The potential value of echocardiography is ischemic heart disease
lies in two areas: assessment of left ventricular function and
diagnosis of complications that arise as sequelae of infarction.
Unfortunately, many patients with ischemic heart disease are
overweight or heavy smokers, and have large `barrel' chests with
hyperinflated lungs. These factors make complete echocardiographic
visualization of the left ventricle difficult. Even a limited
examination is at times impossible in some patients. Such limitations
must be borne in mind when assessing the potential clinical value
of an echocardiographic study.
 |
| Fig. 48 |
Left ventricular wall motion characteristics are altered by transmural
myocardial infarction. The changes are usually regional and may
be detected by echocardiography provided that the ultrasound beam
traverses the affected area and that image quality is satisfactory.
 |
| Fig. 49 |
(Fig.
48) demonstrates an akinetic septum resulting from an anteroseptal
infarction while
(Fig.
49) shows akinesis of the posterior wall.
 |
| Fig. 50 |
Two-dimensional echocardiography is usually superior for this
purpose because its wider field of view provides the ability to
locate and determine the extent of the infarcted myocardium. Cases
of extreme systolic wall thinning and/or dyskinesia are readily
apparent from inspection of sequential two-dimensional echocardiographic
frames. (Fig.
50) shows extensive thinning and akinesis of the septum from
a patient with a massive anteroseptal infarction.
 |
| Fig. 51 |
Usually, such wall motion abnormalities are best evaluated by
comparison of the diastolic and systolic images. (Fig.
51) shows paired short axis views from a patient with normal
wall motion characteristics. Note the symmetry of the ventricle
in both diastole and systole.
 |
| Fig. 52 |
It must be kept in mind that the heart moves through the interrogating
plane as it cycles through diastole and systole. This gross movement,
even in normal individuals causes different regions of the myocardium
to be interrogated in systole and in diastole and may lead to spurious
interpretive errors (Fig.
52).
In addition, incorrect orientation of the short axis plane such
that the ventricle appears eliptical rather than circular will cause
any motion of the posteroseptal and lateral walls to appear exaggerated.
Another common error in interpretation of wall motion abnormalities
concerns the relative movements of the endocardium, epicardium and
pericardium. In normal individuals, the movement of the epicardium
and/or pericardium is much less than the endocardium. In patients
with marginal image quality where only a portion of the endocardium
is identified, the interpreter should not compare areas of endocardial
movement to areas of movement where only the pericardium is visualized.
This leads to the incorrect interpretation that asynergy is present
in the poorly visualized segment.
 |
| Fig. 53 |
If images of suitable quality are available, it is possible to analyze
ventricular wall motion on a regional basis and to apply semiquantitative
or quantitative descriptors to each segment of the myocardium. A
number of simple and complex formats for performing such assessment
have been proposed. (Fig.
53) illustrates the most simplistic format where the ventricle
is divided into five segments: septal wall, anterior wall, posterior
wall, inferior wall and apex. Using all the views possible, most
wall segments can be located echocardiographically, albeit some
with difficulty. Wall motion is then scored as normal, hypokinetic,
akinetic or dyskinetic in each of the five segments.
 |
| Fig. 54 |
The most reliable interpretation of these changes comes from assessment
of the moving image rather than still-frames. An inferior area of
hypokinesis is seen in the short axis of the left ventricle shown
in (Fig.
54).
Animal studies have indicated that wall motion abnormalities will
occur almost instantaneously following coronary ligation. The utility
of such an examination depends upon the clinical questions posed.
For example, echocardiography may be used to assess the extent of
damage in a patient with classic EKG and enzyme changes of a myocardial
infarction. In patients without classical changes, echocardiographic
assessment may be helpful in influencing the clinical decision making
process by detecting the presence or absence of wall motion changes.
Recent advances in computer technology have allowed for the digitization
of a single cardiac cycle and for continuous loop replay to assist
the interpreter in detecting wall motion abnormalities. This technology
also allows for the placement of similar views side-by-side on the
same screen before and after exercise. Since only one beat is required,
it can usually be captured despite the patient's heavy breathing
following peak exercise. Such features in instrumentation are referred
to as "cine- loops".
Thus, echocardiography is now growing in use for the exercise evaluation
of patients with suspected coronary artery disease using protocols
roughly equivalent to those used for radionuclide evaluations. When
image quality is adequate, echocardiography serves as a cheaper
alternative that does not require the use of isotopes. Because no
ionizing radiation is involved, patients may be evaluated more often
depending upon the clinical situation involved. Multiple recent
studies have indicated that this approach is as reliable as other
methods and serves as a suitable alternative.
2004