Biomedical subjects

R C Barr

Publications and source records attributed to R C Barr.

At least 73 records · Page 4Linked to original sources

PubMed1976

Origin of epicardial ST-T wave potentials in the intact dog.

Ventricular repolarization was analyzed by measuring epicardial potential distributions in intact dogs with single or multiple ectopic foci and a minimum at the terminal site(s) of excitation. During the latter half of the T wave the distributions became more complex, and two maxima evolved from the initial one at each ectopic site. The measured epicardial potentials were simulated by means of a model of ST-T wave events that is suitable for study of single and multiple ectopic beats with fusion, a a model we call 'SI model.' Intracellular potentials around the ventricles during repolarization were calculated from measured excitation sequences and known action potential shapes. The extracellular potentials around the ventricles were computed from the intracellular ones by a simplified ventricular geometry. The satisfactory agreement between the theoretical and measured extracellular potential distribution shows that the complex changes which occur throughout the ST-T wave are predicted well on the basis of changes in the intracellular potential distributions. In contrast to the well known lability of the T wave from beat, the results show that for any single beat the events of repolarization proceed in an entirely repeatable and deterministic fashion. The results present a way to directly represent cardiac extracellular events during the ST-T wave, a method analogous to the use of isochromes during QRS, and they imply that in the future it will by possible to achieve a more precise quantitative understanding of the events of the ST-T wave than thus far has been possible for QRS.

Action Potentials↗

PubMed1975

Ventricular intramural and epicardial potential distributions during ventricular activation and repolarization in the intact dog.

Ventricular intramural and epicardial potential distributions were measured during normal excitation and repolarization in intact dogs. Potential distributions were chosen because they can be unambiguously measured, are useful in understanding the shapes of wave forms at many specific sites, and provide a direct measure of repolarization. Unipolar wave forms were recorded from intramural and epicardial electrodes and converted into potential distributions. Well-known shapes of wave forms recorded at the inner and outer layers of the ventricles as well as peak-to-peak voltages were shown by the potential distributions to be determined primarily by superposition effects of distant excitation waves. These effects were most prominent before epicardial breakthrough and then receded during the last half of the QRS complex. However, the potential distributions became more complex as excitation waves merged, collided, and terminated. During terminal depolarization, there were scattered positive repolarization potentials intramurally. Normal repolarization was characterized by positive potentials over the ventricular epicardium while there were changes intramurally and on the atrium. Throughout the T wave, there was a predominant transmural unidirectional gradient with the inner wall being more negative than the outer wall. This finding confirms that the sequence of repolarization is from the epicardium to the endocardium with the middle layers having an intermediate time.

Action Potentials↗

PubMed1975

Anaylsis of ventricular activation and repolarization from intramural and epicardial potential distributions for ectopic beats in the intact dog.

Ventricular activation and repolarization were examined by measuring intramural and epicardial potential distributions during ectopic sequences in intact dogs. Potential distributions were used because they provided a direct measure of all of repolarization. Ectopic sequences produced almost unidirectional excitation across the heart along with repolarization events that were different from normal. During ectopic repolarization, positive potentials occurred over a broad area surrounding the ectopic focus, and negative potentials occurred over a large area on the opposite side of the heart where excitation terminated. The potentials in the walls of both ventricles were more positive in the outer layers and more negative in the inner layers, a gradient similar to normal. A maximum initially was at the ectopic site with a magnitude greater than that of the minimum, but the maximum subsequently decreased in magnitude and shifted toward the minimum while the minimum increased in magnitude. The steepest gradients were initially around the maximum, and they then shifted toward the minimum. The results show that ventricular repolatization potential distributions during ectopic beats are predominantly influenced by gradients from one side of the heart to the other (transventricular gradients) in contrast to normal repolatization distributions which are predominantly influenced by gradients across the wall (transmural gradients).

Animals↗

PubMed1973