Many patients with coronary heart disease have no chest pains or other symptoms indicative of ischemia (diminished blood flow and oxygen to the coronary arteries that supply the muscles of the heart). As such, this silent (asymptomatic) type of ischemia is treacherous and increases the risk of sudden and unexpected death and other cardiac events.
Symptoms, in any illness, are the body’s defense alert system, a good warning sign that allows the affected individual time to do something pre-emptive to protect itself and prevent serious complications, like in seeking prompt medical help. Silent ischemia could strike an individual surreptitiously, causing heart attack or even cardiac arrest. These are the sudden deaths we all hear about every now and then, where the victims do not even know or realize the dangerous situation they are in.
The mechanism
The muscles of the heart require oxygen and nutrition to function properly. These vital ingredients are in the blood which is supplied to these structures by the coronary arteries. If the blood supply is diminished because the coronary arteries are narrowed or blocked by arteriosclerosis (hardening of the arteries that reduces the luminal diameter of these arteries), the muscles are deprived of vital oxygen and nutrition. As a result, theoretically, angina pectoris (heart pains) ensues. But a significant number of heart patients, even with their coronary arteries narrowed, some of them blocked severely, somehow do not develop chest pains. These are the asymptomatic or silent ischemia patients who could be a walking time bomb.
Why “silent”?
When there is myocardial ischemia, it is logically expected that the individual will have chest pains, much like lack of blood to the leg will cause “Charlie Horse”-type pains, medically termed claudication (pain and spasm of leg muscles) and even gangrene. The explanation for silent ischemia of the heart muscles (asymptomatic patients) is not fully understood. Some of the theories include: the patient may have a high threshold for pains; the size of the affected muscles in the heart may be small; there may be some collateral circulation to the ischemic area; the ischemia may be of short duration; some persons may have self-denial; the person may have a defective “warning system,” related to some past brain injury, past heart attack (known or unknown), diabetes, past heart bypass or transplantation.
Etiology
The etiology or cause of narrowing of the arteries is multi-factorial. While heredity plays a role in the pathogenesis of arteriosclerosis, lifestyle appears to be the major culprit. This includes a high-cholesterol, high-fat, high-carbohydrate, low-fiber diet of red meat, eggs, dairy products, bread, potato, rice, pasta, cakes, and sweets, instead of fish, vegetables, fruits, nuts and grains. The other important factors are smoking, the lack of daily regimented physical exercises, excess body mass index (weight), and poor stress management. Alcohol abuse, inadequate treatment of existing or undiagnosed hypertension (high blood pressure) and diabetes mellitus are aggravating conditions that hasten the build-up of cholesterol plaques in the inner walls of the arteries that lead to blockages and resultant ischemia.
The minimum test
Obviously, the early detection of myocardial ischemia, especially among those asymptomatic (silent) cases, is essential. This can prevent sudden cardiac death. Since many of these persons have no indication whatsoever about the state of their coronary arteries and they all may be feeling “100 percent healthy,” the only prudent strategy is to do prophylactic (preventive) investigation. Based on medical statistics, the minimum test recommended is a stress electrocardiogram (Stress EKG) for those with chest pains or other symptoms suspicious of coronary heart disease. Those with a strong family history of coronary heart disease or heart attack and/or hypercholesterolemia and diabetes, regardless of age, should also have Stress EKG every 2 to 5 years, depending on the severity of their hypertension, hypercholesterolemia, diabetes or hyperthyroidism. For those with none of these illnesses and with no familial history of coronary heart disease, Stress EKG is nonetheless advisable when they are 45 and older, especially for those who smoke, and a mandatory test for pilots and some giant corporate executives. There are other more sophisticated tests available.
The supreme court of heart tests
To arrive at the final confirmatory diagnosis, a cardiac cath is performed. This is the “court of last resort,” the “supreme court” of heart tests, that will tell us, once and for all, with 100% accuracy, if there are stenoses (blockages) in the coronary arteries or not, how powerful or weak the ventricular contraction is, the integrity of the heart muscles, in segments and as a whole, and if there are any other cardiac abnormalities present, like heart valve disease, etc. If there are coronary artery stenoses present, this angiogram, which is recorded in a video film (movie of the heart in action), will also show which arteries are blocked, how many percent obstruction there is (are) and the exact location of the blockage(s). The findings will also help the cardiologist and the cardiac surgeon make a final decision if heart surgery is needed or not, and if it is, what procedure to do, which arteries to bypass, blocked arteries) will be, the percentage of risk of the surgery, and the prognosis.
Clinical highlights
Various investigative studies have been done to address this particular issue on silent ischemia, its diagnosis and treatment. To of these trials are the ACIP (Asymptomatic Cardiac Ischemia Pilot) and the ASIST (Atenolol Silent Ischemia Study). The findings are as follows: (1) Silent cardiac ischemia could lead to sudden cardiac death; (2) In the ACIP trial, it has been shown that revascularization, using coronary angioplasty or bypass surgery provided more effective relief of the ischemia than medical (pill) therapy alone; (3) In the ASIST study, those treated with Atenolol showed great reduction of ischemia and the risk of future events compared to those who were given placebo (“sugar” pills, in the controlled group); (4) the prevalence and risk of cardiac events have been much less where ischemia has been treated with revascularization; (5) that risk factor modification (lifestyle and behavioral changes: cessation of smoking, abstinence from red meat and eggs, a diet of fish, vegetables, fruits, nuts and grains, daily exercises), together with aggressive treatment as in numbers 2 and 3 above, reduces or eliminates myocardial ischemia, left ventricular dysfunction, and the incidence of sudden cardiac death. It is obvious that a pre-emptive strike, a prophylactic strategy, on everyone’s part is the only way to beat sudden cardiac death.
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Philip S. Chua, MD, FACS, FPCS, Cardiac Surgeon Emeritus in Northwest Indiana and chairman of cardiac surgery from 1997 to 2010 at Cebu Doctors University Hospital, where he holds the title of Physician Emeritus in Surgery, is based in Las Vegas, Nevada. He is a Fellow of the American College of Surgeons, the Philippine College of Surgeons, and the Denton A. Cooley Cardiovascular Surgical Society. He is the chairman of the Filipino United Network – USA, a 501(c)(3) humanitarian foundation in the United States. Email: [email protected]
