To the Editor:
First of all, I would like to thank Dr García Cosío for his interest in our work on the ECG-MRI correlation,1-3 which we summarized in an editorial published in the Revista Española de Cardiología last October.4 In response to his letter, I would like to make the following comments.
For more than 40 years,5 the true posterior wall of the heart has been considered the portion corresponding to the inferobasal part of the inferior wall. This area was believed to curve upward. An infarction therein causes a necrosis vector running from back to front, which explains the R-wave in V1 that was the key electrocardiographic criterion of posterior infarction. Nonetheless, magnetic resonance imaging has shown that1-3: a) curvature of the inferobasal part of the inferior wall is uncommon (about 20%); b) even though a posterior wall might exist, we have proven that infarction of this area does not originate an R-wave in V1 because the necrosis vector runs toward V3-V4, and not toward V1; c) in contrast, with the same correlation, when necrosis occurs in the anterior or posterior parts of the lateral wall (particularly middle and low), the necrosis vector runs toward V1 and explains the R at this lead; and d) following the work done by Durrer,6 necrosis of the inferobasal part of the inferior wall, classically called the posterior wall, cannot cause Q-wave in the leads on the back or R-wave in V1 because this area depolarizes after 30 to 40 ms. Therefore, infarction of the so-called posterior wall may naturally exist, but does not cause the R-wave in V1 that is observed in some lateral infarctions.
Dr García Cosío states that "computerized navigation reconstruction of the left ventricle allows models of the left ventricle to be created in its true position and shows infarction areas in a posterior position." The area that he marks with the arrows in his Figure 2 as a posterior infarction corresponds to the posterior part of the lateral wall. The true posterior wall, if it exists, would be located to the right of the arrows (segment 4 of the Cerqueira classification6). Often, the entire lateral wall is the part affected when there is R-wave at V1, and not just the posterior part of the wall. What Dr Cosío points out as the posterior wall in his Figure 1 on the left is actually the lateral wall, which is opposite to the septal wall, and what he indicates as the posterior left ventricle on the right side of the figure is the posterior part of this lateral aspect, but not actually a posterior wall. The posterior wall of the heart from the time of Perloff has been considered the basal-most part of the inferior aspect.
In summary, I would like to express appreciation for the letter because it has allowed me to point out several aspects that were perhaps unclear and are summarized below: a) the title may cause confusion if our studies are understood to indicate that there is no posterior myocardial infarction; the fact is that there is no posterior wall—considering as such the part of the inferior wall that curves upward—; if the posterior wall existed and were infarcted, it would not produce high R-wave in V1 for the reasons we explain in our editorial; and b) R-wave in V1 is due to infarction of the lateral wall, the wall opposite the septal wall which, naturally, has an anterior portion and another posterior portion, although R-wave in V1 is often seen when both parts of the lateral wall are necrotic.