exercise echocardiography

Exercise Echocardiography Thomas Ryan, MD, and Harvey Feigenbaum, MD

Exercise edtacardlography is a versatile, nonin- vaslve dhgmstk test that hwohes the recordi* and interpretation of 2dhnensknal echocardk- grams prim to, duw and after exercise. By analyzing and comparing wall mot3on at each stage, a predctknaboutthspresence or absence of coc- onary artery disease can be made. lhs develop- mentofawallmotianabnormalitylsbothsensl- ttveandspecificforthepresence ofasignlfkant coronary stenosis. Changes in regknal systolic fhmctkn during exerciss enable the dinSdan to

&-uWh between infarction and ischemia. lhus,thatestyle4dsinfonnationonthe4pressnce, extent, severity, and kcatkn of -wartery dkea!w.EchocardkgRqhycanbeadaptedto ahnost anyfotm of stress, although treadmYl or bkyde exercise are most commonly employed. Anadvantageofbkyckstressechocardiography is the opportunity to Image during exercke, ratharthanrelyingonpostexerciserecordI~ This conwbutes to enhanced sensitivity, although false=posJtive results may increase due to the dilfkulties of awdyzhgwaU motion durhg strenuousexercise.Exercke~rdiiphy hweasesthsdiagwstkaccuracyofstresstest- ing in a manner similar to radonuclida pwfuskn imaging. It is partkularly useful in the set&g of an ambiguous stress electrocardiography (ECG) or when a false-nepzative or fake-posJthfe result issuspwted.lthasbeensucce&u Ily applied to patienkfotlowingrevas&dartzatknandyields useful pro@mstk data in a variety of clhdcal situations. Exerctse echocardkqgraphy is being in- cfeasingIyutWedasasafeandaccuratetestin

From the Krannert Institute of Cardiology, Department of Medi- cine, Indiana University School of Medicine, William N. Wishard Memorial Hospital, and Roudebush Veterans Administration Medical Center, Indianapolis, Indiana. Supported in part by the Herman C. Krannert Fund; grants HL-06308 and HL-07182 from the National Heart, Lung, and Blood Institute of the National Institutes of Health, U.S. Public Health Service; and the American Heart Association, Indiana Athliate, Inc.

Address for reprints: Thomas Ryan, MD, Krannert Institute of Cardiology, 1111 W. 10th Street, Indianapolis, Indiana 46202- 4800.

patiints with known or suspected coronary ar- terydii.

(Am J Cardiol1992;66S2H-66H)

0 ver the past decade, exercise echocardiography has developed into a clinically useful tool, providing prognostic and diag-

nostic information on patients with known or suspected coronary artery disease. The test is fundamentally based on 3 assumptions: (1) that the induction of ischemia will result in an area of left ventricular (LV) dyssynergy, (2) that such regional abnormalities developing during exercise are relatively specific for ischemia, and (3) that changes in regional wall motion can be recorded accurately using 2-dimensional echocardiography.

Because decreases in wall thickening and endo- cardial excursion are early and sensitive manifestations of ischemia,ig2 the first 2 assumptions appear well founded. It is only in the past several years, however, that convincing evidence has accrued to support the third assumption. There is now a growing awareness that the addition of echocardiographic monitoring to routine exercise testing enhances the test’s ability to detect, localize, and quantify myocardial ischemia. The purpose of this review is to summarize this body of evidence supporting the clinical application of exercise echocardiography.

AN HISTORICAL PERSPECTWE The earliest report on the use of ultrasound to

monitor LV wall motion during exercise was pub- lished in 1970.3 Later reports, using M-mode echocardiography, provided insight into various aspects of cardiac function and physiology.4 The ability to record LV dimensions and to detect changes in chamber sizes and shortening fraction made exercise echocardiography a valuable tool for understanding exercise physiology.4J

The use of exercise M-mode echocardiography for the detection of ischemia was first reported in 1979.6,7 Although the demonstration of transient wall motion abnormalities was exciting, the inher- ent limitations of the M-mode technique precluded

82H THE AMERICAN JOURNAL OF CARDIOLOGY VOLUME 69 JUNE 18, 1992

clinical application. The use of 2-dimensional echocardiography in conjunction with stress testing was also first reported in 1979.* The advantages of this imaging modality were obvious, although widespread use was hampered by image quality and the difficulties of videotape analysis. Successful imaging was possible in only 7040% of patients9-l3 and overall image quality was marginal. This factor, combined with the respiratory interference inher- ent with exercise, made videotape analysis of the early exercise 2-dimensional echocardiograms quite challenging. These obstacles, coupled with the emergence of radionuclide scan techniques to assess ischemia, discouraged widespread clinical acceptance and relegated exercise echocardiography to the research laboratory.

In the mid 198Os, 2 occurrences contributed to a resurgence of interest in exercise echocardiography. First was the general improvement in image quality attributable to various technologic advances in ultrasound equipment. Imaging success rates improved to an acceptable and competi- tive level and this trend has continued to the present. Today, success rates of 90-95% are the norm.

The second factor that propelled stress echocardiography into the clinical arena was the development and application of digital processing techniques to echocardiographic imaging.r4 This technology allowed the conversion of analog ultrasound information to digitized images. Initially, this was accomplished “off-line” by processing of videotaped records.15 Later, “on-line” methods became available, permitting digitization of ultrasound data directly from the scan converter. Through the implementation of these methods, exercise echocardiography became a more accurate, feasible, and convenient diagnostic test. The impact of these innovations was profound and led directly to a dramatic increase in the availability and acceptance of the technique.

TECHNICAL CONSIDERATIONS: EXERCISE METHODOLOGY

In practice, echocardiography can be adapted to many forms of stress. Most often, 2-dimensional echocardiography is combined with either treadmill or bicycle (supine or upright) exercise. In all cases, the goal is to record and compare LV wall motion before, during, and after exercise. With treadmill testing, imaging is only feasible before and immediately after exercise. Although attempts have been made to develop devices to permit imaging during treadmill exercise,16 most investiga-

TABLE I Clinical Features in Patients with Wall Motion Abnormalities That Persist into Recovery Compared with Those Exhibiting Rapid Recovery

Exercise duration (set)

Maximum heart rate (bpm)

Patients with angina (%)

Patients with collaterals (%)

Adapted from J Am Sot Echo.21

Persistent Rapid Recovery (n = 22) (n = 7)

247 2 119 266 + 124

138k 21 138 rt 18

38 71

29 57

tors have relied exclusively on immediate postexercise recording. l”,13~17 Thus, wall motion abnormalities must persist into early recovery to be detected. Although this occurs in the majority of patients, “rapid recovery” of dyssynergic segments can lead to false-negative results.18 Wann et al8 described occasional cases of postischemic hyperkinesis in areas rendered akinetic during exercise.

Despite the theoretical limitations of relying on postexercise imaging, the technique is currently enjoying widespread application for a variety of reasons. Because treadmill testing is the most widely available form of exercise testing in this country, it is generally more expedient to adapt stress echocardiography to an established treadmill laboratory. Also, by avoiding the need to image at peak exercise, both performance and interpretation of the test are simplified. Finally, monitoring the rate and completeness of recovery of wall motion abnormalities may provide addi- tional diagnostic or prognostic information.lg

Using bicycle exercise, imaging throughout the exercise protocol is feasible. During supine bicy- cling, all views can generally be recorded, whereas in the upright posture imaging is limited to the apical and subcostal windows.20 The ability to image at peak exercise enhances the sensitivity of the test to detect transient ischemia.“l However, the clinical importance of peak exercise imaging has not been proven, and there are disadvantages to the bicycle technique. In addition to the greater complexity of bicycle compared with treadmill exercise echocardiography, the level of stress obtained is sometimes lower. Elderly patients, in particular, are often incapable of exercising ade- quately in the recumbent position.

The diagnostic accuracy of peakversus postexercise imaging has been compared in one study using upright bicycle exercise.21 In this series of 96 patients, 29 developed an induced wall motion abnormality (Table I). These transient wall motion abnormalities were more frequent at peak exercise, resulting in a higher sensitivity for the detection of

A SYMPOSIUM: FUTURE OF ECHOCARDIOGRAPHY 83H

1Ml.E II Advantages of Digital Imaging

0 Side-by-side display of rest and stress images allows subtle differences to be detected, improving sensitivity.

0 Acquisition time is reduced because only a single cardiac cycle is re- qurred of each view to construct the clne loop.

0 By selecting the cardiac cycle to be used for the tine loop, respiratory interference is minimized.

0 Digital techniques facilitate storage, interpretation and retrieval of the exercise echocardiograms.

l The convenience of the method enhances teaching and communication with referring physicrans.

angiographic coronary artery disease. Of the 29 new wall motion abnormalities, 10 had resolved completely at the time of postexercise imaging. The reasons for this phenomenon are unknown, although some conclusions can be drawn. Intercor- onary collaterals were more common in patients demonstrating rapid resolution of wall motion abnormalities, and these patients were also more likely to experience angina during the stress test. The authors concluded that well-developed collat- eral vessels may lead to rapid resolution of wall motion abnormalities and may account for some cases of false-negative postexercise cchocardio- graphic results. Duration of ischemia may also be a factor. Because the rate of recovery of systolic function is directly related to the duration of ischemia,**,*” rapid recovery would be more likely in patients who stop exercising earlier in the course of ischemia. Patients in whom ischemia was associated with chest pain may have their test terminated earlier than those who fail to manifest angina. This could partly explain the increased likelihood of rapid recovery in patients with angina.

There are few data directly comparing these different stress methodologies. Some reports have suggested a slightly higher sensitivity, but lower specificity, using bicycle versus treadmill exercise.24 Most recent studies have confirmed that both techniques arc feasible and provide accurate diagnostic information.2”2x

In summary, the opportunity to image at peak exercise is an advantage of bicycle exercise. This may contribute to greater sensitivity, perhaps at the expense of lower specificity, for the detection of coronary artery disease. As yet, there arc no data comparing peak bicycle imaging to posttread- mill imaging. Because of differences in workload achieved, one cannot assume that postexercise imaging following bicycle and treadmill testing are equivalent. Wall motion abnormalities may persist longer into recovery following treadmill exercise, facilitating echocardiographic detection. Both exercise modalities are currently being used succcss-

fully in many laboratories, and as yet there is no compelling evidence that one is clearly superior to the other.

ADVANTAGES OF DtGlTAl IMAGING The field of stress echocardiography has bene-

fitted in recent years from the application of digital recording methods (Table II).i4,i5 This technology permits the creation and display of a “tine loop,” that is, a series of images (usually 8) played in an endless-loop sequence. By convention, the loop begins with the R-wave and is composed of either the entire cardiac cycle or, more commonly, only systole.

Once digitized, the images can be displayed in a variety of ways. For example, a quad screen display can be created in which each quad is an g-cell sequence, synchronized to the R-wave. This format allows analogous views at rest and with stress to be displayed side-by-side. Such a display greatly facilitates comparison of baseline and stress images. This is much preferable to videotape analysis and facilitates detection of subtle differences, thus enhancing sensitivity.

Digital recording also reduces image acquisition time. Since only a single cardiac cycle is needed to create the tine loop, the recording time of each view can be abbreviated. This is particularly important for immediate postexercise imaging, when minimizing recording time is crucial to avoid miss- ing transient wall motion abnormalities. The prob- lems of respiratory interference can also be par- tially eliminated through the use of these methods.

Digital techniques also contribute to the convenience of stress echocardiography. Storage, retrieval, and display of stress echocardiograms are favorably affected. An entire stress study can be stored on a single floppy disk. The images can be readily recalled, either from the floppy disk, optical disk, or from the computer’s hard disk. Teaching and communication with referring physicians are enhanced by these features.

Digital recording is readily adapted to all forms of stress echocardiography and has a favorable impact on accuracy and convenience. The equipment is affordable and can be directly incorporated into the ultrasound machine. Attempting stress echocardiography without the digital recording approach should generally be discouraged.

IHTERPREl’AllOH OF STRESS ECHOCARDIOGRAMS

When compared with other stress imaging modalities, an advantage of echocardiography is its

84H THE AMERICAN JOURNAL OF CARDIOLOGY VOLUME 69 JUNE 18, 1992

ability to record LV wall motion in multiple tomo- graphic planes. By comparing regional wall motion before, during, and after exercise, one can distin- guish: (1) the normal hyperdynamic response to exercise; (2) evidence of prior infarction (or perhaps hibernating myocardium), characterized by a stable wall motion abnormality; and (3) evidence of ischemia, identified by the development of a new wall motion abnormality during stress.

In general, the absence of a hyperdynamic response to exercise should be considered abnormal. However, there are several notable exceptions to this rule which must be considered in order to avoid false-positive results. This is particularly true when analyzing postexercise images. In this situation, wall motion that appears normal and un- changed from baseline (but not necessarily hyperdynamic) should be interpreted as “normal.” Causes of a lack of hyperkinesis in the absence of coronary artery disease include cardiomyopathy, markedly increased blood pressure, B-blocker ther- apy, and a low level of exertion.

The development of a new regional wall motion abnormality during or immediately after exercise is quite specific for ischemia. In fact, any degree of deterioration of wall motion should be considered evidence of ischemia, provided that wall motion is normal at rest. Worsening of a preexisting wall motion abnormality during exercise represents a diagnostic dilemma. Although some investigators have considered this an ischemic response, others suggest that it is nonspecific, possibly representing either ischemia or prior infarction.

The uncertainty exists because unfavorable alter- ations in local loading conditions could lead to a deterioration in regional systolic function in the absence of ischemia. Thus, one of the unresolved issues in exercise echocardiography is how to interpret a worsening wall motion abnormality. Is it possible to detect induced ischemia within an area of prior infarction? A preliminary study has suggested that this may not be feasible.29 At Indiana University, a hypokinetic segment that becomes akinetic or dyskinetic with stress is labeled isch- emit, whereas an akinetic area that worsens with stress is considered evidence of infarction (in which the issue of ischemia cannot be addressed).

Exercise echocardiograms can be interpreted using a variety of qualitative and quantitative approaches. Each interpretive method has its advantages and disadvantages, although all provide useful diagnostic data with an acceptable degree of reproducibility. 3o It should be recognized that a learning curve exists for proper interpretation, and

a training period of at least 100 studies may be required before optimal results can be expected.31

DIAGNOSTIC ACCURACY OF EXERCISE ECHOCARDIOGRAPHY

The reported accuracy of exercise echocardiography varies somewhat, partly due to differences in technique, patient population, and criteria used to define an abnormal response. Earlier studies reported sensitivities for the detection of coronary artery disease in the range of 50-90%.8-10J2J7 In this era, prior to the advent of digital imaging methods, adequate images could be obtained in approximately 7040% of patients. Some studies have included a relatively high percentage of patients with myocardial infarction (MI), most of whom had resting wall motion abnormalities. This tends to inflate sensitivity, since the diagnosis of coronary artery disease is readily apparent by virtue of a baseline abnormality.

More recent studies, using digital technology, have demonstrated higher sensitivity and feasibility (Table III). Armstrong et aP* examined 123 patients before and immediately after treadmill exercise and stratified the cohort on the basis of prior infarction and extent of angiographic disease (de- fined as 250% coronary artery narrowing). Over- all sensitivity was 88% and specificity was 86%. Sensitivity was higher in patients with multivessel disease (93% vs 81%) and in patients with prior MI. This latter result would be anticipated on the basis of resting asynergy. In a subsequent study in which patients with rest wall motion abnormalities were excluded,33 sensitivity was lower (78%) and specificity was improved. Although the overall accuracy was acceptable, the ability of the test to detect multiple wall motion abnormalities specifi- cally in patients with multivessel disease was limited. Subsequent reports have largely confirmed the overall accuracy of the test and have demonstrated its particular value in those patients with a nondiagnostic stress electrocardiogram (ECG).34

As experience grows and technology continues to evolve, accuracy predictably improves. Crouse et a125 recently reported their experience in 228 patients studied with treadmill exercise echocardiography and coronary angiography. These investigators insisted on the development of hyperdynamic wall motion postexercise to be considered normal- absence of hyperkinesis was interpreted as evidence of disease. Using these criteria, they reported a sensitivity of 97% overall and 100% in those patients with multivessel disease. Accuracy was substantially greater compared with the stress

A SYMPOSIUM: FUTURE OF ECHOCARDIOGRAPHY 8!jii

i TABLE III Accuracy of Treadmill Exercise Echocardiography.

I

Sensitivity*

Study Year

Maurer and Nandalo 1981

Robertson et aI17 1983

Limacher et al’* 1983

Heng et aI16 1984 West et alI5 1985

Armstrong et aP 1986 Armstrong et aP 1987

Ryan et aI33 1988

Sawada et aI24 1989

Sheikh et al.26 1990

Crouse et alz5 1991

No. Overall Patients (%)

48 86

30 100

77 91

47 100 96 85

95 88 123 a7

64 78

38 80

34 74

228 97

NoMl w

83

100

- -

80 78

78

-

74

-

Specificity (%I

92

75

88

93 71

87 86

100

94

91

64

Success+ (%)

85

92

99

a7 -

100 -

100

100

100

Sensitivity is presented for the entire study (overall) and, when possible, for the cohort of patients without prior myocardial infarction (No MI). tPercentage of patients in whom technically adequate echocardiograms were obtained.

ECG, and multiple wall motion abnormalities were detected in 93 of 106 patients with multivessel disease. Not surprisingly, specificity was rather low (64%).

No study of comparable size has examined the overall accuracy of bicycle exercise echocardiography. Duchak et al’s reported a series of 72 patients, all of whom underwent bicycle stress testing prior to coronary angiography. Sensitivity for the detection of coronary artery disease was 94% for the entire group and 88% for the subset of patients with normal wall motion at rest. Of 33 patients with multivcssel disease, 28 had either an induced wall motion abnormality or multiple abnormalities at rest. Inclusion of the peak exercise images improved sensitivity by identifying 9 patients with abnormalities not present on the postexercise images. However, 4 of these were false- positive results, which reduced overall specificity to 70%.

Two recent studies have addressed the potential for exercise echocardiography to predict the severity of coronary artery narrowing. Sheikh et al*” examined 34 patients with single-vessel disease and normal wall motion at rest, using treadmill exercise and coronary angiography. They demonstrated that wall motion abnormalities were frequently associated with stenoses 275% (by visual estimate) and were rare with stenoses 125%. How- ever, in patients with moderate coronary narrowing (approximately 50%) wall motion response was variable. Using quantitative angiographic techniques, a close correlation between wall motion and minimal luminal diameter was found.

Agati and his colleagues27 obtained similar results studying 57 patients with single-vessel disease. They correlated several quantitative angiographic

parameters with segmental area changes using echocardiography. The severity of coronary narrowing was related to the decrease during exercise of the segmental fractional area change. Although the quantitative echocardiographic approach was effective for detecting severe coronary stenosis, changes in wall motion were variable in patients with less severe narrowing.

These 2 clinical studies confirm the ability of exercise echocardiography to detect severe coronary disease and to provide an estimate of the physiologic significance of the lesion. The consistent observation that wall motion response is variable in the setting of “moderate” disease suggests that the measurement of arterial narrowing is not the sole determinant of inducible ischemia. Thus, changes in wall motion can provide an independent measure to assess the functional significance of “borderline” coronary lesions.

COMPARISDN WITH OTHER IMAQlNG MODAWES

Several early studies compared exercise echocardiography with radionuclide techniques. Crawford et a135 examined the ability of bicycle exercise echocardiography and radionuclide angiography to detect changes in ejection fraction during exercise. This was the first study to demonstrate that LV volume and ejection fraction could be measured during exercise using 2-dimensional echocardiography, with acceptable intra- and interobserver variability. For the detection of coronary artery disease, most investigators have found that the 2 tests are comparable. r2,r3 At least one study has suggested that exercise echocardiography may be more sensitive for the identification of patients with single-vessel disease,‘* although this has not

86H THE AMERICAN JOURNAL OF CARDIOLOGY VOLUME 69 JUNE 18. 1992

been a consistent finding.‘” The advantages of exercise cchocardiography over radionuclide vcn- triculography arc several. Echocardiography is to- mographic rather than planar, thus permitting a more complete assessment of LV wall motion. Because echocardiography is a real-time examina- tion, it allows instantaneous beat-to-beat recording rather than averaging the imaging data over several minutes. Finally, echocardiographic methods arc cost effective and totally noninvasivc.

Studies comparing echocardiography with myocardial perfusion scintigraphy have generally demonstrated concordant results.8J0J5,3” The largest series to date, a preliminary report by Haichin ct a1,29 examined 145 patients with treadmill exercise echocardiography and single photon emission computed tomography (SPECT) thallium-201 imaging. Agreement as to the presence or absence of coronary disease occurred in 90% of casts. One potential advantage of perfusion imaging may be to detect ischemia within areas of prior infarction. In this study, 15 patients had a “mixed” perfusion defect in an area of resting akinesis. The signifi- cancc of worsening wall motion in regions of prior infarction has not been carefully investigated with exercise cchocardiography. Thus, thallium-201 imaging may be advantageous in this setting.

More recently, Pozzoli et a13’ compared the diagnostic accuracy of upright bicycle exercise echocardiography and technetium-99m MIBI SPECT in 75 patients. Concordance was 88% and both echocardiography and scintigraphy were supc- rior to the stress ECG. Although the 2 tests were equally sensitive for the detection of multivcssel disease, echocardiography was significantly less sensitive for the detection of patients with singlc- vessel disease. The difference could be explained almost entirely by an inability of exercise echocardiography to identify left circumflex coronary artery disease. Although upright bicycle ergometry was used, peak exercise imaging was not performed and this may account for some of the false-negative results.

Thus, exercise echocardiography and perfusion imaging techniques provide similar information on the presence of inducible ischcmia or prior infarction. Most studies to date could be criticized because one or the other method is not considered “state-of-the-art.” As yet, no large series exists in which both imaging modalities arc optimally pcr- formed and then correlated with coronary angiography. Despite this, a high degree of concordance has been demonstrated by several investigators. Scintigraphic methods may bc advantageous in

TABLE IV Indications for Exercise Echocardiography

0 Patients who have had a prior nondiagnostic stress test

0 Patients with a high likelihood of a false-positive stress ECG, such as women or those taking digitalis

0 Patients with conduction or repolarlzation abnormalities rendering the stress ECG drficult to Interpret

0 Patients with a high pretest likelihood of disease In whom the test IS done to determlne the extent and/or location of ischemla

0 Patrents who had or will have an intervention to assess the physlo logic significance of a lesion or to determme the success of the intervention

0 Patients recoverlngfrom Ml In whom prognostic informatlon is needed

Adapted from a Positron Paper of the Amerean College of Cardiology Approved by the ACC Board of Trustees. October 22, 1989.

ECG = electrocardiogram; MI = myocardlal Infarction. J

some situations, such as patients with single-vessel disease or to detect ischemia within an area of prior infarction. Echocardiography is considerably less expensive and more convenient. There is no exposure to radiation and patients are not required to return later for redistribution imaging. Echocar- diography also yields ancillary information on val- vular and pericardial disease.

CLINICAL INDICATIONS FOR EXERCISE ECHOCARDIOGRAPHY

The improved accuracy and supplemental information provided by exercise cchocardiography must be balanced against the added complexity of imaging. Clearly, all stress tests do not require the addition of echocardiographic monitoring. In which situations are the added cost and inconvenience of imaging justifiable? Several studies have addressed this issue and the American College of Cardiology has recently provided some guidelines (Table IV).

It is well established that echocardiography improves the sensitivity and specificity of exercise testing. It also provides information on the extent and location of disease. Thus, to use exercise echocardiography properly one must consider 2 issues: (1) the clinical question that is being asked, and (2) the likelihood that routine stress testing will not provide the entire answer. The most common scenario involves the patient who either has had or likely would have a nondiagnostic stress ECG. In this situation, the inclusion of echocardiography significantly increases the yield of the test.

Armstrong et al 34 demonstrated that the prcs- ence or absence of coronary artcry disease can be correctly predicted using cchocardiography in approximately 75% of patients with an ambiguous or false-negative treadmill ECG. Depending on the population, as many as 60% of patients could be included in this category. Women seem particularly prone to such nondiagnostic results, due to


TABLEV Use of Exercise Echocardiography to Predict Clinical Outcome in Patients Recovering from Myocardial Infarction

No. Study Patients Sensitivity Specificity Criteria

Jaarsma et alLr. 43 75% 78% Transient remote asynergy

Applegate et aI45 67 63 80 New/worse WMA

Ryan et al&s 40 80 95 New WMA

WMA = wall motion abnormality.

their lower prevalence of disease and increased likelihood of a false-positive stress ECG. Sawada et a124 examined the utility of stress echocardiography in this important subset of patients. In a series of 57 women patients, a correct diagnosis was obtained in 85% of women patients and the accuracy was preserved in those with atypical symptoms (84%) and a nondiagnostic stress ECG (82%).

There are several other situations in which exercise echocardiography has proven valuable. Following revascularization, for example, the test is useful to confirm a successful intervention, to detect residual ischemia, and to help plan subsequent management. Two clinical studies have addressed the role of exercise echocardiography following coronary bypass surgery.38,3g Both have demonstrated the ability of the test to detect and localize nonrevascularized vessels and/or graft disease. The superiority of wall motion analysis over the stress ECG was confirmed in both clinical trials.

A similar approach is possible in patients under- going angioplasty. 4o-42 Prior to the procedure, the stress test can detect and localize ischemia. After- ward, an improvement in rest wall motion can often be demonstrated. The stress echocardiogram can confirm a successful intervention by detecting resolution or a reduction in inducible regional dyssynergy. It may also bc possible to detect early restenosis, even when other manifestations of ischemia are absent. Finally, the test can provide a baseline for later comparison, should symptoms recur.

The prognostic value of exercise echocardiography has also been evaluated. Among patients referred for exercise testing because of suspected coronary artery disease, a normal exercise cchocar- diogram is highly predictive of a good prognosis.43 If one series of 148 patients followed a mean of 28 2 9 months after a normal treadmill exercise echocardiogram, the event rate was very low. During follow-up, 4 patients had coronary bypass surgery, 2 patients had MI, and there were no

deaths. All 6 events occurred in patients who exercised to a work load <6 METS or achieved < 85% of their age-predicted maximum heart rate.

Valuable prognostic data can also be obtained in patients recovering from MI. Scvcral investigators have studied patients during the convalescent phase following MI and have demonstrated the fundamental relationship between inducible ischcmia and outcome (Table V).- The presence of multiple resting wall motion abnormalities (suggesting multivessel disease) or an induced wall motion abnormality following exercise (suggesting ischemia) identify patients at increased risk for cardiac events over 6-12 months follow-up. Exercise echocardiography would appear ideally suited to provide prognostic information. This likely reflects the fundamental importance of regional LV wall motion as a marker for ischemia.

CONCLUSION Exercise cchocardiography is a technique that

can be adapted to a variety of forms of stress testing. It is safe, versatile, cost-effective and clinically useful. It is now established that wall motion analysis increases the accuracy of stress testing to detect coronary artery disease. The increased yield is similar to that provided by nuclear imaging methods, although cost and convenience are clear advantages of echocardiography. It appears likely that the clinical application of this diagnostic test will continue to grow and that it will assume an expanding role in the management of patients with coronary artery disease.

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