Mirror image electrocardiograms and additional electrocardiographic leads: new wine in old wineskins?
Background: Mirror image electrocardiograms (ECGs), obtained by inverting the original signals, and additional precordial leads have been proposed as means to improve ECG diagnosis. The theoretical backgrounds of these proposals are discussed. Methods: In 746 body surface potential maps, the mirror areas of the 6 precordial leads, V3R, and 2 more leads higher up and 1 lower down the thorax have been determined. The similarity between the original signal and its mirror image was expressed by a similarity index. This was done separately for QRS and ST-T; for the first and second parts of QRS; and for the categories normal, left ventricular hypertrophy, and infarct. Results: In general, high similarity scores were obtained. The mirror images of V1and V2are almost diametrically located on the back. Inverting these leads could render the V8and V9leads. The other mirror areas may deviate considerably from where generally expected. Conclusion: Mirror images can be obtained consistently from all locations, supporting the dipole representation of cardiac electrical activity. Neither mirror image ECGs nor additional chest leads contribute essentially to ECG diagnosis.