is used, depending on the location of the stenosis. Both of these interventional concepts are also the current standard treatment of coronary arteriosclerosis. If these treatments are unsuccessful or the patient is deemed to be unsuitable for them, amputation of nonviable portions of the foot or leg is the only remaining surgical recourse. Approximately 2 to 10 percent of patients with critical ischemia will require amputation of the affected limb.
Deciding on a surgical treatment for large-vessel atherosclerosis involves an analysis of the risk/benefit ratio for each patient. In other words, is the risk of morbidity and mortality greater than the probable benefit of the surgery for the patient? The methodology of determining this ratio involves looking at epidemiological surgical outcomes and application of the data to the individual patient. It has traditionally been felt that elderly patients carry a greater risk than benefit for vascular reconstruction, and amputation has thus principally been the procedure of choice for these patients. However, many studies looking at this population have been incomplete and/or flawed, leaving the question open to debate.
Amputation carries high rates of mortality (13 to 23 percent) in elderly patients. Reasons for this high mortality is multifactorial, and contributing factors include a multi-system disease, associated comorbidity, and inadequate nutrition. Additionally, it has been shown that up to twothirds of elderly amputees (depending on the level of amputation) are unable to be adequately rehabilitated, resulting in further functional disabilities. Anesthetic techniques that avoid a general anesthetic and increased use of invasive and noninvasive surgical techniques have substantially decreased morbidity and mortality in elderly patients following vascular procedures. Additionally, octogenarians with critical ischemia have an average life expectancy of four years. For these reasons, utilization of more aggressive interventions appear warranted.
Medicine EncyclopediaAging Healthy - Part 4Vascular Disease - Atherosclerosis, Arterial Aneurysms, Varicose Veins