If you have one or more risk factors for coronary heart disease, your doctor is likely to recommend that you undergo one or more diagnostic tests beyond the basic physical exam (during which a medical professional measures your blood pressure, takes your pulse, and listens to your heart with a stethoscope). These additional cardiac tests can help determine if you may already have had a silent heart attack (the kind with no symptoms). Remember that about half of all persons with coronary heart disease have the asymptomatic version, or silent heart disease.
If it’s determined you already have had a heart attack, the tests can also determine how much of your heart was damaged and also what degree of coronary artery disease you may have. The tests screen your heart and help the doctor determine what treatment and lifestyle changes will help keep your heart healthy and prevent serious future medical events.
If that sounds scary, it shouldn’t. Most cardiac tests today are noninvasive or minimally invasive. There are scores of cardiac tests available today, and in this chapter we’ll review the most widely used ones.
Perhaps nothing better illustrates how far cardiac diagnostic testing has come than the history of the Holter monitor, whose origins harken back to the 1930s. That’s when physicist Norman J. Holter began his pioneering studies in the electric potentials of muscles, nerves, and brain waves. The rapid advancements in electronic technology in the early twentieth century, such as the cathode ray oscilloscope (the same technology used in TV sets and computer monitors before the advent of flat screens) and other innovations developed during World War II, enabled the design of a system for sending electrical impulses from the human body through the air to a recorder.
Holter’s device marked the beginning of radio-electrocardiography. Previously, cardiologists were limited to examining a patient’s heart with the standard electrocardiogram for a one-minute period, during which time they might have sixty to seventy heartbeats to review. Holter’s device permitted an evaluation of up to ten hours of heart action, and because the device was portable, the measurements could be taken in real-world circumstances, like a patient’s home or workplace, not just in the physician’s office or a researcher’s laboratory. As a result, for the first time, measurement of the effects of the stress of ordinary life and work activities on heart action provided a much more accurate evaluation of cardiac health.
It was a miracle! Nevertheless, the first Holter “portable” devices weighed eighty-five pounds, and the first patients to use them literally had to wear a backpack to carry them. The invention of the transistor in 1952 permitted miniaturization of the early transmission equipment into a relatively light, four-pound recording device. The need for NASA to measure astronauts’ vital functions in space further refined and miniaturized the equipment. Fast-forward to the twenty-first century and today’s version of the Holter, which only weighs four ounces and can be worn around the neck on a chain. Competing cardiac monitors, or ambulatory electrocardiography devices, include the popular Zio, which is the size of a Band-Aid and is applied to the skin in the same way, with no loose wires or batteries to charge.
On a personal note, the Holter device was instrumental in my first published findings on silent heart disease fifty years ago. My research colleagues and I analyzed literally tens of thousands of magnetic tapes, which was how Holter devices recorded patients’ electrocardiograms at the time, to help formulate our underlying theory that reduced blood flow to the heart (ischemia) could occur without pain. Our findings were published in a paper titled “Clinical Applications of Dynamic Cardiography,” but in retrospect perhaps we should have simply called it, “Thank you, Dr. Holter.”
Today’s cardiac monitor devices essentially perform the same function as the early Holter devices—recording the electrical activity of the heart during daily activities. In developing your cardiac risk profile, your doctor may ask you to wear a monitor to see if you have an arrhythmia —that is, a slow, fast, or irregular (uneven) heartbeat. Or your doctor may use it to see how well your medicines are working to treat these problems. If you have a pacemaker and feel dizzy, a monitor could determine if your pacemaker is working properly.
The monitors pose no risk, and wearing one isn’t painful. You can carry the monitor in a pocket or pouch, slung across your shoulders or worn around your neck like a purse or camera, or attached to your belt. You can perform all your usual activities while you wear the monitor with these exceptions: don’t bathe, shower, swim, or have X-rays while wearing the monitor, and stay away from high-voltage arc metal detectors or large magnets.
A technician will teach you how to keep a diary of your activities and symptoms during the test. It’s important to keep an accurate diary. If you feel symptoms such as chest pain, shortness of breath, uneven heartbeats, or dizziness, note in your diary the time of day they began, how long they lasted, and what you were doing at the time. Your diary will be compared to the changes in your EKG recorded by the Holter monitor.
Now, your doctor may deem your wearing a portable cardiac monitor unnecessary and conduct an electrocardiogram in the office for a onetime measurement. Whether done via portable monitor or in the office, the test measures the same thing, recording the electrical activity of the heart, including the timing and duration of each electrical phase of your heartbeat.
With each beat, an electrical impulse (or “wave”) travels through the heart. This wave causes the heart muscle to squeeze and pump blood from the heart. An EKG will show the timing of the heart’s upper and lower chambers. The right and left atria, or upper chambers, make the first wave, called a “P wave.” The line flattens while the electrical impulse goes to the bottom chambers. The right and left bottom chambers, or ventricles, make the next wave, called a “QRS complex.” The final wave, or “T wave,” represents electrical recovery, or return to a resting state for the ventricles.
An EKG gives two major kinds of information. First, by measuring time intervals on the EKG, a doctor can determine how long the electrical wave takes to pass through the heart. Finding out how long a wave takes to travel from one part of the heart to the next shows if the electrical activity is normal or slow, fast or irregular. Second, by measuring the amount of electrical activity passing through the heart muscle, a doctor may be able to find out if parts of the heart are too large, are overworked, or are not working properly.
The goal for each type of EKG is also the same—to determine if there’s an arrhythmia, to discover if a heart attack has occurred in the past or is presently occurring, and to help predict if a heart attack is developing by monitoring changes in heart rhythm and other functions of the EKG.
Using an X-ray, pictures are taken of the structure and organs inside your chest, like your heart, lungs, and blood vessels. They can show if there are signs of heart failure, including whether the heart is enlarged or fluid is accumulating in the lungs as a result of heart failure. However, a chest X-ray doesn’t show the inside structures of the heart.
In this test, a technician positions the patient next to the X-ray film. An X-ray machine will be turned on for a fraction of a second. During this time, a small beam of X-rays passes through the chest and makes an image on special photographic film. Sometimes two pictures are taken—a front and side view. The X-ray film takes only a few minutes to develop. Sometimes your cardiologist needs more than just the front and side chest X-rays.
There’s no pain involved, and the amount of radiation used in a chest X-ray is very small—one-fifth the dose a person gets each year from natural sources, such as the sun and the ground. While this small amount of radiation isn’t considered dangerous, the levels of exposure for a given test need to be considered in the context of other radiationutilizing tests that may be part of the cardiac diagnosis, since the possible cumulative effects of repeated radiation exposure are of concern. However, pregnant women should avoid even this low level of radiation whenever possible.
This is a common test in which a handheld device, placed on the chest, uses high-frequency sound waves (ultrasound) to produce images of your heart’s size, structure, and motion. It helps your doctor check if there are any problems with your heart’s valves and chambers and to see how strongly your heart pumps blood. An echocardiogram performed before and after exercise is also used to detect areas of the heart where the blood supply through the coronary arteries to the heart muscle is reduced (see “exercise stress test” below).
Also known commonly as a CT or CAT scan, computer imaging (tomography) refers to several noninvasive diagnostic imaging tests that use computer-aided techniques to gather images of the heart. A computer creates a three-dimensional image of the heart’s chambers and coronary arteries supplying blood to the heart. It can show blockages caused by calcium deposits in the coronary arteries.
When contrast dye (iodine) is given during the scan, the test can be used to show blockages in the heart arteries. This is useful in patients with chest discomfort to see if the discomfort comes from lack of blood flow to the heart muscle caused by blocked heart arteries (angina). If the heart arteries are normal, the doctor can confidently look into other causes of chest pain that aren’t related to the heart. A CT scan can also be used to check if coronary artery bypass grafts remain open, check for congenital heart defects (problems present at birth), and also check how the ventricles are working.
In this test, also known as treadmill or exercise cardiac stress test, a monitor with electrodes is attached to the skin on the chest area to record your heart function while you walk and/or run in place on a treadmill. Many aspects of your heart function can be checked, including heart rate, breathing, blood pressure, EKG, and how tired you become when exercising. It also can help determine your safe level of exercise and helps predict dangerous heart-related conditions such as angina pectoris (chest pain) or heart attack.
In a magnetic resonance imaging (MRI) test, you lie on a table inside a long tubelike machine that produces a magnetic field, which aligns atomic particles in some of your cells. Radio waves are broadcast toward these aligned particles, producing signals that create 3-D images of your heart.
When your heart muscle has been damaged, as in a heart attack, your body releases substances into your blood. Blood tests can measure the levels of these substances and show if, and how much of, your heart has been damaged.
A common test after a heart attack checks the level of troponin in your blood. Troponin is a group of proteins found in cardiac muscle fibers that regulate muscular contraction. Increased troponin levels occur when the heart muscle is strained or during the course of an acute heart attack.
Blood tests are also done to measure the level of other substances in your blood, such as blood fats (e.g., cholesterol and triglycerides) and minerals. For example, a blood test can measure levels of vitamin D, which is normally obtained via sunlight and foods such as mushrooms and fortified foods. A low vitamin D level has been associated with high blood pressure, arterial damage, congestive heart failure, poor brain health, and other important problems.
Another widely available blood test can measure Lipoprotein-a, or Lpa, an inherited form of low-density lipoprotein (LDL) bound to a special protein. Studies have shown a correlation between high levels of LDL and early cardiovascular disease.
Another blood test determines your level of ferritin, a protein in the blood that binds with iron. An iron overload can oxidize cells in the arteries, leading to heart disease, and can make blood more prone to clotting. Yet another blood test can measure uric acid. An elevated level is linked to cardiovascular damage and generalized cell membrane dysfunction.
As noted in Part II, a blood test can determine the level for a biomarker for inflammation, which may occur during a heart attack. A high C-reactive protein level is usually a red flag that something in your lifestyle or health is amiss and should be eliminated or otherwise corrected.
Research over the last forty years has revealed that increased levels of homocysteine, an amino acid, may be associated with increased risk of vascular damage. A safe homocysteine level, as determined by a blood test, is under ten micromoles per liter, and patients with high levels can be treated with B complex vitamins, which is a pretty simple solution.
Beyond these commonly used tests, your cardiologist today has an arsenal of more specialized cardiac diagnostic tools. Here’s a quick rundown of some the most widely used of them:
•Advanced cholesterol panel: Two people with an LDL level of 100 mg/dL can have different heart disease risks because it’s possible that they have widely different particle numbers and sizes. An advanced cholesterol panel blood test can tell you more about your LDL particle number and size, which may yield important clues to silent signs of clogged arteries.
•Carotid intimal medial thickness (CIMT) test: This exam uses an ultrasound machine to see inside the major carotid artery in the neck, which connects the heart to the brain. The ultrasound shows the thickness of the inner two linings of the wall of the artery (if these walls are getting too thick, it’s a sign of early atherosclerosis). This test has received a high recommendation from the American College of Cardiology, and more than five hundred scientific studies speak to its effectiveness.
•Endopat: Healthy arteries spring back quickly after being squeezed, for example, by a blood pressure cuff. When blood vessels don’t spring back, it is a sign of diseased arteries. When Mayo Clinic researchers did this test on more than 250 people and tracked their health for six years, those with poor blood flow had a higher risk of heart attack or death. Note: It’s possible to have full-blown coronary artery disease (and even to have undergone bypass surgery or stenting) and still have normal artery function.
•Cardiac catheterization: This test examines the inside of your heart’s blood vessels using a special X-ray imaging technique called angiography. A thin hollow tube called a catheter is threaded through a blood vessel in the arm, groin, or neck to the heart. Dye is injected from the catheter into blood vessels to make them visible by X-ray. This test is also particularly helpful in evaluating chest pain to show if plaque is narrowing or blocking coronary arteries and in measuring blood pressure within the heart and the amount of oxygen in the blood.
Which cardiac tests are best for you will be decided by you and your doctors. However, doctors do follow sets of general guidelines that classify your condition to identify your risk factors and begin early, more aggressive treatment to help prevent heart attacks or heart failure. The two systems used to classify cardiac failure are these:
•New York Heart Association classification. This symptom-based scale classifies heart failure into four categories. In Class I heart failure, you don’t have any symptoms. In Class II heart failure, you can perform everyday activities without difficulty but become winded or fatigued when you exert yourself. With Class III, you’ll have trouble completing everyday activities. Class IV is the most severe, leaving you short of breath even at rest.
•American College of Cardiology/American Heart Association guidelines. This stage-based classification system uses letters A to D. The system includes a category for people who are at risk of developing heart failure. For example, a person who has several risk factors for, but no signs or symptoms of, heart failure is designated as Stage A. A person who has heart disease but no common symptoms of heart failure, such as fatigue or shortness of breath, is designated as Stage B. Someone who has heart disease and is experiencing or has experienced signs or symptoms of heart failure is designated as Stage C, and a person with advanced heart failure requiring specialized treatments is designated as Stage D.
These scoring systems are not independent of each other, and your doctor might use them together to help determine your most appropriate treatment options. Once your tests are complete, your doctor can help you interpret your score and plan your treatment based on your condition.