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The following is excerpted, with permission, from the Manual for Stress Echo by Larry DeBord. This was written several years ago when the only digital acquisition systems (frame grabbers) were stand-alone computers.  Some of the comments and suggestions apply specifically to one of those systems, the Tom-Tec (Freeland).  While the concepts and basic protocol as described are fundamentally useful, you may find that your integrated frame grabber's software may not be flexible enough to perform some of these actions.

Chapter 13
How We Perform the
Supine Bike Stress Echo Exam

• Components of Stress Echocardiography
• Electrocardiogram
• Heart Rate
• Blood Pressure
• Exercise
• Patient Symptoms
• Echocardiography
• Setting Up the Equipment
• Supine Bike Stress Echo & the Preferred Protocol
• Preliminary Stage
• REST Stage
• Criteria for Correctly Acquired Systolic Loop
• Exercise Stage
• Respiration Effects
• Imaging Techniques
• PEAK Stage
• Indications to Stop Exercise
• Immediate Post Exercise (IMPOST) Stage
• FINAL Stage

This chapter reviews every step of the supine bike stress echo exam according to the "Preferred Protocol", a more complex and thorough protocol that evolved in our lab through the trials of over 7000 stress echoes.  These pages should first be read briefly, then reviewed during early practice, and finally once again in detail after performing a few dozen exams.

In the stress echo clinical setting, the ultrasound images are not read in a double-blinded manner and the final diagnosis will not be made without conscious or unconscious consideration of the ECG, the blood pressure, the heart rate, the patient’s symptoms and the patient’s history. But as much as possible, the loops of wall motion should be read as objectively as possible, with minimal reference to the patient’s history. The doctor’s final diagnosis, however, will take all the other parameters into consideration.

A 12-lead ECG (with electrode placement modified to allow access to the windows) is recorded at rest, at the end of each 2-minute stage of exercise and at the end of the test when all changes are resolved. The doctor monitors the ECG carefully throughout the exam. If abnormalities begin to develop, the doctor may announce PEAK earlier than otherwise and ask the echocardiographer to hasten the acquisition of the images. The abnormal ECG response is defined as > 1 mm of horizontal or down sloping ST segment depression 80 msec after the J-point in a lead normal at rest. Because the electrode placement is non-standard and may vary in different exams, caution should be exercised in including the stress echo’s electrocardiogram in a serial study of the patient.

Heart Rate

The predicted maximal heart rate (PMHR) is determined by subtracting the patient’s age from 220. An adequate stress test is conventionally considered to be 80-85% of this value. (A 100 & 85% Heart Rate Chart is in the Appendix.) At the doctor’s discretion, our patients are usually asked to discontinue their beta-blockers and calcium channel blockers on the day of the exam (or even the day before the exam) to allow higher heart rates. Heart rates achieved by the patient on the supine bike will not be as great as those achieved by treadmill exercise (see Chapter 6).

Blood pressure is taken at rest, at each 2-minute stage of exercise, and following exercise until it returns to resting values. With increasing levels of exercise, systolic pressure increases, often exceeding 200 mmHg when using the supine bike. Blood pressure response to exercise on the supine bike is significantly than achieved by treadmill exercise (Chapter 6). The rate-pressure product (peak HR x systolic BP/100) obtained from supine bike exercise and treadmill exercise are insignificantly different, suggesting that the work loads are insignificantly different. A 10 mmHg drop in systolic pressure is abnormal and may be an indicator of left ventricular dysfunction. If hypotension occurs with ECG changes and/or chest pain, start thinking ahead - where is the nitro? where is the crash cart? Keep imaging and keep taping.

A normal response to exercise is increased stroke volume and an increase in systolic blood pressure. However there is a group of people that presents with exercise a lack of increase or even a decrease of these values. Fisman et al. [1989] studied a group of 23 men. Each was normal on physical exam, lacking cardiac history, with no known CAD risk factors, no previous ST-changes, no rhythm disturbances, but presented with a decrease in systolic blood pressure with exercise. Following supine bike exercise their blood pressure and LV volumes were measured (Table 13-1).

Resting Vs. Immediate Post Exercise Hemodynamic Values in Hypotensive Patients [Fisman 1989]

They concluded that exertional hypotension appears in a subgroup of apparently healthy individuals on routine screening. It is not postural or a result of exhaustive exercise, but it is accompanied by abnormal LV performance.

In an earlier study Fleg [1986] studied post exercise hypotensive patients. In a 4-year follow-up one-third of these patients developed ST-changes after exercise. These studies suggest a close follow-up of post exercise hypotensive patients.

Most labs elect to exercise their patients on treadmills and obtain the images post-exercise. Others have elected to utilize upright bicycle. We have found it significantly more useful to obtain the images during exercise while the patient lies supine, pedaling an ergometer integrated into the exam table. See the Discussion and Summary of Advantages of Supine Bike Stress Echo in Chapter 6.

Some evidence indicates that only about one half of CAD patients have recognized symptoms during myocardial ischemia [Mark 1989]. The Framingham study found that about 25% of heart attacks are without symptoms. It sometimes appears that the most common symptom accompanying coronary artery disease is no symptoms. Studies have been unable to agree on the cause or correlations of silent ischemia.

Marwick, Nemec, Torelli [1992], using post treadmill stress echo, studied 71 consecutive patients with significant CAD in order to investigate the relationship between angina and LV dysfunction. The authors found that exertional angina is unrelated to the occurrence of electrocardiographic changes of ischemia, the degree of deterioration of regional function, or to the number of ischemic segments involved and thus, is unrelated to the extent or severity of ischemia as defined by echocardiography.

Up to 30% of patients referred for catheterization for chest pain syndromes are found to have normal coronary arteries [Kern 1992]. These findings - angina, but normal coronaries - are termed Syndrome X. [Kemp 1973]. Assey [1993] reviewed this topic and listed the following nonatherosclerotic causes for angina-like pain:

In our stress echo lab, it is routine to see a wall become dysenergetic, followed later by ST-drops, and, still later, the patient’s report of chest pain. But it is not unusual for us to see the development of dramatic wall motion abnormalities and ECG changes occur without any chest discomfort, and yet the patient feels good and proud of his performance. The term silent ischemia is used to describe this condition of documented CAD but without chest pain or other angina equivalents.

There is another interesting group of patients with truly silent ischemia. These documented CAD patients not only have no chest pain, but no ECG changes either [Hecht DeBord Sotomayor 1994]. Stress echo exams on Syndrome X patients and those with silent ischemia best demonstrate this procedure’s value.

The final component of the exam is echocardiography in the conventional taped format and the digital form. Images in all useful orthographic views are recorded on video tape and on the digital frame grabber in the resting position. Depending upon the mode of exercise chosen, more images are obtained during peak exercise and/or immediate post exercise and (optional) at a "final" period some minutes later. These digital images are arranged and played back at a slower rate for analysis, comparing and scoring the wall motion of each of the LV segments at REST, PEAK and IMPOST.

Summary of the Preferred Protocol for
Supine Bike Stress Echocardiography

• Acquire digital loops at REST, PEAK & IMPOST (& FINAL if necessary), using supine bike exercise.

• Imaging must be in the correct orthographic plane or all is invalid

• Endocardium must be visible in order to be read

• Set trigger and acquisition delays to accurately capture and demonstrate systole.

No more. No less. (see Criteria for the Correctly Acquired Systolic Loop)

• Capture five orthographic planes: PSLA, PSSA, Ap-4, Ap-2 & Ap-3

• Save and format duplicate views of each plane at each stage to reveal ambiguity and/or to increase the confidence that the loops truly characterize the myocardium’s behavior

    It may appear unnecessarily complicated to capture five instead of four views, and to obtain multiple views of each instead of just one. And it may seem far too laborious to spend so much time imaging 6 or 7 minutes of exercise and 1 or 2 minutes of PEAK, another minute of IMPOST and maybe a minute or two of FINAL instead of simply acquiring 60 seconds during IMPOST. We have demonstrated, however, that this extra effort increases the accuracy of the exam. Here, exactly, is how we do it.

P r e l i m i n a r y

• Just to the side of the sector and within the perimeter of the ROI Box, I enter the patient’s initials. These identification notes will be digitized with the images, minimizing mistaken identities.

R E S T

Acquire the REST loops of the 5 views (PSLA, PSSA, Ap-4, Ap-2, Ap-3). It is important to acquire these images following the resting echo rather than before because the windows usually improve after the patient has relaxed on the table for those 10-15 minutes. This may be due to calmer breathing, more complete exhalation or more relaxed intercostal muscles.

Check the ECG signal. Make sure you have a good, steady TTL (this digital ECG signal may display on your monitor as a flashing light or blinking heart). Pay particular attention to the leads that make up the TTL. Make adjustments if necessary.

Place the patient in the conventional left lateral decubitus with the right arm resting on the right hip. If the right arm is held up near the head, as many patients tend to do, the windows may suffer (perhaps by increasing the chest volume?) Occasionally, after wrestling with poor REST images for 10 minutes, I have discovered that when the patient rolls to supine and places his feet in the bike pedals in preparation for exercise, the images pop into view. I am not sure why this is so. Some have suggested because of increased venous return. Maybe. But for reasons that are never entirely clear to me, a new position, any new position, will often improve the window. Be aggressive in rolling the patient forward backward, arch the back, extend the left arm . . . whatever.

During the resting study and during the acquisition of the REST loops, I usually leave the table flat, but some patients are more comfortable and breathe easier if the head is elevated slightly. If the head of the bed is not raised to the extreme, this will not compromise the imaging. (This emphasizes the need for an exam table with easily controlled powered elevations.)

It seems too obvious to say, but make sure your ultrasound system’s monitor is at eye-level and that during frame grabbing the screen is free of reflections.

[Freeland Users: Clear the RAM if necessary. Select the REST imaging stage. Check the HR and select the proper acquisition delay of 50 or 67. If you require a Trigger Delay, set it now for a resting HR. One of my systems requires a 50 msec trigger delay for REST. Another system varies its demands so I have to check it each time.]

Re-check the image processing, the position of the ROI Box, focus, depth, and screen documentation. Get the best window, best cut, best patient position, and best point in the respiratory cycle to get the best endocardial image.

Begin taping and acquiring.

[Freeland users: I suggest always using Multi-loop, even for the REST acquisitions. Ideal images are seldom acquired in only four heart beats.]

Improve the image if possible by changing patient position and controlling patient breathing. Check the playback immediately for image quality and to assure that the loops properly include beginning systole and end-systole. Judge the loops on this basis:

• Frames #7 and #8: LV chamber sizes are equal in size or LV chamber size is slightly larger in #8 indicating first moment of diastole

If the above conditions are not met, correct the triggering problem.

Lock the images you prefer and continue acquiring the remaining views. Save extra loops from all windows to clarify any irregular motion or structure. I frequently save many extra REST images to improve my chances of their matching the cuts obtained during PEAK and IMPOST imaging.

Ask the patient to roll to supine and try to improve the images in this position. It is not unusual to get better images here, particularly the parasternals of the obese. I usually acquire extra supine apicals, especially Ap-4’s, as this view is most subject to change relative to patient position. Frequently, this Ap-4 will better match the PEAK Ap-4 cuts, though the image quality may not be as good as those taken in left lateral decubitus.

Save these selected REST loops. Leave these preferred REST images on the screen (in RAM) for the doctor to see just before exercise begins. Important: the sonographer should point out any resting wall motion abnormalities.

Record the resting ECG, resting heart rate and resting blood pressure. With the patient supine, strap his feet to the pedals of the ergometer and ask him to practice pedaling. Adjust the bike’s position to fit the patient’s leg length. While applying the BP cuff, giving the patient the hand straps, buckling the safety belt and preparing for exercise, I deliver the patient instructions:

As you give the patient instructions, monitor his level of understanding. If it is clear that the instructions are not understood, vary your words to match the patient's level of understanding. I generally say something to the effect of . . .

I look for confusion and clarify if necessary.

E x e r c i s e

Adjust the bike to fit the patient’s legs. The knees should not lock, but be slightly bent when the legs are extended. If the patient is too far from the bike he will not be able to put full power into his exercise and he is likely to jerk with each leg stroke, seriously affecting the stability of the images. If the patient is too close, and is generous in mass, the thighs will pummel the abdomen and will set off periodic tidal waves of belly and breasts. This provides a rather jolly sight, but it makes imaging the heart entirely too challenging.

I generally elevate the back of the bed slightly. This not only makes the patient more comfortable but for many, allows them to pedal longer by reducing the strain on the tops of their thighs. Patients lying completely flat will be tempted to quit early due to leg pain or leg fatigue, before their hearts are completely stressed. Encourage the patient to pull with his feet as well as push, and his legs muscles will suffer less. Make sure the patient is not chewing gum.

I give the patient his hand strap. . . again. For reasons not known to science, the moment a supine person begins to pedal, his nose itches and he must drop the hand strap to scratch the offense.

When pedaling commences, begin taping. Recording this early stage of exercise may seem to be a waste of tape, but it often reveals early onset of a wall motion abnormality. Cardiologists who have always used treadmill exercise have never seen what may happen next:

(This early onset of wall motion abnormality is also thought by some to indicate greater severity of disease.) The best images of the entire study, including the rest, may occur during this first minute or two of exercise, but as respiration increases with continuing exercise, this quality will diminish. So this may be this best opportunity to see developing hypokinesia.

Initially we set the ergometer at 25 watts. With younger, fitter patients, we may start at 50 watts. We have elected to have exercise proceed in two minute stages rather than the three of the Bruce protocol, but I encourage experimentation with this. The studies typically last for three to six stages. Every two minutes the blood pressure and ECG are recorded and the resistance on the bike is increased by 25 or 50 watts depending upon the patient.

I see little value in using ergometers that automatically progress through pre-set work loads. The work loads should be set manually to optimize the work done by the patient. It is only after the patient begins pedaling can it be determined the best course of action. Younger patients may perform better by advancing 50 watts per stage. But they may surprise you four minutes into exercise and you have to reduce that increase to only 25 watts per stage. People with arthritis may suddenly stop pedaling due to leg pain unless the work load is immediately reduced, allowing them to continue. The automatic systems look logical, but they are not useful, and adjusting the bike’s resistance control once every two minutes is not a challenge for most technicians or doctors.

During the entire time of exercise I continually look for the best windows and work with the patient to find the inhalation-exhalation method that provides the best images for each cut.

Near the end of the exercise period I may begin to tilt the bed slightly to slowly accustom the patient to this awkward position.

At the risk of making the reader nauseous with repetition, we will talk just a little more on the manipulation of patient breathing. Breathing control techniques are more important to image quality than is the selection of the ultrasound system or the tweaking of the array of settings and adjustments that crowd the control panel.

It seems that every cardiologist who ever wrote a paper on stress echo felt obligated to emphasize the troublesome respiratory interference. Limacher [1983] stated that "movement artifact . . . has rendered the success rate of (bicycle exercise) unsatisfactory." He noted that in post treadmill imaging "the heart was frequently visible for only one or two beats at end-expiration." One worker mentions the respiration problem rather fatalistically: "With excessive breathing the examiner obtains only an occasional glimpse of the heart." He then seems to place his faith in chance: "Because the respiratory rate is usually quite rapid, the likelihood is high that one of the four cardiac images will be satisfactory." Crawford [1991] wrote "it is difficult when only one or two expiratory images are encountered every five or six heartbeats."

One must conclude they all thought this was an unsolvable problem, for no one mentioned minimizing the interference by controlling the patient’s respiration.

I observe the effects of the patient’s normal respiration on the image while I perform the resting echo. As I acquire the REST loops, I begin experimenting with different points in the respiratory cycle. I request that the patient take a big breath in, to slowly release that breath, and finally to force out the remaining air. I watch the effects on image quality.

For example, the best image of the PSSA is often at that point in mid- expiration when the lung interference just moves off the right side of the cardiac image. If the image does not appear, I continue through the full range of requests for the patient to

. . . breathe in . . . breathe out . . . take a half breath in . . . one third breath in . . . force all the air out . . . exhale normally and hold it . . . breathe normally . . . take a big breath in and slowly let it out until I say stop.

Very commonly, the transducer site for the best Ap-4 window will show absolutely nothing until the patient takes a big breath in. Finding the optimal point within the respiratory cycle at rest, unfortunately, does not guarantee that the search will not have to be repeated when the patient is supine and pedaling the bike. The whole search procedure begins anew during early exercise as I again make seemingly impossible demands upon the pedaling patient to

" . . . breathe in . . . breathe out . . . hold it right there!" This is difficult to do, but nearly all patients can comply. Another important value in pausing respiration is that it prevents the respiratory swing of the heart. Reducing cardiac motion makes it easier to read wall motion.

Effectively controlling a patient’s respiration is a skill that takes time to learn. Do not underestimate its value or the difficulty in learning the technique. Learn to time your commands to be consistent with the patient’s normal breathing cycle. Don’t ask him to take in a big breath when he is exhaling. Be very aware of how long the patient has held his breath. Don’t make him unnecessarily uncomfortable.

You may be surprised to see the image quality dramatically improve with exercise. Usually it will be to degrade as we approach that final moment of truth, but even at PEAK it is not unusual for the endocardial definition to be superior to that seen at REST. This was also noticed in the early days [Maurer, Nanda 1981].

If the patient’s back has been elevated, I may lower it to horizontal, just prior to PEAK, to open the imaging windows. This is especially true for short, pot-bellied people. I may try to improve the images by tilting the table to the side. There are a few people who cannot tolerate this tilt without near panic, so use judgment. Rarely, very rarely, a better window appears if the patient raises his left arm up beside his head. Try anything.

I lay a hand cloth on the patient’s chest to allow a quick cleanup of excess gel on the transducer or the patient’s chest. I rest the side of my left palm and little finger on the chest to secure the transducer in an attempt to steady the image from the rocking of heavy breathing and bouncing. I try to move the transducer in concert with the breathing rhythms. It becomes a dance.

During the final moments of exercise we all cheer the patient on to pedal longer than he really wants or thinks possible. Care must be taken to avoid setting the workload so high that the patient begins to strain excessively, for this will close up the windows. Toward the end of exercise I allow the patient to pedal at his own rate (surprisingly, this is often faster than is dictated), for what is important is that his work load continue to climb as expressed by his blood pressure and heart rate.

P E A K

We don’t necessarily believe the patient when he says he is exhausted and claims the need to quit. We "encourage" him to go longer, following the doctor’s lead who is assessing the patient’s condition. The doctor announces PEAK when he sees that stress level has been achieved (85% PMHR), when we truly feel the patient can pedal for only 60 more seconds or if he exhibits any of the end points listed below. During these final moments of exercise I make the decision about which views to acquire first.

The physician must make the choice of stopping the test early, at the first arrival of any of the above mentioned end points (or at the onset of a wall motion abnormality) or to continue the exercise to see if additional walls become asynergetic. Only by extending the test can all the diseased arteries be identified. Ryan [1993] reported that upright bike stress echo underestimated the extent of CAD in 22% of his patients. That is, in 68 patients who had multivessel disease, the test identified only one diseased artery in each. Perhaps if the test had continued a bit longer, the additional wall motion abnormalities would have been provoked. Fewer than one percent of our patients have suffered such chest pain or shortness of breath that nitroglycerine was administered. Emergency treatment is beyond the scope of this manual except to mention that the technologist is responsible for knowing the location of all equipment and supplies for such events: crash cart, oxygen tank, mask, bed board, defibrillator and medications.

When the doctor declares PEAK I quickly check the HR, make an acquisition delay adjustment if necessary (33 or 50 msec), replace "Exercise" with "PEAK" on the ultrasound screen, and adjust the ROI box. While making these adjustments I tilt the bed to the side. I then begin acquiring my five PEAK views.

This is the moment when you best see the advantage of capturing your images during PEAK exercise instead of rushing to grab your views in the 60 seconds following treadmill exercise. As long as you can keep the patient’s heart rate up, even if it requires slightly reducing the workload (reducing the bike’s resistance), you can continue to improve your images and to capture diagnostic PEAK information. The patient is often surprised to find that he is not really in the final moments of life as he believed earlier, and can actually continue pedaling for two or even three more minutes. This gives us the luxury of time to improve the quality of the study.

During PEAK acquisitions I use the pause pedal frequently. I capture only when I feel I am getting diagnostic images. Perhaps this patient’s images pop out only with complete exhalation; if so, the only time I lift the pedal and acquire is during those moments of held exhalation. When I have acquired all the PEAK images, I step on the pause pedal and announce the immediate post exercise (IMPOST) stage.

[Freeland users only: It is important to use the memory efficiently and to ration it wisely. I hear reports of people taught by the frame grabber applications specialists to merely lift the pedal and forget it until you have raced through all the views. That shotgun approach may work if you have 128 megabytes of RAM, but if you have one of the older systems with only 16 megs, I suggest you exercise discretion in acquisition and budget the memory. I usually use about 75% of the (16 megabyte) RAM on the PEAK loops, leaving the remainder for the easier and less important IMPOST images.]

Imaging Note:  The echocardiographer is not really performing at his best until he/she stops thinking about the transducer and the ultrasound machine and digital acquisition and all the buttons and instead concentrates on diagnosing wall motion in real time. Ideally, while capturing the images during PEAK exercise, the technologist will look at each segment of each wall and ask "Has it augmented from the its resting motion?" or "Is the motion about the same as it was at REST?" or "Has this wall motion worsened with exercise?" The sonographer should determine this at the moment of imaging and then document his/her conclusion and not merely take a series a pictures and hope that the doctor can make some sense out it.

I M P O S T

At the end of the PEAK stage, I ask the patient to gradually slow down his pedaling to maintain the high heart rate as long as possible and to give me a few seconds to change the ultrasound system’s screen documentation to "IMPOST" and select IMPOST on the Freeland.

The assistant and I snap off the seat belt and foot straps. The assistant uses the Bundle Block to quickly roll the patient up onto his left side. With the Bundle Block in place, the patient can relax and catch his breath but he is unable to roll back into supine.

I adjust the ROI box if necessary. Considering the heart rate, I adjust the acquisition delay as necessary. I instruct the patient to relax, breathe smoothly and not to talk. This is frequently defeated by the patient wanting to celebrate his feat by crowing and yodeling. I acquire the IMPOST images, attempting to observe the 60 second rule, though these images are of secondary importance if I have gotten good PEAK pictures.

Occasionally I leave the patient in the supine position, with feet remaining elevated in the pedals to acquire the IMPOST images. I will do this if the images are better than those taken in left lateral decubitus or if I feel the patient will be unable to roll over quickly enough due to obesity or lack of coordination or understanding.

A question frequently asked by technologists is, "which views do you get first?" The answer is, it depends. If the inferior wall is infarcted and scarred, you probably would not begin with the Ap-2. Instead, you would look for the wall that is critical to the diagnosis: the anterior or postero-lateral walls, for example. Image quality may determine which views to get first. If there are poor parasternals, begin with the apicals. Or if the apicals were very poor while the patient was exercising in the supine, go for the apicals as soon as the patient rolls onto his side.

F I N A L

There is no formal definition of the FINAL stage. It merely denotes any image obtained later than one minute after pedaling stops. If there is a provoked wall motion abnormality, I continue taping this FINAL stage until it resolves. It makes a nice presentation to digitize a FINAL loop for inclusion in the study to assure the reader that the wall motion abnormality was a provoked one, and that it eventually returned to normal.

The doctor may wish the patient to rest for a few more minutes while ECG changes resolve, and/or to continue taking blood pressures. At this time I immediately start stepping through the primary loops just acquired and begin selecting the loops I wish to save for interpretation.

In our lab, the doctor now leaves the room to see other patients or attend to other duties for the ten minutes or so it takes me to dismiss the patient and to arrange the loops for reading.

When the patient has completed his exercise and caught his breath, he suddenly becomes talkative and rather excited - sort of jazzed - as though he has just come through an adventure. He is congratulated on his performance as the ECG cable, electrodes and gel are removed. The assistant and I cautiously escort the rubber-legged patient from the table, guarding against a fall, and answer his remaining questions. We offer him a drink and ask him to dress and to wait 10 minutes for the results.

Our next job is to review the digital images we have captured, select those that are diagnostically useful and to format them in a way that facilitates accurate judgment about myocardial contractility as affected by the exercise. See Formatting the Digital Study.

References

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Content revised: January 24, 2004