Electrical activation of the ventricular myocardium of the crocodile Crocodylus johnstoni: A combined microscopic and electrophysiological study

We mapped the sequence of ventricular depolarization in the crocodile Crocodylus johnstoni. We also attempted to find specialized conduction tissue within the ventricular myocardium. Electrical recordings with miniature multi-point electrodes revealed two strands of rapidly conducting tissue (channels) within the interventricular septum, suggestive of conductive tissue pathways. From these septal channels, wavefronts of excitation swept around each ventricle. Electrical recordings did not indicate that there was conductive tissue in the wall of either ventricle. Similarly, microscopic studies of the septal channels provided no indication of specialized conductive tissue. We suggest that the channels of early septal depolarization provide the crocodile heart with a high speed depolarization pathway functionally analogous to a rudimentary conductive system

The Dynamics of Sustained Reentry in a Loop Model with Discrete Gap Junction Resistance

Dynamics of reentry are studied in a one dimensional loop of model cardiac cells with discrete intercellular gap junction resistance ($R$). Each cell is represented by a continuous cable with ionic current given by a modified Beeler-Reuter formulation. For $R$ below a limiting value, propagation is found to change from period-1 to quasi-periodic ($QP$) at a critical loop length ($L_{crit}$) that decreases with $R$. Quasi-periodic reentry exists from $L_{crit}$ to a minimum length ($L_{min}$) that is also shortening with $R$. The decrease of $L_{crit}(R)$ is not a simple scaling, but the bifurcation can still be predicted from the slope of the restitution curve giving the duration of the action potential as a function of the diastolic interval. However, the shape of the restitution curve changes with $R$.Comment: 6 pages, 7 figure

A Validation Study of the Trio Measure of Visual Processing Ability

Trio is a newly developed group-administered instrument designed to measure visual ability for application in cognitive styles research. This study investigated the validity of Trio as seen in its convergence or divergence with two established tests, one conceptually related and one conceptually unrelated. The correlation of Trio scores with scores on these other two tests was examined using a sample of undergraduate students. The analysis of the relationship between scores on Trio and on the conceptually related Learning Figures Test failed to provide evidence that these two tests are measuring the same construct. At the same time, Trio\u27s correlation with the unrelated ACT English section was shown to be fairly low. This second finding supports the conclusion that Trio scores are not severely confounded by verbal ability level

Effect of Pacing Site on the Atrial Electrogram at Target Sites for Slow Pathway Ablation in Patients with Atrioventricular Nodal Reentrant Tachycardia

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/75513/1/j.1540-8159.1994.tb02394.x.pd

Genetic Background Can Result in a Marked or Minimal Effect of Gene Knockout (GPR55 and CB2 Receptor) in Experimental Autoimmune Encephalomyelitis Models of Multiple Sclerosis

PMCID: PMC379391

Toward the optimal lead system and optimal criteria for exercise electrocardiography

To define the optimal lead system for exercise electrocardiography, data of the whole body surface potential distribution were analyzed in 25 normal subjects and in 25 patients with coronary artery disease at rest and during exercise. All patients had a normal electrocardiogram at rest. The sensitivity of the standard chest leads was 60 percent; it improved to 84 percent with the body surface map whereas both methods had a 100 percent specificity. On the basis of these data, and reports from other centers, it is concluded that a single bipolar lead from the right subclavian area to lead V5 is adequate in those laboratories that are restricted to testing subjects with a normal electrocardiogram at rest. In patients with a previous infarction or other abnormalities in the electrocardiogram at rest three (pseudo) orthogonal leads or several standard leads are necessary. Recommendations for optimal measurements from the exercise electrocardiogram are based on quantitative computer analysis of the selected leads in larger groups of patients. Best results were obtained with a combination of S-T amplitude, S-T slope and heart rate. The improvement in sensitivity from 50 percent with visual analysis to 85 percent with computer was similar to that obtained with body surface mapping. Changes of the P wave and QRS complex during exercise appeared to be of little diagnostic value. The pathophysiologic mechanisms that contribute to the changes of the electrocardiogram during exercise are discussed

Progressive age-associated activation of JNK associates with conduction disruption in the aged atrium.

Connexin43 (Cx43) is critical for maintaining electrical conduction across atrial muscle. During progressive aging cardiac conduction slows and becomes susceptible to disruption, predisposing to arrhythmias. Changes in Cx43 protein expression, or its phosphorylation status, can instigate changes in the conduction of the cardiac action potential. Our study investigated whether increased levels of activated c-jun N-terminal kinase (JNK) is the mechanism responsible for the decline of Cx43 protein and intercellular communication during progressive aging. We examined right atrial muscle from guinea pigs between 1 day and 38 months of age. The area of the intercalated disc increased with age concurrent with a 75% decline in total C43 protein expression and spatial re-organisation of the remaining protein. An age-dependent increase in activated-JNK correlated with a rise in phosphorylated Cx43. The data also correlated with slowing of the action potential conduction velocity across the right atria from 0.38±0.01 m/s at 1 month of age to 0.30±0.01 m/s at 38 months of age. The JNK activator anisomycin increased levels of activated JNK in myocytes and reduced Cx43 protein expression paralleling the aging effect The JNK inhibitor SP600125, was found to eradicate almost all trace of Cx43 protein from the intercalating discs. We conclude that in vivo activation of JNK increases with age leading to the loss of Cx43 protein from atrial myocytes. This progressive loss results in impaired conduction and is likely to contribute to the increasing risk of atrial arrhythmias with advancing age

The Effect of Electrode Configuration on the Unipolar His-Bundle Electrogram

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/75654/1/j.1540-8159.1989.tb06148.x.pd