Spectral turbulence analysis of the signal-averaged electrocardiogram and its predictive accuracy for inducible sustained monomorphic ventricular tachycardia.

This study was designed to assess the accuracy of a new noninvasive frequency analysis method for predicting patients with inducible sustained monomorphic ventricular tachycardia (VT) at electrophysiologic study and hence the risk of spontaneous ventricular tachyarrhythmias. Signal-averaged electrocardiograms from 3 orthogonal bipolar surface leads were evaluated using a microcomputer-based frequency analysis system that performs analysis of conventional time-domain late potentials as well as incorporating a new technique for spectral analysis of relatively short, overlapping signal segments spanning the whole QRS complex. The spectral analysis technique measured abnormalities anywhere in the entire QRS complex and did so without dependence on any arbitrarily defined frequency, duration or amplitude cutoffs. The hallmark of arrhythmogenic abnormality was hypothesized to be frequent and abrupt changes in the frequency signature of the QRS wave front velocity as it propagates throughout the ventricle around areas of abnormal conduction, resulting in a high degree of spectral turbulence. One-hundred forty-two subjects were studied, including 71 totally normal control subjects ("true negatives"), 33 with both late potentials by time-domain analysis and inducible sustained monomorphic VT ("true positives"), 28 with late potentials but no evidence of spontaneous or inducible sustained monomorphic VT ("false positives") and 10 with inducible sustained monomorphic VT but absence of time-domain late potentials ("false negatives"). The frequency analysis technique correctly classified 100% of the true negatives, 97% of the true positives, 86% of the late potentials false positives and 60% of the late potentials false negatives. The total predictive accuracy of frequency analysis for all groups was 94%, compared with 73% for time-domain late potential analysis. The results suggest that a high degree of spectral turbulence of the overall QRS signal during sinus rhythm may provide a more accurate marker for the anatomic-electrophysiologic substrate of reentrant tachyarrhythmias than detection of late potentials in the terminal QRS region by either time- or frequency-domain analysis. Spectral turbulence analysis is applicable to patients irrespective of the QRS duration and the presence or absence of bundle branch block.

The signal-averaged electrocardiogram and late potentials. A comparative analysis of commercial devices.

The authors used two separate protocols to compare four commercially available devices for recording of the signal-averaged electrocardiogram and "late potentials" to assess their degree of concordance in identifying abnormalities. In one protocol, studies were performed using each system. In 19% of recordings the results from one system were discordant in at least one numeric parameter. In the second protocol identical averaged data files were used to identify discordancies due solely to differences in analysis algorithms used for QRS offset determination by the various devices. This disclosed 23% discordant findings, mostly in the root mean square amplitude of the terminal 40-msec segment resulting from small differences in the estimate of QRS offset point. To improve concordance between commercial systems, there is an urgent need for adoption of a rigorously standardized algorithm for analysis of baseline noise and QRS offset.

Effects of analyzed signal duration and phase on the results of fast fourier transform analysis of the surface electrocardiogram in subjects with and without late potentials.

A microcomputer-based system capable of performing time- and frequency-domain analysis on the same set of acquired and signal-averaged raw data was used to correlate late potentials detected in the time domain with the results of frequency-domain analysis. Ten patients with spontaneous or inducible sustained ventricular tachycardia (VT) known to have abnormal late potentials in the time-domain signal-averaged electrocardiogram and 10 normal subjects without late potentials were studied. Fast Fourier transform analysis was performed on a segment that comprised the last 40 ms of the QRS and the ST segment up to the onset of the T wave as identified visually. The high-frequency signal content, expressed as the area ratio or the peak magnitude, was found to be markedly dependent on the length of the analyzed QRS-ST segment. A change of as little as 3 ms in the duration of the estimated QRS-ST segment changed the results of the frequency analysis across proposed boundaries of normalcy in normal subjects and in patients with VT. This resulted in both false-negative and false-positive conclusions. Similar results were obtained when the effects of varying analyzed signal length or phase were studied using a pure synthesized sine wave signal. For frequency analysis to be clinically useful and reproducible, standards of normalcy must be established for a signal region of fixed duration or the technique must be modified so as to be insensitive to duration of signal sample.

Noninvasive His Bundle electrogram: value of three vector lead recordings.

Studies were conducted in 45 patients to determine whether the reliability of the measurement of the His bundle potential from the body surface was increased by signal averaging of three simultaneously recorded electrocardiographic potentials from horizontal (X), frontal (Y) and sagittial (Z) axes as opposed to recording of any of these. Potentials from the X, Y and Z leads were amplified by 250,000, filtered between 80 hertz (12 dB/octave) and 200 hertz (24 dB/octave) and signal averaging of 1,000 beats was performed. The His bundle potential could be clearly defined in 25 of the 45 patients in the X, Y, or Z lead. His bundle potentials were evident in the X lead in 17 (68 percent) of these 25 patients, in the Y lead in 19 (77 percent) and in the Z lead in 11 (44 percent). No single lead gave satisfactory His bundle electrographic potentials in all patients. In 20 patients the His bundle electrogram could not be recorded because terminal atrial activity overlapped activity of the His bundle potential. The three lead system defined the His bundle potential in a significantly greater number of patients than did the best single lead because it (1) displayed the vectorial lead with the largest His bundle potential, (2) permitted validation of the His bundle potential in more than one lead, and (3) displayed the vectorial lead with the most isoelectric terminal P wave. It is concluded that reliable His bundle potential measurements are obtained in a significantly greater number of patients with use of the simultaneous three lead system than with use of any single lead.

A clinical evaluation of an improved Holter monitoring technique for artificial pacemaker function.

This paper discusses shortcomings of conventional Holter monitoring in paced patients and describes a new technique which permits reliable detection of intermittent pacemaker malfunction and counts pacemaker activity during the recording period. Evaluation of the system of 64 consecutive patients revealed 15 with unsuspected episodic pacemaker dysfunction.

Myocardial infarction following acute aortic dissection.

Acute aortic dissection may present a clinical picture simulating myocardial infarction, including electrocardiographic changes. The mechanism underlying this mode of presentation has not heretofore been documented during life. We present here for the first time, a patient with acute aortic dissection and the clinical picture of acute myocardial infarction, where the mechanism of infarction has been demonstrated, by preoperative angiographic studies, probably to be due to compression of the extramural portion of the right coronary artery by the false channel of the dissecting hematoma.