Some aspects of the wideband recording of the electrocardiogram

Abstract

Summary:The physiological mechanisms responsible for the high frequency components of the electrocardiographic signals in different frequency ranges are still unknown. These components have been studied in the frequency domain as well as in the time domain. Numerous clinical and experimental studies have focused upon the incidence and interpretation of high frequency notches and slurs under different conditions in the myocardium. However, the analysis of the high frequency components appeared to be tedious and imprecise, and the interpretation of its results difficult and controversial, and strongly dependent upon empirically determined standards which still require thorough evaluation. Digital methods for processing electrocardiographic signals developed during the last decade have given rise to a variety of fast and reliable approaches for analyzing the information carried by the electrocardiogram. Many researchers have applied such methods to various clinical situations in human studies and to different kinds of interventions in animal studies. These developments prompted us to review research in the field of wideband recording of the electrocardiogram and to briefly discuss some of the aspects that still require elucidation.Key words: frequency response of electrocardiographs, high fidelity ECG, high frequency components, QRS notching and slurring, high frequency content of QRS, digital filtering, morphology of high frequency QRS

Real-Time 12-Lead High-Frequency QRS Electrocardiography for Enhanced Detection of Myocardial Ischemia and Coronary Artery Disease

“…Mass reproduce only with permission from Mayo Clinic Proceedings. Table 1 had a QRS interval greater than 120 ms, cardiomyopathy, or left ventricular hypertrophy (ie, conditions that can cause notches and slurs in the conventional QRS and therefore possible RAZ formation even in the absence of CAD 14,29 ) or arterial collaterals of grade 2 or higher to a singularly diseased culprit vessel at catheterization, a pacemaker, right axis deviation, persistent arrhythmia, or preexcitation syndrome. Using the same statistical analysis noted previously and considering only patients with no prior MI, the incidence of all 3 types of RAZs was significantly increased in patients with (vs without) critical stenoses at catheterization (1-sided P values for the test of no mean increase were .04, .004, and .004 for the RAZ Ns, RAZ APs, and RAZ As, respectively).…”

“…Although the HF QRS ECG is clearly more sensitive than the conventional ECG for identifying myocardial ischemia and MI in monitoring situations, 4,5,7 its use in the diagnosis of CAD requires further study and verification before it can enter the clinical mainstream. For example, because loss of energy in the higher-frequency (150-250 Hz) QRS range often corresponds to an addition of energy (and therefore notching and slurring) in the conventional QRS complex, 14 it is not surprising that notch-producing pathologic conditions such as ventricular hypertrophy, 30,31 collagen diseases affecting the heart, 32 and noncoronary cardiomyopathies 32 are, according to our preliminary data, also commonly associated with extensive RAZ formation, even in the absence of advanced CAD at catheterization. Although no published studies have specifically investigated the 150-to 250-Hz HF QRS in the context of these other cardiac conditions, idiopathic dilated cardiomyopathy is clearly associated with the formation of multiple local maxima and minima within the higher frequencies of the QRS.…”

“…The 2 most commonly measured parameters of HF QRS signals are the root mean squared (RMS) voltage 4,5,[7][8][9]11,12 and the presence vs the absence of a splitting phenomenon known as a reduced-amplitude zone (RAZ). [6][7][8][12][13][14][15] Whereas RMS voltage provides an estimate of the total energy or amplitude of an HF QRS signal, the presence of a RAZ provides a morphologic indicator of potential pathology. As originally defined by Abboud, 7 a RAZ occurs in an HF QRS signal when at least 2 local maxima of the signal's upper envelope or 2 local minima of the signal's lower envelope are present (Figure 1, B-D).…”

“…Reduced-amplitude zones are important because they often are formed in the HF QRS complexes of individuals with CAD and during ischemia, even when there is no simultaneous change in the conventional ST segments. 3,7,13,14,[16][17][18] Abboud et al 19 have successfully modeled both HF QRS complexes and the generation of RAZ phenomena using a computer simulation that includes the torso as a volume conductor, the cells of the myocardium, and a ventricular conduction system that branches 7 or more times in a fractal (self-similar) fashion. When an ischemic activation process is simulated in the model by reducing the conduction velocity in a small ventricular region that includes the late-branching Purkinje fibers, the local myocardial cells, or both, a RAZ is formed.…”

High‐frequency QRS electrocardiogram

“…One possible explanation is the utilization of different frequency ranges in different studies. The precise frequency range utilized is of critical importance, as directional changes occurring in RMS voltages in the 150–250 Hz band might often be opposite to those occurring in wider or lower HF bands (Mor‐Avi & Akselrod, 1990a). For example in dogs, Mor‐Avi & Akselrod (1990b) have specifically observed power shifts from higher frequencies to lower frequencies (sometimes accompanied by the appearance of ‘notches and slurs’) during slowing of conduction caused by myocardial ischaemia.…”