Coronary Artery Regions

Systole

A3C I Diastole

Fig. 2. Pseudo-dyskinesis in 54-yr-old male with end-stage liver disease. Left ventricular walls in this 54-yr-old male with end-stage cirrhosis owing to chronic alcohol use and hepatitis C virus infection was normal during diastole (A-C). Apparent hypokinesis/ dyskinesis in the postero-inferior walls (B,D, arrows) was a result of external pressure from tense ascites secondary to his end-stage liver disease. (Please see companion DVD for corresponding video.)

echocardiographic findings in acute mi

Wall Motion Abnormalities

Among the earliest detectable changes in myocardial ischemia or an acute MI are regional LV and potentially also right ventricular wall motion abnormalities. The LV can be divided into 17 anatomic segments, which can be viewed as a composite from the standard echocardiography views, and have standardized nomenclature as recommended by the American Heart Association (AHA) (see Chapter 5, Figs. 1 and 10). Normal wall motion (normally kinetic segments) is seen as wall thickening, caused by the contraction of individual myocardial fibers; on echocardiography, this is seen as the radial distance between the epi- and endocardial borders, which increases by at least 10-20% during systole. Abnormal wall motion owing to insufficient blood supply to the myocardium may be graded as hypokinetic (thickening, but less than normal), akinetic (no thickening), and dyskinetic or aneurysmal (no thickening, with outward movement of the segment during systole, owing to increased intraven-tricular pressure on a scarred and noncontractile area of myocardial fibrosis). In general, myocardium that is transmurally infarcted tends to have more severe dysfunction, with akinetic or dyskinetic motion.

It is important to carefully distinguish between wall thickening, as opposed to just epicardial or endocardial border movement during systole. Pitfalls in diagnosing wall motion abnormalities abound: these include both false-positives owing to poor visualization of the endocardium (the artifact of echo "dropout"), superior angulation of the probe such that the membranous, nonmuscular portion of the upper interventricular septum is misinterpreted as an infarct, extracardiac compression of the inferior wall by ascites or abdominal contents ("pseudodyskinesis," see Fig. 2; please see companion DVD for corresponding video), and para

Fig. 1. (Continued) ventricular regions supplied by the left anterior descending coronary artery during systole. Compare these regions to the segments and coronary artery territories depicted in Figs. 3-5. (Please see companion DVD for corresponding video.)

Coronary Arter Bulls Eye

Fig. 3. "Bull's eye" left ventricular segmentation (American Heart Association [AHA]) with corresponding coronary artery territories. "Bull's eye" left ventricular segmentation (AHA nomenclature) with corresponding coronary artery supply. There are six basal segments (1-6), beginning with the antero-basal segment, and numbering in an anti-clockwise direction The next six middle segments (7-12) follow the same pattern, followed by the next four apical segments, and the last segment (17) occupying the tip. Compare this to the anatomical schema shown in Figs. 4 and 5.

Fig. 3. "Bull's eye" left ventricular segmentation (American Heart Association [AHA]) with corresponding coronary artery territories. "Bull's eye" left ventricular segmentation (AHA nomenclature) with corresponding coronary artery supply. There are six basal segments (1-6), beginning with the antero-basal segment, and numbering in an anti-clockwise direction The next six middle segments (7-12) follow the same pattern, followed by the next four apical segments, and the last segment (17) occupying the tip. Compare this to the anatomical schema shown in Figs. 4 and 5.

doxical or dissynchronous septal motion owing to bundle branch blocks or postsurgical states. False-negatives, i.e., missing a wall motion abnormality that is present, can also occur owing to poor image quality or off-axis imaging. In some cases, the injection of an intravenous contrast agent can help delineate endocardial borders.

The main epicardial coronary arteries supply distinct territories that should be individually evaluated during the ultrasound exam. In general, the LV can be divided into anterior, inferior, septal, and lateral quadrants. At the basal and midventricular levels, the septal and lateral walls are further subdivided into anterior and inferior sections. (Many cardiologists refer to the basal-most and more lateral portion of the inferior wall as the "posterior" wall.) Each wall is further divided along the long-axis into basal, mid, and apical thirds, with the distal apex designated as a separate segment, giving a total of 17 wall segments under the AHA scheme (Fig. 3; Chapter 5, Figs. 1 and 10).

Coronary Artery Territories

The majority of the blood supply to the heart is from the left main coronary artery, which normally arises from the left coronary cusp and divides into the LAD artery and left circumflex (LCx) (see Fig. 4). The LAD supplies most of the anterior ventricular wall (proceeding from base to apex, segments 1, 7, 13 [Fig. 5], and its septal branches also supply the anterior two-thirds of the septum [segments 2, 8, 14]). In addition, diagonal branches of the LAD supply the anterolateral wall (segments 6, 12). Large LADs can occasionally "wrap around" the apex of the heart and supply the distalmost portion of the inferior wall (segments 15, 17). The LCx runs in the atrioventricular groove and its branches (obtuse marginals) supply the inferolateral and lateral wall (segments 5, 11, 16). The right coronary artery (RCA) arises from the right coronary cusp, and supplies blood to the inferior one-third of the septum and the inferior wall (segments 3, 9, 14). It also supplies the right ventricle (RV) as well.

In an acute MI, a blockage in the coronary artery owing to a ruptured plaque and intraluminal thrombus causes partial or complete occlusion of the arterial lumen. This in turn reduces blood flow to the supplied segments, reduces contraction (and relaxation) of

\ ^Left Main Coronary LMCA ^ Artery (LMCA)

Right Coronary I . jAfl

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Coronary Artery (LCx)

LAO straight"^ Posterior Descending Artery (PDA)

Fig. 4. Coronary blood supply. Anatomical sketch depicting coronary blood supply. Still frames of right and left coronary angiograms appear as inserts. These main epicardial arteries give rise to intramural branches that further subdivide into subepicardial and subendocardial arterioles and capillary plexuses. In the normal heart, anastomotic branches and networks connect the major coronary arteries. These serve as the framework for collateral circulation development following total or near-total occlusion of a major epicardial artery.

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Responses

  • cora goodchild
    What is basal inferolateral dyskinesis?
    4 years ago

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