Letter by Del-Carpio Munoz et al Regarding Article, “Masking Inferior Infarction by Anterior Myocardial Injury”
To the Editor:
In the July 25th, 2006, issue of Circulation, Deng and Das1 conclude that an old inferior myocardial infarction (Figures 1 and 3 of their article) was masked by an acute anterior-wall injury pattern (Figure 2 of their article). They state that the possible mechanism is a well-known electrocardiographic principle: Electrical forces in one zone reciprocally change the QRS vector on the opposite myocardial zone. We agree with this principle, but we disagree with the interpretation of the tracings.
If carefully analyzed, although the second ECG tracing certainly shows the disappearance of the inferior myocardial infarction, there are new and similar pathological Q waves in the left lateral leads (I, aVL). We believe that this ECG demonstrates changes attributable to improper limb–lead positioning, with the left-arm and left-leg electrodes reversed. This conclusion explains all of the ECG changes: Lead I in the original tracing is similar to lead II in the second tracing, and lead II in the first tracing is similar to lead I in the second tracing. Lead III in the first tracing is the opposite (reversed) lead III. Likewise, aVL in the first tracing is similar to aVF in the second tracing, and aVF is similar to aVL in the second tracing. Lead aVR remains unchanged because this cable was correctly placed on all tracings. Finally, the P-wave morphology in leads I and II is reversed.
This ECG presentation emphasizes the importance of adequate ECG interpretation, not only regarding the accurate diagnosis on the basis of theoretical approach, but also in a more practical one. The possibility of technical errors such as lead misplacement should be kept in mind.