The Quest for Quality Electrocardiographic Recording

Heden et al., reported that 2% of the 11,000 ECGs analyzed showed interchanged electrode placement. Thus, if 300 million ECGs are performed annually in the world, 6 million are erroneously recorded. This figure could even triple if one includes other frequent mistakes, such as vertical displacement of precordial electrodes and the distal placement of these on the limbs instead of the trunk. Few manuals on electrocardiography have devoted space to warn about the effects of ECG recordings that do not conform to standards, but it seems that this is changing.


The Quest for Quality Electrocardiographic Recording
Javier García-Niebla. 1 For correct electrocardiography (ECG) diagnosis and interpretation, it is important not only to distinguish normal from pathological electrocardiograms, but also to ensure that they have been properly recorded.
Heden et al., 1 reported that 2% of the 11,000 ECGs analyzed showed interchanged electrode placement. Thus, if 300 million ECGs are performed annually in the world, 6 million are erroneously recorded. This figure could even triple if one includes other frequent mistakes, such as vertical displacement of precordial electrodes and the distal placement of these on the limbs instead of the trunk. 2 Few manuals on electrocardiography have devoted space to warn about the effects of ECG recordings that do not conform to standards, but it seems that this is changing. 3 This issue of the Journal contains two interesting articles by Rosen et al., who form part of the research group led by Dr. Adrian Baranchuk, which address the most common mistakes made in daily practice in relation to improper placement of limb and precordial electrodes, as well as tell-tale signs for their detection. 4,5 In this editorial we will elaborate on certain issues directly related to possible errors on performing an ECG.

Is it important to prepare the patient for an ECG?
Yes. Patients must be informed of the procedure to be performed, emphasizing that it is painless and harmless but they must lie still, breathe normally and refrain from talking. Nervousness and sweating are to be resolved before starting the procedure. Proper skin preparation, with shaving if necessary, is required to reduce impedance and ensure adhesion of the electrode. This greatly helps to minimize the appearance of artifacts that can sometimes cause significant diagnostic errors. 6

Is it easy to identify ECG patterns obtained with reversal of limb electrodes?
Yes. They are generally easy to identify. Only one pattern, resulting from the reversal of left arm and left leg electrodes, may be easily overlooked, even by experts. The presence of a P wave in lead I with greater amplitude than that in lead II and a positive terminal P wave morphology (-/+) in lead III can sometimes alert us to this error. 7 Given the low specificity of these criteria, it is advisable to check for this error and repeat the ECG to ensure correct electrode placement.

Can limb electrodes be placed on the trunk?
No. Proximal placement of limb electrodes or their placement on the trunk is not compatible with a standard ECG. 8 The advent of easily applicable adhesive electrodes with decreased muscle noise has favored this practice (Figure 1). 9 ECG changes are clearly visible when limb electrodes are placed on the trunk. In these cases, there is a QRS axis deviation to the right, which decreases the voltage of the R wave in leads I and aVL and increases it in leads II, III, and aVF. In a patient with necrotic Q wave in leads II, III and aVF, placing limb electrodes on the trunk may reduce both the voltage and the duration of the

Editorial
wave. If for any reason we need to perform the ECG with this non-standard placement (a patient with Parkinson's, for example), this should be expressly recorded in writing and taken into account in the interpretation.

Is it necessary to place the precordial electrodes exactly on their established sites?
Yes, precordial lead electrodes must be placed exactly on their specific internationally established anatomical locations. 10 Several published studies have described the ECG changes that occur when the electrodes are misplaced. 11,12 Do professionals who regularly perform ECG demonstrate better electrode placement?
No. Even technicians with an average of 15 years or more experience and who perform over 30 ECGs a day can make important mistakes. 11 However, their theoretical knowledge about precordial lead placement is superior to that of other professionals (Figure 2). 13 The most common mistakes include: A) High placement of V1-V2. B) V5-V6 placed too low in some cases or located along the curvature of the 5th intercostal space.

Once the ECG has been obtained, what are the tell-tale signs of high V1-V2 placement?
Three morphologies help identify high placement of these electrodes (Figure 3) 14,15 : a) a negative P wave in V1 only. Under normal conditions, the P wave in V1 is positive or biphasic +/-, more positive than negative with a mild slope. b) The rSr' morphology with a negative P wave is exclusive to ECGs recorded with high placement of the V1 electrode on the 2nd intercostal space. It is seen in 17% of cases of inappropriate placement in healthy individuals. c) A negative component of the P wave or a flattened P wave in V2 are indicators of high placement.
High positioning of the electrodes V1-V2 can mimic a Brugada type 2 pattern. However the r` in this case is narrow with the base of the lower triangle measuring less than 4 mm. 16,17 Can ECG filter settings affect the ECG? Yes. When filters are applied to prevent unwanted noise and obtain better quality recording of the cardiac signal, the ECG can sometimes be markedly affected unless the recommended cutoffs are applied: Figure 3. The P wave is positive in V1-V2 (arrows) when the electrodes are correctly placed (A) on the 4th intercostal space (ICS). When V1-V2 electrodes are misplaced on the 3rd ICS (B), the low-voltage or flattened P wave in V2 (arrow) is the tell-tale sign of high placement. And when the V1-V2 electrodes are misplaced on the 2nd ICS, one sees a negative P wave and rsR' (red arrow) which indicate high placement of the electrodes (C).

Figure 4.
Effect of a high-pass filter in lead V4. Note how the voltages of the R wave (14.84 mm to 12.82 mm) and the S wave (6.68 mm to 2.52 mm) are reduced when applying a non-standard 25Hz filter.