Electrocardiogram read by the computer as arm-lead reversal.

T he electrocardiogram shown in Figure 1 was read by the computer as arm-lead reversal. Th e computer reading went on to say that no further analysis would be attempted. Th is clearly is a programming mistake because the precordial leads make the diagnosis. Although we would estimate that 95% of electrocardiograms with negative P, QRS, and T waves in lead I are due to armlead reversal, a small number are due to situs inversus totalis with mirror-image dextrocardia. In this condition, the left-sided precordial leads show progressive diminution in the size of the complexes from leads V1 to V6 as the leads are placed ever farther away from the right-sided heart (Figure 1). In contrast, the left-sided precordial leads are unaff ected by simple arm-lead reversal. Another diagnostic point is that the QRS morphology is similar in leads I and V6 in mirror-image dextrocardia, whereas it is quite diff erent in those leads in simple arm-lead reversal (1). Situs inversus totalis with mirror-image dextrocardia is perhaps the most common of the congenital cardiac malpositions From the Sections of Cardiology, Louisiana State University Health Sciences Center and the Touro Infirmary, New Orleans, Louisiana.