Revascularization: Bypass Surgery and Angioplasty
REVASCULARIZATION: BYPASS SURGERY AND ANGIOPLASTY
Ischemic heart disease is the commonest form of heart illness. It increases in frequency with increasing age, and outcomes are much worse in elderly patients. Ischemia is caused by narrowings or blockages in the coronary arteries, resulting in an inadequate blood supply to the heart. The disease spectrum ranges from subclinical disease (no symptoms) to angina, and, finally, to a heart attack (myocardial infarction, or MI). Typical angina is marked by exertional chest pain and shortness of breath that settles with rest. With stable angina, people may limit their activities to avoid symptoms, but it is generally well-tolerated and can be controlled with medication.
With acute ischemic syndromes, which include both unstable angina and myocardial infarctions, the risks are much greater. Unstable angina is marked by an increase in the severity or duration of pain or symptoms—and having them occur with lower levels of activity or at rest. If unstable angina progresses in a crescendo pattern, it may lead to a myocardial infarction. With a myocardial infarction, the ischemia to the heart is so severe that permanent damage occurs to the muscle. Major complications from heart attacks include life-threatening arrhythmias, congestive heart failure, and death.
Mortality rates from myocardial infarction for patients younger than sixty-five are generally less than 5 percent, while mortality rates for those over the age of seventy-five are greater than 20 percent.
There are six medications used to treat ischemic heart disease. Aspirin, cholesterol-lowering medications, and ACE inhibitors all reduce the risk of future heart attacks and strokes but have no other effect on the symptoms of angina. Beta blockers help reduce the symptoms of angina and the risk of heart attacks and strokes. Calcium channel blockers and nitroglycerin also help control symptoms of angina. As patients get older, especially diabetics and women, they are more likely not to have typical chest pain and angina, which can lead to misdiagnosis.
Coronary artery bypass grafting
If angina cannot be controlled adequately with medications, or if patients have severe side effects such as asthma or depression with beta blockers or severe headaches with nitroglycerin, then revascularization may need to be considered. This consists of opening clogged arteries or replacing blocked arteries with a patient’s own veins or arteries to bypass the blockage. Coronary artery bypass grafting (CABG) is open-heart surgery, and it has been available since the early 1970s. In the mid 1980s, nonsurgical revascularization was developed using balloons guided to the coronary arteries through X-ray equipment. This is known as percutaneous transluminal coronary angioplasty (PTCA).
Patients with unstable angina, or those who are felt to be at high risk, are referred for coronary angiography. This is a specialized X ray used to determine exactly where the blockages to the coronary arteries exist. An intravenous catheter is inserted into the femoral artery in the groin or into the brachial artery at the elbow. Through this sheath long catheters are guided using X-ray equipment through the major arteries to the heart. Dye is injected into the coronary arteries and X rays measure the extent of blockages.
Cardiac catheterization does carry a small but real risk, including allergic reactions (one in one thousand patients), MI (one in one thousand), stroke (one in two thousand), or death (one in one thousand). Other complications include renal failure. Risk factors that predispose to heart disease and that increase with age (e.g., diabetes, hypertension) also increase the risk for renal disease.
Patients are required to lie on their back for five to six hours after the catheter has been removed to prevent significant bleeding. Even with precautions, large bruising may occasionally result. This will resolve spontaneously, but may take days or even weeks.
Following angiography, the type or extent of blockage and the number of coronary arteries involved determines the best treatment. Studies comparing surgery to medical therapy have determined what degree of blockage most benefits from surgery. Unfortunately, patients over the age of sixty-seven were excluded from these trials. Because older patients have an increased risk of dying from surgery, as well as other complications such as stroke, renal failure, postoperative infection, and prolonged hospitalization, it is difficult to be certain that this same benefit is present. By benefit we understand a reduction in mortality. The original trials showing the benefit of surgery also tended to exclude women, who make up more than 50 percent of the elderly population. In addition, these trials were conducted in the 1970s, and since then there have been considerable improvements in both medical therapy and surgical therapy.
The rationale for surgical intervention is that risks taken at the time of surgery will pay off with long-term benefits. A review by Yusuf, Zucker, Peduzzi, et al. of the trials comparing bypass surgery and medical therapy show that the peak benefit of surgery over medical therapy occurs at five years after surgery. At this point, mortality rates are 10.2 percent for surgical patients vs. 15.8 percent for those having medical therapy in the under sixty-five age group.
Expected mortality for patients under the age of sixty-five who undergo bypass surgery and have no other major medical problems is less than 1 percent. Over the age of seventy, operative mortality may increase to 2 to 5 percent; and over the age of eighty this increases to 5 to 10 percent. Depending on operative risk factors, which are certainly increased in older patients, mortality may climb to 20 percent, and emergency surgery has a ten-fold increase in risk to 35 percent. The major risk factors include an ejection fraction (fraction of blood pumped out of the heart with each beat) less than 20 percent, repeat surgery, emergency surgery, female sex, diabetes, age greater than seventy, left main disease (two of the three arteries to the heart branch of the short left main artery; if it is blocked fifty percent, this is considered a significant risk), recent MI, and/or three-vessel coronary artery disease. The incidence of coronary artery disease also increases with age, and the greatest growth in the use of bypass surgery has been in the elderly. Older age also predisposes to other risk factors for heart disease, such as underlying lung disease, kidney problems, cerebrovascular disease, diabetes, and problems with infection and healing postoperatively.
Stroke is another possible operative complication. The risk of stroke is less than 2 percent for those under age seventy and greater than 6 percent for those over age seventy. A less well-documented area of concern is that of cognitive change or decline following bypass surgery. While more difficult to measure, this may have great significance for patients’ independent living and quality of life postoperatively.
Renal failure also increases with increasing age after bypass surgery. It occurs in less than 1 percent of patients under the age of seventy, but is present in almost 2 percent of patients over the age of eighty. Predisposing factors would be renal failure preoperatively, diabetes, and hypertension. Older patients tend to have longer hospital stays postoperatively.
The long-term mortality rates are three to four times greater for older patients at five to ten years after surgery. It is, therefore, somewhat difficult to extrapolate older data on younger patients to older patients, who clearly have greater risks but may not have as much benefit regarding survival. The reasons to undertake any intervention, whether it be medication or surgery, are either to prolong life or to improve symptoms. While the evidence for bypass surgery prolonging life in patients over the age of sixty-five remains unclear, there certainly is improvement in symptoms of angina and quality of life in older patients, provided major complications are avoided.
Bypass surgery is done under general anesthesia, usually lasting three to four hours. The chest or sternum is split, while a specialized pump maintains circulation to the vital organs. The heart is then stopped and arteries or veins are attached to the aorta. The other ends are reattached to the native arteries beyond the blockages. Veins are generally harvested from the leg; arteries from the forearm or chest. Although there are three major arteries supplying the heart, these all have multiple branches, and patients may have up to five or six bypasses done during surgery. During the first twenty-four to forty-eight hours after surgery, the patient is placed in the intensive care unit. Following this, the patient is transferred to a regular hospital ward for mobilization and monitoring of complications. The great majority of patients do very well with this surgery and return to a full and active life.
Revascularization can also be accomplished using percutaneous transluminal coronary angioplasty (PTCA), which is much less invasive. This is done using catheters, which are passed through the femoral or brachial arteries to the heart, as with coronary angiography. Wires are then passed through the catheter and down the coronary arteries past the narrowings. A balloon, which is deflated, is passed over the wire to the point of greatest narrowing. The balloon is then inflated, compressing the plaque or obstruction. When the balloon is deflated, the artery usually remains open. Blood thinners are used to prevent immediate clotting while the area heals over, and oral antiplatelet agents also prevent blood clots from forming on the torn or damaged artery. Twenty to 30 percent of arteries reocclude following the procedure, with up to one-half of these occurring in the first twenty-four hours. While many of these can be reopened with a balloon and kept open using a coil or stent, occasionally a dissection or acute closure results in the need for emergency surgery. These complications are more common in the elderly. Gregorio, Kobayashi, Albiero, et al. found that 3.7 percent of angioplasty patients over the age of seventy-five required emergency CABG, compared with 1.4 percent for those under the age of seventy-five. They also found that mortality was markedly increased, at 2.2 percent for the older patients, compared with 0.1 percent for the younger group. This procedure is very operator-dependent, and experience certainly results in better outcomes. While complication rates are lower than for bypass surgery, they are more significant with increasing age. Bypass surgery results in more complete revascularization and better reduction of symptoms than PTCA, but it has not been shown to prolong survival. Diabetics, the BARI (Bypass Angioplasty Revascularization Investigation) trial showed, have had improved five-year mortality with bypass surgery compared to angioplasty (5.8 percent vs. 20.6 percent).
The most striking difference between the two procedures is the need for repeat revascularization procedures. Less than 10 percent of bypass surgery patients require another procedure in five years, compared to 50 percent of angioplasty patients. Further, not all blockages are amenable to angioplasty. Experience of the physician performing the angioplasty (interventionalist) is critical with more difficult lesions.
Following angioplasty or coronary artery bypass grafting, risk management is important to maintain artery patency. This includes the use of aspirin and antiplatelet agents, aggressive lipid lowering, smoking cessation, and managing blood pressure and diabetes. Revascularization may reduce the need for antianginal medication. These treatments should not be considered curative; patients must still be aware of the possibility of recurrence of angina and ischemic heart disease.
The utilization of coronary angiography and subsequent revascularization varies considerably within different jurisdictions and health care systems. An interesting study compared patients over the age of sixty-five having a heart attack from a United States Medicare database and an Ontario, Canada database. Catheterization rates in the United States approached 40 percent, compared to 10 percent in Ontario, and revascularization rates were 28.5 percent versus 6.3 percent, respectively. Despite this marked increase in revascularization in the United States, mortality rates at one year were identical. Symptom control was not assessed, however.
In summary, while ischemic heart disease and associated risks increase with increasing age, there is also increased risk with revascularization procedures. In addition, comorbidities such as diabetes, hypertension, renal failure, prior strokes, lung disease, heart failure, and deconditioning may also be increased with increasing age. If medical therapy cannot adequately control symptoms of ischemic heart disease, then revascularization procedures must be considered. While angioplasty carries less risk, it is not always technically possible, and the need for repeat procedures is greater than with bypass surgery. Bypass surgery carries far greater risk but may provide the greatest benefit. Further, there seems to be an increasing physiological variability with aging. Multiple organ systems are at risk during bypass surgery and complications may be more devastating if coping skills and general health are reduced. There is no substitution for an open and frank discussion with physicians and family before embarking on revascularization. Technical expertise of surgeons, physicians, and the entire health care team are crucial to achieve optimal outcomes.
See also Anesthesia; Heart Disease; Surgery in Elderly People; Quality of Life.
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