Case Studies In Small Animal

Cardiovascular Medicine

Home Up .    Radiographs ECG 2D Echo M-Mode Color Flow Doppler Diagnosis

Case 10

M-mode Echocardiography

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This M-mode echocardiogram shows a markedly enlarged left ventricular end-diastolic diameter (7 cm [normal = 4.7 cm]) and a moderately enlarged end-systolic diameter (5 cm [normal = 3.2 cm]). The shortening fraction is 29% which is within the normal range (25% to 40%). Even though the shortening fraction is within normal range, myocardial contractility is at least moderately decreased as evidenced by the moderate increase in end-systolic diameter (note that the shortening fraction is within the normal range because the end-diastolic diameter is larger than normal). Myocardial contractility, however, is not homogeneous as evidenced by discrepancies in wall motion between the interventricular septum and left ventricular free wall. The motion of the interventricular septum (IVS) is increased (hyperdynamic) while the free wall motion (LVFW) is reduced (in a normal heart the motion of the interventricular septum is less than that of the left ventricular free wall). Wall thicknesses of the left ventricle are normal (about 1 cm). This means the left ventricle must have grown larger since pure dilation would be characterized by a larger diastolic chamber diameter and thinner than normal walls. Consequently, there is eccentric or volume overload hypertrophy present. This is usually produced by sarcomeres (contractile elements) replicating within myocardial cells (myocytes) in series (end to end) resulting in the myocytes growing longer. Note that the left ventricular free wall continues to move upward (toward the interventricular septum) for a short time after the end of systole (where the markers have been placed. If one places the markers slightly to the right, at the peak of the left ventricular free wall motion, the distance between the interventricular septum and the left ventricular free wall are exactly the same as they are in the position above. This means the last portion of the motion is due to the whole heart moving toward the transducer, not due to actual contraction.

This dog's E point to septal separation (EPSS) was 16 mm which is at least moderately increased from the normal of less than 6 mm. His left atrial diameter on a short-axis basilar view was 48 mm compared to an aortic diameter of 20 mm for a ratio of 2.4 (normal is less than 1.5).

 

Mark D. Kittleson, D.V.M., Ph.D. All rights reserved.