Brief Report

Electrocardiographic artifacts due to electrode misplacement and their frequency in different clinical settings^B

Alain Rudiger MD^a,*, Jens P. Hellermann MD MSc^b, Raphael Mukherjee^c, Ferenc Follath MD^d, Juraj Turina MD^c

^aWolfson Institute of Biomedical Research, University College London, WC1E 6BT London, UK

^bCardiology, Hospital Altsta?tten, CH-9450 Altsta? tten, Switzerland

^cDivision of Cardiology, Department of Medicine, University Hospital Zurich, CH-8091 Zu? rich, Switzerland

^dDivision of Internal Medicine, Department of Medicine, University Hospital Zurich, CH-8091 Zu? rich, Switzerland

Received 30 May 2006; revised 16 June 2006; accepted 21 June 2006

Abstract Misplacement of electrodes can change the morphology of an electrocardiogram (ECG) in clinical important ways. To assess the frequency of these errors in different clinical settings, we collected ECGs routinely performed at the cardiology outpatient clinic and the intensive care unit. lead misplacement was suspected when one of the following morphological changes occurred: QRS axis between 1808 and -908, positive P wave in Lead aVR, negative P waves in lead I and/or II, very low (b0.1 mV) amplitude in an isolated peripheral lead, or abnormal R progression in the precordial leads. We analyzed 838 ECGs and identified 37 ECGs suspicious for electrode misplacement, from which 7 were confirmed. The frequency of ECG artifacts due to switched electrodes was 0.4% (3/739) at the outpatient clinic and 4.0% (4/99) at the intensive care unit ( P = .005). In conclusion, errors in ECG performance do occur with an increasing frequency in an Acute medical care setting.

D 2007

Introduction

The 12-lead electrocardiogram has become an essential medical investigation worldwide since its introduc- tion in clinical practice in 1942 [1]. There has been a lot of

This article has been presented at the annual meeting of the Swiss Society of Internal Medicine in 2005.

^B Dr Alain Rudiger was supported by the Stiefel Zangger and the

Swiss National Science Foundations (Grant PBBSB-107757).

* Corresponding author.

E-mail addresses: [email protected] or [email protected] (A. Rudiger).

debate about in what circumstances the ECG morphology can change with different lead placements and even in healthy subjects. This might be of clinical importance, hence, the picture of Inferior myocardial infarction leads to erroneous decisions and therapy initiations [2-6]. Despite the common use of the ECG, only little information on ECG artifacts are available in standard cardiology textbooks [7-10]. Possible criteria to identify ECG changes due to misplacements of the precordial [11-14] and peripheral [15-20] leads have been described, but their diagnostic value for clinical practice is unknown. Thus, the aim of this study was to detect artifacts due to erroneously switched ECG electrodes and to investi- gate their frequency in 2 distinct clinical settings. In addition,

0735-6757/$ - see front matter D 2007 doi:10.1016/j.ajem.2006.06.018

Fig. 1 This ECG of a 56-year-old man showed a QRS axis of 1638; concordant Negative T waves in I, II, and aVL; positive P and R waves in aVR; and negative P waves in aVL and was therefore suspect for electrode misplacement to both the investigators and the automated ECG analyzer.

we wanted to unravel the value of the published criteria used for the identification of these artifacts.

Methods

The place of investigation was the University Hospital Zurich, which serves as tertiary care medical center. The protocol for this prospective study was approved by the local ethics committee. All technicians, nurses, and physicians performing ECGs were blinded for the study aims. During 2 weeks, copies were collected from all ECGs routinely performed at the cardiology outpatient clinic (OC). Here, the ECGs were recorded by specializED technicians using a Philips Recorder M 2483A (Philips AG Medical Systems, Switzerland). Additionally, copies of ECGs were collected from the medical and cardiosurgical Intensive care units . There, the ECGs were recorded by nurses or physicians in charge using a Marquette MAC 500 or a Hellige EK 512 (both from GE Healthcare, Switzerland). Electrocardiograms suspicious for lead misplacement were compared with previous or subsequent ECGs of the same patient. Doubtful ECGs were reanalyzed by 2 senior experts in electrocardiography, who were aware of the patient’s history.

Electrocardiographic artifacts due to switched electrodes were suspected when one of the following morphological changes occurred:

• • in the peripheral leads:
    • Abnormal QRS axis between 1808 and -908
    • Abnormal P axis with positive P wave in aVR and/ or negative P waves in lead I and/or II
    • Very low (b0.1 mV) amplitude in the lead I, II, or III
    • Concordant negative QRS and T waves in the leads I, II, III, and/or aVF
  • in the precordial leads:
    • Abnormal R progression in the leads V1 to V6, especially when the R wave amplitude increased after an initial decrease in the precedent leads

All ECGs in which the automated ECG analyzer sus- pected an erroneous electrode placement were redone and analyzed separately. Pacemaker ECGs were included in the analysis. However, abnormal QRS and P axis could not be used as criteria for electrode misplacements in these ECGs. Statistical comparison of frequencies was made with the use of a v² test, and the null hypothesis was rejected with a 2-sided P value of less than .05. The precision of our morphological criteria was calculated as follows: [correct positive test/(correct positive test + false- positive test)].

Results

We analyzed 838 ECGs from 568 patients with a mean age of 61 F 16 years. Two or more ECGs were performed in 121 patients. The technicians at the OC performed 739 ECGs, and 99 ECGs were collected at the ICU. We

Fig. 2 The control ECG of the 56-year-old man with proper electrode placement showed sinus rhythm, a heart rate of 93 per minute, and a QRS axis of 278.

identified 37 ECGs suspicious for electrode misplacement in

36 patients. Control ECGs were available in 35 of the

37 cases, and an artifact due to switched electrodes could be confirmed in 7 of the 37 ECGs. In the 2 cases without available control ECG, expert opinion rejected the presence of electrode misplacement. The test precision of our criteria varied between 0.17 and 0.6 (see Table 1 for details). Two examples for erroneously recorded ECGs identified in our

study are shown in the figures (Figs. 1 through 4). The frequency of artifacts due to switched electrodes was 0.4% (3/739 ECGs) at the OC and 4.0% (4/99 ECGs) at the ICU ( P = .005). The automated ECG analyzer suspected electrode misplacement in 12 ECGs. In 3 of these 12 cases, both the investigators and the machine suspected switched electrodes. All patients, whose ECG was suspicious to the machine, had at least 1 control ECG. An artifact due to

Fig. 3 This ECG of a 63-year-old man showed an isoelectric line in II and negative P waves in I and aVL, and was therefore suspect for electrode misplacement.

Fig. 4 The control ECG of the 63-year-old man with proper electrode placement showed sinus rhythm, heart rate of 72 per minute, first- grade AV block, complete Right bundle branch block, and a QRS axis of -238.

switched electrodes could be confirmed in only 1 of the

12 cases. This single ECG was also identified by our morphological criteria.

Discussion

Using basic morphological criteria, we were able to identify ECG artifacts due to switched electrodes. In contrast to published reports [3,5], we are not aware that one of these ECG artifacts caused any harm to our patients. The frequency of electrode misplacement was below 1% in the OC and increased to 4% in the ICU setting.

The overall frequency of erroneous ECG recordings in our study was lower than the estimations by Hede’n et al [18,21]. They used artificial neural networks and found lead reversals in nearly 2%, although they only investigated left arm-left foot reversals and erroneous placements of the precordial leads. Several factors may explain the higher rate of ECG artifacts in the ICU in comparison to the OC. First, nurses and doctors in the ICU had less experience and routine in recording ECGs than the specialized technicians in the OC. Second, ICU staff might have suffered a higher workload and more distraction while recording the ECG, which have been demonstrated to increase the rate of errors in the ICU setting in general [22]. Donchin et al [23] demonstrated that the ICU environment is hazardous for Medical errors and that potentially detrimental mistakes occurred on the average twice a day in their 6-bed unit (although ECG artifacts were not included in their report). Recently, Rothschild et al [24] showed that errors in their ICU were most commonly slips and lapses rather than rule- based or knowledge-based mistakes. Error rates in medicine

can be minimized by training of the personal, the use of standardized equipment and procedures, and state-of-the art technology [25]. In our instance, possibilities for improve- ment include clearer labeling of the ECG electrodes and instruction of staff that a misplacement of leads can change the ECG morphology significantly. Doctors should adapt their routine in ECG analysis, so that they become able to detect ECG artifacts due to misplaced electrodes. They must not rely on the automated analysis by the ECG machine, which was of no additional value for the detection of ECG artifacts due to switched electrodes in the present survey.

We identified 37 ECGs suspicious for electrode misplacement, some of

them showing more than 1 morphological criterion. Artifacts due to switched electrodes were confirmed in 7 of the 37 cases. The test precision was calculated as follows: [correct positive test/(correct positive test + false-positive test)].

0.17

1

6

0.21

0.18

3

2

14

11

0.17

1

6

confirmed precision

3 0.60

to observer

5

QRS axis between

1808 and -908

Isoelectric line in leads I, II, or III

Abnormal P wave Concordant negative

QRS and T wave in I, II, III,

and/or aVF Abnormal R

progression in V1-6

Table 1 Morphological criteria and their precision to identify

electrode misplacement in the routine 12-lead electrocardiogram

ECG suspect Misplacement Test

This supports results from our previous study in healthy volunteers, in which the ECG machine made wrong diagnoses and recognized lead misplacements only in a minority of cases [15].

Our study is limited by the fact that not all 568 patients had a control ECG. Hence, we cannot exclude the possibility that originally pathologic ECGs may have turned normal after accidentally switching the electrodes. We described this phenomenon earlier in patients with ECG signs of chronic inferior myocardial infarction, in whom electrode misplacement provoked a normalization of the ECG [15]. This lack of a gold standard makes the calculation of sensitivity and specificity for our criteria impossible. Future studies using rigorous control ECG are needed to resolve this problem. Surprisingly the precision of our criteria was less than expected, especially for the abnormal QRS axis and the isolated isoelectric lines in lead I, II, or III. We explain this phenomenon by our heterogeneous population including many patients with complex congenital heart disease or cardiomyopathies.

In conclusion, this study shows that errors in the performance of the ECG do occur and that their frequency increases in an acute medical care setting. Hence, clinicians should know the typical ECG changes resulting from electrode misplacements and stay alert to identify these errors in their daily practice.

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