ECG Quiz 54 – Discussion: Right arm – Left leg lead reversal
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Lead I shows inverted P waves, which in the absence of features of dextrocardia in the chest leads (regression of amplitude of QRS complexes as you move from V1-V6) should make one suspect lead reversal. But this is not the common right arm – left arm lead reversal pattern when you look at the inferior leads. At one look, the inferior leads makes you think of an evolved inferior wall myocardial infarction. But the clue is the inverted P waves in inferior leads (blue arrows). Uniform negativity of the QRS complex (violet arrows) and T waves (red arrows) along with P waves makes one suspect a misplaced left leg electrode. When the left leg electrode is placed on the right arm and vice versa, the P wave, QRS and T waves which usually have downward vectors, get inverted. In fact such an ECG is usually misdiagnosed as inferior wall infarction unless one is careful to go in a sequential manner starting from the P wave as is usually taught in ECG lessons.
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