Search

This paper presents a new, quantitative approach to measuring abnormal intra-QRS signals, using the high-resolution electrocardiogram (HRECG). These signals are conventionally known as QRS 'notches and slurs.' They are measured qualitatively and form the basis for the ECG identification of myocardial infarction. The HRECG is used for detection of ventricular late potentials (LP), which are linked with the presence of a reentry substrate for ventricular tachycardia (VT) after a myocardial infarction. LP's are defined as signals from areas of delayed conduction which outlast the normal QRS period. Our objective is to quantify very low-level abnormal signals that may not outlast the normal QRS period. In this work, abnormal intra-QRS potentials (AIQP) were characterized by removing the predictable, smooth part of the QRS from the original waveform. This was represented as the impulse response of an ARX parametric model, with model order selected empirically from a training data set. AIQP were estimated using the residual of the modeling procedure. Critical AIQP parameters to separate VT and non-VT subjects were obtained using discriminant functions. Results suggest that AIQP indexes are a new predictive index of the HRECG for VT. The concept of abnormal intra-QRS potentials permits the characterization of pathophysiological signals contained wholly within the normal QRS period, but related to arrhythmogenesis. The new method may have other applications, such as detection of myocardial ischemia and improved ECG identification of the site of myocardial infarction, particularly in the absence of Q waves. Index Terms - Autoregressive processes, electrocardiography, modeling.

The time-frequency plane Wiener (TFPW) filter is a new method, based on a posteriori Wiener filtering principles, to enhance the performance of ensemble averaging. This paper develops the mathematical aspects of the TFPW filter, and assesses its performance with elementary signals, such as sine waves and chirps, and authentic high-resolution electrocardiogram (HRECG) ensembles. The principal feature of the TFPW filter is its use of the time-frequency plane to accommodate signal nonstationarity. Using a posteriori computed statistics of the ensemble, the filter matches itself to the time-frequency structure of the signal to be estimated. The method is sufficiently general to be applicable to any class of repetitive signal with a deterministic time-frequency structure and additive noise in the ensemble. It is concluded that significant improvements in both estimated signal fidelity and noise reduction are possible with the TFPW filter, compared to conventional ensemble averaging. Index Terms - Electrocardiography, time-varying filtering, Wiener filtering.

This paper introduces the concept of a posteriori Wiener filtering (APWF), performed in the time-frequency plane. The objective is to improve the signal-to-noise ratio (SNR) of the ensemble-averaged high-resolution electrocardiogram (HRECG). APWF was developed to address the problem of a limited ensemble size for estimating ensemble-averaged evoked potentials. For the HRECG, we identify the major challenge as adapting the time-frequency structure of the filter to that of low-level cardiac signals. Technical limitations and the characteristics of HRECG signals make time-frequency analysis of the ensemble average problematic. Normal and abnormal signal components are difficult to distinguish due to low time-frequency energy concentration and limited spectrotemporal resolution. However, considering the entire ensemble of repetitive ECG records, signal and noise components are separable in the time-frequency plane. This forms the basis of the new time-frequency plane Wiener (TFPW) filter, applicable to any ensemble averaging problem involving repetitive deterministic signals mixed with uncorrelated noise. Index Terms - Electrocardiography, time-varying filtering, Wiener filtering.

Abstract: This article introduces a novel concept of abnormal intra-QRS potentials (AIQPs) associated with myocardial ischemia. AIQPs are microvolt-level potentials—subtle alterations in the QRS of the high-resolution electrocardiogram (ECG)—isolated from the unfiltered signal-averaged ECG (SAECG) by a method of mathematical modeling. The aims of the study were (1) to determine the characteristics of potentials in the SAECG related to ischemically altered activation during percutaneous transluminal coronary angiography (PTCA), (2) to determine their relationship with standard 12-lead ECG variables, and (3) to investigate whether AIQPs have a specific pathophysiologic basis in myocardial ischemia. Continuous high-resolution ECG data were acquired from 12 patients before, during, and after PTCA. SAECGs were computed every 60 seconds using an enhanced method of signal averaging. AIQP, ST-segment deviation, and changes in standard ECG QRS duration were measured in each 1-minute SAECG. AIQP amplitudes increased significantly during balloon inflation, compared with the preinflation state. AIQPs exhibited a greater prevalence (12 of 12 patients) than ST-segment deviation changes of more than 100 μV (7 of 12 patients), or measurable changes in standard QRS duration (4 of 12 patients). In patients with significant changes in 12-lead ECG variables during balloon inflation, AIQPs were strongly correlated with both ST-segment and QRS-duration changes. AIQP timing was correlated with the artery occluded, suggesting a specific, ischemia-influenced origin of the signal. AIQPs show promise as a time-localized, sensitive new ECG marker of ischemically altered ventricular activation. [Copyright &y& Elsevier]

This article reports that the Department for Culture, Media & Sport will streamline operations by coordinating activities between their four key branches. Museums, Libraries & Archives Council, Arts Council England, Sport England and English Heritage will now work together, hopefully, resulting in savings that will be put back into new services.