~Cardiovascular Disease Comprehensive 18 - Invasive vs Noninvasive Testing
INVASIVE VERSUS NONINVASIVE TESTING AND HEART PROCEDURES
Facts to Consider Before a Final Decision Is Made
Invasive heart treatment ranks ninth among the top 10 causes of death. Because of the obvious seriousness of any procedure involving the heart, consenting to invasive testing and surgery should be made rationally rather than emotionally. The intent of this protocol is not to steer the patient in regard to cardiac testing and treatment but rather to enlighten the reader concerning both options and risks. Fortunately, researchers have removed many of the uncertainties from the dilemma.
The detection of a heart problem can be made by several noninvasive tests, medical history, physical examination, electrocardiogram, stress tests, blood tests, and an echocardiogram. An echocardiogram provides a graphic outline of the movements of the heart structures, showing the valves and the action of blood flowing through them, the ability of the left ventricle to pump blood, the walls of the heart (considering thickness), and an assessment of the membrane around the heart (the pericardium). It does not show the coronary arteries well enough to determine blood circulation directly to the heart. For this evaluation, the echocardiogram should be combined with a cardiac stress test. This combination will show the workings of the various parts of the heart during stress compared to rest.
The blood tests are valuable because they confirm or refute uncertainties arising from early-stage diagnosis of a heart attack. Creatine kinase (CK), a small fraction of the CK enzyme (CK-MB), and troponins are heart damage markers or cardiac enzymes measurable in the blood. CK-MB shows an increase above normal about 6 hours after the onset of a heart attack. It typically reaches its peak level within 9-30 hours and usually returns to normal within 48-72 hours (Cardiac Biomarkers 2000).
Blood tests to measure troponins, specifically T (cTnT) and troponin I (cTnI) -- cardiac muscle proteins -- have been developed. These proteins control the interaction between actin and myosin, muscle proteins that contract or squeeze the heart muscle. Identifying troponins specific to heart muscle allowed for the development of blood assays that can detect heart muscle injury with great sensitivity and specificity. The normally low level of cTnT and cTnI increases substantially within 4-6 hours of heart muscle damage. Peak levels occur at 14-20 hours, usually returning to normal 5-7 days later (American Heart Association 2000; Cardiac Biomarkers 2000; Sobki et al. 2000).
It is now considered possible to use troponin testing to identify individuals at either low or high risk for a coronary event. Even modestly elevated troponin levels are associated with larger numbers of tiny coronary artery blood clots, complex arterial lesions, and impaired blood flow through the vasculature.
Compared to patients with the lowest levels of troponin T, those with the highest troponin T levels are almost 13 times more likely to die over a 37-month period (Lindahl et al. 2000). The type of troponin blood test used by most clinical laboratories is troponin I. If levels exceed 0.4 ng/mL, antiplatelet and antithrombotic therapy should be considered. Nutrients with an antiplatelet and antithrombotic therapeutic profile are highlighted in the Therapeutic section of this protocol.
Researchers at University of Texas Southwestern Medical Center (Dallas) have discovered another impressive cardiac marker, brain natriuretic peptide (BNP), showing remarkable accuracy in regard to predicting cardiac morbidity and mortality. BNP is a neurohormone synthesized in the muscular wall of the left ventricle of the heart that is released into the circulation in response to ventricular dilation and pressure overload. BNP, a counterregulatory hormone, promotes excretion of salt by the kidneys and dilates blood vessels.
To determine the predictive value of BNP, 2525 patients were enrolled in a study (half having experienced a heart attack and the other half displaying unstable angina or chest pains). After a 30-day analysis, the researchers found that levels of BNP were higher among patients who died. Also, it was observed that patients with higher BNP were more likely to have a new or recurrent heart attack, develop heart failure, or experience progression of the disease process. Even in patients who had no detectable heart damage from a previous attack, elevated BNP levels identified individuals at high risk of dying or developing life-threatening cardiac complications (de Lemos et al. 2001).
An angiogram, referred to as cardiac catheterization, is a mechanism in which coronary arteries are luminated by injections of dye, a process that aids in diagnosing blocked arteries. A catheter is introduced through an incision into a large vein, usually of an arm or a leg, and threaded through the circulatory system to the heart. As the dye wends its way through the vasculature, blockages are detected by changes in flow rate at points of occlusion. An angiogram is a popular diagnostic tool, but it is not without risks. It is possible that the catheter will damage the artery or loosen a piece of plaque lining the artery wall. The dislodged plaque can block the flow of blood, causing a stroke. Thrombophlebitis, local infection, and cardiac arrhythmias are other valid concerns.
Data reported in the JAMA debated the relevancy of widespread angiogram usage (Graboys et al. 1987, 1992). A study chronicled 168 patients who were advised to have an angiogram to determine the need for either angioplasty or cardiac surgery: 80%, or 134, of the 168 patients who were evaluated noninvasively were determined not to need catheterization. From the 168 patients, an annual fatal heart attack of 1.1% was observed over a 5-year period compared to a 5-10% mortality rate from coronary bypass surgery and a 1-2% mortality rate from angioplasty. The conclusion of the published report was that noninvasive testing to access the heart's performance is a better and safer determinant of a suitable therapeutic program than searching for blocked arteries. If the patient fails some of the noninvasive tests, an angiogram is warranted to determine the need for surgery (Murray 1999).
Magnetic Resonance Imaging
Up to 70% of heart attacks occur in blood vessels that appear normal on an angiogram. The journal Circulation reported that plaque without any calcium deposits is not detectable by angiograms or CT scans, but it is the most common cause of sudden death from a heart attack. While calcification may lead to a more extensive form of heart disease, it is less likely to lead to a heart attack (Fayad et al. 2000, LEF 2000).
Fatty buildup on arterial walls, although not detectable by an angiogram, can result in a small fraction of plaque breaking free. The circulating particle ultimately increases the risk of a heart attack or stroke.
A special type of MRI, with a sensitive screening technique, is promising in regard to detecting even a slight buildup in coronary arteries, including plaque without calcium deposits. This is especially praiseworthy since coronary arteries are very small and the constant movement of the heart makes a clear image difficult. The newer technique, black blood imaging, blacks out the blood and produces an image of just the artery. Besides being of much greater advantage in diagnosing early-stage heart disease, this process is noninvasive. It is hoped that this newer, more responsible means of assessing the health of coronary arteries will become part of a routine check-up (Fayad et al. 2000).
Coronary Bypass Surgery
Blocked arteries are not always prognosticators of an impending heart attack. The Coronary Artery Surgery Study (CASS) demonstrated that heart patients with healthy hearts, but with one, two, or three of the heart vessels blocked, did amazingly well without heart surgery. The number of blockages did not alter the 1% a year death rate observed in the study groups (Hueb 1989; Alderman et al. 1990).
A study conducted by researchers in Iowa and published in the New England Journal of Medicine evaluated the efficiency of arteries that were 96% blocked (diagnosis made by angiogram) (White et al. 1984; CASS Principle Investigators, 1983, 1984). The researchers found that arteries blocked 96% had a greater thrust of blood than similar arteries only 40% blocked. The conclusion of the report was that the degree of closure did not correlate to the briskness of blood flow. Michael Murray, N.D., states that the most critical assessment regarding the heart's performance is how well the left ventricular pump is working, not necessarily the degree of closure (Murray 1999).
It seems that aggressive procedures to open the vessels do not influence the course of the disease, except in the most advanced stages of atherosclerosis. Bypass appears most helpful when the ejection fraction is less than 40%. Many bypass procedures are performed when the ejection fraction is greater than 50%, a percentage that appears adequate for meeting the demands of circulation. (White et al. 1984; Winslow et al.1988; Murray 1999).
A study by Harvard Medical School's Department of Public Health revealed that 84% of patients who obtained a second opinion after being scheduled to undergo a heart bypass procedure were told that they did not need it. During the study's 2-year follow-up, there were no deaths in the group who canceled their surgeries based upon the second opinion (Perlmutter 2002). Often individuals undergoing the surgery live no longer and with no more quality than a matched group of patients treated without surgery. Conversely, if coronary bypass surgery or angioplasty is appropriately advised, the procedures definitely increase long-term survival and give symptomatic relief to about 85% of patients (Murray 1999).
Although coronary bypass surgery can bring relief to many patients, the procedure is weighted with danger and chance. Infections, problems with blood coagulation, nerve damage, and the possibility of a heart attack or stroke are risks that must be factored into the patient's final decision. According to Harvard researchers, up to 30% of patients have their heart arteries reclog badly in just a year. Few patients survive 10 years without needing retreatment, and high risk patients -- such as those who already have undergone repeat surgery -- reclog at even greater rates. It should be noted that morbidity and mortality rates vary considerably between hospitals. If considering any heart procedure, ask for an analysis of patient outcome.
Steven Whiting, Ph.D., states that although the odds of surviving bypass surgery have improved since the operation was first introduced, the risk of experiencing a decline in mental function following surgery has remained consistent since the 1980s. Signals of this type of decline may include difficulty following directions, mood swings, and short tempers. Many doctors have downplayed the importance of alterations in intellectual abilities that occur in about 50-80% of patients following bypass surgery, believing the decline to be temporary. It now appears a transient display of incompetency may predict an increased risk of intellectual instability several years later.
Researchers (reporting in the New England Journal of Medicine) followed 261 bypass patients for 5 years. Enrollees in the study underwent intellectual testing before and after surgery, as well as at the 6-week, 6-month, and 5-year interval. Intellectual function declined by 20-53% considering presurgical and postsurgical mental status. The decline was 36% at 6 weeks and 24% at 6 months. In 5 years after surgery, 41% of the patients had experienced neurocognitive impairment. The researchers concluded that an intellectual decline in patients following heart surgery was significantly associated with diminished mental abilities 5 years postsurgery (Newman 2001).
In 1977, Dr. Andreas Gruentzig introduced the procedure known as balloon angioplasty, and by 1980 balloon angioplasty had become a popular cardiac option. Angioplasty is used 3-10 times more often in the United States than in other developed nations.
Balloon angioplasty widens coronary arteries by inserting a specially designed catheter (a long, thin, bendable tube) with a balloon on its tip into a blocked coronary artery. After centering the tip of the catheter in the blocked area, the balloon is inflated, stretching the artery and compressing the plaque. The arteries do not fully constrict, which leaves a larger opening than before. Unfortunately, any procedure using an arterial catheter may cause plaque to be dislodged (resulting in a cardiovascular event) or the wall of an artery to be torn. Other concerns associated with angioplasty are arterial spasms and blood clots, fluid accumulation in the lungs, and impaired kidney function.
From the University of Giessen (Germany) comes a detailed analysis of 300 patients who underwent primary angioplasty for an acute myocardial infarction. At 1 year, 34% had experienced a cardiac event, 23% required repeat angioplasty, and 6% had died from cardiac disease (Peterson et al. 1994; Noninvasive Heart Center, Waldecker et al. 1995).
Dr. Eric Peterson (and associates) at Duke University Medical Center reported the following survival statistics among various age groups undergoing angioplasty:
Mortality After Angioplasty in 225,915 Patients
Chart extracted from material provided by The Noninvasive Heart Center, 2550 Fifth Avenue, Suite 706, San Diego, California 92103 firstname.lastname@example.org (619) 544-0200.
|Ages||30 Day||1 Year
After collaborating with several universities, Ian Gilchrist, M.D., cardiologist at the Penn State Milton S. Hershey Medical Center (Philadelphia, PA), announced that 178 angioplasty patients (from a total of 2064 subjects) experienced a heart attack, required additional surgery, or died, and 82% of those numbers experienced the trauma within 18 hours of the procedure. Gilchrist said that despite efforts to minimize risk, angioplasty complications are nonetheless common (Gilchrist et al. 2000).
The original focus of the trial was to establish the worthiness and dosage of eptifibatide, an IV platelet inhibitor. Dr. James Tcheng (associate professor of medicine at Duke University Medical Center, Durham, NC) reported that eptifibatide, a cost-effective drug, reduced the risk of major complications during angioplasty 40% in the first 48 hours following the procedure. While evaluating the worth of eptifibatide (a landmark study in itself) researchers were able to target the period requiring greatest watchfulness among angioplasty patients.
Continued . . .
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