Clockwise rotation III 2 I 2 II AVL AVF

Incorrect electrode cable connections during electrocardiographic (ECG) recording can simulate rhythm or conduction disturbance, myocardial ischaemia and infarction, as well as other clinically important abnormalities. When only precordial or only limb cables, excluding the neutral cable, have been interchanged the waveforms in the different leads are re-arranged, inverted, or unchanged, whereas the duration of intervals is not changed. Themistake canbe recognizedby thepresenceof unusual P–QRSpatterns (e.g. negative P–QRS in lead I or II, positive in lead AVR, P–QRS complexes of opposite direction in leads I and V6, etc.), change in the P–QRS axis, or abnormal precordial QRS–Twave progression. Interchange of limb cables with the neutral cable distorts Wilson’s terminal and the morphology of all precordial and unipolar limb leads. The telltale sign of the mistake is the presence of (almost) a flat line in lead I, II or III. Interchange of evenoneof the limb cables, except for the neutral cable,with aprecordial cabledistorts the morphology of most leads and leaves not more than one lead (I, II, or III) unchanged. Computerized algorithms for detection of lead misplacement, such as those based on artificial neural networks, or on correlation between original and reconstructed leads, have been developed.