ECG of the Month Presentation is on p 262.
DIAGNOSIS: Arm-lead reversal; normal sinus rhythm; right atrial enlargement and right ventricular enlargement sug- gesting 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. Progres- sively larger QRS complexes in standard chest leads V 1 to V 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 V 1 , S waves in leads V 5 and V 6 , SV 5 > 7 mm (where 10 mm = 1.0 mv), and RV 1 + SV 5 > 10 mm suggest right ventricular enlargement. 1,2 The 2 mm P waves in lead V 2 indicate right atrial enlarge- ment, 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 inminiscule P, QRS, and T voltage in that lead, are easy to recognize, as are gross chest lead misplacements, such as placing the V 1 lead in the V 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 posi- tions involved in lead misplacement can be recognized, an electrocardiographic diagnosis usually can be made. REFERENCES 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 :631–670. 2. Surawicz B, 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.
J La State Med Soc VOL 166 November/December 2014 263
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