The Noninvasive Heart Center
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ABOUT STRESS TESTS


Most cardiologists believe that stress tests can be used to detect the presence of coronary artery disease in patients believed to be at increased risk whether or not they have symptoms such as chest pain. The stress part of such tests is commonly carried out on a treadmill or bicycle ergometer while recording an electrocardiogram, a nuclear imaging procedure or an echocardiogram. Because some patients are unable to exercise on a treadmill, a drug is administered intravenously to these individuals to increase their heart rate. This is called a pharmacological stress test. Regardless of which stress is used, the goal of the stress test is to increase the patient's heart rate to a predetermined rate that is determined by the patient's age. It is believed by most doctors that if the test is abnormal, then this means the patient has obstructive coronary artery disease of sufficient degree to interfere with flow of blood to the heart muscle. When this happens, the heart muscle is said to be ischemic.

Ischemia does not occur at normal heart rates in most patients because at rest, with a normal heart rate, the heart muscle's need for blood is comparatively small, and the amount of obstruction of the coronary arteries is not great enough to reduce the flow of blood to the heart muscle. During stress, however, when the heart rate speeds up, and the heart has to work harder, the heart muscle requires a great deal of extra blood to generate the energy needed to perform the extra work. Now, the obstruction to the coronary arteries may be great enough, to prevent the blood flow from increasing, and the heart muscle will become ischemic. Think of a 4 lane freeway with one or two blocked lanes. When traffic is light there will be no slowing of traffic. During rush hour, however, marked slowing of traffic will take place.

Ischemia produces distinctive changes in an electrocardiogram, in a nuclear perfusion study, and in the contraction of the heart muscle that can be seen on an echocardiogram. When these tests are abnormal, most cardiologists immediately assume that one or more coronary arteries are severely obstructed, and that coronary artery bypass surgery or angioplasty will be necessary to eliminate the blockage.

Little or no consideration is given to the possibility that there may be other reasons for the test being positive. Nor is there consideration of the fact that if there is obstructive coronary artery disease, it may have been present in silent form for years, and that there is another cause for both the patient's chest pain and for the test becoming abnormal. Indeed, there are multiple reasons to explain why stress tests become abnormal, and those reasons have nothing to do with the coronary arteries being obstructed. Failure to consider these other explanations in patients with coincidental and asymptomatic coronary artery disease has resulted in hundreds of thousands of such patients undergoing unnecessary angiograms, angioplasty or coronary artery bypass surgery every year!

OTHER EXPLANATIONS FOR POSITIVE STRESS TESTS

The most common cause of abnormal stress tests in the absence of obstructive coronary artery disease is hypertension. Blood pressure invariably rises during stress tests, particularly so in those patients who have hypertension. Both the patient and doctor are often unaware of the hypertension because such patients frequently have relatively normal blood pressures at rest. However, their blood pressures will rise to very high levels during stress.

The mechanism of how hypertension can cause chest pain and ischemia of the heart muscle is similar to the changes that occur when a blood pressure cuff is inflated while taking someone's blood pressure. Air is pumped into the cuff until the pressure in the cuff exceeds the pressure within the artery. When that happens the pressure within the cuff is transmitted to the tissues of the arm to the brachial artery causing it to collapse. In fact, in case of injury to an extremity from an accident, a blood pressure cuff can be inflated above the arterial pressure. It will now act like a tourniquet and stop any bleeding that might be present.

In the case of the heart, the elevated pressure within the circulatory system during a stress test is transmitted back to the heart's chambers, specifically the cavity of the left ventricle. If that amount of pressure were transmitted to the inside of the stomach, it would inflate the stomach like a balloon. However, the heart muscle is too thick to be distended. In addition, the tough membrane around the heart known as the pericardium will prevent the heart from becoming larger. Consequently, the high pressure within the cavity of the left ventricle is transferred directly to the heart muscle in the same way the pressure within a blood pressure cuff is transmitted to the arm and brachial artery.

Depending upon the amount of elevation of the blood pressure within the cavity of the left ventricle, the small blood vessels within the heart muscle will all be compressed causing a reduction in the amount of blood that can reach the heart muscle cells. If the reduction in blood flow is great enough, the heart muscle will become ischemic causing the stress test to become abnormal, and the patient to experience chest pain. Numerous research studies, particularly in the European medical journals, have reported patients with high blood pressure, chest pain, abnormal stress tests, and normal coronary angiograms. In other words, the abnormal stress test is not due to blockages within the main coronary arteries.

A second important reason why stress tests are often artifactually abnormal is the marked increase in heart rate that takes place, by design, in patients undergoing such testing. A little bit of background information is necessary to understand what happens when the heart rate speeds up. In a subject with a heart rate of 60, each heart beat lasts for one second. Approximately 0.3 second is occupied by the contraction of the heart. The remaining 0.7 second is for the relaxation of the heart. While all tissues of the body receive blood continuously throughout both contraction and relaxation of the heart, this cannot occur within the heart muscle itself while the heart is contracting for reasons described in the preceding paragraph. In other words, the high pressure that is generated within the cavity of the left ventricle to provide the pressure to circulate the blood, prevents any flow of blood within the heart muscle itself. Thus, blood can only flow within the heart muscle while the heart is relaxing. The actual amount of time available for the heart muscle to receive its blood supply is a little less than 0.7 second.

For whatever reason evolution has made the heart the way it is, when the heart rate speeds up, it does so more at the expense of the time available for relaxation than for contraction. Accordingly, at a heart rate of 150 per minute, each heart beat lasts only about 0.4 second. Contraction now takes about 0.2 second and relaxation also takes only about 0.2 second. That's not a lot of time---hardly enough time for the heart muscle to receive the amount of blood it requires to work that hard. What happens? The muscle becomes ischemic regardless of whether there is any blockage in the subject's coronary arteries.

The third reason why heart muscle may become ischemic during a stress test in the absence of significant obstructive coronary artery disease is similar to what happens when a telephone switchboard literally becomes overloaded with incoming calls during a catastrophe. All the calls cannot get through because of circuit overload. All of us develop coronary artery disease as we get older---it is an aging phenomena. If there are areas of narrowing, the heart rapidly adapts and grows new blood vessels around the narrowed artery through a process called angiogenesis. In a sense the heart puts in its own bypasses. This is the same process that grows new blood vessels for cancer cells and tumors within the body, since such growths cannot survive without a blood supply. Indeed, one of the ways of treating cancer is to destroy its blood supply.

The network of new vessels that grow around narrowed coronary arteries, are known as collateral vessels, and are too small to be seen on an angiogram. Nevertheless, such vessels not only allow a normal flow of blood to the heart muscle, but ensure normal contraction of the heart muscle as well. This network of collateral vessels that develop around obstructed coronary arteries keep the heart muscle well oxygenated as long as the heart rate is not too high. Incidentally, these small vessels cannot be seen on an angiogram, and this explains why cardiologists often tell patients their arteries are blocked and they are in danger of a heart attack. Since the angiogram technique does not allow visualization of either these small vessels nor the heart muscle they supply, and since there is no blockage of blood flow, such interpretations are often grossly inaccurate and unwarranted.

Like a telephone switchboard that becomes overloaded, or in the same way that multiple small roads cannot carry the volume of traffic that a four lane freeway can, these small vessels are also limited in the amount of blood they can carry. Accordingly, at very rapid heart rates, when the heart muscle requires large increases in blood to perform the increased work it must do, the circulatory system is unable to keep up with the increased load. This causes the heart muscle to become ischemic, the stress test to become abnormal, and the victim to have chest pain.

Now combine reasons one, two and three, and it should be obvious that not only are stress tests unreliable to detect coronary artery disease, they should never be used! In medical terms, stress tests that are carried out to extremes of heart rate and blood pressure increases cause physiological ischemia. If I put my hands around your neck and choke you until you turn blue, and take an electrocardiogram, and it is abnormal, it does not mean you have heart disease anymore than if you were to get short of breath after you ran up five flights of stairs. This, then, is physiological ischemia. Pathological ischemia would be present if ordinary activities such as walking across a room or getting dressed produced chest pain or shortness of breath. But one doesn't have of undergo a stress test to find out that information.

The tragedy of all of this is that the most commonly used noninvasive test for the detection of coronary artery disease leads to an even more inaccurate invasive test-the coronary angiogram. Massive amounts of medical studies over the past 45 years have testified to the inaccuracy of angiograms. Yet they continue to be used upon an unsuspecting and uninformed public, are proclaimed to be the "gold standard" and like a black hole that sucks everything in, even light, stress tests continue to suck patients into undergoing unnecessary interventions, procedures, and surgery that are not only not effective but kill more people than they save.

ALTERNATIVE TO STRESS TESTS----MECHANOCARDIOGRAPHY

BACKGROUND: One of the techniques the Noninvasive Heart Center uses to study the heart is called mechanocardiography, or the science of studying the mechanical function of the heart. To put things in perspective, the heart may be likened to an automobile. An automobile has two systems: (1) an electrical system for the lights, horn, ignition, radio, etc, and a mechanical system for turning the wheels. Similarly, the heart has two systems: (1) an electrical system for electrically activating the heart so it can beat once a second, and (2) a muscle system to contract and pump blood from the heart's chambers, followed by relaxation so that it can fill with blood for the next heart beat. One would not check the voltage of a car battery to determine the performance of a car. Similarly, an electrocardiogram cannot be used to study the function and performance of the heart. For example, an individual might have a terrible looking electrocardiogram but be able to play basketball or run a marathon race. Conversely, a patient might have chest pain with walking less than a block due to coronary artery disease, but have a completely normal electrocardiogram. Experience has taught us that survival and prognosis are not related to the electrical output of the heart (the electrocardiogram) any more than the voltage of a battery will predict the life of a car.

In the same way that the electrocardiogram cannot provide information about the heart's function, neither will listening to the heart with a standard stethoscope provide this kind of information. The diseased heart does develop abnormal sounds and murmurs. Unfortunately, in all but the most advanced states of disease, those abnormal sounds and murmurs are of such low or high frequencies that they cannot be heard by the human ear.

As a result of these limitations, a variety of noninvasive procedures have evolved over the years. One of these procedures is called mechanocardiography and enables doctors to obtain mechanical and functional information about how the heart contracts and relaxes on a moment to moment basis throughout the cardiac cycle. This is accomplished by the graphic recording of physiological and pathological events from the heart by external recording instruments that are placed directly over the heart and blood vessels.

Such instruments record the exact moment the pressure begins to rise within the left ventricle as the cardiac muscle begins its contraction, the moment the heart valves (the mitral and tricuspid valves) close, and the force with which they close, the duration of time in milliseconds it takes for the heart to generate the required pressure to force the aortic valve (the exit valve) open, the precise moment the aortic valve opens and allows blood to leave the heart, the duration of time it takes for blood to be ejected from the heart, the exact moment the aortic valve closes allowing the heart to relax, the duration, also in milliseconds, of how long it takes for the heart to relax, the amount of time required for the initial filling of the heart, the relative pressure required to do this, and the relative amount of pressure and time required for contraction of the left atrium.

In addition, the analog readout provides an accurate picture of how well, or how poorly the ventricle is contracting. At the same time, the instrument records other physiological or pathological events of the heart's contraction and relaxation such as any abnormal sounds or heart murmurs, how rapidly blood is ejected into the circulation, and whether there is any obstruction to blood flow at the aortic valve. The duration of these various intervals of the cardiac cycle reflect the performance of the heart in the same way that timing how long it takes for a car to go from zero to 60 miles an hour is a reflection of the performance of a car. In a like manner, how long it takes for an engine to start after turning the key in an ignition, how long it takes to accelerate, how long it takes to brake or stop each reflect different components of a car's performance.

Similarly, the duration of the various phases of the contraction and relaxation of the heart reflect the performance or function of a different part of that heart. For example, a heart that takes 375 milliseconds rather than the normal 300 milliseconds to eject its quota of blood during a single heart beat has an entirely different problem, and requires a different treatment than a heart that takes 175 milliseconds to relax instead of the normal 100 milliseconds. Yet, both abnormalities may cause identical symptoms. Thus, modern technology can serve as an early warning system to identify component failure and correct it, rather than to wait for total failure of the whole heart, as is currently being done. In the former instance, specific drug treatment can be selected. In contrast, most conventional methods of examination do not become abnormal until there is total system failure. When drug therapy is recommended with total system failure, there is little understanding of what specifically is wrong, and what specific drug should be used to counteract it. Instead, the doctor guesses, and often, unfortunately, guesses wrong.

Another important group of noninvasive tests that are now incorporated into the technique of mechanocardiography is echocardiography, including color and spectral Doppler. The following data is just some of the information that can be obtained from this cardiac imaging group of tests.

  • Localized abnormalities of motion of heart muscle due to obstructive coronary artery disease.

  • Flow of blood in heart muscle.

  • Thickness of heart's muscular walls.

  • Presence of scar formation from prior heart attacks.

  • Dimensions of the heart's chambers.

  • Blood clots within the heart's chambers.

  • Structure and motion of its valves.

  • Obstruction or leakage of valves.

  • Presence of calcium in heart valves.

  • Heart murmurs: their origin, and the volume, velocity and pattern of blood flow through each valve.

  • Systolic and diastolic heart function.

  • Fraction of blood ejected each beat.

  • Presence of tumors and congenital heart defects.

The parameters that are measured are placed in a database for that patient. The information can be used in a stand alone fashion to evaluate the function of the patient's heart and to arrive at a predicted prognosis. At future office visits, repeat recordings are obtained and compared to prior recordings. The patient's medical program is then adjusted accordingly.

The various parameters that are recorded by this technology allow a doctor experienced in their interpretation to identify heart disease at a very early stage long before symptoms or complications appear. He also may determine how advanced the patient's disease is, track its progression, determine the effect of drug treatment, modify that treatment to optimize it, and identify unpredictable changes in cardiac function so that they can be reversed. The information provided allows almost all patients to avoid future coronary artery bypass surgery, angioplasty, heart attacks, congestive heart failure, and unexpected cardiac death.

In summary, most cardiologists depend upon a stress test and only the angiogram to provide the necessary information on which to make a decision as to how a patient should best be treated. Both kinds of tests are highly inaccurate, and lead to unnecessary interventions with angioplasty, stents and bypass surgery all of which have their own set of complications. Noninvasive tests, in contrast, are vastly more informative, far less costly, very safe, and can be repeated as often as necessary to track a patient's disease.