DK2985_C000 1..28 - AlSharqia Echo Club

Segmental Ventricular Function and Ischemia 167V. SEGMENTAL SYSTOLIC FUNCTIONCHANGESStudies and clinical experience have shown that segmentalwall motion abnormalities occur in the area supplied bythe obstructed artery within seconds after the interruptionof myocardial blood flow, well before (minutes) the developmentof ischemic electrocardiographic changes andchest pain (if they appear). Most quantitative methodsare based on the evaluation of wall motion. A segmentalwall motion abnormality is defined as hypokinesis whencontraction is normally directed but reduced in magnitude,akinesis when it is absent, or dyskinesis when there is systolicbulging (Table 8.1).A semiquantitative assessment of regional left ventricularcontraction is provided by the wall motion score index(WMSI). The LV is divided into 17 segments (2) assuggested by the American Society of Echocardiography(ASE) and a score is assigned to each segment, accordingto its contractility (18). A score of 1 is given to a normallycontracting or hyperkinetic segment, 2 for an hypokineticsegment, 3 for akinesis, and 4 in the presence of a dyskineticsegment (Table 8.1). Of note, there is no specificscore for compensatory hyperkinesis. The WMSI is equalto the sum of the regional scores divided by the numberof evaluable segments and can vary between 1.0 (fornormal ventricular contraction) and 3.9 (for severe systolicdysfunction). Because CAD causes segmental dysfunction,which can be accompanied by compensatory hyperkinesisof nonischemic segments, regional assessment of systolicfunction is more sensitive for the detection of ischemiathan global approaches. Furthermore, the prognosticvalue of the motion score has been shown in clinicalstudies. Among a group of patients admitted with acutemyocardial infarction, those with favorable indices (bestquintile) had an incidence of cardiovascular death of 8%at 1 year. In contrast, patients with motion indexes in theworst quintile had a mortality of 51% at 1 year (19). Kanet al. (20) also examined the value of WMSI in patientswith acute myocardial infarction and found a significantlyhigher mortality rate in the group with the most abnormalscore indexes compared with those with more favorableones (61% vs 3%, respectively). Quantitative evaluationof regional left ventricular systolic function requireshigh-quality images with good endocardial resolution.The centerline method is a quantitative approach for assessingregional ventricular function, which first involves theconstruction of a line halfway between the end-diastolicand end-systolic endocardial perimeters (21). The endocardialexcursion is determined along 100 equally spacedchords perpendicular to this centerline. Motion is then normalizedfor heart size by dividing by the length of the enddiastolicperimeter. The normalized length of each line isthen converted into units of standard deviation from themean excursion along a given chord, which allows theregional heterogeneity of ventricular contraction to betaken into account. By convention, negative and positivevalues indicate hypokinetic and hyperkinetic chords,respectively. The extent of abnormal wall motion is calculatedas the number of chords with hypokinesis equal to ormore severe than 2 standard deviations (SD). The severityof wall motion abnormalities is calculated as the area underthe curve below the 0 SD line.Compared with multilead electrocardiographic monitoringand invasive hemodynamic monitoring, transesophagealechocardiography has proved to be superior atdetecting acute ischemia as reflected by new regional wallmotion abnormalities (3,22). In a group of patients at highrisk for intraoperative ischemia undergoing coronaryartery bypass or major vascular surgery, Smith et al. (3)found that 24 (48%) of the 50 patients demonstrated newsegmental wall motion abnormalities while only six (12%)patients presented new ischemic ST changes. Furthermore,Leung et al. (23) demonstrated that wall motion abnormalitiesoccurred in the absence of hemodynamic changes andwere predictive of adverse outcomes after cardiac surgery.In contrast, van Daele et al. (22) have shown the lack ofsensitivity of hemodynamic measurements in predictingischemia or postoperative cardiac complications. A fewlimitations and pitfalls of TEE for the assessment ofregional systolic function should be mentioned. The segmentalwall motion analysis system must first compensatefor global motion of the heart, usually by a floating frame.When viable and nonischemic, the interventricular septumthickens during systole but its asynchronous motion canbegin slightly before or after the inward motion of theother walls. Experimental and clinical studies have alsodefined important regional differences in normal myocardialcontraction (24). As mentioned previously, it is importantto realize that contraction of the inferobasal wall is oftenslightly more limited than that of the other ventricular segmentsand that not all systolic wall motion abnormalities areindicative of ischemia. Patients with myocarditis, septicshock, ventricular pacing, and bundle branch block canpresent segmental wall motion abnormalities (Fig. 8.9).Tethering of nonischemic myocardium adjacent to anischemic or infarcted myocardium is a frequent cause ofoverestimation of the infarct size with echocardiographycompared with postmortem examination (25). Force et al.(25) found that although tethering does lead to an unavoidableoverestimation of the infarct size within 1 cm of theischemic area, the amount of myocardium involved issmall and relatively predictable. Altered loading conditionsmay also result in segment wall motion abnormalities ormay unmask areas of scarring. For example, an acuteelevation of the blood pressure may retard the contractionof an already damaged myocardial segment more thanthat of a normal one.