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ECG in a 44-year-old man with chest pain.

DIAGNOSIS: Arm-lead reversal; normal sinus right atrial enlargement and right ventricular enlargement suggesting an ostium secundum atrial septal defect; acute inferior myocardial infarction.

Negative P waves, QRS complexes, and T waves in lead I suggest arm lead reversal or situs inversus. Progressively larger QRS complexes in standard chest leads [V.sub.1] to [V.sub.5] exclude situs inversus. When the arm leads are reversed, true lead I is inverted, producing the negative P, QRS, and T; lead II is actually true lead III; lead III is true lead II; lead aVR is true lead aVL; lead aVL is true lead aVR; and lead aVF and the precordial leads are unchanged.

The presence of an incomplete right bundle branch block pattern in true lead aVR and in lead V1, S waves in leads [V.sub.5] and V6, S[V.sub.5] > 7 mm (where 10 mm = 1.0 mv), and R[V.sub.1] + S[V.sub.5] > 10 mm suggest right ventricular enlargement. (1,2) The 2 mm P waves in lead [V.sub.2] indicate right atrial enlargement, (3) helping to confirm right ventricular enlargement and to suggest a fossa-ovalis type (ostium secundum) atrial septal defect. The atrial septal defect was confirmed by echocardiography.

Correcting for arm-lead reversal, one can also recognize the changes of acute inferior myocardial infarction: large Q waves, ST-segment elevation, and T-wave inversion in the inferior leads with reciprocal tall R waves, ST-segment depression, and upright T waves in true leads I and aVL.

Misplaced electrocardiographic leads are common. Some misplacements, such as arm lead reversal or both electrodes of a bipolar lead on the legs resulting in miniscule P, QRS, and T voltage in that lead, are easy to recognize, as are gross chest lead misplacements, such as placing the [V.sub.1] lead in the [V.sub.6] position and vice versa or placing all of the chest leads on the right side of the chest. Many lead misplacements, however, go unrecognized. When the positions involved in lead misplacement can be recognized, an electrocardiographic diagnosis usually can be made.


(1.) Milliken JA, Macfarlane FW, Lawrie TDV. Enlargement and hypertrophy. In: Macfarlane PW, Lawrie TDV, editors. Comprehensive Electrocardiology: Theory and Practice in Health and Disease. New York: Pergamon Press; 1989: Volume 1 :631677.

(2.) Surawicz Knilans T. Chou's Electrocardiography in Clinical Practice, Adult and Pediatric, 5th edition. Philadelphia: W B Saunders; 2001:44.74.

(3.) ibid. 28-43.

Dr. Glancy is a Professor and Dr. Jain is an Associate Professor in the Sections of Cardiology, Departments of Medicine, Louisiana State University Health Sciences Center and the Interim LSU Hospital, New Orleans.

D. Luke Glancy, MD; Neeraj Jain, MD

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Title Annotation:ECG of the Month
Author:Glancy, D. Luke; Jain, Neeraj
Publication:The Journal of the Louisiana State Medical Society
Date:Nov 1, 2014
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