PubMed Health⌕ Search

Biomedical subjects

Thomas Paul

Publications and source records attributed to Thomas Paul.

34 records · Page 2Linked to original sources
PubMed2003

Origin of electrical activation within the right atrial and left ventricular walls: differentiation by electrogram characteristics using the noncontact mapping system.

Clinical data using the noncontact mapping system (Ensite 3000) suggest that characteristics of the reconstructed unipolar electrograms may predict the origin of electrical activation within the atrial and ventricular walls (endocardial vs myocardial vs epicardial origin). Experimental data are lacking. In ten open-chest pigs (mean body weight 62 kg) cardiac pacing was performed at a cycle length of 600 ms with a pulse width of 2 ms and twice diastolic threshold from the endo-, the myo-, and the epicardium, respectively. Pacing was undertaken at three right atrial and three left ventricular sites, and cardiac activation was recorded with the Ensite system. Reconstructed unipolar electrograms at the location of earliest endocardial activation assessed by color coded isopotential maps were analyzed systematically for differences in morphology. The positive predictive value of atrial electrograms exhibiting an initial R wave during pacing for a subendocardial origin (i.e., myocardial or epicardial) was 0.96. The negative predictive value was 0.48. Electrograms generated during myocardial pacing exhibited increased maximal negative voltage and maximal dV/dt (-3 +/- 1.8 mV, -798 +/- 860 mV/ms, respectively) than the electrograms obtained during endocardial (-2 +/- 1 mV, -377 +/- 251 mV/ms, respectively) and epicardial pacing (-2.1 +/- 0.7 mV, -440 +/- 401 mV/ms, respectively, P<0.01 for both parameters). During pacing at the left ventricular wall, occurrence of an initial R wave did not differ significantly between electrograms reconstructed during endocardial and subendocardial pacing. All other characteristics of the unipolar ventricular electrograms analyzed, except latency, did not differ significantly when compared to stimulation depth. Morphological characteristics of unipolar electrograms generated by the noncontact mapping system during pacing of the atrium allowed for discrimination of an endocardial versus a subendocardial origin of activation. At the ventricular level, characteristics of unipolar electrograms did not predict the origin of cardiac activation in this experimental setting.

Analysis of Variance↗
PubMed2003

Complete occlusion of the left circumflex coronary artery after radiofrequency catheter ablation in an infant.

Radiofrequency catheter ablation of a left lateral accessory atrioventricular pathway was performed in a 5-week-old infant with drug-refractory supraventricular tachycardia. Energy application via a 5-French mapping and ablation catheter in the temperature-controlled mode (60 degrees C, 30 W) at the atrial aspect of the mitral valve annulus repeatedly resulted in termination of the tachycardia by conduction block within the pathway. Tachycardia remained inducible subsequently. After a safety energy application during sinus rhythm, significant ST-segment elevation in the inferior, mid precordial, and left lateral leads was noted. Selective left coronary angiography revealed complete occlusion of the circumflex coronary artery. Moderate-to-severe mitral valve regurgitation developed, finally requiring mitral valve replacement.

Arterial Occlusive Diseases↗
PubMed2003

Radiofrequency catheter ablation therapy in the young: current status.

Since 1989, when radiofrequency ablation was introduced into clinical practice for pediatric patients with supraventricular tachycardias, radiofrequency catheter ablation techniques have evolved as the treatment of choice for many forms of tachycardia in young patients. This review discusses the current status of ablation therapy for the four most common forms of supraventricular tachycardias in children, including tachycardias based on accessory atrioventricular pathways, atrioventricular nodal reentrant tachycardia, atrial ectopic tachycardia and the permanent form of junctional reciprocating tachycardia. In addition, the report will focus on the current status and limitations of ablation therapy of ventricular tachycardias and atrial reentry tachycardias in patients after surgical correction of congenital heart defects.

Adolescent↗
PubMed2002

The contrasting kinetics of peroxidation of vitamin E-containing phospholipid unilamellar vesicles and human low-density lipoprotein.

It is well established that alpha-tocopherol, TocH, is an outstanding lipid-soluble, peroxyl radical trapping antioxidant in homogeneous systems. It is also well established that TocH functions as a prooxidant in human low-density lipoprotein, LDL, subjected to attack by peroxyl radicals generated in the aqueous phase by, for example, thermal decomposition of the azo compound, ABAP. This tocopherol-mediated peroxidation, TMP, of LDL involves a three-step chain reaction, one step being hydrogen atom abstraction from the LDL lipids by the tocopheroxyl radical, Toc*. The occurrence of TMP has been attributed to three factors, (i) translocation by TocH of radical character from the aqueous phase into LDL lipid, (ii) isolation of the water-insoluble Toc* in the LDL particle in which it is formed for times sufficient to permit it to react with the lipid, and (iii) the small lipid volume of LDL which ensures that no particle can contain more than a single radical for a significant length of time. This consensus view of TMP implies that it should occur in any TocH-containing dispersion of small lipid particles. However, the present examination of the kinetics of the ABAP-initiated peroxidation of small unilamellar vesicles, SUVs, made from palmitoyllinoleoylphosphatidylcholine and cholesterol with a composition designed to mimic the surface coat of LDL, has shown that TocH functions as an antioxidant in such systems and that TMP does not occur under conditions where it would have occurred if the particles had been LDL. Several possible reasons for the kinetic differences between SUVs and LDL have been considered and ruled out by experiment. It is concluded that TMP can occur in LDL because these particles contain a lipid core in which the Toc* radical "hides" for much of its lifetime well away from the peroxyl radicals in the aqueous phase. In contrast, because SUVs have no lipid core, the Toc(*) radical is always "exposed" and available to aqueous peroxyl radicals with which it reacts rapidly and is destroyed before it can abstract a hydrogen atom from the lipid.

Antioxidants↗
PubMed2002

Intraatrial reentrant tachycardias in patients after atrial switch procedures for d-transposition of the great arteries Endocardial mapping and radiofrequency catheter ablation primarily targeting protected areas of atrial tissue within the systemic venous atrium.

Thirteen patients with d-transposition of the great arteries after the Mustard/Senning procedure underwent electrophysiological study for recurrent intraatrial reentrant tachycardia (IARTs). In 8 patients, a 20-pole electrode catheter and a steerable 7F mapping and ablation catheter were placed in the systemic venous atrium, and via the retrograde route in the pulmonary venous atrium, if required. During IART pace mapping and entrainment mapping were performed in order to localize protected areas of atrial tissue between anatomical and/or surgical barriers of electrical isolation. The systemic venous atrium of 5 patients was studied using the non-contact mapping system (Ensite 3000(TM)). Linear radiofrequency current lesions were induced after mapping of electrical protected areas from the medial aspect of the superior caval vein to the systemic venous atrium and/or intraatrial baffle or the intraatrial suture line in 4 patients, from the medial aspect of mitral valve annulus to the inferior caval vein in 5 patients, from the intraatrial suture line to the posterior systemic venous atrium in 1 patient and in 2 patients from the posterior and inferior pulmonary venous atrium to the tricuspid valve annulus. Subsequently, 14 of the 15 identified IARTs were not inducible during repeated programmed stimulation. Mean duration of the electrophysiological study was 202 min, mean fluoroscopy time was 21.6 min. During follow-up (mean 20 months), 10 of 12 patients with successful procedures are free of tachycardia, 2 patients developed IARTs with a new morphology. In the majority of our patients, curative treatment was feasible by induction of linear radiofrequency current lesions by primarily targeting electrical protected areas of atrial tissue in the systemic venous atrium.

Adolescent↗
PubMed2002

Fontan-type procedures: residual lesions and late interventions.

BACKGROUND: The purpose of this study was to determine the type and incidence of hemodynamic and electrophysiological abnormalities requiring surgical or catheter-based interventions in a single-center long-term experience. METHODS: Eighty-eight patients with a follow-up of at least 5 years (mean follow-up, 9.6 +/- 2.6 years) after Fontan-type procedures were included. All patients had undergone cardiac catheterization either as part of the regular postoperative protocol or because of symptomatic atrial tachycardia or increasing cyanosis. RESULTS: Freedom from reoperation for up to 5 years was documented for 82% of patients and decreased to 76% after 8 years. Late reoperations included conversion of an atriopulmonary anastomosis to a total cavopulmonary anastomosis in 2 patients with atrial dysrhythmia and implantation of an extracardiac conduit in 1 patient with left atrial isomerism and intrapulmonary arteriovenous malformations after a Kawashima operation. Decline in sinus node function with symptomatic bradycardia required pacemaker therapy in 10 patients (11%). Transcatheter interventions included fenestration occlusion in 5 of the 11 patients with initial baffle fenestration. In 6 of 17 patients with aortopulmonary collaterals, coil occlusion was indicated to reduce future systemic ventricular volume load. Various systemic venous collaterals were documented in 11 patients and required coil occlusion in 2. One patient with symptomatic protein-losing enteropathy underwent transcatheter fenestration creation without sustained relief of symptoms. Freedom from transcatheter interventions decreased from 94% to 82% after 5 and 10 years, respectively. CONCLUSIONS: During long-term follow-up, reoperations are rare and mainly involve Fontan conversion to either a lateral-tunnel or extracardiac-conduit procedure. Detailed angiographic evaluation on a routine basis allows identification of the vascular sites of origin of aortopulmonary collateral vessels and systemic venous collaterals potentially developing during long-term follow-up. Transcatheter interventions including fenestration occlusion and occlusion of venous collaterals and aortopulmonary collaterals were performed to maintain and improve the Fontan circulation in clinically symptomatic and asymptomatic patients. During long-term follow-up after Fontan-type operations, a regular postoperative cardiac catheterization protocol is recommended.

Adolescent↗
PubMed2002

Experimental ASD closure using autologous cell-seeded interventional closure devices.

OBJECTIVE: Atrial septal defect (ASD) occluders are permanent implants in paediatric cardiology which serve as mechanical shields until complete overgrowth and incorporation of the occluding device by autologous tissue has occurred. Thereafter, the foreign body material making up the device is dispensable and bears potential long-term adverse effects. Rapid, firm and complete incorporation into the atrial septal wall should be a prerequisite for biodegradable devices. In this study, the feasibility of using autologous cell-seeded devices was investigated by (a) testing the influence of a collagen coating on cellular stress resistance in vitro and (b) comparing the short-term effects between cell-seeded, collagen-coated and acellular ASD occluders in vivo. METHODS: Native and collagen-coated Dacon fabrics and Starflex-devices were pre-seeded with autologous fibroblasts (skin biopsy) and evaluated using various mechanical stress tests. In a sheep model interventionally created ASDs were closed using either autologous pre-seeded or conventional (acellular) Starflex-devices. RESULTS: ASD closure devices were successfully pre-seeded with autologous cells. The incubation period needed, the cellular density achieved and the mechanical stability of the cytolayer after mechanical stressing (implantation) were improved by applying a collagen matrix on the fabric. Compared to the thin layer of ingrown tissue seen on conventional occluders after 30 days in vivo, a thicker layer of organising, newly formed granulation tissue on pre-seeded collagen-coated devices embedded not only the Dacron fabric, but also completely covered the spring arms of the device underneath a layer of neo-endothelium. CONCLUSION: Autologous cell pre-seeding of interventional closure devices is feasible since the cells survive the mechanical stress encountered during implantation. Rapid, firm and complete ingrowth of occluder devices into a thicker layer of young fibrous granulation tissue can be achieved, but an increased thrombogenicity currently limits the in vivo application.

Absorbable Implants↗
PubMed2002

Non-contact mapping and ablation of tachycardia originating in the right ventricular outflow tract.

We performed an electrophysiological study, using non-contact mapping, in an 8-year-old girl weighing 39.9 kg who had suffered recurrent symptomatic episodes of exercise-induced non-sustained ventricular tachycardia. Color-coded isopotential maps of the ventricular tachycardia identified the area of earliest endocardial activation high and anterior in the right ventricular outflow tract. Although partial deflation of the balloon was required to position the ablation catheter at the earliest site of activation, this site was still identified accurately, as demonstrated by termination of the ventricular tachycardia and ectopy upon mechanical pressure, as well as application of radiofrequency current. In this young patient, precise mapping of the earliest endocardial activation using the non-contact mapping system was safe and effective, allowing successful radiofrequency ablation of the tachycardia.

Body Surface Potential Mapping↗
PubMed2002

Complete elimination of incessant polymorphic ventricular tachycardia in an infant with MIDAS syndrome: use of endocardial mapping and radiofrequency catheter ablation.

Experience with radiofrequency catheter ablation of ventricular tachycardia (VT) in pediatric patients is limited. A 5-month-old white female infant (body weight 5.5 kg) with MIDAS syndrome who suffered from incessant polymorphic VT (ventricular rates 250 to 300 beats/min) and was unresponsive to medical treatment resulting in significantly depressed left ventricular (LV) function underwent a total of four catheter ablation procedures during a 5-month period. Each of the procedures reduced the number of morphologies and the rate of the tachycardia, but VT returned after each of the first three procedures, despite concomitant medical therapy. Activation mapping and pace mapping were used to identify the anatomic substrates, which were found at different locations at the LV septum and LV free wall. All forms of VT finally were ablated successfully. There were no significant complications. After the fourth procedure, the patient was in continuous sinus rhythm. Follow-up examination 29 months after the last procedure while the child was not taking any medication showed normal sinus rhythm and normal LV function. This report demonstrates the usefulness and safety of radiofrequency catheter ablation in an infant with polymorphic VT who was unresponsive to medical therapy.

Abnormalities, Multiple↗
PubMed2002

Catheter tip cooling during radiofrequency ablation of intra-atrial reentry: effects on power, temperature, and impedance.

INTRODUCTION: Cooling the catheter tip either passively with increased tip size or actively during radiofrequency catheter ablation (RFCA) has been shown in canine thigh preparations to create larger lesions than standard catheter tips, yielding a theoretical advantage for improving the outcome of RFCA for intra-atrial reentrant tachycardia (IART). METHODS AND RESULTS: The pediatric RFCA database at the Medical University of South Carolina was reviewed for RFCA of IART in patients with structural heart disease. From a total of 31 patients who underwent procedures during the study period, 8 patients in whom ablation with conventional ablation techniques failed and who went on to passive cooling with an 8-mm tip catheter or active cooling with an internally cooled-tip catheter were studied. Power delivery was greater but temperature and impedance were lower during cooled ablation than during conventional ablation. Passive cooling was associated with higher power than active cooling. These changes in RF biophysical characteristics were associated with successful elimination of 11 of 13 IART circuits in 7 of 8 patients. CONCLUSION: Cooling during RF ablation of atrial tachycardia clearly yielded greater power delivery in vivo and was associated with success.

Adolescent↗
PubMed2002

Dissociated conditional-associative learning in anorexia nervosa.

This study assessed the acquisition of conditional-associations using neutral and individually threatening nouns in 16 females with anorexia nervosa (AN), 16 females with bulimia nervosa (BN) and 16 normal controls (NC). Groups did not differ in terms of age, sex, handedness, depression, intelligence, verbal memory and verbal fluency measures. Furthermore, patients and controls were widely comparable on any test assessing neuropsychological functioning. In the conditional-associative learning (CAL) task, anorexic patients displayed an impaired performance with neutral material but not with individually threatening material. Such a deficit was not evident in bulimics or in normal controls. Only anorexics showed a dissociation in the CAL of material with different emotional valence. These findings support the assumptions from functional neuroimaging investigations in AN and justify the assignment of this disorder to the obsessive-compulsive spectrum disorders.

Adolescent↗
PubMed2002

Self-injurious behavior in women with eating disorders.

OBJECTIVE: The authors assessed lifetime and 6-month occurrence and phenomenology of self-injurious behavior in patients with eating disorders. METHOD: Women (N=376) in inpatient treatment for an eating disorder (anorexia: N=119, bulimia: N=137, eating disorder not otherwise specified: N=120) were assessed for self-injurious behavior and completed the Traumatic Life Events Questionnaire, the Dissociative Experience Scale, the Barratt Impulsiveness Scale, and the Yale-Brown Obsessive Compulsive Scale. RESULTS: The lifetime rate of self-injurious behavior occurrence was 34.6%, with the highest rates found in subjects with eating disorder not otherwise specified (35.8%) and bulimia (34.3%); the 6-month rate of self-injurious behavior occurrence was 21.3%. Multivariate comparisons were computed for the factors of self-injurious behavior and diagnostic subgroup: self-injuring patients reported a significantly higher number of traumatic events, showed significantly higher dissociation scores, and exhibited significantly more obsessive-compulsive thoughts and behaviors. Bulimic patients showed significantly higher impulsivity scores. CONCLUSIONS: This study strongly supports the assumption that patients with eating disorders are at risk for self-injurious behavior and points to the necessity of a routine screening for self-injurious behavior as well as the development of a standardized questionnaire. Group comparisons point to the relevance of traumatic experiences and comorbid dissociative phenomenology.

Adult↗
PubMed2002

Heart rate variability in infants with heart failure due to congenital heart disease: reversal of depressed heart rate variability by propranolol.

BACKGROUND: Analysis of heart rate variability (HRV) provides a noninvasive index of autonomic nervous system activity. HRV has shown to be reduced in congestive heart failure and in children with congenital heart disease (CHD). Beta-blockers improve HRV in adults with congestive heart failure, but this improvement remains to be demonstrated in children. MATERIAL/METHODS: HRV was analysed in 14 infants with severe heart failure due to CHD who received a 'standard' therapy with digoxin and diuretics ('Digoxin/Diuretics' group) and in 9 of these patients with an additional propranolol therapy ('Propranolol' group) 17 days later on average and compared with HRV of 70 healthy infants ('Healthy Control'). RESULTS: Comparing the 'Digoxin/Diuretics' group versus 'Healthy Control', we found significantly reduced HRV in the time domain and the frequency domain, that could be abolished in the 'Propranolol' group. None of the HRV parameter were significantly related to age or any hemodynamic parameter but inversely related to ejection fractions within the normal range (pNN50: r= -0.58, p=0.004; rMSSD: r= -0.42; p=0.049). HRV measurements (SDNN, r= -0.48) and plasma norepinephrine levels (r=0.7) were significantly related to clinical symptoms of heart failure, measured by the Ross Score. CONCLUSIONS: HRV represents a noninvasive parameter that is reduced in infants with congenital heart disease depending on the severity of heart failure but not on hemodynamic disturbances. Propranolol but not digoxin therapy effectively reduced the supposed autonomic imbalance in infants with severe heart failure due to CHD.

Adult↗
PubMed1996

Reaction of Phenyl-Substituted o-Quinodimethanes with Nitric Oxide. Are Benzocyclobutenes Suitable Precursors for Nitric Oxide Cheletropic Traps?

In order to elucidate the potential of substituted o-quinodimethanes as reagents for the trapping of nitric oxide (NO) in biological systems, the reaction of alkoxyl- and alkyl-substituted 7,8-diphenyl- and 7,7,8-triphenyl-o-quinodimethanes with nitric oxide in solution was investigated by ESR spectroscopic and UV/vis stopped-flow techniques. Photolytic decarbonylation of 1,3-diphenyl- and 1,1,3-triphenylindan-2-ones gave the corresponding phenyl-substituted benzocyclobutenes as the major products and low photostationary concentrations of o-quinodimethanes. During 266-nm laser flash photolysis (LFP) of 1,3-dimethoxy-1,3-diphenylindan-2-one and 1-methoxy-1,3,3-triphenylindan-2-one in acetonitrile, species absorbing in the 400-600 nm range were produced, which were attributed to configurational isomers of the corresponding 7,7,8,8-substituted o-quinodimethanes. The isomeric o-quinodimethanes decayed at significantly different rates, indicating a strong influence of the relative orientation of the terminal substituents on their stability. Reaction of the raw photolysates of the 2-indanones with NO produced strong ESR spectra of the corresponding cyclic nitroxide radicals, isoindolin-2-oxyls. The nitroxide radicals were generated in a two-phase process, the first, rapid phase being attributed to the reaction of NO with the photolytically formed o-quinodimethanes and the second, slow phase reflecting the reaction with small amounts of o-quinodimethanes, generated by thermal ring opening of the phenyl-substituted benzocyclobutenes and probably a direct reaction of NO with the benzocyclobutenes. The kinetics of both steps, as evaluated by stopped-flow UV/vis and ESR spectroscopy, revealed a strong dependence of the rate constants of the o-quinodimethane + NO reaction on the substitution pattern of the o-quinodimethanes, with rate constants spanning a range of 10-4000 M(-)(1) s(-)(1). The rate constants ((0.4-7.5) x 10(-)(4) s(-)(1)) for the reaction of NO with the 7,7,8,8-tetrasubstituted benzocyclobutenes are much less influenced by the substitution pattern. The utility of phenyl-substituted benzocyclobutenes as "reservoirs" for o-quinodimethane-type nitric oxide traps is discussed.

Journal Article↗