The echo - echocardiogram - is the quickest, safest test available that gives so much information about your heart. An echo can detect and measure valve disease, heart size, blood flow, clots inside the heart, EF, heart wall motion, pressures inside the heart, and more. It is less expensive than MUGA and more clinics have the equipment to do an echo. There is no dye or radioactive tracer used. There are no needles and no pain.
Like any test, it's not perfect. It's hard to get good echo results in people with lung disease; The technician's skill affects the test's accuracy; It's no good for checking the right side of the heart. Still, with a skilled technician, EF can be measured with no more than +/- 8% error. The test equipment itself costs about $100,000 and good techs don't come cheap, so an echo costs from $500 to $1000. Echocardiograms are covered by health insurance 99% of the time.
Echos use ultrasound. Ultrasound is sound that is so high pitched it is beyond the range of normal human hearing, at a frequency of 18,000 to 20,000 cycles per second. The echo machine sends sound waves to a transducer (a hand-held sound-sensitive device) that is placed on the chest. The sound waves are reflected by the heart walls and valves back through the transducer to the machine.
High-powered software puts together a picture of your heart from the returned sound for the doctor to examine. That same software also gives a lot of information about your heart's function through the numbers on the monitor screen. The whole test is recorded on video tape.
This test can be done in your doctor's office if he has the equipment, but it is usually done in a clinic or hospital. You will have to strip to the waist, so ask for a gown if you are cold or modest. You may be connected to an EKG machine through small, sticky electrode patches stuck to your upper body (the usual).
You will lie on your left side on a padded table that has a small section cut out of it on one side next to your chest. This sounds uncomfortable but it really isn't. The cut-out is so the tech can easily get to your entire heart area. Some gel will be rubbed on your chest to improve the quality of the sound waves. This stuff is cold!
The tech will place the transducer - it looks like a big electric shaver - against your chest. He will move this around your chest and side to get the information your cardiologist has ordered. At times, he will use a lot of pressure, which can get very uncomfortable but that is fairly brief. You may be asked to change positions slightly now and then for better pictures. You will be asked to hold your breath a few times as well, but not for long.
The pictures will be displayed on a monitor in front of the tech. You can watch the monitor too. You will be able to hear your heart sounds, although often they will sound distorted. An experienced tech doesn't mind conversation and will usually explain whatever you ask about. This can be a very educational and fascinating procedure if you ask enough questions! The software is very sophisticated and the pictures are amazingly clear.
How long the test takes depends on what information your cardiologist told the tech to get. If a lot of info was requested, it may take up to 45 minutes. When it is done just for a few numbers, it can take as little as 10 minutes. When the test is done, the gel is wiped off with a towel, you get dressed and you're done! No pain, no strain, just the way we like it.
A good tech can guess your EF during the echo, but you never know how good the tech really is. Besides, he doesn't know your medical history and that can make a big difference. Echo results are not easy to interpret. For these reasons, take his guess (if he does) with a big grain of salt. Some echo techs have hit my "numbers" on the nose but others have been off by as much as 15%. Your cardiologist will read the echo and write a report for your chart. He will give you the official results and his results are more accurate than the tech's.
As far as I know, there are none.
Don't take your diuretics too soon before the test or you'll have to excuse yourself partway through. Don't eat a big meal before the test.
More than 5 million echos are done each year in the USA. Medicare saw a 170% increase in the number of echos done from 1986 to 1993. They also saw a rise in echo charges from $190 million in 1986 to more than $1 billion in 1994. Echo plays a large role in heart failure diagnosis and treatment.
Given the cost and the huge number of echos done every year, interpreting echo results would seem like a critical quality control issue. However, when we searched journals, textbooks and guidelines for doctor training, we discovered that interpreting echo findings was not even mentioned.
Interpreting measurements To understand how a measurement is interpreted, we look at how lab work and blood testing is done. When ordering a blood test, the question the doctor wants to answer is, "Does the measurement indicate health or illness?" If the measurement seems unhealthy, the next question is "How unhealthy is it?" The doctor compares the measurement to a standard called a reference value, or with previous results of the same test on the same person. The second question is answered by seeing how far the result is under or over the reference value.
Reference Values We don't use the term "normal" anymore. Instead, we use the term "reference values." There are accepted ways to develop reference values. A few basic principles are listed here:
Limits "Reference limits" are measurements taken from healthy people. "Discrimination limits" are the overlap between healthy values and values from people with disease. Finding discrimination limits requires studying a lot of people both with and without disease. A study that describes reference values should describe the population measured, the way participants were chosen, how measurements were taken and under what circumstances, and how the values were calculated.
Partitioning Dividing reference values by age, sex, or other characteristics must be done if measurements are different from one group to the next for a physical reason. For example, you would not group measurements of men's sex hormones with measurements of women's sex hormones; You have to "partition" them into 2 groups - male and female - to get useful results. The issue of partitioning by age has gotten more important due to the general population being older.
Sample Size At least 120 to 200 people are needed for reliable reference limits.
We searched electronic databases, medical textbooks, and scientific tables for echo reference values for adults. There was a lot of variation in reference limits used. Only 3 studies were based on large samples. There were differences in patient selection and in measurement techniques. Most echo reference values were not compared to patient outcomes. The ranges were:
|Reference values used for heart size|
|left atrium||36 to 47 mm|
|aortic root||33 to 44 mm|
|left ventricular end-diastolic diameter||52 to 70 mm|
|left ventricular end-systolic diameter||30 to 40 mm|
|left ventricular wall thickness||11 to 13 mm|
Partitioning When developing cut-points that separate "illness" from "health," testers must decide which measurements to use, because echo dimensions vary according to sex, age, and race. Most reference values we found were not partitioned at all. It was one size fits all, which simply cannot be accurate.
Sex The impact of sex on heart size and measurements is well known. Autopsy data, x-ray studies, and MUGA studies show smaller heart size in women compared to men. Studies show larger heart size in men even after accounting for differences in body size. In other words, men's hearts are usually bigger in relation to their body size than women's hearts.
Race There may also be racial differences in heart structure in healthy people. However, it has not been studied.
Age Whether to have separate echo reference values for the elderly is complicated. We really can't tell which physical changes are caused just by aging and which are caused by heart-related conditions like high blood pressure. For example, high blood pressure used to be considered a normal result of aging, so it was not aggressively treated. Now we know that aggressively treating high blood pressure in older people greatly reduces heart-related death in the elderly.
Indexing/Adjustment Because heart dimensions vary with body size, it seems reasonable to take a person's body size into account when interpreting echo results. Adjusting or "indexing" by body surface area (the "traditional" method) has been criticized because it "forgives" obesity-related variations in echo measurements. There is no agreement about how to adjust measurements for body size.
Subgroups Highly trained athletes and pregnant women are 2 subgroups needing different standards. Healthy members of both groups may have echo measurements that are larger than usual.
The same terms should mean the same thing Cardiologists often use the terms "mild," "moderate," and "severe" to describe the degree of abnormality in heart structure. Non-specialist doctors often interpret echo reports. Although it is useful for a non-specialist to use terms like "mild" or "severe", abnormal values should be divided into precisely defined categories based on just how abnormal they really are.
Relevance We surveyed 35 echo labs in hospitals in eastern Massachusetts to compare their reference values and how they interpret echos. Twenty-nine of the 35 laboratories responded. Many of the labs also provided samples of their echo reports. Reference values were different from lab to lab. Upper reference limits for "normal" varied:
|Upper reference limits used for healthy hearts|
|left atrium||35 to 41 mm|
|aortic root||32 to 39 mm|
|left ventricular end-diastolic diameter||53 to 58 mm|
|left ventricular end-systolic diameter||30 to 40 mm|
Most labs said they sometimes changed their usual echo interpretation when the patient was very tall (or short) or very fat. However, only 5 of 29 labs indexed their measurements by body surface area. Even though the labs routinely used the terms "mild," "moderate," and "severe", they admitted that they had no standard guidelines as to what exactly these words meant.
The Subjective Factor Interpreting echos involves combining one-dimensional measurements with 2D images. This combined information is added to knowledge of the patient's individual health situation to make a final report. This means that interpreting echo results is partly subjective.
Variability The doctor has to take into account the echo technique itself. Sources of variability include the patient, the echo tech, the techniques used to obtain the images, the methods used to analyze the images, the equipment, and the reader. In a study across 3 medical centers and involving nearly a dozen experienced operators, only 25% of images were judged to be "perfectly" positioned. So there can be disagreements in how to read even "standardized" techniques. Echo labs make their measurements in several ways (M-mode, 2-D [on-line, off-line]). Echo measurements are also influenced by test quality, which is affected by the age, weight, body build of the patient, and presence of lung disease.
Technology With rapid changes in imaging technology, it's likely that reference values made with older technology will become obsolete pretty fast. So applying older reference limits to measurements taken with newer equipment and techniques may not work.
Recommendations Progress in setting standard reference values is way behind technical advances. Since millions of echos are done every year, this needs to be corrected. We recommend the following to make interpreting echo measurements more scientific and meaningful:
Conclusions Despite the widespread use of echo, interpreting echo measurements is seriously limited by lack of standards. There is no agreement among operators about adjusting reference values by sex or age; the proper way to adjust for body size; or the precise definitions of terms like "mild" and "severe." These are urgent matters that must be resolved to make echo results more consistent.
Title: Interpretation of Echocardiographic Measurements: A Call for Standardization
Authors: Ramachandran S. Vasan, MD; Daniel Levy, MD; Martin G. Larson, ScD; Emelia J. Benjamin, MD; ScM
Source: Am Heart J 139(3):412-422, 2000
All information on this site is opinion only. All concepts, explanations, trials, and studies have been re-written in plain English and may contain errors. I am not a doctor. Use the reference information at the end of each article to search MedLine for more complete and accurate information. All original copyrights apply. No information on this page should be used by any person to affect their medical, legal, educational, social, or psychological treatment in any way. I am not a doctor. This web site and all its pages, graphics, and content copyright © 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004 Jon C.