Final Feigenbaum’s Echocardiography DIGITAL

Chapter 5 Evaluation of Systolic Function of the Left Ventricle

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Chapter 5 Evaluation of Systolic Function of the Left Ventricle

Evaluation of Systolic Function of the Left Ventricle

FIGURE 5.42. Schematic representation of the simplified methods for determining left ventricular wall stress. Wall stress can be defined as radial, circumferential, or meridional, all of which are mutually orthogo- nal. Meridional wall stress is the simplest to calculate. Circumferential wall stress incorporates the length of the left ventricle and is best cal- culated from the two-dimensional echocardiogram. Bottom: The rela- tionship of location to regional stress with respect to variation of wall thickness ( h ) and local radius of wall curvature ( r ) is depicted.

cross-sectional area of the annulus or of the mitral valve ori€ce is more problematic than determination of an out ow tract area and quantitative ow calculations from the mitral valve are rarely used in clinical practice. Nonischemic Wall Motion Abnormalities ere are several commonly encountered variations on wall motion abnormalities that deserve comment and which may be confused for ischemia or infarction (Tables 5.6 and 5.7). Tardokinesis refers to the delayed contraction of a segment of the le ventricle, typ- ically occurring in the €nal 50 to 100 ms of mechanical systole. Tardokinesis is most oen noted in the proximal inferior or poste- rior wall. It should be distinguished from postsystolic contraction which can be seen in an ischemic segment and may be most reliably detected with strain imaging. Isolated tardokinesis is rarely a man- ifestation of myocardial ischemia and is most oen seen at high heart rates in the stress phase of a stress echocardiogram. Another potentially confusing segmental wall motion €nding is early relax- ation, in which a segment relaxes or moves outward before the rest of the chamber. is €nding is generally considered a normal variant. It is noted most oen with stress echocardiography at high heart rates in individuals with preserved exercise tolerance. It is most commonly seen in the distal septum and apex and its location may not €t anticipated coronary anatomy. Typically one notes an abrupt relaxation of the ventricular wall occurring while the mitral valve is closed. e duration of early relaxation rarely exceeds 50 to 100 ms (Fig. 5.45). Le bundle branch block alters the sequence of electrical acti- vation and hence the sequence of contraction of the le ventricle. Normally, conduction down the le bundle precedes that down the right bundle by 10 to 20 ms, and hence the normal initial activation of the heart is in the proximal midseptum on the le ventricular

changes in forward ow. Figure 5.44 was recorded from patients with various disease states and shows the range in TVI values that can be encountered. Note in panels C and D the variation in TVI is due to rhythm disturbances. In theory, these same principles can be applied to any of the four cardiac valves or out ow or in ow tract dimensions. e right ventricular out ow tract, just below the pulmonic valve, provides information analogous to that for the le ventricular out ow tract. Comparison of the TVI-out ow tract area product at these two sites has been successfully used in congenital heart disease to compare right and le ventricular stroke volume and hence determine shunt ratios in patients with intracardiac shunts. In theory, similar cal- culations can be performed using either the mitral valve annulus or an average mitral valve area. In practice, determination of the

FIGURE 5.43. Schematic representation of the method for determining volumetric flow. This method is applicable for any laminar flow for which the cross-sectional area (CSA) of the flow chamber can be determined. The product of cross-sectional area and the time velocity integral (TVI) is stroke volume (SV). Cardiac output (CO) can be calculated as the product of stroke volume and heart rate. See text for further details.

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