ABSTRACT
Background
Identification of a possible ventriculoatrial (VA) dissociation in wide QRS complex tachycardias is one of the most reliable criteria for differentiation of tachycardia origin. The Lewis lead has been proposed for detection of atrial activity during ventricular tachycardias.
Hypothesis
A modified Lewis‐lead‐ECG will be superior to the standard‐lead ECG for detection of ventriculoatrial conduction during ventricular tachycardia.
Methods
Forty‐seven patients underwent electrophysiological study, stimulated with a fixed cycle length of 400 ms in the ventricle. During stimulation, a standard‐lead ECG and a modified Lewis‐lead ECG were recorded. Simultaneously, VA conduction was documented by intracardiac electrograms. Surface ECGs were presented to 6 blinded examiners for VA conduction assessment.
Results
Type of VA conduction was correctly diagnosed in significantly more ECGs in the Lewis‐lead ECG group (mean, 35.0 [75%]) than in the standard‐lead ECG group (mean, 29.2 [62%]; P = 0.045). Ventriculoatrial dissociation also was significantly more often correctly diagnosed in the Lewis‐lead ECG group (mean, 17.7 [71%]) than in the standard‐lead ECG group (mean, 12.7 [49%]; P = 0.014). Interobserver agreement was moderate in both groups (κ = 0.45 and κ = 0.49, respectively).
Conclusions
Compared with standard‐lead ECG, modified Lewis‐lead ECG is associated with significantly improved detection of VA conduction type during fast ventricular pacing and thus may help improve ECG diagnosis.
Introduction
Wide complex tachycardias represent a common entity in emergency departments. These tachycardias necessitate quick, reliable differentiation between supraventricular and ventricular origin to determine further treatment decisions. Several electrocardiogram (ECG)‐based algorithms have been proposed for better differentiation of wide complex tachycardias.1, 2, 3 One of the most secure criteria leading to the diagnosis of a ventricular tachycardia (VT) is ventriculoatrial (VA) dissociation visible in the standard‐lead ECG.3 Ventriculoatrial dissociation can be found in about 50% of patients with wide complex tachycardias; in the other cases, a 1:1 or 2:1 (Wenckebach) conduction can be found.4, 5 However, reliable detection of VA dissociation in the standard‐lead ECG is often difficult, possible in perhaps a maximum of 50% of cases.4 Recently, the Lewis‐lead ECG has been proposed for detection of atrial activity during VTs in 2 case reports.6, 7, 8 Up to now, no systematic assessment of possible benefits using this lead in the context of wide complex tachycardias has been performed. We evaluated a modified 12‐lead Lewis‐lead ECG as a possible tool for improved P‐wave detection and VA conduction characteristics during ventricular stimulation.
Methods
Study Design
The present study was a prospective, operator‐blinded study for the evaluation of potential benefit of a modified 12‐lead Lewis‐lead ECG registration in comparison with the standard 12‐lead ECG for correct diagnosis of VA conduction during ventricular stimulation. In patients undergoing an electrophysiological study, ECGs were registered during ventricular pacing. Standard‐lead ECG and modified Lewis‐lead ECGs of the documented wide complex tachycardias were presented to blinded examiners, who were informed about the ventricular origin of the presented ECGs. The blinded examiners judged the ECGs on the presence of visible P waves and VA conduction ratio.
Study Population
The ECGs in this study were acquired prospectively according to a study protocol approved by the ethics committee of the Charité–University Medicine Berlin. Written informed consent was obtained from all patients prior to participation in the study protocol. We evaluated 94 ECGs from 47 patients. Patients underwent electrophysiological investigation for different types of ablation, such as paroxysmal supraventricular tachycardias, atrial fibrillation, differential diagnosis of syncope, and the evaluation and ablation of VT.
Ventricular Stimulation and Lewis‐Lead Electrocardiogram Registration
In the course of the electrophysiological procedure, patients were catheterized with at least 1 ventricular and 1 atrial catheter to reliably document the ventricular as well as the atrial excitation. Ventricular stimulation was performed via a catheter positioned in the right‐ventricular apex with a constant cycle length of 400 ms for about 10 seconds. Intracardial electrograms for documentation of VA conduction type were recorded. Simultaneously, a standard‐lead ECG registration over a length of 2 pages—including Einthoven leads I, II, and III; Goldberger leads aVL, aVF, and aVR; and precordial Wilson leads V1 through V6—was performed using a registration speed of 50 mm/sec. Thereafter, ECG electrodes were moved to allow a modified Lewis‐lead ECG registration (Figure 1). The right arm electrode was moved to the second intercostal space, right sided, adjacent to the sternum; the left arm electrode was moved to the fourth intercostal space, parasternal right, sided likewise. The other body surface electrodes remained in the same place. The now‐varied lead I was the actual Lewis lead. For the purpose of our study, a modified 12‐lead Lewis‐lead ECG version was recorded, which included the recording of the additional now‐modified leads of Einthoven II and III; Goldberger leads aVL, aVF, and aVR; and precordial Wilson leads V1 through V6. This 12‐lead ECG will be referred to as the modified Lewis‐lead ECG in the text of this article. Ventricular stimulation was repeated from the same stimulation site and with the same cycle length of 400 ms, as before. Registration duration and ECG speed remained unchanged (Figure 2).
Figure 1.
Electrode configuration for the modified Lewis‐lead ECG registration. The right arm electrode is moved to the second intercostal space parasternal right and the left arm electrode to the fourth intercostal space parasternal right. Then, a modified 12‐lead Lewis‐lead ECG was recorded. Abbreviations: ECG, electrocardiogram; F, foot; L, left; LL, Lewis lead; N, neutral; R, right.
Figure 2.
Two ECGs from the same person: a modified Lewis‐lead ECG on the left and the standard‐lead ECG on the right. Both ECGs display a retrograde 2:1 conduction. Arrows indicate the P waves. Abbreviations: ECG, electrocardiogram.
Electrocardiographic Evaluation
All ECGs were presented to 6 blinded examiners. The ECGs were anonymized and presented in random order. No further information than the 12‐lead ECG and its distinct ventricular origin was provided to the examiners. The examiners were all physicians specializing in cardiology and cardiac electrophysiology. Each examiner assessed the ECGs on the presence of detectable P waves and on the type of VA conduction. Three different types of possible VA conduction could be selected: VA dissociation, 1:1 conduction, and 2:1 conduction.
Thereafter, the examiners were asked to select the 1 out of all 12 leads in the modified Lewis‐lead ECG and in the standard‐lead ECG that allowed the best detection of P waves and VA conduction type.
Statistical Analysis
Differences in continuous variables were determined with the t test in normally distributed values and the Wilcoxon test in case of non‐normal distribution. Distribution pattern was analyzed with the 1‐sample Kolmogorov‐Smirnov test. Continuous variables are shown as mean ± SD and range. Categorical variables were compared by the χ2 test or Fisher exact test when expected cell values were <5. Categorical variables are presented as percentages. The κ statistic was used to quantify overall interobserver agreement. Overall interobserver agreement was defined as good if κ > 0.6, moderate if 0.6 > κ > 0.4, and poor if κ < 0.4. All P values are 2‐sided, and a P value of <0.05 was considered statistically significant. Statistical analysis was performed with SPSS for Windows, version 22.0 (IBM Corp., Armonk, NY).
Results
Baseline Electrocardiographic Data and Patient Characteristics
All together, 94 ECGs from 47 patients were presented to the examiners. All ECGs showed a cycle length of 400 ms. Mean patient age was 63 ± 13.21 years (20–83 years), and 28 (60%) were male.
The following VA conduction types were documented: In the standard‐lead ECG group, 13 (28%) ECGs showed a 1:1 conduction, 8 (17%) ECGs showed a 2:1 conduction, and 26 (55%) ECGs showed a VA dissociation. In the modified Lewis‐lead ECG group, 13 (28%) ECGs displayed a 1:1 conduction, 9 (19%) ECGs displayed a 2:1 conduction, and 25 (53%) ECGs displayed a VA dissociation.
Differences Between Electrocardiographic Leads
The VA conduction type was significantly more often correctly detected in the modified Lewis‐lead ECGs than in the standard‐lead ECGs (mean, 35.0 [75%] vs 29.2 [62%]; P = 0.045). Details on the distribution of correct diagnosis concerning VA conduction type in each of the 6 examiners are displayed in Figure 3. The VA dissociation was significantly more often correctly detected in the modified Lewis‐lead ECGs than in the standard‐lead ECGs as well (mean, 17.7 [71%] vs 12.7 [49%]; P = 0.014). Details on the distribution of correct diagnosis concerning VA dissociation in each of the 6 examiners are presented in Figure 4.
Figure 3.
Diagram displaying the percentage of accurately detected overall VA conduction ratio in standard‐lead ECGs and modified Lewis‐lead ECGs in different raters. Abbreviations: ECG, electrocardiogram; VA, ventriculoatrial.
Figure 4.
Diagram displaying the percentage of accurately detected VA dissociations in the standard‐lead ECGs and modified Lewis‐lead ECGs in different raters. Abbreviations: ECG, electrocardiogram; VA, ventriculoatrial.
The interobserver agreement was moderate in the standard‐lead ECG group (κ = 0.45) as well as in the modified Lewis‐lead ECG group (κ = 0.49).
The examiners rated lead V1 as best lead for correct detection of VA conduction type in the standard‐lead ECG group. Details on all leads in the standard‐lead ECG group are displayed in Figure 5. In contrast, lead I was rated the best lead for correct detection of VA conduction type in the modified Lewis‐lead ECG group. This would be the original Lewis lead. Details on all leads in the modified Lewis‐lead ECG group are displayed in Figure 5.
Figure 5.
Blinded examiners' ratings for best lead for correct VA conduction type in the standard‐lead ECGs (top) and modified Lewis‐lead ECGs (bottom). Abbreviations: ECG, electrocardiogram.
Discussion
The majority of wide complex tachycardias are of ventricular origin (about 70% to 80%).2, 9 Because of their potential hemodynamically compromising impact, a quick and reliable differentiation of wide complex tachycardias is inevitable. Misdiagnosis of those tachycardias often occurs and might lead to a poorer outcome.10 Although several ECG‐based algorithms have been proposed,1, 2, 3 differentiation of ventricular or supraventricular origin still can be challenging. Differentiation criteria such as the Brugada criteria3 were, after being published, evaluated in the clinical setting by various study groups.11, 12 In the clinical setting, those criteria showed less sensitivity and specificity than the initial publication suggested.11 Furthermore, several of the morphological criteria favoring VTs were found in patients with intraventricular conduction defects during sinus rhythm,12 suggesting a lower specificity of those criteria in this patient group. Possible reasons for misdiagnosis of wide complex tachycardias can include insufficient clinical experience of treating physicians; on the other hand, complexity of the available ECG criteria can be a relevant problem as well, especially in the emergency situation.
A detectable VA dissociation during wide complex tachycardia has been described as one of the most reliable criteria to identify a ventricular origin.3 Nevertheless, detection of VA dissociation is present in only about 50% of those tachycardias, and only a fractional amount of them can be recognized by the observer.4 In our series, all ECGs were of ventricular origin because of fixed frequent ventricular pacing. Ventriculoatrial dissociation was present in 53% of ECGs in the modified Lewis‐lead ECG group and 55% of ECGs in the standard‐lead ECG group. This was correctly identified in significantly more patients in the modified Lewis‐lead ECG group than in the standard‐lead ECG group (mean, 71% vs 49%).The inter‐rater agreement for correct detection of VA conduction type was moderate in both ECG groups, which emphasizes the difficulty of correct P‐wave detection during VTs.
In our study, all ECGs were recorded at paper speeds of 50 mm/sec, and only 2 ECG pages were presented to the examiners. It remains speculative whether a longer ECG registration strip and additional registrations with a paper speed of 25 mm/sec would have enhanced the differences between the 2 groups. Additional ECG registration with different paper speed has been shown to improve the accuracy of rhythm diagnosis in narrow QRS‐complex tachycardias.13
We present the first systematically prospective comparison of the standard‐lead ECG with a modified 12‐lead Lewis‐lead ECG. Originally, the Lewis lead was described by Sir James Lewis with the objective of enhancing P‐wave amplitudes for better identification of atrial excitation in atrial fibrillation.6 The initially described Lewis lead corresponds to lead I in our modified 12‐lead Lewis‐lead ECG. It has been occasionally used by clinical physicians to improve differential diagnosis in different arrhythmias. The Lewis lead recently has been described in 2 case reports as a crucial diagnostic tool in 2 patients with different wide complex tachycardias.7, 8 It is easy and quick to apply and available nearly everywhere.
The most probable reason for the varying visibility of P waves with the 2 groups of ECG leads is the different lead vector in relation to the excitation vector. This might cause a different P wave‐to‐QRS amplitude relationship, and thereby change visibility of P waves. P amplitude itself has been shown to be not higher in the Lewis‐lead ECG than the lead with the highest amplitude in the standard‐lead ECG.14
In our study, in addition to the originally described Lewis lead, which is only lead I, the other lead electrodes remained in their positions and the resulting “modified 12‐lead Lewis‐lead ECG” was presented to the examiners. Because right and left arm electrodes of the standard‐lead ECG were thereby changed, not only the single Lewis lead itself, but also the Goldberger leads as well as the Wilson leads, were changed in their vector. Changing the position of the right and left arm electrodes will change the average potential of the Wilson's central terminal, which is used as negative pole for the 3 augmented limb Goldberger leads and the 6 precordial leads. This explains why the modified 12‐lead Lewis‐lead ECG appears to be different in all 12 leads (Figure 2). Thereby, possible additional leads for better detecting P waves and VA dissociations emerged.
The ECG examiners were asked to name the ECG lead of each presented ECG that allowed the most reliable P‐wave detection. The examiners were blinded to whether the presented ECG was a standard‐lead ECG or a modified Lewis‐lead ECG, and all ECGs were presented in random order. In the modified Lewis‐lead ECG group, lead I was selected for the most reliable P‐wave detection, compared with lead V1 in the standard‐lead ECG group. Lewis lead I presents the originally described single lead by Sir James Lewis. However, a relevant number of examiners still voted for other leads in the Lewis‐lead ECG group. So for clinical practice, the modified 12‐lead Lewis‐lead ECG seems to be preferable.
Clinical Implications
The additional recording of a modified Lewis‐lead ECG in cases of unclear wide complex tachycardias might help to properly differentiate the origin of a tachycardia and, as a consequence, guide safer and faster treatment of patients with unclear wide QRS complex tachycardias.
Study Limitations
Our study has some limitations. First, we present a single‐center study. Further evaluation of our interrogation with a larger, multicenter study will be necessary. Second, the VTs in our study were all focal tachycardias, simulated by fixed ventricular pacing from the right ventricular apex. Ventricular fixed frequent pacing in our study was only performed at a cycle length of 400 ms. We did not evaluate the Lewis‐lead ECG during faster tachycardias or in the context of scar‐related re‐entry tachycardias and preexisting intraventricular conduction disturbances. And third, the evaluation of VTs in our study was performed in a nonemergency setting. The clinical value of an additional modified Lewis‐lead ECG in the emergency setting, implying less time and possibly less experience of the treating physician for ECG analysis, is still unclear.
Conclusion
During fast ventricular pacing, the modified Lewis‐lead ECG shows a significantly enhanced detectability of P wave and VA conduction type compared with the standard‐lead ECG.
The authors have no funding, financial relationships, or conflicts of interest to disclose.
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