Redbud Medical Systems, Inc.
Custom-made beds for Supine bike stress echo, Post treadmill imaging exercise echo, & Resting echo

*p<0.01 versus POST † p>0.05 versus POST § p<0.0001 versus POST

Specificity was the same for PEAK and IMPOST. However, significantly greater sensitivity was obtained for detection of disease in each of the three major coronary arteries by imaging during exercise compared to post-exercise. (We do not presume that this comparison is equivalent to testing PEAK supine bike vs. IMPOST treadmill exams, but it does allow cautious conclusions.)

Upright Bike vs. Supine Bike

The upright bike method allows imaging during peak exercise and we prefer it to post-treadmill imaging, but it has a few disadvantages. A brief summary of the differences between supine bike and upright bike follows:

Supine Bike vs. Upright Bike

The Need for an Improved Protocol

In 1988 Presti described the digital exercise echo protocol.

This protocol has not changed in the many intervening years, even though it is limited in the amount of data it provides and even though advancing computer technology long ago removed many of the handicaps and limitations imposed on the original developers of digital echo.

This simple protocol is still endorsed and encouraged by industry. There is no profit in modifying the software. Portraying the exam as a more complex procedure could be detrimental to sales.

Much of the literature and many of the stress echo luminaries who make the speaking circuit persist in presenting their familiar protocol with an attitude that discourages innovation or any departure from the "standard protocol."

The Golden Rules of Exercise Echo seem to be:

Brevity seems to be the primary concern. In all the papers cited here, very very few have one single word to say about quality and how to attain it. We proposed proposed an alternate protocol that is primarily concerned with quality and not ease, a protocol that is based on the following rationale:

Preferred Protocol: Multiple Loops of Each View to Reveal Ambiguity

One worker wrote what is so commonly and hopefully and mistakenly believed: "one only needs one good cardiac cycle per view." If "good" means "perfect," I agree, but I suggest you not expect perfection in ultrasound. Ever. That requires a cloak of Faith that only the Pope should wear. Ultrasound images are wonderfully useful but under the best of conditions they are mere murky suggestions of the cardiac structure and behavior. And when the heart is pounding at 130 beats/min. and swinging back and forth and twisting and thrusting apically and the left lung is being a pest and the chest is heaving and when the sonographer is weary and frustrated . . . forget Faith in perfection. Under these conditions, you subscribe to Hope, not Faith. The several loops acquired of the same (attempted) orthographic plane are going to be different. If you expect all exercise apical-2s in a patient to show the same wall features and the same contractility, you will be disappointed. All experienced techs understand how any wall can be made to appear different than it really is. The inferior wall of the PSSA can be made to look severely hypokinetic with under rotation. That same inferior wall in the apical-2, even if akinetic, can be made to look normal by cutting it off-axis and/or truncating it.

If the sonographer is allowed only a few seconds to acquire each view (posttreadmill), it should not come as a surprise that digital loops of the apical-2, for one example, could suggest different contractility patterns: one loop could make the inferior wall look hyperdynamic, another loop could make the same wall look akinetic. If only one of these loops is shown to the reader for interpretation, which will it be? The "normal" one or the "diseased" one? It will be the one selected by the sonographer. Who has diagnosed this study? The sonographer or the physician?

Even with all the chances that 128 megabytes of RAM offer, the captured loops nearly always contain ambiguities. One PSLA loop has a normal looking septum. The next PSLA loop is from a very slightly lower window and the septum looks hypokinetic. The reader should see this ambiguity in order to make a responsible judgment. When you (the reader) are looking for subtle differences between the contractility of small segments in the REST, the PEAK and the IMPOST walls, the more information you have, the more confidence you will have in your diagnosis. There will be times when you will see so much ambiguity within a study that you will admit defeat and conclude that you cannot make a confident prediction. The imaging just wonÂ’t allow it. YouÂ’ll have to pass. Contrast this situation with the sonographer protecting you from that trauma by choosing one loop and one loop only. Without contradictory data, you can make your decision easily. Rightly or wrongly. Which would you prefer?

The more loops you have to read, the greater confidence you will have in your calls. To restrict yourself to one cardiac cycle per view is to unnecessarily handicap yourself. The sonographer can save and format the multiple loops of each view in only a few minutes of additional time (as described briefly below and in more detail in the Exam Chapter). Even if the reader helps select the final views for reading, it is useful in the final analysis to have the multiple loops side by side for comparison.

Preferred Protocol: Additional Views - More than the Usual Four

The PSLA, PSSA, AP-4 & Ap-2 are the planes acquired in the conventional protocol. We have added the routine acquisition of the Ap-3 or "apical long axis" view to our studies. The Ap-3, in more than half the cases, provides a better look at the posterior wall than does the PSLA. It permits another look at the septum and, usually, one more view of the apex. It is difficult to explain, but the sonographer also has more "control" over this view, greater flexibility to include or exclude the pap muscle, to line up with the aortic valve, etc. It seems easier to match the REST and PEAK views of the AP-3 than it is for the PSLA. Occasionally, the most useful window is somewhere between the parasternal and apical positions. Rarely, we include the sub-costal window if that is helpful.

Including extra views and the additional loops of each view requires more archival space. For reasons not clear to me, this threatens some people. For example, I once heard a popular speaker explain that the entire study should be condensed to one floppy disk. "If there are two disks," he explained, "you will lose one." Another luminary wrote, "it is inconvenient to require multiple disks to store one study." IsnÂ’t the value of additional data for the diagnosis worth that small risk of loss and that "inconvenience" to the staff? Archiving to optical discs minimizes inconvenience and the probability of loss.

Some will complain that the inclusion of this extra view and the extra loops per view also requires more time to time to read. A well known cardiologist was overheard to say vehemently, "I donÂ’t want to spend more than two minutes reading a stress echo study!" I can understand that. If economy of your time is most important, I suggest having the sonographer diagnose the study for you by choosing 4 REST and 4 IMPOST loops for your quick review. More time can be saved by having the tech dictate the final report.

Preferred Protocol: Higher Quality Images

Supine bike stress echo allows increasing the quality of the images by providing more time to perfect the images. During the several minutes of exercise, before PEAK is achieved, the sonographer becomes familiar with the changing windows and is able to learn the fine-tuning required to optimize the images. The sonographer works with the patient as he pedals, practicing the breathing methods that will optimize the images when PEAK finally arrives. The sonographer has the opportunity to see the onset of wall motion abnormalities and can plan his imaging to optimize the images to show that abnormality. At termination of exercise, the patient is merely rolled to left lateral decubitus, or left in the supine position, so the IMPOST imaging can begin immediately. If it takes a little longer to optimize these images, it is now less important, for these are secondary to the PEAK images.

Preferred Protocol: Data that is more Valid
The validity of acquiring the data during peak exercise when ischemia is at its maximum, rather than while ischemia and wall motion abnormalities are resolving has already been discussed in detail.

Preferred Protocol: Reading
Optimally, the study should be read immediately while the tape and digital studies are loaded and while the images are fresh in the cliniciansÂ’ minds. The physician should take advantage of the sonographerÂ’s skills by including her/him in the reading for the sonographer has valuable input about the views, artifacts, triggering, angulation, planes, etc. Two qualified readers are better than one.

In summary:

The Preferred Protocol Format
The loops are assembled as follows. Each page displays loops of REST, PEAK, PEAK, and IMPOST of one orthographic plane.  See Formatting the Digital Images for details.  

It may be useful to speculate on the application of this new protocol to Dr. Tom RyanÂ’s excellent 1993 paper. Of the 309 patients he studied with upright bike exercise echo, 66% of the 392 lesions were identified. More than half of those lesions not identified were in the left circumflex. Why should this sensitivity be so low? The conventional upright bike protocol provides only one loop that gives information about the circumflex during PEAK exercise: the AP-4. (Remember that the parasternals are not usually visualized in an upright patient.)

Especially in consideration of these difficulties, the standard upright bike protocol provides disappointingly few images of the circumflex territory, and most of these are post exercise:

(Not much circumflex information here - 1 PEAK loop and 3 IMPOST loops)

The Preferred protocol provides the reader with much more information about the circumflex territory:

Instead of only one PEAK and three IMPOST loops of the circumflex, the preferred protocol can easily show 16 PEAK views and 8 IMPOST views of the circumflex territory.

More data is better than less.

Using the Preferred Protocol with supine bike exercise, we [Hecht DeBord Sotomayor 1993] correctly identified circumflex disease 78% of the time compared 36% in Dr. RyanÂ’s study.

Acquiring Data During PEAK Exercise:
Summary of Advantages

Increased Validity of Images

• Acquiring the data at PEAK exercise provides greater validity of data: the Peak images are obtained while maximum ischemia is occurring, when a functional response would be expected to be the most obvious. Impost images are obtained while ischemia is resolving and when subtle wall motion abnormalities are obliterated by the sudden "rebound" of the myocardium when the afterload is reduced. Intuitively, peak imaging is more valid. Would you consider acquiring your 2-D images only after the dobutamine pump was turned off? obtaining the electrocardiogram only after the treadmill exercise? injecting thallium-201 only after exercise was terminated?

Increased Quality of Images

More time during PEAK to acquire images permits:

One author wrote confidently "Because one only needs one good cardiac cycle per view, the examination can be greatly shortened. . . . theoretically each view could be obtained in no more than 4 or 5 seconds." Whenever you see that word "theoretically," you know it most likely doesnÂ’t happen. How many images will you capture in 4-5 seconds? What is the quality of these fast-grabs? Are they in the right plane? Same plane as the REST images? See any endocardium? Is there cardiac swing? Respiratory artifact?

It disappoints me that the literature and educational programs place so much emphasis on speed and so little on quantity and quality. For the sonographer to be performing at his optimum, he must be diagnosing the study as he images. He must be asking, am I in the absolutely right plane? Is the LV at its maximum size? Can I see all the walls? The true apex? Is this inferior wall moving? Is it really thickening more than it did at REST? Is this apex augmenting, dilating or is it off-axis? Is this the endocardium I am looking at, or chord? Or an artifact?

Quality work is not attained by the sonographer who is pressured to hurry. To put this in perspective, imagine being asked to do an aortic stenosis study in 60 seconds. How would the quality of the exam be affected if you had only one minute to get outflow tract diameter, outflow tract velocity and peak AV velocity in one minute?

PEAK imaging provides the echocardiographer with the time to optimize the images, to exercise judgment, to reduce errors and to have more confidence in the diagnosis.

A Comment on Patient Motion

Virtually every paper written about stress echo mentions, usually in one sentence, that stress echo is "technically demanding," and if PEAK exercise is mentioned, it is described as "more technically demanding." And then the author grieves over the patientÂ’s body motion, respiratory artifact, and translation (heart swing). Typical statements describing the convenience treadmill brings to the study are:

Well . . . yeah. But there are techniques to minimize these disrupting movements (see the Exam Chapter). The difference between the movement problems of a post-treadmill patient and a supine bike patient has been highly exaggerated. When the patient is provided with a hip strap, hand straps to the side (not overhead), a properly positioned bike, and when the patient is given the correct instructions and is directed to control his breathing, the movements are not as destructive to the study as the literature would have you believe.

Increased Quantity of Images -
Some is information is good. More is better.

Maintaining the patientÂ’s pedaling at peak exercise allows three or four times as much data to be collected. The patient can usually be persuaded to pedal for two full minutes at his "peak" exercise. If we still have difficulty getting good images, we may lower the bike resistance slightly to extend the patientÂ’s duration. This additional time allows us greater control of the patientÂ’s movement and respiration, thereby increasing the imaging "yield."

Additional information is gained by seeing the entire exercise in real time while it occurs. This not only provides the sonographer the valuable opportunity to discover the best windows (they change with exercise) and to perfect the other imaging parameters that increase the yield, but allows the physician to obtain more information by seeing the onset of ischemia We agree with Quiñones [1991] who wrote:

The immediate post exercise images are still obtained in addition to the exercise images, and no time is lost by the patient walking to the bed. In many cases, we do not even ask the patient to roll to his side, but merely to stop pedaling. In this case, there is no delay in the beginning of acquisition of the IMPOST images, which results in more IMPOST data collected within that 60 second period. Supine Bicycle Exercise allows the capture of more data.

Other Issues of PEAK Imaging - Rebound effect

Related to ShneiderÂ’s study, cited earlier, is the difficulty of identifying small or subtle segmental wall motion abnormalities immediately following exercise due to the immediate increase in ejection fraction at the termination of exercise. In an early study, Wann [1979] noted this problem following treadmill exercise: "segments of the left ventricle that had moved abnormally during exercise appeared to return to normal and then to contract more vigorously than at rest." This early observation of increased EF is consistent with ours and with SchneiderÂ’s radionuclide angiographic studies. We refer to this as rebound. As the heart rate rapidly decreases, stroke volume increases [Cumming 1972; Goldberg 1980]. This sudden hyperdynamic motion of the normally perfused walls, often conceals those small abnormally perfused segments. The hypokinetic wall segment is dragged inward by the surrounding healthy myocardium, making it impossible to identify the hypokinesia.

Reproducibility

The reproducibility of treadmill exercise echo has been demonstrated [Oberman 1989]. Maurer [1981] and Fortuin [1977] observed that the treadmill is controlled by the clinician and the patient has no capacity to regulate the workload but must struggle to keep up the pace as directed, but in contrast the workload on the bike is determined by the patient. In light of this, they concluded that the treadmillÂ’s workload is more reproducible than the bikeÂ’s and thus the post-treadmill data is more reproducible.

I suggest an alternate perspective on this. For all practical purposes, in a clinical setting, a patient that pedals 50 rpm through four 2-min. stages of exercise that increase by 25 watts per stage has performed in a way that is easily and accurately recorded and reproduced. If, for instance, a patient is exercised before and after PTCA can we not make a reasonable comparison between the two exams with assurance of the "reproducibility" of the workload?

But there is another factor of "reproducibility" that is far more important than workload - the quality of the images acquired and the similarity of the images throughout the series. If, for instance, you feel that all "apical-2Â’s" acquired post exercise from a poor imaging patient show the same endocardium in the same way, and present the wall contraction in the same way, you have deluded yourself. Under the best of circumstances it is difficult to acquire several loops that all show the exact same orthographic plane, and having only a few seconds to devote to this view seriously affects the sonographerÂ’s ability to grab the perfect plane. But if the sonographer has the time to watch the walls of this view throughout 6 or 7 minutes of exercise and to become familiar with the changing window and with the wall behavior, and then has two full minutes to optimize the scanning, it is much more likely that he can reproduce the ideal cuts.

I feel that a 10% difference in certainty of equal workloads in a series of exams is insignificant compared to the "reproducibility" of the images obtained by having more time to acquire the data.

Patient Familiarity

Maurer [1981] was the first to mention another popular defense of treadmill: "Exercise in the upright position is more familiar to the majority of the population." Presti [19] wrote "many patients are more accustomed to treadmill exercise, which allows for achievement of higher workloads." Familiarity is important only if a significant portion of our cardiac patients are so uncoordinated and so dull that they are unable to adapt to pedaling in the supine position for a few minutes. I am not impressed from my experience of thousands of stress echoes that our patients are so handicapped. While we will always encounter an occasional elderly patient who cannot coordinate his/her legs to pedal circularly, and a few unmotivated souls that complain they absolutely-positively-completely-cannot-will-not-donÂ’t-even-ask-me-to tolerate the novel supine exercise posture, they are the rare exception.

Normalization of SWMAs

Having both the PEAK and the IMPOST images allows the reader to see the resolution, or lessening, of the severity of a wall motion abnormality during IMPOST. This increases confidence in identifying a segmental wall-motion abnormality during PEAK.

Physically Compromised Patients

Supine Bike Stress Echo allows testing of patients with physical disabilities: even those with severe arthritis, severe physical deconditioning, etc. A patient shuffled into the office, completely dependent upon his walker. His left foot was paralyzed, and he could not consider keeping up with a treadmill. He was surprised and pleased to learn that while lying on his back he could pedal quite vigorously. Another patient suffered dizziness and would not walk on treadmill for fear of falling. He felt very secure on the bed and was able to exercise to a diagnostically useful level.

Reduced Stress on the Sonographer

Lacking the "60 second imperative," the supine bike protocol reduces stress on the sonographer. Hurrying can increase imaging sloppiness, increase errors in command entries, and decrease quality of judgment.

Safety

SBSE allows greater safety. The supine patient cannot fall. The patientÂ’s supine position allows easier detection and quicker response to untoward events such as a fall in BP or potentially dangerous arrhythmias. More importantly, the earlier indicator of problem, the wall motion, can be constantly monitored. The physician has greater control of an emergency situation with the patient on the exam table.

Convenience

Supine bike stress is more convenient and easier for the patient and much easier for the technologist. Neither the patient nor the technologist is required to move between exercise and IMPOST.

Economics

A supine bike bed with a small electrocardiograph costs less than a conventional treadmill and exam table.

Space requirements

Supine bike stress echo requires minimally only enough room for the bed, the ultrasound system, and a small cart for the frame-grabber and EKG. It is physically possible (but not recommended) to perform SBSE in a room as small as 8Â’ x 9," Post-treadmill requires that same minimal space plus the additional space for the treadmill and for maneuvering the patient. Even upright bike requires more room than SBSE.

Post Treadmill Imaging:
Summary of Advantages

To boast of obtaining four views within 60 seconds post-treadmill is to miss the important issues: how many cardiac cycles were captured? What is the endocardial image quality? Do these few images exactly match the resting images? Were these few images all triggered correctly? Was there distracting cardiac swing? Did the provoked wall motion abnormalities begin to resolve before the images were captured? What is their diagnostic value? How much usable data was collected in that brief period of time?

Discussion

It is a bit perplexing to me that treadmill echo is so popular considering the number of workers who have recognized the additional value of peak exercise imaging

[Wann 1979; Presti 1988; Duchak 1990; Mahony 1990; Marwick 1992; Ryan 1993; Hecht 1993]. Our data lead us to the conclusion that there is a clear-cut advantage to obtaining the images during exercise compared to following exercise. We demonstrate to ourselves, on a daily basis, the very obvious difference between PEAK exercise wall motion and immediate post exercise wall motion. It is routine for us to see wall motion abnormalities develop during exercise and then completely resolve within 30 seconds after termination of pedaling. Perhaps these transient abnormalities (which do correlate with positive angiographic tests) occur only in those patients with mild disease. Is it not an important application of stress echo is to identify these patients?

This discussion is not to imply that the impost images are without value. Quite the contrary. For a small subset of patients, the treadmill may be the preferred method of exercise. These patients, for whatever reasons, mental or physical, cannot achieve a suitable work level on the supine bike. But when they are coerced to keep up with the treadmill, they improve their performances. The IMPOST images are important to compare with the REST and PEAK. In some cases the difference between the IMPOST and PEAK are as useful as the comparison of the REST with PEAK. It is useful to see how quickly the SWMA normalizes [Athanasopoulos 1991].

If the technologist is charged with the responsibility of collecting the necessary data, if the technologist accepts the responsibility of getting the necessary data to make his own diagnosis, he will prefer the technique that gives him more time and more control over that acquisition. It takes no more time or energy to image PEAK and IMPOST than it does to image IMPOST alone. The only difference is while the patient is walking the treadmill, the tech can merely chew gum. Or his nails if he is fretting over getting the necessary data in 60 seconds. It is not nearly so much more difficult to image a pedaling patient as the literature would lead us to believe. By controlling the patientÂ’s breathing and judiciously using the pause pedal to budget memory, PEAK imaging can be less demanding than impost imaging.

References

In 1999 Badruddin, et al.confirmed our reports in their work and concluded:

Patients achieve a similar rate-pressure product during [supine bike echocardiography] and [treadmill echocardiography]. However, ischemic wall motion abnormalities at the time of imaging are more frequent and more extensive during supine bicycle echocardiography, which may increase the detection of CAD and facilitate interpretation of ischemia. These findings along with patient and sonographer preference make SBE a useable stress echocardiography modality in the evaluation patients with CAD.

Shamim-M. Badruddin, MD, Anwar Ahmad, MD, Judith Mickelson, MD, FACC, John Abukhalil, RT,William L. Winters, MD, NIACC, Sherif F. Nagueh, MD, FACC,, William A. Zoghbi, MD, FACC. Supine Bicycle Versus Post-Treadmill Exercise Echocardiography in the Detection of Myocardial Ischemia:  A Randomized Single-Blind Crossover Trial.  Journal of the American College of Cardiology.  Vol. 33, No. 6, 1999.

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Content revised: January 24, 2004