PubMed Health⌕ Search

Biomedical subjects

D W Benson

Publications and source records attributed to D W Benson.

At least 55 records · Page 3Linked to original sources
PubMed1992

Supraventricular tachycardia mechanisms and their age distribution in pediatric patients.

To better define the natural history of supraventricular tachycardia (SVT) in young patients, age distribution of SVT mechanisms was examined in 137 infants, children and adolescents. Patients with a history of cardiac surgery or neuromuscular diseases were excluded. An electrophysiologic study was performed in each patient: transesophageal (110 patients) or transvenous (14 patients) or both (13 patients). Mechanisms were classified as SVT using accessory atrioventricular (AV) connection (SVT using accessory connection, including orthodromic and antidromic reciprocating tachycardia), primary atrial tachycardia (including chaotic, automatic and reentrant atrial tachycardia), and tachycardia due to reentry within the AV node. SVT using accessory connection occurred in 100 of 137 patients (73%) and was the most prevalent mechanism. Primary atrial tachycardia and reentry within the AV node were present in 19 of 137 (14%) and 18 of 137 (13%) patients, respectively. Using a multinomial logit model, relative probabilities for tachycardia mechanisms for 5 age groups--prenatal, less than 1, 1 to 5, 6 to 10 and greater than 10 years--were determined. Primary atrial tachycardia (11 to 16%) and SVT using accessory connection (58 to 84%) appeared throughout infancy, childhood and adolescence. On the other hand, tachycardia due to reentry within the AV node (0 to 31%) rarely appeared before age 2 years. Mechanisms of SVT appear to have age-dependent distributions. SVT using accessory connection is the most common mechanism in young patients. We speculate that the propensity to tachycardia due to reentry within the AV node occurs during postnatal development.

Adolescent↗
PubMed1992

Echocardiographic evaluation of the aortic root and mitral valve in children and adolescents with isolated pectus excavatum: comparison with Marfan patients.

Pectus excavatum, mitral valve prolapse (MVP), and dilated aortic root occur frequently in patients with Marfan's syndrome (MS). Patients with isolated pectus excavatum (IPE) have a high prevalence of MVP, but it is not known whether aortic root dilatation is a risk in those patients. To test the hypothesis that IPE and MS represent a spectrum of connective tissue dystrophy with MV and aortic root involvement, two-dimensional (2D) echocardiography was used to measure the aortic root diameter and assess for MVP in IPE (n = 31), MS (n = 14), and normal (n = 16) gender- and age-matched patients. Aortic root was measured in parasternal long- and short-axis views, just above the aortic sinuses, at end systole, in six cardiac cycles, and averaged. Parasternal long-axis view was used to assess for MVP. Aortic root diameter in IPE patients was not different from that in normal subjects, 24 +/- 4 mm vs 22 +/- 4 mm (p = NS), respectively, both were significantly smaller than that in MS patients (30 +/- 5 mm; p less than 0.05). MVP was present in 17 of 31 (55%) IPE patients vs 12 of 14 (86%) MS patients (p = NS) and in only 1 of 16 (6%) normal subjects (p less than 0.05) vs both IPE and MS. We conclude that young patients with IPE represent an isolated form of connective tissue abnormality because of the presence of pectus excavatum and MVP, but this is different from the systemic involvement of MS because of the lack of other systemic findings, including aortic root dilatation and changes in body habitus.

Adolescent↗
PubMed1992

Relationship between cardiac cycle length and ventricular relaxation rate in the chick embryo.

We hypothesized that during chick embryo cardiac development, cycle length decrease (heart rate increase) may be associated with developmental changes in the ventricular relaxation rate constant, tau, which can be estimated from ventricular pressure decrease by the function P(t) = P0e-t/tau, where P0 = pressure at the time of minimum time derivative of ventricular pressure and t = time. Natural logarithm conversion results in a linear relation between In P(t) and t with slope of -1/tau. We determined tau in Hamburger-Hamilton stage 17-27 (d 3-5) embryos (n = 35) at intrinsic cycle length and in stage 24 embryos (n = 5) during cardiac cycle length perturbations with the hot-cold probe technique. Regression analysis of In P(t) from the minimum dP/dt until t = 30 ms was used to estimate tau. Intrinsic cycle length decreased during development from stage 17 to 27 and tau decreased linearly as cycle length decreased (r = 0.39, p less than 0.005). Thus, during early development, both tau and cycle length decrease (relaxation rate and heart rate increase). In stage 24 embryos, cycle length perturbation yielded a nonlinear cycle length-dependent relation with tau, with a plateau at cycle lengths less than intrinsic, i.e. tau decreased with cycle length decrease to intrinsic cycle length, then tau plateaued with further cycle length decrease. These findings demonstrate that ventricular relaxation rate is both maturation and cycle length dependent. The plateau effect of the tau-cycle length relationship may be due to developmental limitations of the calcium transport system.

Animals↗
PubMed1992

Pediatric cardiology research in 1990: a review of abstracts submitted to the Society for Pediatric Research, American Academy of Pediatrics, and American Heart Association Scientific Sessions.

We assessed pediatric cardiology research by reviewing pediatric cardiology abstracts submitted in 1990 to the Society of Pediatric Research, American Academy of Pediatrics, and American Heart Association national meetings. Included were accepted and rejected studies. Abstracts were reviewed for disease being studied, methodology used to answer the research question, study design, and acceptance/rejection. Abstracts were analyzed from 123 institutions, 81 American and 42 foreign. Out of 423 abstracts, 307 (72.6%) were clinical and the remainder were basic science investigations. Slightly more than half of the clinical submissions were related to congenital heart disease. Coronary artery disease and inflammatory diseases accounted for 12% of clinical submissions. Echocardiography, clinical outcome measures, and electrophysiology were the most common research methodologies. Almost 80% of basic science research was performed in normal tissues; animal physiology, fetal physiology, and cellular/biochemical studies were the most common methodologies. With regard to study design, half of the clinical studies were retrospective and only 6% were either prospective epidemiologic or prospective controlled intervention trials. For basic sciences, 38% of abstracts were descriptions of phenomena and 62% were hypothesis testing, with developmental hypotheses being most common. Acceptance rates favored higher quality study design. However, areas of greatest interest to cardiologists, congenital heart disease, cardiomyopathy, and electrophysiology, had poorer quality study design than did other areas. We have shown broad interest in pediatric cardiology research. However, clinical studies frequently were retrospective or had uncontrolled study designs. Basic science research was performed at a small number of institutions and emphasized either description of phenomena or developmental biology of normal tissues.

Abstracting and Indexing↗
PubMed1992

Ventricular volume growth after cardiac transplantation in infants and children.

BACKGROUND: Intermediate-term survival after pediatric cardiac transplantation continues to improve. However, little is known about cardiac function and especially ventricular growth in young patients after cardiac transplantation. The purpose of this study was to evaluate serially the hemodynamics, left ventricular (LV) volume, and ventricular function after cardiac transplantation in infants and children. METHODS AND RESULTS: Indications for cardiac transplantation were dilated cardiomyopathy (eight patients), hypoplastic left heart syndrome (six patients), and postoperative structural congenital heart disease (three patients). The age at time of transplant ranged from 7 days to 15 years (median, 3.5 years). The mean follow-up was 30.3 months (range, 13-46 months). Serial annual cardiac catheterizations were performed 1 year (17), 2 years (15), and 3 years (seven) after transplant. Measurements included right and left heart pressures, cardiac index, and LV volume and ejection fraction (Lange). Cumulative results (expressed as mean +/- SD) were pulmonary artery pressure, 14.9 +/- 3.2 mm Hg; LV end-diastolic pressure, 7.7 +/- 2.6 mm Hg; cardiac index, 3.5 +/- 0.52 l/min.m-2; and pulmonary vascular resistance, 2.02 +/- 0.76 units/m2. LV end-diastolic volume increased as patients grew, so that left ventricular end-diastolic volume remained 90 +/- 14% of that predicted for body surface area. The ejection fraction was 99 +/- 6% of that predicted. There was no evidence of chronic rejection by endomyocardial biopsy. No accelerated coronary artery atherosclerosis was identified. CONCLUSIONS: Serial studies in these young patients demonstrate normal hemodynamics and LV function after cardiac transplantation. Cardiac transplantation is associated with normal LV volume growth despite immunosuppression and denervation.

Adolescent↗
PubMed1991

Complex ventricular ectopic activity in patients less than 20 years of age with or without syncope, and the role of ventricular extrastimulus testing.

To assess the potential for ventricular tachycardia (VT), ventricular extrastimulus testing was performed in 33 young patients with complex ventricular ectopic activity defined as multiform ventricular premature complexes (VPCs), couplets or nonsustained VT, or a combination, found during electrocardiographic monitoring. There were 21 male and 12 female patients with a mean age of 11 years (range 1 to 18). Patients were divided into 2 groups based on the presence (14 patients) or absence (19 patients) of syncope. Patients with syncope had ostensibly normal hearts (9 patients) or miscellaneous heart disease (5 patients). Patients without syncope had ostensibly normal hearts (8 patients) or miscellaneous heart disease (11 patients). Ventricular stimulation protocol consisted of burst pacing and 1 to 4 programmed extrastimuli decreasing to refractoriness at 3 drive-train cycle lengths, and at 2 pacing sites (right ventricular apex and outflow tract) during the drug-free baseline state and isoproterenol infusion. No patient had VT induced with 1 or 2 extrastimuli. VT was induced in 13 of 14 patients (93%) with syncope, and in 9 of 19 patients (47%) without syncope (p less than 0.05). Using a 3-extrastimuli protocol, 8 of 14 patients (57%) with and 3 of 19 patients (16%) without syncope had VT induced (p less than 0.05). These findings suggest that VT may be the cause of syncope in young patients with complex ventricular ectopic activity.

Adolescent↗
PubMed1991

Use of amiodarone for short-term and adjuvant therapy in young patients.

Limited data are available defining the safety of amiodarone for short-term use or as part of combination antiarrhythmic therapy in pediatric patients. Results of amiodarone in 47 young patients for an average treatment duration of 12 months were examined. There were 21 male and 26 female patients (age range of 23 weeks gestation to 29 years). Patients were divided into 4 groups: group 1--electrocardiographic documented ventricular tachycardia (n = 7); group 2--syncope of unknown cause (n = 16); group 3--primary atrial tachycardia (n = 11); and group 4--supraventricular tachycardia (n = 13). Amiodarone was clinically useful in 32 (68%) patients. Amiodarone was considered effective as a sole antiarrhythmic agent in 21 (45%) patients. Treatment was ineffective but was continued in 11 (23%) patients; in 10 of these 11 patients amiodarone was adjuvant to other antiarrhythmic drugs. Amiodarone was considered ineffective and was withdrawn in 15 (32%) patients. No patient required cardiac pacemaker implant during therapy. Torsades de pointes and cardiac arrest occurred in 1 patient each after 9 and 14 days of therapy, respectively. Two patients underwent successful cardiac transplant after 2 and 14 months of amiodarone administration, respectively. Amiodarone was used as short-term treatment (less than 18 months) in 7 infants (age less than 18 months), and after cessation of treatment there was no recurrence of tachycardia for 4 to 24 months. Results of this study confirm reports of successful amiodarone use in pediatric patients with a variety of rhythm disturbances.(ABSTRACT TRUNCATED AT 250 WORDS)

Administration, Oral↗
PubMed1991

Decreased myofibrillar protein breakdown following treatment with clenbuterol.

Daily treatment of Fischer-344 rats for 14 days with the beta 2-adrenergic agonist, clenbuterol, increased gastrocnemius muscle mass and protein content. Coadministration with the beta-adrenergic antagonist, nadolol, significantly reduced these anabolic effects of clenbuterol. Although clenbuterol treatment reduced food intake during the first 4 days, clenbuterol-treated rats were hyperphagic during the second week of drug administration. Nadolol treatment also blocked these effects of clenbuterol on feeding. In a second experiment, in vitro incubation of extensor digitorum longus muscles taken from post weaning food-deprived rats demonstrated decreased release of 3-methylhistidine by clenbuterol-treated rats, suggesting decreased breakdown of myofibrillar protein. Protein synthesis was not increased in vitro in the soleus muscles taken from these rats. These experiments demonstrate that the anabolic effect of clenbuterol is due in part to beta-adrenergic activity and may involve reduced myofibrillar protein degradation. These results appear to have direct application to nutrition and protein repletion in various catabolic diseases.

Adrenergic beta-Antagonists↗
PubMed1991

Proarrhythmia, cardiac arrest and death in young patients receiving encainide and flecainide. The Pediatric Electrophysiology Group.

The potential for proarrhythmic responses to the class IC sodium channel-blocking drugs encainide and flecainide has not been well described in young patients. Therefore, data were retrospectively collected from 36 institutions regarding 579 young patients who were administered encainide or flecainide for treatment of supraventricular tachycardias (encainide 86 patients, flecainide 369 patients) or ventricular arrhythmias (encainide 21 patients, flecainide 103 patients) to assess the frequency of proarrhythmia, cardiac arrest and death during therapy (adverse events). The two drugs were similar in regard to efficacy (flecainide 71.4%, encainide 59.8%) and rate of proarrhythmic responses (flecainide 7.4%; encainide 7.5%). However, patients receiving encainide more frequently experienced cardiac arrest (encainide 7.5% vs. flecainide 2.3%, p less than 0.05) or died during treatment (encainide 7.5% vs. flecainide 2.1%, p less than 0.05). Detailed data were provided for 44 patients experiencing one or more adverse events. Patient age, previous drug trials, concomitant therapy and days of inpatient monitoring were similar for patients receiving encainide or flecainide. However, echocardiographic left ventricular shortening before treatment was lower among patients receiving encainide (0.23 +/- 0.09) than among those receiving flecainide (0.34 +/- 0.06, p less than 0.05). Plasma drug concentrations were rarely elevated. Cardiac arrest (12 patients) and deaths (13 patients) occurred predominantly among patients with underlying heart disease, particularly among patients receiving flecainide for supraventricular tachycardia (8.3% vs. 0.3%, p less than 0.001). Fifteen patients with an ostensibly normal heart and normal ventricular function experienced proarrhythmia during treatment for supraventricular tachycardia, but only 3 of the 15 had a cardiac arrest or died. The relatively high incidence of adverse events should be considered when contemplating treatment with encainide or flecainide, particularly among patients with underlying heart disease.

Anilides↗
PubMed1991

Heart rate perturbation in chick embryos: a comparison of two methods.

This report compares the effects of two methods of heart rate (HR) perturbation on stroke volume and dorsal aortic flow in the Hamburger-Hamilton stage 24 chick embryo. The sinus venosus was paced at intrinsic HR and at 150, 125, 75, and 50% of intrinsic HR (n = 23). Alternatively, a 1-mm steel probe heated to increase and cooled to decrease HR was applied to the sinus venosus (n = 15). All studies were performed in ovo at 37-38 degrees C. Aortic flow (mm3/S) and stroke volume (mm3/beat) were calculated from aortic velocity, aortic cross-sectional area, and HR. Atrioventricular (AV) inflow velocities were measured during pacing (n = 10) or probe application (n = 11) technique. Dorsal aortic flow was maximum at intrinsic HR and decreased at both increased and decreased HR. Stroke volume decreased proportionally to HR during rate increase. At decreased HR, when AV synchrony was disrupted (pacing), stroke volume was unchanged from intrinsic values. However, when AV synchrony was maintained at decreased HR (cold probe), the embryonic ventricle significantly increased stroke volume.

Animals↗
PubMed1991

The effect of cardiac cycle length on ventricular end-diastolic pressure and maximum time derivative of pressure in the stage 24 chick embryo.

We hypothesized that developmental increases in both ventricular end-diastolic pressure (EDP) and the maximum time derivative of pressure (dP/dt) observed in stage 12 to 29 chick embryos are the result of observed cardiac cycle length (CL) decrease (heart rate increase). To test this hypothesis, we evaluated EDP and dP/dt changes that occur during acute CL alterations in the Hamburger-Hamilton stage 24 chick embryo (n = 18). Ventricular pressure measurements were obtained with a servo-null pressure system and digitally recorded at 500 samples/s. A 1-mm steel probe, heated (decrease CL) or cooled (increase CL), was applied to the sinus venosus. The average baseline CL was 454 ms. The heart rate perturbation resulted in CL that varied over a range of 200-2966 ms, assimilating the range of CL change observed during development. Changes in EDP ranged from 0.014 to 0.130 kPa (baseline = 0.061 kPa) and maximum dP/dt ranged from 0.33 to 13.33 kPa/s (baseline = 5.99) kPa/s). In each study, EDP varied directly with CL (R2 = 0.70). Conversely, maximum dP/dt changes were inversely related to CL alterations (R2 = 0.54). Thus, we found that there is a direct relationship between changes in CL and EDP in the stage 24 chick embryo, whereas CL and dP/dt vary inversely. During cardiac development, observed increases in maximum dP/dt may be attributed to CL decreases. In contrast, developmental increases in EDP cannot be explained by CL decrease and must be accounted for by maturational changes in cardiac function in the chick embryo.

Animals↗
PubMed1991

Intermediate term results of infant orthotopic cardiac transplantation from two centers.

Orthotopic cardiac transplantation has become established for selected infants with severe forms of congenital heart disease. This study reviews the combined experience and intermediate term results of infants undergoing orthotopic cardiac transplantation from Children's Memorial Hospital, Chicago, and Kosair Children's Hospital, Louisville. From June 1986 through December 1989, 20 orthotopic cardiac transplantations were performed in 19 patients. Sixteen patients had variants of hypoplastic left heart syndrome. One infant had anomalous origin of the left coronary artery with severe ischemic cardiomyopathy. Two infants had aortic stenosis with endocardial fibroelastosis, and one had extracorporeal membrane oxygenation as a bridge to transplantation. Immunosuppression included cyclosporine, azathioprine (Imuran), and corticosteroids with an effort to wean the patients from steroids by 6 months to 2 years. Three early deaths resulted--from technical errors in two patients and from hyperacute rejection in one patient at 3 days. Four late deaths have occurred. Two patients died at 2 and 13 months of acute rejection. One patient died at 15 months of acute rejection after retransplantation. One patient died at 7 months of respiratory syncytial viral pneumonia. The remaining 12 patients are surviving 5 to 47 months (means 20 months) after orthotopic cardiac transplantation. Rejection surveillance in the first 6 months is by clinical signs supplemented by echocardiography, electrocardiography, and cell cycle analysis; endomyocardial biopsy is used after 6 months of age. For the cumulative series, 24 episodes of suspected rejection have been treated during 277 at-risk patient months with intravenous methylprednisolone (Solu-Medrol) (n = 18) and monoclonal antibody (OKT3) (n = 6), for an incidence of 1.04 episodes of rejection per patient per year. Serious posttransplantation infections including endocarditis, catheter sepsis, meningitis, and colonic perforation were successfully treated in four patients. Subjectively, their quality of life is excellent as shown by normal growth and developmental milestones and a low hospital readmission rate (1.4 episodes per patient per year). These encouraging intermediate term results warrant continued application of infant orthotopic cardiac transplantation for severe forms of congenital heart disease.

Antibodies, Monoclonal↗
PubMed1990

Is there a circulating proteolysis-inducing factor during sepsis?

Muscles from fed or 72-hour fasted rats were incubated in the presence of plasma from septic rats, recombinant interleukin 1 alpha (rIL-1 alpha), or recombinant tumor necrosis factor alpha (rTNF alpha), and breakdown of total and myofibrillar protein was assessed by determining release of tyrosine and 3-methylhistidine, respectively. Septic plasma stimulated total protein breakdown in muscles from 72-hour fasted rats by 10% to 20%, while myofibrillar protein breakdown was not affected. When septic plasma was added to muscles from fed rats, neither tyrosine nor 3-methylhistidine release was altered. Various concentrations of recombinant interleukin 1 alpha or recombinant tumor necrosis factor alpha did not affect total or myofibrillar protein breakdown. Since septic plasma did not stimulate myofibrillar protein breakdown, the role of a circulating factor for muscle proteolysis during sepsis remains unclear.

Animals↗
PubMed1990

Heart rate and blood pressure response to upright tilt in young patients with unexplained syncope.

Syncope in apparently normal patients has been attributed to an inhibitory reflex originating in cardiac sensory receptors. The reflex may be elicited by upright tilt with or without isoproterenol infusion. In this study, an upright 90 degree tilt protocol was evaluated in 20 young patients aged 7 to 22 years with syncope but with normal cardiac and neurologic evaluations. The electrocardiogram and blood pressure were noninvasively recorded at 1 min intervals while the patient was supine (5 to 10 min) and during tilt (15 min) in the baseline state. The protocol was repeated during isoproterenol infusion at increasing doses until symptoms of syncope or near syncope were provoked or the maximal isoproterenol dose was achieved (0.07 to 0.1 microgram/kg per min). Mean heart rate, mean blood pressure and RR interval variability, expressed as the standard deviation and the mean of the absolute difference between consecutive RR intervals, were assessed. Symptoms were elicited during tilt in 16 of the 20 patients (in 4 at baseline and in 12 with isoproterenol infusion); no symptoms were induced in 4 patients.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1990

Exit block in pediatric cardiac pacing. Comparison of the suture-type and fishhook epicardial electrodes.

Ninety-seven consecutive permanent epicardial pacemaker implantations were performed with either suture-type (group I, n = 52) or fishhook electrodes (group II, n = 45). In addition to epicardial fixation of the electrodes at the collar area, the suture-type was further secured in place by tying the electrode's suture at its exit to another nonabsorbable pledget-supported suture. Acute thresholds and slew rates were not significantly different between the two groups. Although the R wave was lower in group I (8.4 +/- 3.5 mV) than in group II (11.8 +/- 6, p less than 0.01), no sensing problems occurred. The larger surface area of suture-type electrode led to lower resistance in group I (271 +/- 61 omega) compared with group II (356 +/- 72, p less than 0.001); however, the difference in pacemaker generator longevity did not appear significant (group I, n = 12, mean 4.7 +/- 1.6 years; group II, n = 4, mean 5 +/- 0.6 years). The incidence of exit block was significantly higher in group II (40%, 18/45) than in group I (8%, 4/52, p less than 0.01). The length of the stimulation tip and better fixation of the suture-type electrode probably accounted for the observed difference in the incidence of exit block between the two electrodes.

Adolescent↗
PubMed1989

Effect of intravenous propranolol or verapamil on infant orthodromic reciprocating tachycardia.

The effects of intravenous verapamil (0.15 mg/kg) and propranolol (0.2 mg/kg) with regard to atrioventricular (AV) conduction and tachycardia termination during paroxysmal atrial tachycardia were compared in 2 groups of infants (verapamil n = 14, propranolol n = 18, mean age 80 +/- 21 days, range 1 to 364). Using transesophageal recording techniques, tachycardia cycle length, AV intervals and ventriculoatrial intervals were measured before and after drug administration. Both intravenous propranolol and verapamil significantly prolonged tachycardia cycle length and AV interval (cycle length--propranolol 230 +/- 30 to 262 +/- 33 ms, p less than 0.05, verapamil 223 +/- 38 to 245 +/- 32 ms, p less than 0.05; AV interval--propranolol 98 +/- 26 to 126 +/- 38 ms, p less than 0.05, verapamil 96 +/- 19 to 109 +/- 24 ms, p less than 0.05). Neither drug prolonged the ventriculoatrial interval. Tachycardia terminated after intravenous verapamil in 11 of 14 infants (79% efficacy rate). Tachycardia terminated in 0 of 18 after intravenous propranolol (0% efficacy rate). In 8 infants an atrial deflection was recorded on the esophageal electrocardiogram at the time of tachycardia termination after intravenous verapamil, which suggested that tachycardia terminated by block occurring in the AV node. In 2 infants a ventricular deflection was recorded at the time of tachycardia termination after verapamil, which suggested that block occurred in the accessory connection. Both drugs prolonged tachycardia cycle length by prolonging AV conduction to a similar degree.(ABSTRACT TRUNCATED AT 250 WORDS)

Electrocardiography↗