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Biomedical subjects

N K Roberts

Publications and source records attributed to N K Roberts.

At least 55 records · Page 3Linked to original sources
PubMed1979

Morphology of the atrioventricular node, bundle and proximal bundle branches: a study employing computerized reconstruction.

The morphology of the human atrioventricular node, atrioventricular bundle and bundle branches is described. A block of tissue bounded by the ostium of the coronary sinus, the pars membranacea, the septal leaflet of the tricuspid valve and the atrial and ventricular septa is removed. The block is then sectioned serially from the right endocardial surface in the frontal plane of the heart. Sectioning in this way produces fewer sections than from techniques previously described. Outlines of the atrioventricular node, atrioventricular bundle and proximal bundle branches are digitally registered and stored in a computer. Three dimensional reconstructions of the structures are then generated by computer and displayed on an oscilloscope so that the entire three dimensional image can be rotated in any plane. Stereoscopic image pairs are produced to assist perception of the shape of the atrioventricular node, bundle and branching patterns of the bundles. This technique is unique in that it describes a method from which a relatively small number of histologic sections are generated permitting not only a complete histologic examination, but also a study of the morphology of the area.

Adult↗
PubMed1979

Left axis deviation: a reassessment.

This report deals with the ramifications of the concept of left axis deviation. In early life, the leftward shift of the frontal plane QRS axis is determined chiefly, if not solely, by the relative weights of the ventricles. Once adult ventricular weight ratios are reached, there is a long period of axis stability, then a gradual leftward drift of the QRS, governed principally by left anterior fascicular conduction. Thus, the normal QRS axis is age-dependent, and left axis deviation must be considered accordingly.

Adult↗
PubMed1978

Adaptation of the rat myocardium to endurance training.

The purpose of this study was to assess cardiac adaptation to endurance training in rats. After 11 wk of progressive treadmill exercise (1 h/day), gastrocnemius cytochrome c oxidase activity was 38% higher (P less than 0.01) in the trained (n = 20) as compared to control (n = 20) rats. Cardiac Mg2+-stimulated myofibril ATPase activity (0.308 +/- 0.012 vs. 0.324 +/- 0.006 micrometer.mg-1.min-1) did not change nor was there any change in myofibril protein concentration (60.0 +/- 1.12 vs. 59.9 +/- 0.85 mg.g-1). The isolated left ventricular papillary muscle showed no significant change in time-to-peak tension (TPT) or half-relaxation time. Tension output, however, was significantly increased with training, 2.2 +/- 0.3 vs. 1.5 +/- 0.1 g.mm-2 (P less than 0.025). Furthermore, when the papillary preparations were perfused with 0.5 mM lanthanum (La3+) to displace membrane-bound Ca2+, the time course for tension decay was significantly prolonged in the trained muscles (P less than 0.001). We conclude that endurance running of this type does not necessarily increase myofibril ATPase activity or the time course of the isometric twitch of rat papillary muscle. However, tension output per unit area does increase and this appears to be due to a greater amount of Ca2+ being made available to the contractile apparatus.

Adaptation, Physiological↗
PubMed1977

Diagnosis of trifasicular damage following tetralogy of fallot and ventricular septal defect repair.

We evaluated the usefulness of the surface electrocardiogram to predict the presence of postoperative trifascicular damage. We used the pre and postoperative electrocardiograms and postoperative His bundle electrograms from 50 patients an average of 3.8 years following tetralogy of Fallot (TF) and ventricular septal defect (VSD) repair. Right bundle branch block (RBBB) and RBBB with left anterior hemiblock (LAH) developed in 88% and 18% respectively, and 22% had transient postoperative complete heart block (CHB). Mean P-A and A-H conduction times were 16.6 and 84.9 msec and were not different from 37 are-matched normal patients and 61 patients with unoperated TF and VSD. The mean H-V conduction time of 48.5 msec was significantly increased compared to the other two groups. Ten postoperative patients had H-V times of 55 msec or greater, indicating trifasicular damage. Of these, five had electrocardiographic bifascicular block (RBBB with LAH) with or without additional 1 degrees A-V block. The remaining five patients' electrocardiograms did not suggest trifascicular damage. Since postsurgical trifascicular damage may progress to late onset CHB, conduction studies are indicated to identify patients at risk, despite surface electrocardiographic findings.

Adolescent↗
PubMed1977

The atrioventricular node, His bundle and bundle branches-a new histologic technique.

A technique for examination of the conducting system of the heart is described. A block of tissue embracing the ostium of the coronary sinus, the pars membranacea, the septal leaflet of the tricuspid valve, and appropriate amounts of interatrial and interventricular septum is flattened and fixed in a Kaiserling I solution. Blocks are subsequently cleared in methyl salicylate and trimmed. Sections are cut from the blocks after paraffin embedding beginning from the endocardial surfaces of the right heart chambers. The sections are mounted and stained on 35 mm unperforated leader film and covered with an acrylic preservative. For examination of the conducting system many fewer sections are required than with previous techniques.

Atrioventricular Node↗
PubMed1977

Electrophysiologic study of the condition system in normal children.

Values for cardiac conduction intervals obtained from normal children are reported so that the data will be available for comparison with patients who are suspected of having abnormalities. Sinus node recovery time correlated linearly with the resting PP interval. The mean intra-atrial conduction was considerably shorter in children (less than 25 msec) than in adults (42 msec). The atrioventricular node had similar electrophysiologic properties in the child and adult. With aging, the His bundle to Purkinje fiber time increased significantly (P less than .01).

Adolescent↗
PubMed1976

Sinus node function in children. Factors influencing its evaluation.

Overdrive atrial stimulation was performed in 20 electrophysiologically normal children at the time of routine diagnostic cardiac catheterization, for the determination of the sinus node recovery time (SNRT). Measurements were made at pacing rates of 120, 150, 180, and 200 beats/min. The absolute recovery times demonstrated wide range of values (420-1280 msec). Expressed as a percent of the resting P-P interval, values at pacing rates of 120 and 150 beats/min were 109-166%, with significantly less overdrive suppression (P less than 0.001) occurring at the two faster pacing rates. Atropine diminished the maximum SNRT in all patients tested. This study reports normal values for the SNRT in children. Factors which influence the SNRT are the resting heart rate, the rate of overdrive, and the autonomic tone. In children, the sinus node recovery time should be expressed in terms of the resting sinus interval.

Adolescent↗
PubMed1970

Arrhythmias in children with pulmonary stenosis.

Arrhythmias have been recorded in association with congenital pulmonary stenosis. Of six patients who had arrhythmias before operation, anatomical conduction defects were present in two and the arrhythmias persisted after operation. In four, the arrhythmic episodes have not been recorded after operation. No specific causative factors were evident in the pre-operative group. Acute and often fatal arrhythmias have occurred in the early post-operative period. High risk patients were those with cyanosis, high right ventricular pressure (in excess of 175 mm. Hg), and gross right ventricular hypertrophy. There is evidence to suggest that these arrhythmias develop in association with myocardial ischaemia.

Acute Disease↗