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Biomedical subjects

R M Arthur

Publications and source records attributed to R M Arthur.

8 recordsLinked to original sources
PubMed1991

Diagnostic implications of spectral and temporal analysis of the entire cardiac cycle in patients with ventricular tachycardia.

BACKGROUND: Available methods for analysis of signal-averaged electrocardiograms (ECGs) have a low-positive predictive accuracy for identifying patients at risk for ventricular arrhythmias. Identification of the spectral and temporal features in ECGs that distinguish patients prone to ventricular tachycardia (VT) is a prerequisite to implementing refinements in methods that increase the diagnostic power of the signal-averaged ECG. METHODS AND RESULTS: Fast Fourier transforms and time-domain reconstructions based on inverse fast Fourier transforms were computed over the entire cardiac cycle of signal-averaged ECGs of sinus beats from 40 patients with myocardial infarction and sustained VT, 41 with infarction without VT, and 20 normal controls. Ventricular depolarization and repolarization were analyzed by procedures that obviate limited resolution due to short data segments and window functions. Spectral magnitudes of ECGs from patients in each group were compared, and the phase data were used for time-domain reconstructions to determine the temporal distributions of distinguishing frequency bands during the cardiac cycle. Magnitudes of 1-7-Hz frequencies were increased (from p less than 0.05 to p less than 0.00001), and magnitudes of 13-56-Hz and 70-128-Hz frequencies were decreased (from p less than 0.05 to p less than 0.00001) in the spectra of ECGs from patients with VT compared with patients without VT. Time-domain reconstructions demonstrated that 1-7-Hz frequencies were detectable throughout the QRS complex, ST segment, and T wave in ECGs from each group. The 13-56-Hz and 70-128-Hz frequency bands not only contributed to the terminal QRS and ST segment but were also detectable throughout the QRS complex of ECGs from patients with VT. CONCLUSIONS: Results define new spectral and temporal features in signal-averaged ECGs from patients with VT that are excluded from analysis by available techniques that limit the bandwidth or restrict interrogation to portions of the cardiac cycle. These findings provide an objective basis for developing new indexes for signal-averaged ECG analysis.

Electrocardiography↗
PubMed1990

Noninvasive detection of patients with ischemic and nonischemic heart disease prone to ventricular fibrillation.

Abnormalities in the fast Fourier transforms of signal-averaged electrocardiograms (ECGs) obtained during sinus rhythm appear to distinguish patients with ischemic heart disease and sustained monomorphic ventricular tachycardia from those without ventricular tachycardia. This study was performed to determine the power of frequency analysis to detect patients with a history of ventricular fibrillation, to determine the extent to which spectra of signal-averaged ECGs from patients with ischemic and nonischemic heart disease are comparable and to compare results of signal-averaged ECG analysis in patients with ventricular fibrillation with results of programmed ventricular stimulation. Signal-averaged ECGs were obtained during sinus rhythm from 60 patients with sustained ventricular tachycardia (Group I) and 34 patients with ventricular fibrillation (Group II). Results of signal-averaged ECG analysis were abnormal in 92% of patients with ventricular tachycardia and 85% of patients with ventricular fibrillation (p = NS). Abnormal spectra were detected in the signal-averaged ECGs from 90% of patients with ischemic and from 86% of patients with nonischemic heart disease (p = NS). In contrast, the results of programmed stimulation differed markedly between the two patient groups. Sustained ventricular arrhythmias were induced in 91% of the patients with ventricular tachycardia compared with only 46% of those with ventricular fibrillation (p less than 0.0001). Moreover, ventricular tachycardia was inducible in 81% of patients with ischemic heart disease compared with only 50% of those with nonischemic heart disease (p less than 0.02). Thus, abnormalities in the spectra of signal-averaged ECGs were found in the majority of patients with ventricular fibrillation and were detectable even in those whose arrhythmia was not inducible by programmed stimulation. These results broaden the potential clinical application of noninvasive interrogation of signal-averaged ECGs to include the prospective identification of patients with ischemic or nonischemic heart disease prone to ventricular tachycardia or ventricular fibrillation.

Cardiac Pacing, Artificial↗
PubMed1990

Respiratory problems in the racehorse.

Racetracks are ideal environments for the promotion of lower respiratory disease. The stabling is close and unclean, the population is nationally and internationally mobile, and the work the racehorse performs is traumatic to the respiratory tract. The running horse must complete a respiratory cycle with each stride. This relationship requires 130-150 breaths a minute in the running horse. Minute volume has been measured at 1300 L per minute and peak flow rates of 60 L/second in horses traveling at a modest 8 meters per second. As a comparison, the fastest running horse approaches 18 meters per second. The traumatic nature of racing to the respiratory tract is demonstrated by the fact that over 80% of the Thoroughbred racehorses show signs of exercise-induced pulmonary hemorrhage. Treating respiratory disease is a major part of racetrack practice.

Animals↗
PubMed1977

A dipole plus quadrupole lead system for human electrocardiography.

A lead system was constructed to extract dipole and quadrupole components of cardiac sources from surface electrocardiograms (ECGs) recorded at 16 sites. The lead system was based on an analysis of a computerized model of a multipole equivalent cardiac generator in a homogeneous torso. The model was previously determined from extensive geometric and electrocardiographic data obtained from one subject. Dipole components estimated with the lead system were 89% accurate for the original subject. Evaluation of the lead system on this subject and in 59 other subjects included calculation of the effect of non-dipolar sources on the values of the estimated dipole components, comparison of the consistency of equivalent sources found independently at two origins in the heart region, and reconstruction of ECGs from lead system components. Dipole consistency at the origins was maintained over the wide range of age, weight, and body shape which characterized the subject population. Whereas quadrupole terms did not agree as well as the dipole terms, inclusion of the quadrupole reduced ECG reconstruction errors by a factor of about three compared to errors for the dipole alone. Together, the dipole and quadrupole accounted for almost 90% of the electrocardiographic information measured on the body surface with the D/Q lead system.

Computers↗