Search PubMed⌕ Search

Biomedical subjects

N K Roberts

Publications and source records attributed to N K Roberts.

At least 37 records · Page 2Linked to original sources
PubMed1984

Cardiac involvement in myotonic muscular dystrophy (Steinert's disease): a prospective study of 25 patients.

The presence, degree and frequency of disorders of cardiac conduction and rhythm and of regional or global myocardial dystrophy or myotonia have not previously been studied prospectively and systematically in the same population of patients with myotonic dystrophy. Accordingly, 25 adults with classic Steinert's disease underwent electrocardiography, 24-hour ambulatory electrocardiography, vectorcardiography, chest x-rays, echocardiography, electrophysiologic studies, and technetium-99m angiography. Clinically important cardiac manifestations of myotonic dystrophy reside in specialized tissues rather than in myocardium. Involvement is relatively specific, primarily assigned to the His-Purkinje system. The cardiac muscle disorder takes the form of dystrophy rather than myotonia, and is not selective, appearing with approximately equal distribution in all 4 chambers. Myocardial dystrophy seldom results in clinically overt ventricular failure, but may be responsible for atrial and ventricular arrhythmias. Since myotonic dystrophy is genetically transmitted, a primary biochemical defect has been proposed with complete expression of the gene toward striated muscle tissue, whether skeletal or cardiac. Specialized cardiac tissue and myocardium have close, if not identical, embryologic origins, so it is not surprising that the genetic marker affects both. Cardiac involvement is therefore an integral part of myotonic dystrophy, targeting particularly the infranodal conduction system, to a lesser extent the sinus node, and still less specifically, the myocardium.

Adult↗
PubMed1981

Nodoventricular accessory atrioventricular connection associated with dual atrioventricular pathways: a case report and review of the literature.

A case is presented of a patient free from tachyarrhythmias or prior evidence of pre-excitation syndrome, in whom electrophysiologic study revealed evidence of dual AV nodal pathways associated with a nodoventricular bypass tract. Programmed atrial extrastimuli testing revealed that conduction through the fast AV nodal pathway was associated with a normal HV interval and normal QRS morphology. Conduction through the slow AV nodal pathway was always associated with a short HV interval and ventricular pre-excitation. No tachyarrhythmias could be induced with atrial extrastimuli or rapid atrial pacing. Previously reported cases of this pre-excitation variant (all of whom were symptomatic from tachyarrhythmias) are reviewed and the features summarized. This pre-excitation syndrome can occur in individuals without clinical evidence of tachyarrhythmias or overt pre-excitation and as such may be more common than previously suspected.

Adult↗
PubMed1981

Influence of exercise on excitation-contraction coupling in rat myocardium.

The present studies were conducted to investigate further the mechanisms by which the myocardium adapts to exercise training. Sixty female rats were randomly divided into sedentary control (group C) and trained (group T) groups. Group T was progressively trained for 12 wk. After the rats were killed, left ventricular papillary muscles were mounted in a tissue bath for mechanical studies. Muscles from group T generated greater peak isometric twitch tension per unit cross-sectional area than muscles from group C with [Ca2+]o ranging from 0.25 to 3.5 mM. Analyses of these data indicated that the Km for Ca2+ was not different but that the predicted number of sarcolemmal Ca2+ binding sites was 63% higher in group T. The ATPase activity of the purified cardiac myofibrils was not different between the two groups in the pCa range of 8.53-4.42. Action potentials were recorded with microelectrodes impaled into left ventricular muscle fibers of the subendocardium. Although there was no difference in the resting membrane potential, overshoot, or 90% duration, there was a significant prolongation of the action potential at 0 mV (20.2 +/- 1.0 vs 30.0 +/- 1.3 ms) in group T. These data further support the hypothesis that treadmill exercise enhances cardiac performance by increasing Ca2+ availability to the contractile element. This adaptation is mediated, at least in part, by a sarcolemmal adaptation induced by the exercise paradigm.

Action Potentials↗
PubMed1981

The prevalence of conduction defects and cardiac arrhythmias in progressive systemic sclerosis.

A prospective noninvasive electrocardiographic study was done on 50 patients with progressive systemic sclerosis. Thirty-two percent had abnormalities on the resting electrocardiogram, of which the commonest were left anterior fascicular block (16%) and first-degree heart block (8%). The 24-hour ambulatory continuous tape-recorded electrocardiograms showed serious abnormalities in 62% of the patients: supraventricular tachycardias (32%), conduction disturbances (14%), coupled ventricular extrasystoles (20%), and ventricular tachycardia (10%). Intracardiac electrophysiologic data were obtained in 20 of these patients, and functional abnormalities of the sinus node, atria, and atrioventricular node were noted in seven, nine, and 10 patients, respectively. One patient had prolonged His-Purkinje conduction time. Of the 20 patients who had electrophysiologic studies, only six had entirely normal findings. These results suggest a much higher degree of cardiac involvement in progressive systemic sclerosis than previously believed. We postulate that the first-degree heart block and supraventricular tachycardias may derive from a similar pathologic process, namely, fibrous atrophy of the proximal atrioventricular node.

Adult↗
PubMed1980

The changing face of congenital heart disease. A method for predicting the influence of cardiac surgery upon the prevalence and spectrum of congenital heart disease.

The influence of surgery upon the natural history of congenital heart disease is great. Children with many types of congenital heart lesions are now living to adult life. Most of these children will, however, require continuing medical care, care which traditionally has been given by the pediatrician. We have developed a method by which incidence figures and a knowledge of the natural history may be used to obtain prevalence estimates of congenital heart disease. We estimate that in the United States in 1995 there will be nearly 300,000 children under 21 years old with congenital heart disease; 38 per cent of these will have had one or more surgical procedures. In the last two decades the majority of care for children with congenital heart disease was aimed at the correction of the original lesion; however, we predict that in the next two decades an increasing fraction of medical resources will be directed toward the residua and sequelae of cardiac surgical procedures. This alteration in character of congenital heart disease will affect the patient mix seen by the cardiologist with adult patients as well as that of the pediatrician. For ventricular septal defect, pulmonary stenosis, atrial septal defect, persistent ductus arteriosus, coarctation of the aorta and tetralogy of Fallot, we have estimated the nationwide prevalence and the surgical requirements for 1995. Used with more specific local data on population and birth rate, this model can provide important input into planning the delivery of cardiovascular services.

Adolescent↗
PubMed1980

Atrioventricular nodal function in progressive systemic sclerosis: electrophysiological and morphological findings.

Electrophysiological data consistent with atrioventricular nodal dysfunction were obtained in 10 out of 19 patients with progressive systemic sclerosis (scleroderma). Conducting system studies were carried out in a further seven patients with progressive systemic sclerosis. In each the proximal portion of the atrioventricular node was consistently found to be smaller and more slender. It is postulated that there is a relation between proximal atrioventricular nodal structural alterations and impaired atrioventricular nodal function.

Atrioventricular Node↗
PubMed1980

An unusual mechanism for a fistulous communication between the aorta and right side of the heart.

A case of infective endocarditis is reported in which a fistulous communication developed from the septal tricuspid valve leaflet, throught the membranous ventricular septum, into the non-coronary aortic cusp. From a nidus of infection in the uterus, the tricuspid valve was seeded, leading eventually to the fistula. The particular course of the perforation avoided conduction system damage until late in the clinical course, when idioventricular rhythm and eventual cardiac arrest supervened.

Adolescent↗