Electrocardiographic lead reversals

Abstract

Misplacement of cables during the recording of a 12-lead electrocardiogram [ECG] poses a non-negligible risk of creating panic and confusion at the bedside in daily clinical practice. Clinical awareness about the manifestations of commonly encountered electrode misplacements is imperative for avoiding misdiagnosis. A basic understanding of the electrophysiology behind these anomalous ECG tracings is likely to aid in prompt suspicion, accurate detection, and appropriate rectification in most cases. We discuss the abnormalities produced on 12-lead ECG tracings by the misplacement of electrode cables, with a focus on the clinical implications of the same. We suggest a mnemonic - 'SPIRAL' - as a quick screening criterion to detect commonly encountered lead reversals.

Fig. 1

12-lead-ECGs and the corresponding schematic representations of the electrocardiographic limb lead vectors. 1A. Normal ECG tracing and Einthoven's triangle; 1B. LA-RA lead reversal depicting a) inversion of lead I, b) swapping of leads II and III, c) swapping of leads aVL and aVR, and d) unaltered aVF; 1C. LA-LL lead reversal depicting a) inversion of lead III, b) swapping of leads I and II, c) swapping of leads aVL and aVF, d) unaltered aVR, and e) P wave amplitude in lead I > lead II; 1D. RA-LL lead reversal depicting a) inversion of lead II, b) swapping of leads I and III with their polarities inverted, c) swapping of leads aVR and aVF, and d) unaltered aVL; 1E. Clockwise rotation of LL-RA-LA leads depicting swapping of leads I, II and III; and counter clockwise swapping of augmented leads; 1F. Counter clockwise rotation of LA-LL-RA leads depicting swapping of leads I, II and III; and clockwise swapping of augmented leads [The schematic illustrations are adapted from reference 2].

Fig. 2

Schematic representation of the electrocardiographic vectors in limb lead misplacements involving the neutral [RL] electrode. 2A. RA-RL[N] reversal showing collapsed Einthoven's triangle with LA lead at the apex. Lead III is unaltered. Lead II records zero voltage. 2B. LA-RL[N] reversal showing collapsed Einthoven's triangle with RA lead at the apex. Lead II is unaltered. Lead III records zero voltage. 2C. RA-RL and LA-LL (bilateral arm-leg) reversal showing collapsed Einthoven's triangle with misplaced LL lead at the apex. Lead I records zero voltage. 2D. LA-RL and RA-LL reversal (bilateral arm-leg cross reversal) showing collapsed Einthoven's triangle with misplaced LL lead at the apex. Lead I records zero voltage. 2E. Clockwise rotation of RL-RA-LA-LL leads showing collapsed Einthoven's triangle with misplaced RA lead at the apex. Lead III records zero voltage. 2F. Counter clockwise rotation of LA-LL-RL-RA leads. [The schematic illustrations are adapted from reference 2].

Fig. 3

12-lead ECG tracings of limb-precordial lead misplacement. 3A. Left arm [LA] and V6 lead reversal showing altered morphology in lead V6 tracing, and precordial-like amplitude in leads I, III, aVL. 3B. Right leg [RL] and V6 lead reversal showing lead V6 tracing which resembles the unaugmented VF tracing. 3C. 12-lead ECG tracing with standard lead placement depicting acute ST elevation myocardial infarction of inferior wall; 3D. 12-lead ECG tracing of the same patient, with the LA and LL electrodes switched, suggesting the misdiagnosis of acute high lateral wall ST elevation myocardial infarction.

Fig. 4

Algorithm for detection of limb lead reversals which do not involve the neutral electrode, by polarity of P waves. Except for LA-LL reversal, all other electrode misplacements in this category have positive P waves [with or without positive QRS/T] in lead aVR. All the polarities mentioned above are in specific reference to the P waves in sinus rhythm, as the polarity of QRS/T may vary based on their polarities in the baseline ECG. LA-LL reversal can be identified by a greater P wave amplitude in lead I relative to lead II.

Fig. 5

Algorithm for detection of limb lead reversals which involve the neutral electrode. Except for LL-RL reversal [which does not alter the ECG significantly], and counter clockwise rotation [which is similar to the counter clockwise rotation without involvement of the neutral electrode – depicted in Fig. 4], all other electrode misplacements in this category are characterized by an isoelectric [flat] tracing in one of the bipolar leads.