Edmund A Bermudez Md Mph and Ming Hui Chen MD MMSc

Contents

Introduction Indications Stress Protocols Interpretation Pitfalls

Suggested Reading introduction

Stress echocardiography is a common diagnostic procedure used in the evaluation of coronary artery disease. In fact, stress echocardiography is now a widely accepted test utilized for the diagnosis, prognostication, and risk stratification of ischemic heart disease (Fig. 1). Imaging is most often coupled with treadmill stress, however, it can be easily coupled with pharmacological stress, bicycle exercise, or pacing. In skilled hands, stress echocardiography is safe, versatile, and accurate, providing important information on segmental wall motion and overall ventricular function.

The interpretation of echocardiography images is based on changes in regional myocardial thickening with stress. In the setting of significant coronary artery disease, regional myocardial thickening will decrease as a result of oxygen supply-demand mismatch. The area supplied by the stenosed coronary artery will, therefore, display a change in contraction, enabling the identification and extent of underlying coronary ischemic disease. In the absence of hemodynamically significant coronary stenoses, an increase in systolic wall thickening should be observed in all coronary territories with a decrease in the size of the left ventricular cavity. Therefore, localization and burden of ischemic heart disease can be routinely assessed.

indications

Stress echocardiography is indicated in the diagnosis of coronary artery disease in those with an intermediate likelihood of coronary artery disease and an abnormal electrocardiogram (Fig. 1, Table 1). Those individuals with left bundle branch block, Wolff-Parkinson-White syndrome, left ventricular hypertrophy, digoxin use, or more than 1 mm ST segment depression on electrocardiogram should undergo imaging with stress as interpretation of ST segments are an unreliable marker of ischemia in these settings. If the patient is able to exercise, treadmill stress, or bicycle stress (supine or upright) should be performed. When this is not feasible, dobutamine stress may be used. In the United States, vasodilator stress is an uncommon modality for stress echocardiography.

In peri-operative evaluations for noncardiac surgery, stress echocardiography can aid in risk stratification. According to the American College of Cardiology/ American Heart Association guidelines, stress echocardiography is indicated when there are intermediate predictors of cardiovascular risk with low functional capacity or when a high-risk surgical procedure is planned. When high-risk results are obtained (extensive inducible wall motion abnormalities) from this testing, coronary angiography is usually warranted. However,

From: Contemporary Cardiology: Essential Echocardiography: A Practical Handbook With DVD Edited by: S. D. Solomon © Humana Press, Totowa, NJ

Clinical Exercise Testhttp://www.acc.org/clinical/guidelines/exercise/fig1.htm.)"/>
Fig. 1. American College of Cardiology/American Heart Association (ACC/AHA) guideline update on stress testing. (Modified from ACC/AHA Exercise Testing Guidelines: http://www.acc.org/clinical/guidelines/exercise/fig1.htm.)

when no wall motion abnormalities can be induced with adequate stress, surgery can usually be performed at relatively low risk for perioperative events.

Stress echocardiography can be used for prognostic purposes in those with chronic coronary artery disease and in post-myocardial infarction. As in risk stratification, the extent and severity of ischemia as evidenced by inducible wall motion abnormalities is a main determinant of prognosis, as well as overall left ventricular function. Among individuals with known or suspected coronary disease, a normal stress echocardiogram portends a more benign prognosis compared to those with abnormal stress echocardiography results. In addition, the presence of viability with dobutamine echocardiog-raphy (biphasic response) in those with coronary artery disease can identify those in whom revascularization and functional recovery is more likely (see Chapter 5, Fig. 17).

Finally, stress echocardiography can be utilized with Doppler to evaluate valvular function. In those individuals

Table 1

Overview of Qualitative Reporting of Left Ventricular Wall Motion Abnormalities During Stress Echocardiography

Wall motion/endocardial thickening at baseline

Wall motion/endocardial thickening at peak stress

Interpretation

Normal Normal Hypokinetic

Akinetic (± wall thinning) Hypokinetic/akinetic

Hyperdynamic

Hypokinetic-akinetic

Worsening hypokinesis

Akinetic-dyskinetic

Augmentation with lower dose of dobutamine; deterioration with high dose (biphasic response)

Normal Ischemic Ischemic Infarcted

Viability with ischemia

Augmentation with lower dose of dobutamine; deterioration with high dose (biphasic response)

Stress Echo Protocol
Fig. 2. Exercise stress echocardiography protocol.

with small, calculated aortic valve areas, low ejection fractions, and low transaortic gradients, stress echocar-diography can be used to increase cardiac output and further define the severity of aortic stenosis by calculating changes in aortic valve area with stress. In a similar fashion, mitral stenosis can be evaluated and pulmonary systolic pressures calculated after or at peak stress. Therefore, in situations where the severity of stenotic valve lesions is questioned, stress echocar-diography may provide important information to guide management decisions.

stress protocols

Exercise Echocardiography (Fig. 2)

Standardized images are acquired before the initiation of exercise and immediately after exercise. Two paraster-nal views (parasternal long axis and parasternal short axis) and two apical views (apical four-chamber and apical two-chamber) are used to assess endocardial wall motion (Fig. 3; please see companion DVD for corresponding video). A common practice is to hold atrioven-tricular nodal blocking agents prior to testing, as the attainment of at least 85% of predicted maximal heart rate is desirable. It is important that the acquisition of images occurs immediately postexercise when using the treadmill machine. If images are acquired late after exercise, the heart rate may decrease substantially, giving time for any peak wall motion abnormalities to subside and, therefore, go undetected. The use of a supine bicycle machine may improve the timing of image acquisition, as images can be acquired at almost any time point during exercise and give true peak stress imaging. It is, therefore, believed that supine bicycle imaging may improve the sensitivity of testing over treadmill exercise.

Pharmacological Stress Echocardiography (Fig. 4)

Pharmacological stress echocardiography is utilized when patients are unable to exercise maximally. In the diagnosis of the coronary artery disease, stress to maximal

Immediate Post-Exercise

Peak Systolic Frames

Immediate Post-Exercise

Peak Systolic Frames

Fig. 3. This 45-yr-old man with a history of hypertension and new right bundle branch block exercised for 12 min on a standard Bruce protocol, stopping secondary to fatigue. Heart rate and blood pressure at peak exercise was 179 bpm and 168/78 mmHg, respectively. There was 1-mm ST segment depression in lead III, becoming upsloping in V4-V6. Baseline left ventricular dimensions were within normal limits with estimated ejection fraction of 60-65%. No regional wall motion abnormalities were present. Immediate postexercise imaging showed appropriate decrease in left ventricular chamber size with augmented contractility of all ventricular (A,B). (Please see companion DVD for corresponding video.)

Stress Echo Protocol
Fig. 4. Dobutamine stress echocardiography protocol.

levels is an important component in the evaluation. However, in regard to viability testing, dobutamine echocardiography is primarily utilized over exercise stress in the identification, localization, and extent of viable myocardium.

Dobutamine is the most commonly utilized pharmacological agent that is combined with echocardiography for the assessment of coronary artery disease. This cardiac inotrope provides stress through pi receptor stimulation and increasing myocardial oxygen consumption. Typically, dobutamine is infused in 3-5 min stages starting at low doses (5 ^g/kg/min) and increased until the maximal predicted heart rate is achieved or peak infusion levels are reached (40 ^g/kg/min) (Figs. 4 and 5). Additional intravenous injections of atropine may be used to augment the heart rate in some individuals whom higher heart rates are needed. At peak levels, it is not uncommon to observe a drop in systolic blood pressure, owing to the mild vasodilatory effects of dobutamine. In contrast to exercise stress, this drop is not specific for severe coronary ischemia.

Echocardiography images are obtained in the same views as treadmill testing, i.e., the parasternal long, parasternal short, apical four-, and apical two-chamber views. Images are acquired at rest before infusion, low dose infusion (5 or 10 ^g/kg/min), peak infusion, and postinfusion. Images are displayed in quad-screen format (the four views mentioned previously on one screen) for each stage and routinely digitized for interpretation (Fig. 5; please see companion DVD for corresponding video). This protocol is often augmented when resting wall motion abnormalities are seen on the echocardiographic images. In this case, images are often acquired at both low dose levels (5 and 10 ^g/kg/min) to capture any changes in wall motion with low-dose infusion.

Vasodilator and Pacing Stress

As in nuclear stress testing, vasodilator stress has been used in combination with echocardiography. The agents typically used are dipyridamole or adenosine, both of which cause coronary vasodilation and perfusion mismatch with subsequent ischemia when significant stenoses are present. This approach has not been routinely applied in the United States, however, has been more extensively used in Europe.

Pacing can be used when exercise and pharmacological means are not feasible because of contraindications. Pacing is more favorably achieved via the atrium, as ventricular pacing may cause differential wall contraction and theoretically pacing induced wall motion abnormalities. Atrial pacing can be accomplished through esophageal pacing leads. This modality has not gained wide use, because it appears more invasive than pharmacological stress and may cause discomfort in some patients. Nonetheless, this modality offers an alternative

Abnormal Stress Echo

Fig. 5. (See legend facing page)

Diastolic Frames

Fig. 5. (See legend facing page)

to pharmacological measures, and ensures the ability to achieve maximal heart rates.

interpretation

The myocardium is divided into 16 segments (see Chapter 5, Fig. 10A) corresponding to different coronary territories: left anterior descending distribution, right coronary artery distribution, and left circumflex distribution. In general, the anterior, septal, and apical segments are supplied by the left anterior descending, lateral, and basal posterior segments by the left circumflex, and the inferior and posterior segments by the right

Fig. 5. A 64-yr-old female with coronary artery disease and aortic valve disease underwent dobutamine stress echocardiography. Graded doses of dobutamine were infused in 3 min stages to a peak dose of 40 |g/kg/min. Atropine (0.4 mg X 3) was given to achieve heart rate targets. Maximal heart rate achieved was 118 bpm (74% of predicted heart rate) and blood pressure was 110/82 mmHg. Patient had no symptoms. Baseline electrocardiogram showed normal sinus rhythm with ST abnormalities suggestive of a digitalis effect. Baseline echocardiogram showed dialated ventricular cavity size with estimated ejection fraction (EF) of 40-45% with akinesis and thinning of the basal-to-midanteroseptal and anterior wall. Images at peak infusion showed no increase in global systolic function (estimated EF 40%). The akinetic anteroseptal and anterior segments became progressively dyskinetic during the infusion—consistent with a transmural infarct/scarring. In addition, the inferior wall, mildly hypokinetic at baseline, becomes akinetic at the high dose of dobutamine. Overall study was consistent with a large anterior and anteroseptal infarct with no significant peri-infarct ischemia. Sensitivity was limited because target heart rate was not achieved. (Please see companion DVD for corresponding video.)

Fig. 5. A 64-yr-old female with coronary artery disease and aortic valve disease underwent dobutamine stress echocardiography. Graded doses of dobutamine were infused in 3 min stages to a peak dose of 40 |g/kg/min. Atropine (0.4 mg X 3) was given to achieve heart rate targets. Maximal heart rate achieved was 118 bpm (74% of predicted heart rate) and blood pressure was 110/82 mmHg. Patient had no symptoms. Baseline electrocardiogram showed normal sinus rhythm with ST abnormalities suggestive of a digitalis effect. Baseline echocardiogram showed dialated ventricular cavity size with estimated ejection fraction (EF) of 40-45% with akinesis and thinning of the basal-to-midanteroseptal and anterior wall. Images at peak infusion showed no increase in global systolic function (estimated EF 40%). The akinetic anteroseptal and anterior segments became progressively dyskinetic during the infusion—consistent with a transmural infarct/scarring. In addition, the inferior wall, mildly hypokinetic at baseline, becomes akinetic at the high dose of dobutamine. Overall study was consistent with a large anterior and anteroseptal infarct with no significant peri-infarct ischemia. Sensitivity was limited because target heart rate was not achieved. (Please see companion DVD for corresponding video.)

coronary artery (see Chapter 7, Figs. 3-5). However, there can be considerable overlap in perfusion territories and depends on coronary dominance, which should be taken into consideration when interpreting segments that may belong to more than one coronary distribution. More recently, a 17-segment model has been developed that takes into account the true apex (see Chapter 5, Fig. 10B). This model has neither been routinely used, nor made a significant change in interpretation of stress echocardiography images to date.

First, each myocardial segment is assessed for systolic thickening at rest and overall ventricular function. Areas of prior infarction are identified by thinned segments of hypokinesia or akinesia. Thickening is the primary measure of regional function, not myocardial motion itself. Second, the myocardial segments are examined at peak stress or post stress. Normal myocar-dial segments should sufficiently thicken to a greater extent with stress. The stress images are then analyzed in addition to the size of the left ventricular cavity,

Baseline

Dobutamine

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The Donts of Treadmill Buying

The Donts of Treadmill Buying

Though competitive runners are advised to run on the road, there are several reasons why you should buy treadmills anyway. You might have a family which means that your schedule does not have the flexibility it once had.

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