Left Bundle-Branch Block With Technical Right-Axis Deviation
Figure 1 shows complete left bundle-branch block (LBBB) with marked right-axis deviation. The tracing was obtained during a routine clinic visit from an asymptomatic 64-year-old man with systemic hypertension and primary conducting system disease. All previous tracings had consistently shown LBBB with slight left-axis deviation. Because of the latter and the fact that the person obtaining the ECG was an insufficiently trained pulmonary technician, electrode misplacement was suspected. Fortunately, the electrodes were still attached to the patient. Surprisingly, we found that the technician had placed the left arm electrode on the chest between the V2 and V3 electrodes, so that 7 electrodes were on the precordium and none were on the left arm. Because of this arrangement, aVL displayed the rS morphology expected to be recorded by a unipolar precordial electrode reflecting the electrical activity of the previously mentioned anatomic site. This new aVL resulted in the mandatory change in morphology of aVR and aVF (and of leads I and III) to conform to the equation of the central terminal (aVR + aVL + aVF=0), thus explaining the right-axis deviation. Proper positioning of the electrodes resulted in the ECG shown in Figure 2, which was similar to the previous ones.
In this case, it was not difficult to suspect electrode misplacement. The problem was determining which electrodes were involved. The attending and assistant physicians initially thought that the left arm and, possibly, the V2 electrodes had been switched. When this happens, however, the morphology of the normal AVL (large R wave) should appear in the electrocardiographic position corresponding to V2 and that of V2 in aVL. This was subsequently corroborated by intentionally interchanging the latter electrodes (Figure 3).
The editor of Images in Cardiovascular Medicine is Hugh A. McAllister, Jr, MD, Chief, Department of Pathology, St Luke’s Episcopal Hospital and Texas Heart Institute, and Clinical Professor of Pathology, University of Texas Medical School and Baylor College of Medicine.
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