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Simple Diagnosis of Limb-Lead Reversals by Predictable Changes in QRS Axis

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Background: Limb-lead reversals (LLRs) remain clinically problematic. Because the frontal QRS axis is derived from an equilateral Einthoven triangle and LLRs either rotate (180 ° horizontally (mirror-image (M)) and/or 120 ° vertically (clockwise (C)/counterclockwise (CC)) or distort the triangle (by forcing a bipolar lead to record across the lower extremities (LE) where electrical potentials approach zero (zero-potential lead)), we hypothesize that LLR axes changes from a baseline value (n) are predictable.

Methods: Three hundred and sixty ECGs with all 24 limb-lead combinations from 15 individuals were analyzed. Predicted and actual QRS axes were compared using linear regression.

Results: Twenty-four lead combinations produced only 12 (11 abnormal) ECG patterns and diagnosis depended upon identifying upper extremity (UE) cable configurations. Predicted formulas for rotation-type LLR axes (M, C, CC, MC, and MCC) were 180 − n, n − 120, n + 120, 300 − n, and 60 − n, respectively. Corresponding mean differences between predicted and actual values were 4 ± 5 °, 4 ± 2 °, 7 ± 10 °, 5 ± 7 °, and 3 ± 4 ° (all r = 0.99 − 1.00, P < 0.0001). The predicted formula for distortion-type LLR axes is (zero-potential lead axis) ± 90 °. Actual mean values for zero-potential lead I, II, and III were 90 ± 7 ° or 266 ± 17 °, −31 ± 6 ° or 148 ± 14 °, and 26 ± 14 ° or 209 ± 9 °, respectively. The mean difference between predicted and actual values for all LLRs was 5 ± 8 ° (r = 1.00, P < 0.0001).

Conclusions: LLR axes are predictable within an average of 5 °. This might help differentiate an acute axis shift due to an LLR from serious medical conditions that may require treatment.

(PACE 2006; 29:272–277)
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Keywords: computing; electrocardiogram

Document Type: Research Article

Affiliations: 1: Department of Medicine, Division of Cardiology, Thomas Jefferson University Hospital, Philadelphia, Pennsylvania 2: Department of Medicine, Division of Cardiology, University of California at San Francisco, San Francisco, California

Publication date: 01 March 2006

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