A total of 3186 articles were identified from the initial search strategy, reducing to 3131 after duplicates were removed. Full text screening was performed utilising NICE Healthcare Database Advance Search (HDAS)[24] was conducted on 78 articles, according to the eligibility criteria, which resulted in 7 included studies, Table 1 (Systematic Review Synthesis and Data Extraction) and Figure 1. PRISMA flow diagram, detailing searches strategy of systematic review.
Data Extraction and Synthesis:
Five themes were derived from the Systematic Review Synthesis and Data Extraction Table 1. The chief characteristics of included studies and themes derived are as follows:
Theme 1 - Misplacement of Electrodes:
It is well documented within the literature that misplacement of precordial electrodes is long-standing, continues to remain a common occurrence and finding that, so far, has not been effectively addressed.[13] Of concern, are the subsequent clinical and diagnostic/prognostic ramifications for the patient.[28] The findings of this review support this notion, with V1 and V2 being consistently erroneously misplaced superiorly in the 2nd intercostal space rather than in the 4th intercostal space at the right sternal border and left sternal border respectively.[13][10][29][14][28] [32]
Potentially harmful treatment and/or therapeutic procedures may ensue. Typically, erroneous electrode placement has the potential to affect and alter ECG waveform morphology, clinical interpretation, lead to misclassification of ischemic changes, and a misdiagnosis of arrhythmia. [13][10][29][14][28] Consequently, superior misplacement of V1 and V2 spearheads to spurious ECG abnormalities that may include: poor R-wave progression; ventricular hypertrophy; anteroseptal infarct; QRS complex and T-wave alterations; incomplete right bundle branch block (IRBBB); false positive and false negative ischemic changes and Type 2 Brugada syndrome.[30][14][28] A confounding factor and one worthy of consideration is, almost all of the included papers allude to the frequency of misplaced precordial leads V1-V6. [13][10][29][14][28]
Reasons for such erroneous placement are multi-factoral and can include poor training, a lack of appreciation of consequences of misplacement, a failure to understand and utilise anatomical landmarks such as the sternal notch (Manubriosternal joint/Angle of Louis), and the Xiphoid process for correct identification of the 4th intercostal space.[30]
Furthermore, levels of undress and the desire to preserve patient modesty, particularly in females, are factors that evidence significant impact. Fewer cardiac investigations are evidenced in women with ACS than in men. Subsequently, such inequities result in less treatment and prove potentially detrimental. [31]
Theme 2 - Anatomical Differences:
Anatomical differences between male and female patients provide additional challenges in electrode placement and accurate ECG acquisition. SCST guidelines and recommendations state, by convention electrodes V4, V5 and V6 ought be placed beneath the breast when breast tissue overlies the correct anatomical positions. [19]
A study conducted by Wallen et al, (2013) [31] noted 52% of women preferred electrodes placed on the breast tissue, deeming it less intrusive, 38% were indifferent and 10% preferring under the breast.[31] Review of the wider literature and that of the included studies of this review allude to difficulties, particularly on women with large breast tissue mass and, in obese patients, in accurately identifying bony landmarks as anatomical reference points to aid in the correct placement of electrodes. However, current evidence pertaining to misplacement because of women’s breast tissue and obesity is inconclusive and warrants further investigation. [13][30][28]
In contrast, a prospective observational study by McCann et al, (2007) [10] evidenced greater lateral chest electrode discordance (V4-V6), irrespective of gender, than those of central chest electrodes (V1-V3), however, identification of anatomical landmarks and accurate location were impeded particularly in older, larger women and the obese. [10][30] This was further supported by the findings of the PULSE multi-site randomised clinical trial, (2018), where < 50% of both male and female participants were found to have accurate electrode placement. [29] PULSE concluded no significant difference in accuracy for precordial electrode placement between men and women.
Theme 3 - Operator Error & Causes of Misplacement:
Inter-operator variability, even among senior clinicians, is a factor widely acknowledged for the occurrence of electrode misplacement.[10] Causes of misplacement extend to both modifiable and non-modifiable patient factors, such as body habitus, body position, lack of anatomical awareness, lack of confidence, competence or even over confidence.[10][13] However, confidence is no substitute for competence.[19] Cardiologists in particular fall prey to such over confidence. Assuming the position of V1 and V2 electrodes in the 2nd intercostal space rather than that of the 4th, which may arise from a complacency through regularly listening to auscultations of heart sounds at 2nd intercostal level.[13]
It is postulated that particularly amongst paramedics, operator error is compounded by a hesitancy to expose the female breast. The connotation that the female breast is a secondary sexual organ provides ensuing embarrassment. [31]
Theme 4 - Clinical Impact on Diagnosis, Treatment & Management:
Correlation between misplaced precordial electrodes with changes to ECG morphology dominates the theme of the majority of papers included in this review. Such alterations have the potential to significantly impact clinical interpretation and diagnosis, leading to over, under or even a missed diagnosis. Conversely, superior misplacement of V1 and V2 has proven beneficial in the detection of ST-segment elevation myocardial infarction (STEMI), Non-ST-segment elevation myocardial infarction (NSTEMI) and Brugada syndrome, with no noted significant change to specificity. [28] However, studies have purported a shift in placement by as little as 2cm; can affect interpretation and diagnosis in as much as 17-24% of patients. [30]
Theme 5 - Education & Training:
Overarching consensus of included papers, place education and training as tantamount, and of paramount importance to accurate ECG acquisition. Thus, optimising sound clinical diagnosis and practice. Implementation and adherence to SCST and the American Heart Association (AHA) guidelines, yields significant improvement.[29][14] Correct identification of anatomical landmarks, notably, the sternal notch (Angle of Louis), Xiphoid process and the 4th intercostal space for the correct placement of electrodes is essential in the undertaking of ECG. This coupled with on-line education and strategies to change current erroneous practice, through raising awareness and knowledge, are fundamental to good clinical practice, quality of care and outcomes for patients, with a reduction in patient morbidity and mortality.[10][29]