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S Nath

Publications and source records attributed to S Nath.

At least 37 records · Page 2Linked to original sources
PubMed1996

Atrial rhythm after atrioventricular junctional ablation.

Atrioventricular (AV) junctional ablation followed by pacemaker implantation is an established treatment for patients with refractory paroxysmal atrial arrhythmias. The stability of the underlying atrial rhythm after AV junctional ablation is unknown. This study evaluates the atrial rhythm after AV junctional ablation in 49 patients with medically refractory atrial arrhythmias. The group included 25 men and 24 women, of whom 36 had known structural heart disease. Paroxysmal atrial fibrillation was the primary rhythm disturbance in 41 patients, whereas 8 manifested either atrial tachycardias or atrial flutter. All patients had failed therapy with > or = 1 antiarrhythmic drug. Chronic pacing modes were DDIR or DDDR, with mode switching in 15 patients and VVIR in 34 patients. After AV junctional ablation, chronic antiarrhythmic drug therapy was prescribed in only 4 patients (8%). Routine electrocardiograms (ECGs; 6.5 +/- 6.1/patient) during long-term follow-up (18.6 +/- 15.6 months) showed that 7 patients (14%) had an atrial arrhythmia detected on all ECGs, 30 patients (61%) had sinus or atrial-paced rhythms on all recordings, and 12 patients (25%) had both atrial arrhythmias and sinus rhythm documented. Sinus or an atrial-paced rhythm was present on the last available ECG in 33 of 49 patients (67%). Pacing mode was not a predictor of continued sinus rhythm. In conclusion, most patients with a history of paroxysmal atrial tachyarrhythmias will not convert to chronic atrial arrhythmias after AV junctional ablation, even in the absence of antiarrhythmic drug therapy. Use of dual-chamber pacing modes will allow maintenance of at least intermittent atrial function in these patients.

Aged↗
PubMed1996

Sensing lead-related complications in patients with transvenous implantable cardioverter-defibrillators.

The widespread use of the redesigned Endotak lead (CPI, St. Paul, Minnesota), which combines transvenous pacing, sensing, and defibrillation on a single transvenous lead in patients receiving transvenous implantable cardioverter-defibrillators (ICDs), has reduced morbidity and shortened length of hospital stay after ICD implantation. We describe the incidence and management of Endotak sensing lead-related failures in a series of 348 consecutive patients from 4 institutions who underwent implantation between 1990 and 1995. We retrospectively reviewed the databases for patients receiving an ICD with an Endotak lead for the incidence of lead-related sensing abnormalities. Ten patients (2.8%) with lead-related sensing abnormalities were detected at a mean of 15 +/- 11 months after ICD implantation. Sensing abnormalities were detected in 6 patients after they received inappropriate shocks. Noise or oversensing was noted in 7 patients from interrogation of the devices' data logs. Eight patients had a new transvenous sensing lead placed, 1 patient had a new Endotak lead placed, and 1 had a chronic pacemaker sensing lead converted to function as a sensing lead. No further sensing problems were noted in 8 of 10 patients during a mean follow-up of 14 +/- 8 months. The site of the sensing lead failure was localized to the subrectus pocket in 5 patients and to the clavicle-first rib area in 3 patients; it was undetermined and presumed to be in the clavicle-first rib area in the other 2 patients. One patient had late failure of the defibrillation lead. We conclude that Endotak sensing lead failure does not require insertion of a new Endotak lead, but can be managed with close follow-up and insertion of a new transvenous sensing lead. Endotak lead fractures are frequently localized to the ICD pocket.

Aged↗
PubMed1996

Effects of dispersive electrode position and surface area on electrical parameters and temperature during radiofrequency catheter ablation.

Positioning of the dispersive electrode has no significant effect during radiofrequency ablation. Doubling the surface are of the dispersive electrode results in a lower impedance, higher current delivery, and increased tip temperatures, particularly if the baseline impedance is >100 ohms. These findings may have important implications for optimizing radiofrequency energy delivery using currently available radiofrequency generators.

Cardiac Catheterization↗
PubMed1996

Paediatric plastic surgery in the University Teaching Hospital, Lusaka, Zambia: a 13-year audit.

An audit of paediatric plastic surgical procedures performed over a period of 13 years (1981-1993) at the University Teaching hospital, Lusaka, Zambia is presented. There are few publications of precise data from developing countries and no audit of this nature has been published from the area of Africa encompassed by this study. The purpose of the audit was to analyse the number and pattern of paediatric plastic surgical cases and to identify problems associated with their management. The pattern could be considered representative of the whole of sub-Saharan Africa. In addition to the audit, the basic principles of management and associated problems of some of the conditions have been outlined with particular respect to the local circumstances. It is hoped that an audit such as this will serve to upgrade the plastic surgical services and lead to the subject being incorporated into the undergraduate and postgraduate curriculums. It might also form the basis for establishing regional and provincial paediatric plastic surgical units. A balanced improvement in the provision of both general and plastic surgery within the health care services of the African continent is seen as important. Finally, this audit might enable surgeons in more developed nations to understand the pattern of disease and need in Africa and familiarise those who intend to work in the continent with the situation.

Burns↗
PubMed1996

Conjoined twins in Zambia.

The University Teaching Hospital (UTH) is based in the Zambian capital, Lusaka. It is the main referral centre for the country, which has a population of over 8 million (census 1992). Thirteen sets of conjoined twins have been seen over the 24 year period between 1970 and 1993. Out of 13 cases of conjoining twins three were stillborn (reported in 1978). Ten cases of our personal series were analysed including three successful separations. An attempt has been made to establish the incidence of conjoined twins in Zambia. Basic principles of management have been suggested and the constraints encountered in developing countries have been discussed.

Abnormalities, Multiple↗
PubMed1995

Correlation of temperature and pathophysiological effect during radiofrequency catheter ablation of the AV junction.

BACKGROUND: Accelerated junctional rhythms have been observed before the development of AV nodal block during radiofrequency (RF) catheter ablation of the AV junction. However, the time course and temperatures required to induce an accelerated junctional rhythm and AV nodal block during this procedure have not yet been characterized. METHODS AND RESULTS: Nineteen patients underwent RF ablation of the AV junction with a thermistor ablation catheter. RF energy was initially delivered at 10 W for 9 seconds and then increased by 5-W increments for 9 seconds at each power level up to a maximum power of 50 W. If a junctional rhythm was observed during the power titration, a 30- to 60-second RF application was then delivered at the same power level. The power was then further increased to a maximum of 50 W if AV nodal block was not observed after 20 seconds of RF delivery. The procedure was successful in all 19 patients. A median of one RF application (range, one to eight applications) was required to produce permanent AV nodal block. An accelerated junctional rhythm was observed during 89% of successful attempts versus 70% of unsuccessful deliveries (P = NS). The median time to onset of the junctional rhythm was significantly shorter during successful compared with unsuccessful applications (1.8 versus 7.7 seconds, respectively; P < .001). Similarly, the mean time to appearance of AV nodal block was significantly shorter during successful compared with unsuccessful attempts (19.6 +/- 9.4 versus 36.8 +/- 19.0 seconds, respectively; P < .01). The catheter tip temperatures associated with the development of an accelerated junctional rhythm were significantly lower than those associated with the appearance of AV nodal block (51 +/- 4 degrees C versus 58 +/- 6 degrees C, respectively; P < .001). Mean temperatures in the range of 60 +/- 7 degrees C were required to produce permanent AV nodal block. CONCLUSIONS: The development of an accelerated junctional rhythm within 5 seconds and the appearance of AV nodal block within 30 seconds of RF onset were both highly characteristic of successful target sites during RF ablation of the AV junction. The accelerated junctional rhythm and AV nodal block were both highly temperature dependent. The temperatures associated with the onset of AV nodal block were significantly higher than the temperatures resulting in an accelerated junctional rhythm.

Aged↗
PubMed1995

The effect of radiofrequency catheter ablation on myocardial creatine kinase activity.

INTRODUCTION: The primary mechanism of myocardial injury during radiofrequency (RF) catheter ablation in the heart is presumed to be thermal. Creatine kinase has been measured in serum to assess the volume of myocardial injury after ablation. However, its thermal inactivation by RF ablation could lead to underestimation of the true volume of injury. METHODS AND RESULTS: Serial RF lesions were created in 10 canine left ventricles in vivo, and serial serum creatine kinase activities were measured and compared to lesion volume. To assess the stability of myocardial creatine kinase during RF catheter ablation, 29 RF ablations were made on the epicardial surface of porcine left ventricle in vivo and a 2-mm core biopsy was rapidly removed. The cores were rapidly frozen, sectioned longitudinally in 1-mm slices, and homogenized in 0.3 M Tris buffer solution containing EDTA and dithiothreitol for subsequent analysis of creatine kinase activity. An additional 19 tissue cores from RF lesions were stained and used to determine mean lesion depth. Normal tissue biopsies were exposed to 60 seconds of hyperthermia (37 degrees to 85 degrees C, n = 190), or high-density RF current at 50 degrees C (0 to 100 mA/mm2, n = 50), and tissue creatine kinase activity was measured. There was no evidence of creatine kinase washout within the first 2 hours, and peak values were measured 5 to 7 hours postablation. Tissue creatine kinase activity in the first mm depth of RF lesions averaged 10% of control values and increased over the first 5 mm of lesion depth. The mean creatine kinase activity within the hemisphere of ablated myocardium was calculated to be 31% of control. Creatine kinase activity declined significantly at temperatures above 65 degrees C, but no difference in tissue creatine kinase activity was observed among differing levels of RF current exposure in the absence of significant heating. CONCLUSIONS: Creatine kinase activity in myocardial tissue is significantly diminished within the RF lesion. Creatine kinase activity is not stable at temperatures above 65 degrees C, which are routinely achieved within the central zone of RF ablation, and is unaffected by RF current in the absence of hyperthermia. Measurements of serum creatine kinase activity after RF catheter ablation may significantly underestimate the volume of myocardial injury.

Animals↗
PubMed1995

New horizons in catheter ablation.

Catheter ablation has evolved into the dominant therapeutic modality in the treatment of a variety of arrhythmias, particularly supraventricular arrhythmias with the mechanisms of atrioventricular (AV) nodal reentry and AV reciprocating tachycardia via an accessory pathway. The mode of catheter ablation used in the great majority of cases is radiofrequency (RF) catheter ablation. This technology is well-suited for the above arrhythmias because the targets and the RF lesions are both small and discrete. Using temperature monitoring may improve the outcome of these procedures by decreasing procedure time and incidence of coagulum formation on the catheter after a sudden rise in electrical impedance. New RF catheter designs and new modalities of creating catheter-induced focal myocardial injury will allow operators to have improved success with the ablation of less approachable arrhythmias, including atrial flutter and reentrant ventricular tachycardia. Studies are currently underway to create a catheter based "maze" procedure for the treatment of atrial fibrillation. As techniques and technologies evolve, a greater proportion of patients with symptomatic or threatening arrhythmias may be approached with catheter ablation as a curative or palliative procedure.

Catheter Ablation↗
PubMed1995

Structure/function studies of mammalian Na-H exchangers--an update.

Four mammalian Na+/H+ exchangers have recently been cloned. Despite the structural similarity, these Na+/H+ exchanger isoforms differ in kinetic characteristics and their response to external stimuli. The present review deals with the recent developments in their functional characterization and their short-term regulation.

Animals↗
PubMed1995

Sexual ambiguity and malformation in Zambia: challenges in surgical management.

This article addresses the complexity in diagnosis, gender assignment and management in patients with sexual ambiguity and malformed sexual organs. Between 1984 and 1993, nine children and 10 adult patients with this ailment were treated in the University Teaching Hospital, Lusaka, Zambia. All children had clitorovaginoplasty and adults had different surgical procedures such as feminisation and masculinisation operations. Methods, means and the manner in which we manage these patients in the midst of a scarcity of expert manpower and sophisticated equipment are discussed. Need for a specialised clinic for better management, teaching and research of this unfortunate and highly sensitive congenital defect has been emphasised.

Adult↗
PubMed1994

Management of postburn contracture of the neck.

Five hundred and sixty-two patients with postburn contractures were treated by a plastic surgeon in the Central Hospital of the capital city Lusaka. There were 37 patients with neck contractures of whom 18 were classified as major, all but two were burned by fire and two-thirds were female. Release of contracture and excision of scar tissue followed by surface cover with skin grafting was the mainstay of treatment and was carried out in 31 of 37 patients. Careful perioperative management and the basics of plastic surgery such as skin grafting are within the competence of many general surgeons. Because burn contractures are common in the developing world, it is recommended that plastic surgery be included in the training of general surgeons and that selected cases be managed by them. The more complex cases should be referred to a plastic surgery centre.

Adolescent↗
PubMed1994

Phosphorylation modulates the function of the calcium release channel of sarcoplasmic reticulum from skeletal muscle.

The modulation of the calcium release channel (CRC) by protein kinases and phosphatases was studied. For this purpose, we have developed a microsyringe applicator to achieve sequential and multiple treatments with highly purified kinases and phosphatases applied directly at the bilayer surface. Terminal cisternae vesicles of sarcoplasmic reticulum from rabbit fast twitch skeletal muscle were fused to planar lipid bilayers, and single-channel currents were measured at zero holding potential, at 0.15 microM free Ca2+, +/- 0.5 mM ATP and +/- 2.6 mM free Mg2+. Sequential dephosphorylation and rephosphorylation rendered the CRC sensitive and insensitive to block by Mg2+, respectively. Channel recovery from Mg2+ block was obtained by exogenous protein kinase A (PKA) or by Ca2+/calmodulin-dependent protein kinase II (CalPK II). Somewhat different characteristics were observed with the two kinases, suggesting two different states of phosphorylation. Channel block by Mg2+ was restored by dephosphorylation using protein phosphatase 1 (PPT1). Before application of protein kinases or phosphatases, channels were found to be "dephosphorylated" (inactive) in 60% and "phosphorylated" (active) in 40% of 51 single-channel experiments based on the criterion of sensitivity to block by Mg2+. Thus, these two states were interconvertable by treatment with exogenously added protein kinases and phosphatases. Endogenous Ca2+/calmodulin-dependent protein kinase (end CalPK) had an opposite action to exogenous CalPK II. Previously, dephosphorylated channels using PPT (Mg2+ absent) were blocked in the closed state by action of endogenous CalPK. This block was removed to normal activity by the action of either PPT or by exogenous CalPK II. Our findings are consistent with a physiological role for phosphorylation/dephosphorylation in the modulation of the calcium release channel of sarcoplasmic reticulum from skeletal muscle. A corollary of our studies is that only the phosphorylated channel is active under physiological conditions (mM Mg2+). Our studies suggest that phosphorylation can be at more than one site and, depending on the site, can have different functional consequences on the CRC.

Adenosine Triphosphate↗
PubMed1994

Ultrastructural observations in the myocardium beyond the region of acute coagulation necrosis following radiofrequency catheter ablation.

INTRODUCTION: We hypothesized that myocardial injury following radiofrequency (RF) catheter ablation may extend beyond the region of acute coagulation necrosis as defined by histochemical staining. METHODS AND RESULTS: Five RF lesions were created in vivo in the left ventricle of two dogs using a 4-mm tipped ablation electrode in which RF power was adjusted to maintain an electrode-tissue interface temperature of 85 degrees C for 60 seconds. The lesions were bisected; one half of the lesions were stained with nitroblue tetrazolium (NBT) and the other half processed for electron microscopy. Three zones of interest were identified extending 0-3 mm, 3-6 mm, and > 6 mm from the visible pathologic lesion border. The degree of ultrastructural injury to the myocardium was scored for each zone. Electron microscopy demonstrated the presence of significant abnormalities of the plasma membrane, mitochondria, sarcomeres, sarcoplasmic reticulum, and gap junctions of myocytes, as well as damage to the microvasculature extending up to 6 mm beyond the pathologic lesion edge. The plasma membrane and gap junctions of myocytes and the microvasculature appeared particularly sensitive to thermal injury, whereas the intercalated discs were relatively thermally resistant. CONCLUSION: RF catheter ablation results in ultrastructural damage to the myocardium extending up to 6 mm beyond the acute pathologic RF lesion border as defined by NBT histochemical staining.

Animals↗
PubMed1994

Basic aspects of radiofrequency catheter ablation.

Radiofrequency (RF) catheter ablation has become the treatment of choice for many symptomatic cardiac arrhythmias. It is presumed that the primary cause of tissue injury by RF ablation is thermally mediated, resulting in a relatively discrete homogeneous lesion. The mechanism by which RF current heats tissue is resistive heating of a narrow rim (< 1 mm) of tissue that is in direct contact with the ablation electrode. Deeper tissue heating occurs as a result of passive heat conduction from this small region of volume heating. Lesion size is proportional to the temperature at the electrode-tissue interface and the size of the ablation electrode. Temperatures above 50 degrees C are required for irreversible myocardial injury, but temperatures above 100 degrees C result in coagulum formation on the ablation electrode, a rapid rise in electrical impedance, and loss of effective tissue heating. Lesion formation is also dependent on optimal electrode-tissue contact and duration of RF delivery. Newer developments in RF ablation include temperature monitoring, longer ablation electrodes coupled to high-powered RF generators, and novel ablation electrode designs.

Arrhythmias, Cardiac↗