Augmentation Of Left Ventricular Wall Segments

Peak Systolic Frames

Fig. 6. A 72-yr-old female patient underwent dobutamine infusion with atropine to achieve targeted heart rate. Baseline echocardiography images showed borderline left ventricular hypertrophy with preserved systolic function. Minimal septal hypokinesis was noted. With increasing doses of dobutamine, augmentation of all segments accompanied by decrease in left ventricular cavity size up to a heart rate of 110 bpm. However, at heart rates more than 115 bpm, left ventricular dilatation accompanied by hypokinesis of the postero-inferior walls from base to apex was observed. These findings were consistent with ischemia in the right coronary/left circumflex artery territory. The septal wall that appeared mildly hypokinetic at baseline augmented during stress testing, suggesting no ischemia in this territory.

which should become smaller with augmentation of ejection fraction. When a myocardial segment thickens less with stress, hypokinesia or akinesia is present and signifies stress-induced ischemia (Fig. 6). Dyskinesia is defined by the presence of outward movement of the myocardium in systole in an area of akinesis (Fig. 5; please see companion DVD for corresponding video). If an abnormal area at rest does not change with stress, this result is likely secondary to infarcted or scarred myocardium. The thought is that the greater the supply-demand mismatch, the greater will be the deficit during systolic thickening. Areas surrounding zones of ischemia may display decreased thickening, or so-called tethering. Overall, the territories corresponding to areas of decreased thickening define the coronary distribution and extent of ischemia (Fig. 7; please see companion DVD for corresponding video).

A qualitative or quantitative approach to interpretation can be used. Qualitatively, each myocardial segment is observed at rest and with stress and an appreciation for single or multivessel ischemia can be assessed. However, quantitative schemes have been developed in order to gain a more objective, standardized interpretation for stress echocardiograms. In this light, each of the 16 myocardial segments is given a score: 1 for normal segments; 2 for hypokinetic segments; 3 for areas of akinesis; 4 for dyskinetic areas; 5 for aneurysmal segments (see Chapter 5, Fig. 1B). Areas that are unable to be visualized adequately are not scored. An overall index for wall motion is then calculated by summing all of the wall scores and then dividing by the number of segments analyzed. This can be done for the rest images and also for the stress images.

When dobutamine is used for the assessment of myocardial viability, the changes in myocardial thickening are assessed at rest, low dose, and peak images (see Chapter 5, Fig. 17). Viable myocardium that is more likely to recover function with revascularization is typical when a biphasic response is observed: hypokinesis at rest, improvement with low-dose dobutamine and worsening with high-dose dobutamine. This is the most specific

Rest

Immediate Post-Exercise

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Peak Systolic Frames

Fig. 7. A 58-yr-old man with a history of aortic insufficiency stopped 1 min 50 s into a standard Bruce protocol. Baseline echocardiogram showed hypokinesis of the basal inferior segment. Despite suboptimal test, peak systolic images showed modest increase in overall systolic function with estimated ejection fraction of 65-70%. All left ventricular segments, including the basal inferior segment, showed augmented contractility, with no inducible wall motion abnormalities. This finding indicates viable nonischemic myocardium with non-flow limiting coronary artery stenosis. (Please see companion DVD for corresponding video.)

Fig. 7. A 58-yr-old man with a history of aortic insufficiency stopped 1 min 50 s into a standard Bruce protocol. Baseline echocardiogram showed hypokinesis of the basal inferior segment. Despite suboptimal test, peak systolic images showed modest increase in overall systolic function with estimated ejection fraction of 65-70%. All left ventricular segments, including the basal inferior segment, showed augmented contractility, with no inducible wall motion abnormalities. This finding indicates viable nonischemic myocardium with non-flow limiting coronary artery stenosis. (Please see companion DVD for corresponding video.)

response for recovery of function following surgical revascularization. A uniphasic response is seen when an area of hypokinesis improves continuously with dobutamine infusion and also indicates myocardial viability but this area appears to be less likely to recover full function after revascularization. The definition of ischemia is the same as with exercise modalities, i.e., worsening of wall thickening with stress infusion of dobutamine.

The range of left ventricular wall motion characteristics seen during stress echocardiography and their interpretation are summarized in Table 1.

pitfalls

Stress echocardiography has its advantages and disadvantages (Table 2). Several caveats should be taken into account during interpretation. False-positive stress echocardiograms can result from a number of issues. First, a hypertensive response has been associated with a higher likelihood of wall motion abnormalities with stress in the setting of nonobstructive coronary artery disease. A hypertensive response has been defined as a systolic blood pressure over 220 mmHg for men and systolic blood pressure higher than 190 mmHg for women or as an increase in diastolic blood pressure higher than 10 mmHg with exercise or diastolic blood pressure higher than 90 mmHg during exercise. The exact mechanisms for this phenomenon are unclear but may be a result of abnormal loading conditions that eventually lead to subendocardial ischemia at the microvascular level.

Left bundle branch block may be a cause for false-positive readings (Fig. 8; please see companion DVD for corresponding video). With left bundle branch block, septal motion may be abnormal with systole as a result of the interventricular conduction delay. In this setting, one should again focus on thickening of the myocardium in the septal area and not on the septal motion. False-positive results may be related to increased heart rates in this setting. Therefore, one might speculate that vasodilator stress may be more specific in this setting, as has been the case with adeno-sine nuclear perfusion imaging.

Finally, interpretation of echocardiographic images can be difficult in certain patients. These patients may be obese individuals in whom inadequate penetration of the ultrasound beam results in poor endocardial resolution. Myocardial diseases, e.g., myocarditis can affect systolic performance and regional wall motion. Stress testing in this setting (for evaluation of chest pain) should be interpreted with caution (Fig. 9). Further, patients with chronic obstructive lung disease and hyperinflated lungs may impede the quality of echocar-diographic images. In situations where endocardial border definition may be tenuous, the addition of intravenous echocontrast agents may help to better delineate

Table 2

Advantages/Disadvantages of Stress Echocardiography

Advantages

Sensitivity and specificity comparable to exercise nuclear imaging Utility in diagnosis, prognosis, and risk-stratification

Assessment of multiple parameters: systolic function, valvular function, and ischemia

Widely available

Portability

Relatively inexpensive No radiation

No need for iodinated contrast agents

Disadvantages

Highly dependent on sonographer and interpreter skills

Difficult acoustic windows can limit imaging. Echocontrast agents may be necessary

Echocardiography

Fig. 8. A 62-yr-old man with baseline left bundle branch block (LBBB) exercised for 3 min, achieving peak heart rate of 115 bpm and peak blood pressure of 110/60 mmHg. Definity® (perflutren lipid microspheres) contrast agent was administered to improve endocardial border definition. Baseline images revealed moderately impaired left ventricular systolic function with abnormal septal motion (likely related to his LBBB) and hypokinesis of the mid- and distal septum. Postexercise images showed no increased contractility and worsening of septal hypokinesis. Findings are consistent with ischemia in the mid- and distal anterior septum—areas supplied by the left anterior descending coronary artery (see Chapter 7, Figs. 3-5; see also companion DVD for corresponding video).

Fig. 8. A 62-yr-old man with baseline left bundle branch block (LBBB) exercised for 3 min, achieving peak heart rate of 115 bpm and peak blood pressure of 110/60 mmHg. Definity® (perflutren lipid microspheres) contrast agent was administered to improve endocardial border definition. Baseline images revealed moderately impaired left ventricular systolic function with abnormal septal motion (likely related to his LBBB) and hypokinesis of the mid- and distal septum. Postexercise images showed no increased contractility and worsening of septal hypokinesis. Findings are consistent with ischemia in the mid- and distal anterior septum—areas supplied by the left anterior descending coronary artery (see Chapter 7, Figs. 3-5; see also companion DVD for corresponding video).

regional endocardial thickening (Figs. 8 and 10; please see companion DVD for corresponding video for Fig. 8). This procedure should be routinely employed should any question arise regarding image resolution on rest imaging. Ideally, if one should use contrast, it should be used for each set of images (rest and stress) so as to compare similar images with one another.

Acquisition of images post-treadmill exercise demands extensive experience in obtaining quality images for

Healthy Echocardiogram

Fig. 9. A 35-yr-old woman with recent onset chest pain and dyspnea exercised for 13 min on the Bruce protocol, stopping owing to fatigue. At rest (heart rate 60 bpm), basal inferior wall hypokinesis with preserved function of the remaining left ventricular segments were present. Immediate postexercise images obtained between heart rates 136-180 bpm showed abnormal septal motion with augmented contractility of the remaining segments. The differential diagnosis included postmyocarditis or a cardiomyopathy with possible exercise-induced septal ischemia at achieved workload. Clinical correlation and/or further evaluation with another investigative modality was recommended.

Fig. 9. A 35-yr-old woman with recent onset chest pain and dyspnea exercised for 13 min on the Bruce protocol, stopping owing to fatigue. At rest (heart rate 60 bpm), basal inferior wall hypokinesis with preserved function of the remaining left ventricular segments were present. Immediate postexercise images obtained between heart rates 136-180 bpm showed abnormal septal motion with augmented contractility of the remaining segments. The differential diagnosis included postmyocarditis or a cardiomyopathy with possible exercise-induced septal ischemia at achieved workload. Clinical correlation and/or further evaluation with another investigative modality was recommended.

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Responses

  • matthias
    How dangerous is an ECO finding that at peak stress the septum appeared relatively hypokinetic?
    1 year ago
  • esko
    Is augmentation in myocardial segments norma?
    8 months ago

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