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ECG: Reversal of limb leads
1. ECG OF THE WEEK Idhayachandran. N. Prof. Sundar’s unit.
2. A 24 year old male patient came to the OPD with complaints of chest pain for the past 2 hours. Pain was retrosternal, pricking type, not aggravated by exertion or relieved by rest. No h/o DM/HT. Smoker & consumes alcohol occasionally. O/E: conscious, oriented, afebrile, hydration fair comfortable at rest. CVS,RS,ABD,CNS-Normal.
4. Rate - 60/min. Normal sinus rhythm. PR interval - 160 ms. QRS duration - 100 ms. QT interval - 400 ms. Right axis deviation. No signs of RVH or LVH. T wave inversion in L1and aVL. Q wave in aVL. Negative P wave in L1 and aVL.
5. INTERPRETATION T wave inversion and QS in L1 and aVL might suggest lateral wall infarction. This is an artefact due to reversal of the two upper limb leads. L1, aVL, V5 and V6 all have similar axes. The morphology of QRS complex should be identical in all these leads. If the polarity of QRS in L1 is opposite to that of the left precordial leads (V5 and V6), as in this case, arm lead reversal should be suspected.
6. Reversal of arm leads is the most common lead placement error and is the easiest to recognize because of negative P wave in L1. In patients with AF or unrecognizable P waves, if the polarity of QRS in L1 is different from that of left precordial leads V5 and V6, arm lead reversal is suspected.
7. In case of reversal of arm leads the morphology of complexes in the limb leads resembles dextrocardia. However dextrocardia and reversal of arm leads can be differentiated on the basis of QRS complexes in the precordial leads. In dextrocardia as we progress from V1 to V6 QRS complex becomes progressively smaller and displays mostly QS or rS in V5 or V6. In reversal of arm leads the progression of QRS from V1 to V6 is normal.
9. + Lead I - - + Lead I RA RA LA LA -> - - - - Lead II Lead III Lead III Lead II + + + + LL LL
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11. If one of the standard limb leads is almost a straight line, the right leg cable was probably switched with other limb cables. In the augmented unipolar limb leads, if the lead aVL shows all negative deflection, the right arm cable has been switched with the left arm. If the lead aVf shows all negative deflection, the right arm cable has been switched with the left leg.
12. Reversal of the left arm cable and the left leg cable is difficult to recognize without having a previous normal ECG for comparison. If the precordial leads are misplaced, the ECG might resemble infarction pattern.
