Inferolateral zone

Both acute coronary syndromes (ACSs) and infarcts in chronic phase affect, as a result of the occlusion of the corresponding coronary artery, one part of the two zones into which the heart can be divided (Figure 1.14A) (1) the inferolateral zone, which encompasses all the inferior wall, a portion of the inferior part of the septum and most of the lateral wall (occlusion of the RCA or the LCX) (2) the anteroseptal zone, which comprises the anterior wall, the anterior part of the septum and often a great part of inferior septum and part of the mid-lower anterior portion of lateral wall (occlusion of the LAD). In general, the LAD, if it is large, as is seen in over 80% of cases, tends to perfuse not only the apex but also part of the inferior wall (Figures 1.1 and 1.14). 

In the classical ECG assessment of an STE-ACS, the leads with electrocardiographic changes give to us an approximate diagnosis of the location of the injury (anteroseptal vs inferolateral zone). However not much information was given regarding what the occluded artery was, where the occlusion was located and how large the area at risk was. Therefore, for example, the classical interpretation of... 

Figure 4.17 Acute myocardial infarction with ST-segment elevation in II, III and VF and ST-segment depression in V1-V3. This pattern corresponds classically to an infarction involving inferior and posterior walls. Nowadays, this is the pattern of STE-ACS of inferolateral zone evolving to inferolateral infarction due to distal occlusion of a dominant RCA (ST-segment depression in I and V1-V3,...

The correlations that will be presented are based on the segmentation of the LV into two zones the anteroseptal and the inferolateral (Figure 1.14 and p. 17). The involvement of the anteroseptal zone corresponds to cases with occlusion of the LADand its branches (Table 4.1A),while the involvement of the inferolateral zone corresponds to the occlusion of the RCA and the LCX (Table 4. IB). We will study 12 different locations of coronary occlusions that define 12 areas at risk, 6 in the anteroseptal zone (Table 4.1 A) and 6 in the inferolateral zone (Table 4. IB). The ECG patterns that match with these different areas will be commented and discussed in all cases. 

RCA occlusion proximal to the RV branches (Figures 4.30-4.32 and Table 4.1B(7)) When the RCA occlusion is proximal to the RV branches (Figure 4.30A), the area at risk involves the RV and part of inferolateral zone, more or less extensive according to the dominance of RCA. In Figure 4.30B, C the involved myocardial area is shown, as well as the polar map in case of balanced dominance. The more affected segments are 3, 4, 9 and 10, and part of segments 14 and 15. 

RCA occlusion distal to the RV marginal branches (Figures 4.33 and 4.34, and Table 4.1B(8)) In case of balanced dominance the area at risk may involve, if the occlusion is just distal to RV branches, similar part of inferolateral zone of the LV than in the case of occlusion proximal to RV branches (see above and Figure 4.30). 

Figures 4.41 and 4.42, and Table 4.1B(12)) When the LCX is very dominant and the occlusion is proximal (Figure 4.41A), the area at risk involves a great part of inferolateral zone that includes the majority of the lateral and inferior wall and even some portion of inferior part of the septum. The involved segments are 3, 4, 5, 6, 9, 10, 11, 12,15 and 16 (Figures 4.41B and C). 

From a clinical point of view, in the majority of cases, usually the most striking ECG abnormality found by the physician is ST-segment elevation located in the precordial leads (V1-V6) (anteroseptal zone) (Figure4.43) or in inferior leads (inferolateral zone) (Figure 4.45). We will see how we can identify not only the culprit artery, but also the occlusion site. 

Figure 5.9). Seven infarcted areas due to first MI have been found to have a good correlation with seven electrocardiographic patterns (Cino et al., 2006). Four of these are located in the anterosep-tal zone, while the remaining three in the inferolateral zone, the former being secondary to occlusions in different segments of the LAD and its branches and the latter due to RCA or LCX occlusion... 

Type and location of the ischemia due to ACS - Usually transmural and homogeneous - Located in anteroseptal (f ST Vi 2 a V3) I or VL) or inferolateral zone (t ST II, III, and sometimes I, VL, Vs and/or [ ST V,-V3. - See atypical patterns (fig 8.3) - Often not easy to locate - When ST depression is in >7 leads with elevation in VR, the injury is very extensive (circumferential) and predominantly subendocardial - non-complete occlusion of the main trunk (LMT) or proximal occlusion of LAD + LCX (equivalent) - The ischemia is regional when the ST depression is only present in a few leads (<6) - Flat or negative T wave is due to delay of repolarization that has no subendocardial predominance. 

On the other hand, the STE-ACS involving the inferolateral zone, presenting with the poorest prognosis, is that with the largest extension, with evidence of significant involvement of the inferior and lateral walls and the RV.Those cases with the highest risk present the following ECG criteria ... 

Figure 8.13 (1) The three types of repolarisation abnormalities that may be seen in an acute phase of myocardial infarction involving the inferolateral zone ...

We will just remind (see p. 137) that seven areas of MI detected by CE-CMR have good correspondence with seven ECG patterns (four in anteroseptal zone - septal, apical-anterior, extensive anterior and mid-anterior - and three in the inferolateral zone - inferior, lateral and infero-lateral) (Figure 5.9 Cino et al., 2006). We have also demonstrated that in clinical practice the presence of these seven ECG patterns correlates well with the corresponding infarction areas detected by CE-CMR, and therefore these have real value in clinical practice (Bayes de Luna et al., 2006a-c) (Table 5.3). Therefore, in chronic infarction the correlation between ECG changes (Q waves of necrosis) and involved area (CE-CMR) is clearly good (88% global concordance). However, the in-farcted area of apical infarction (A-2 type), mid-anterior infarction (A-3 type) and lateral infarction (B-l type) presents the lower concordance. 

The presence of many electrocardiographic criteria showing inferior and lateral involvement represents generally a large infarction that encompasses the cases of worst prognosis of MI of inferolateral zone, especially in case of MI due to very dominant RCA or LCX. The ejection fraction is usually diminished. Therefore, in the acute phase, quick decision should be taken (urgent PCI) to avoid haemodynamic complications. 

From the prognostic standpoint, Mis of inferolateral zone with RV involvement - proximal occlusion of RCA - especially when the artery is dominant, have worst prognosis in the acute phase, as they potentially involve a very large myocardial area at risk. Consequently, carrying out an urgent coronary angiogram is mandatory (Figures 4.31 and 9.6). 

Some Q-wave infarctions may exhibit normal or near-normal ECG recordings in the chronic phase. They are usually but not always small septal, mid-anterior, inferior or lateral infarctions that, generally, in the acute phase exhibit ST-segment elevation in the corresponding leads, accompanied by a Q wave. Relatively often, especially in the inferolateral zone or in septal or mid-anterior infarction, the Q wave disappears over time (Figure 8.12 Bayes de Luna et al, 2006a-c). 

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