On Recording the Unipolar ECG Limb Leads via the Wilson's vs the Goldberger's Terminals: aVR, aVL, and aVF Revisited

The augmented unipolar limb leads aVR, aVL, and aVF, introduced by Goldberger in 1942, are an integral part of the 12-lead ECG.1,2 Leads I, II, and III have 2 dedicated electrodes, but the other 9 leads have a single dedicated electrode, and another one constructed from the averaged inputs of multiple electrodes. This Viewpoint discusses whether an indifferent pole for the recording of unipolar limb leads is best provided by the Wilson's central terminal (WCT), or by inputs from 2 limb electrodes (Goldberger's central terminal) (GCT), as done currently, and whether the latter have any advantages over the former. The term "unipolar", popularized by Wilson, is a misnomer, since no leads can be truly "unipolar", all requiring positive and negative poles. Thus the term unipolar is used herein in the quasi-unipolar sense, as when first introduced by Wilson and Goldberger, who also realized that such leads were not truly unipolar. The popularity of the unipolar leads reflected the quest of recording the ECG from various vantage points of the body, considering the limitations of the 3 bipolar leads, introduced by Einthoven,3 which register the difference of 2 ECG curves recorded at the 2 poles of these leads, and no variation in potential at each of these poles.4 In contrast the unipolar leads were thought to register such variation of absolute potential, something not really true. Initially the WCT was used to record the unipolar limb leads,5 but the amplitude was low, and the inscribed ECGs, then, and for many decades later,6 were thick-lined (≥2 mm) (Figure 1)

Drug-induced QRS morphology and duration changes

Drug-induced ECG changes may affect all components of the ECG curve. The attention of regulatory agencies, researchers and clinicians has been directed towards drug-induced QT-interval prolongation and its well-documented proarrhythmia. This presentation focuses on druginduced changes, i.e., morphology, amplitude and QRS complex duration (QRSd). A great variety of pharmacological agents (e.g., class IA and IC antiarrhythmics, antihistamines, antidepressants, antipsychotics) exert an influence on the QRSd. The QRSd is assessed by a variety of ECG methodologies. Standardization of measurements of QRSd ensures the comparability of results by different ECG modalities, and of serial QRSd assessments. Some analgesics and hypoglycemic agents influence the amplitude of QRS complexes by way of their propensity to cause peripheral oedema (extracardiac mechanism). Perhaps a new culture could evolve in which the entire ECG curve, from the onset of the P-wave to the offset of the U-wave, will be used in the evaluation and monitoring of drug safety, with emphasis primarily on the standard ECG

Suggestions To Evaluate Whether T-wave Alternans Is T-wave Amplitude Dependent

-wave alternans (TWA) has been employed in the selection of patients considered for cardioverter/defibrillator (ICD) implantation, and has been found to have an excellent negative predictive value for sudden death and malignant ventricular arrhythmias in patients with a variety of cardiac pathologies [1]. Although a qualitative approach in the characterization of patients with TWA positive or negative results has prevailed, based on a threshold of ≥1.9 μV, attained during exercise stress testing, employing the frequency domain analysis [2], some have advanced the argument that employment of TWA in quantitative terms may have advantages [3,4]. Indeed even the currently employed qualitative (yes or no) spectral analysis method with the ≥1.9 μV threshold value has a quantitative underpinning, in the sense that non attainment of the threshold value of ≥1.9 μV renders the patient's test negative [2]. Intuitively the magnitude of TWA must be of importance not only because a particular threshold needs to be reached, before the patient is considered positive, but because pathophysiological derangements (e.g., ischemia, volume overload, or myocardial necrosis) result in an increase of the magnitude of TWA or an association of the magnitude of the TWA and the severity of derangement [5-7], while therapeutic interventions (e.g. beta-blockers) lead to a decrease in the magnitude of TWA [8]

The Need for Studies to Evaluate the Reproducibility of the T-Wave Alternans (TWA), and the Rationale for a Correction Index of the TWA

Sudden cardiac death (SCD) due to various cardiomyopathies is currently prevented by the implantation of an automated cardioverter/defibrillator (ICD). ICD impalntation in patients who are not survivors of SCD, or have not suffered potentially lethal ventricular arrhythmias, are based on the presence of cardiomyopathy with a reduced left ventricular ejection fraction. The bulk of patients who are considered suitable for an ICD implantation and receive such devices, do not experience device therapy shocks at follow-up ("false positives"), thus creating a climate of uncertainty among patients and physicians about the soundness of our current eligibility criteria for ICDs. In addition the cost of inappropriate ICDs is staggering, and the undue exposure of "false positive" patients to complications, and hardships is disconcerting. T-wave alternans (TWA) has emerged as a possible "risk detection of SCD" technology, but its reproducibility has not been tested. Peripheral edema (extracardiac) or other cardiac mechanisms, unrelated to the degree of SCD risk, alter the amplitude, and other attributes, of the T-waves. Since TWA may be T-wave amplitude-, or other T-wave attributes-dependent (this is still a speculation), a need may be emerging for its correction by the T-wave amplitude (TWA index); such an index may enhance the reproducibility, and evaluate the true sensitivity, specificity and predictive accuracy of the TWA in detecting future victims of SCD

P-wave duration and dispersion in patients with peripheral edema and its amelioration

BACKGROUND: Attenuation of the P-wave amplitudes in patients with peripheral edema (PERED) has been recently reported, with P-waves regaining some of their amplitude in patients, who subsequently experienced amelioration of their PERED. Changes in the P-waves correlated with the corresponding alterations in the QRS complexes. Also since amplitudes and durations of QRS complexes changed in parallel in patients with PERED, it was hypothesized that similar changes in the P-wave amplitudes, mean P-wave duration (P-du-mean), and P-wave dispersion (P-d), would occur in such patients. METHODS: Measurements of P-wave amplitude, P-du-mean and P-d in patients who developed, or experienced alleviation, of PERED, were carried out and analyzed. RESULTS: Although P-wave amplitudes and P-wave areas decreased with development of PERED (N = 16), and increased with its amelioration (N = 6), P-dur-mean before PERED was 66.8±14.5 ms, and at peak weight gain it was 65.2±11.9 ms, p = 0.66; also at peak weight gain and subsequent lowest weight, in the patients who lost weight, it was 66.5±9.9 ms and 72.3±12.0 ms, respectively, p = 0.38. Similarly the P-d prior to PERED was 62.3±25.2 ms, and at peak weight gain it was 74.3±29.3 ms, p = 0.09; also at peak weight and subsequent lowest weight, in the patients who lost weight, it was 58.8±34.2 ms, and 61.3±13.6 ms, respectively, p = 0.87. CONCLUSION: P-du-mean and P-d did not change in patients who developed PERED; their stability is attributed to the offsetting of the electrophysiologically-mediated real changes, by opposite apparent changes, imparted by PERED

Comments on “QT interval prolongation in Takotsubo syndrome: a frightening feature with no major prognostic impact”

Dear Editor, Pinho et al. reported on the acquired corrected QT-interval (QTc) prolongation in a retrospective analysis of 113 patients (aged 67.6±11.7, 94.7% female)..

ECG Changes and Voltage Attenuation in Congestive Heart Failure

The electrocardiogram (ECG) is invaluable in providing diagnosis, prognosis, and information for decision making in the management of patients with congestive heart failure (CHF). In addition to the traditional applications of the ECG, which are of importance in the management of patients with CHF, and include indeed the bulk of ECG derived information, a recently described association of peripheral edema with attenuated ECG voltage, provides an expanded dimension in diagnostics. These attenuations result in decreased amplitude of QRS complexes, P-waves, and shortened duration of QRS complexes and QT intervals, with significant diagnostic implications. Alleviation of peripheral edema in response to diuresis in patients with CHF reverses all above alterations