**3. Detection of myocardial infarcted segments**

782 Biomedical Science, Engineering and Technology

have shown that surgical ventricular restoration (SVR), in conjunction with CABG, is seen to benefit the ischemic-infarcted heart, by (i) restoration of cardiac remodeling index of 'enddiastolic to end-systolic curvedness change', (ii) reduction of regional wall stresses, and (iii)

In Cardiology, the etiology of congestive heart failure (CHF) is coronary artery disease in approximately two-thirds of cases. The majority of these patients have hearts with myocardial infarcted segments. This infarcted myocardial wall mitigates adequate contraction of the wall. So, the end-result of an infarcted left ventricle (LV) is poor intra-LV velocity distribution and pressure-gradient distribution, causing impaired outflow from the

In the infarcted myocardial segments, the myocardial infrastructure of actin and myosin filaments (and their cross – bridges) is disrupted, and hence there is no contraction within these infarcted myocardial segments. The below figure 1 illustrates a myocardial sarcomere segment's bioengineering model, composed of two symmetrical myocardial structural units (MSUs). In these MSU(s), the contractile elements represent the actin-myosin contractile components of the sarcomere segment. The disruptions of these contractile elements impair the contractile capability of that sarcomere segment. Hence, a LV with infarcted myocardial segments will have diminished contractility, inadequate and improper intra-LV flow, and

Fig. 1. Based on the conventional Hill three-element model and Huxley cross bridge theory, we have developed a myocardial model involving the LV myocardial mass, series-elastic element (CE),. In this figure we have linked the anatomical associations of these myocardial model elements with microscopic structure of the heart muscle. This figure illustrates the sarcomere element contractile model, involving: the effective mass (*m*) of the muscle tissue that is accelerated: elastic parameter k of the series element stress *σSE* (k = elastic modulus of the sarcomere), viscous damping parameter B of the stress *σVE* in the parallel viscous element VE, the generated contractile stress *σCE* between myosin (thick ) and actin (thin )

augmentation of the cardiac contractility index value.

**2. Myocardial infarction: What it entails** 

LV into the aorta.

poor ejection.

filaments.

Now, infarcted myocardial segments can be detected as highly reflectile echo zones (HREZs) in 2-dimensional B-scan echocardiograms. In this context, we have shown how infarcted myocardial segments can be detected (in shape and size), by echo-texture analysis, as highly reflectile echo zones or HREZs. Each myocardial tissue component of the heart generates a grey scale pattern or texture related to the tissue density and fibrous content. In diseased states (such as myocardial ischemia, myocardial fibrosis, and infiltrative diseases), changes in myocardial tissue density have been recognised by employing echo intensity and mean grey level of pixel as the basis for recognition of such myocardial disorders. It is found that hyper-reflectile echoes (HREs) correlated well with diseased cardiac muscle, and that myocardial tissue containing HREs corresponded with foci of sub-endorcardial necrosis and even calcification.

In our study [1], in order to determine highly reflectile echo zones (HREZs), echocardiograms were recorded, and each image was made up of 256 x 256 pixels, with each pixel having a resolution of 0-256 grey scales. The echocardiographic images were digitised into 256 grey scales. Then, echo intensity levels from normal infants were used to delineate the range of echo intensities for normal tissues. The upper bound of the echo intensity was set to 100 per cent in each normal infant, and the intensities from the rest of the image were referenced to this level. Normally, pericardium had the highest intensity level. It was found that the upper-bound of the echo intensity value for healthy tissue (expressed as a percentage of the pericardial echo intensity value) was 54.2.


Table 1. Echo intensity values for various anatomic regions of diseased pediatric hearts (based on long axis view). The numbers in the four rows represent Mean (M), Standard Deviation (SD), Number of Pixels (N), Percentage of Posterior Pericardial Intensity (P). This figure is adopted from Ref [1].

For patients whose echo-texture analysis showed presence of HREs, it was found that the echocardiographic intensities of the HREs from these patients intensities were distinctly higher than the echo intensity range of normal tissue (as depicted in Table 1).

Myocardial tissue pixels having echo-intensity values greater than 200 are generally noted to be infarcted. This region's echo-intensity values can remain unaffected by administration of a myocardial perfusing agent. This infarcted sub-region is seen to be surrounded by an ischemic sub-region whose pixels are noted to have echo intensity values between 100 and 200. This region's echo-intensity can be reduced by the administration of a myocardial perfusing agent. The surrounding healthy tissue has echo intensity less than 100. Figure 2(a) depicts an echo image of an infant with visible scars regions 1 and 2, while figure 2(b) depicts printouts of the echo intensities from these two regions, wherein the infarcted segments are depicted in dark colour and the surrounding ischemic segments are depicted in a lighter shade.

Fig. 2. (a) Long axis view of a pediatric patient's heart showing HRE regions 1 and 2 and a healthy region 3 [1].


Fig. 2. (b) Pixel values correcponding to highly reflectile echo region 1. The central region having echo-intensity values greater than 200 is infarcted, while its immediately surrounding region shown in lighter shade is ischemic.

In this way, in each highly reflectile echo zone (HREZ) made up of , say, N number of pixels, we can determine the number (I) of infarcted pixels. The ratio I/N represents the infarcted potion of that HREZ myocardial segment. The total number of all the infarcted pixels in all the HREZs provides an indication of the amount of infarcted myocardium of the heart or of the LV.
