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Biomedical subjects

M Akhtar

Publications and source records attributed to M Akhtar.

At least 181 records · Page 10Linked to original sources
PubMed1994

Evaluation of a commercial enzyme immunoassay kit (RIDASCREEN) for detection of staphylococcal enterotoxins A, B, C, D, and E in foods.

The RIDASCREEN SET kit (R-Biopharm GmbH, Darmstadt, Germany), a commercial staphylococcal enterotoxin (SE) visual immunoassay kit, was evaluated for its efficacy. The kit utilizes monovalent capture antibodies against SE types A to E (SEA to SEE); therefore, it simultaneously detects and identifies the enterotoxin types. The major advantages of the kit are (i) a high degree of specificity (except for naturally occurring peroxidases, food compositions or ingredients and microbiological products due to growth of nonstaphylococcal microorganisms did not cause false-positive results; additionally, no cross-reactions among reagents of the kits were observed), (ii) excellent sensitivity (minimum detectable limits were 0.20 to 0.30 ng of SEs per ml of extracts of ham, salami, and mushroom and 0.30 to 0.35 ng of SEs per ml of cheese extracts, or 0.50 to 0.75 ng of SEs per g of foods such as noodles, ham, salami, cheese, and turkey), (iii) simplicity (the kit enabled direct assay of SEs in food extracts without the need for lengthy extraction or concentration procedures), (iv) rapidity (it took less than 3 h to complete the analysis of individual enterotoxin types SEA to SEE), and (v) its semiquantitative results (optical density values could be read against a standard curve to estimate the amount of SE in the extract). The RIDASCREEN kit is a convenient, rapid, and reliable tool for the detection and identification of SEs in foods.

Enterotoxins↗
PubMed1994

Wegener's granulomatosis limited to the kidney as a masslike lesion.

We report on a 45-year-old female who presented with end-stage renal disease due to Wegener's granulomatosis limited to the kidneys. Ultrasonography and computed tomography revealed a masslike expansion involving the upper pole of an otherwise small right kidney. Histopathology of a nephrectomy specimen revealed cystic dilatation of renal tubules and active lesions of Wegener's granulomatosis in the upper pole. The lower part of the kidney showed atrophic changes. Wegener's granulomatosis presenting as a renal mass is extremely rare. Only 3 cases have been previously reported in the literature. Wegener's granulomatosis only limited to the kidney is also rare. A brief review of 23 previously reported cases who initially presented with renal disease is presented. All but 2 patients subsequently manifested extrarenal lesions. Our patient continues to be free of any extrarenal involvement 18 months following presentation, although subsequent development of extrarenal lesions cannot be ruled out.

Adolescent↗
PubMed1994

Transcatheter ablation of posteroseptal accessory pathways using a venous approach and radiofrequency energy.

BACKGROUND: The efficacy of transcatheter ablation of atrioventricular (AV) accessory pathways (APs) located in the posteroseptal region using a right atrial approach and radiofrequency energy was evaluated. METHODS AND RESULTS: Fifty consecutive patients with APs in the posteroseptal region underwent radiofrequency catheter ablation. Manifest preexcitation was present in 36 patients and a concealed AP in 14. In 18 patients (group 1), the ventriculoatrial (VA) interval during orthodromic tachycardia was prolonged by 21 +/- 7 milliseconds (range, 10 to 30 milliseconds) with functional left bundle-branch block. In 16 patients (group 2), functional left bundle-branch block caused no VA interval prolongation. The remaining 16 patients (group 3) had no inducible left bundle-branch block during orthodromic tachycardia. Functional right bundle-branch block was induced in 30 patients with no effect on the VA interval. In group 1, of 14 patients with manifest preexcitation during sinus rhythm, 10 patients had a positive delta wave in lead V1. Of 10 group 2 patients with manifest preexcitation, only 5 had a positive delta wave in lead V1. In group 3, of 12 patients with manifest preexcitation, 7 exhibited a positive delta wave in lead V1. All posteroseptal APs were successfully ablated, and this was achieved via a right atrial approach in 48 patients and left ventricular approach in only 2. Successful sites were at the posteroseptal region of the tricuspid annulus (30 patients), within the terminal 1 cm of the coronary sinus including its ostium (16 patients), and at the inferomedial aspect of the right atrium posterior to the coronary sinus ostium (2 patients). The posteroseptal region of the left ventricle was the site of successful ablation in 2 patients. Six patients with a recurrence of AP conduction required a repeat ablation, with successful results in 5. Thirty-five patients had a complete electrophysiological evaluation 2 to 3 months after their successful ablation and were found to have no functioning AP. In 49 patients with a final successful ablation, no recurrence of symptoms was noted during a mean follow-up period of 12 +/- 9 months. Complications occurring in 3 patients were cardiac tamponade requiring surgical drainage and repair of a right ventricular tear, pericardial effusion with no hemodynamic consequence that spontaneously resolved, and a transient 2:1 atrioventricular block. CONCLUSIONS: These data suggest that posteroseptal APs are amenable to successful ablation using a right atrial approach. Success was achieved in 47 cases (94%) in this series even though the ECG and/or electrophysiological characteristics of the posteroseptal APs of some patients were suggestive of "left-sided" pathways.

Adolescent↗
PubMed1994

Castleman's disease of the chest. Magnetic resonance imaging features.

The value of magnetic resonance imaging (MRI) in the evaluation of vascular abnormalities in the chest is well established. To our knowledge, however, MRI in Castleman's disease of the chest had not been reported previously. We present a case of Castleman's disease of hyaline vascular type involving the pulmonary hilum where MRI was equal to computed tomography in showing the extent of the disease, but was more informative in demonstrating its relationship with vascular structures.

Castleman Disease↗
PubMed1994

CT-guided fine needle aspiration biopsy in the diagnosis of mediastinal tuberculosis.

Twenty-two patients with mediastinal tuberculosis were reviewed. The most common symptoms were chest pain, cough, fever, and weight loss. Results of the physical examination were unremarkable. The chest radiographs of all 22 patients showed abnormal mediastinum with no evidence of extramediastinal disease. Most (62%) had right-sided paratracheal lymphadenopathy. Mantoux skin test was positive (> 15 mm) in all patients, whereas sputum smears and cultures for acid-fast bacilli were negative. Computed tomographic (CT) guided fine needle aspiration biopsies (FNAB) were performed in 12 patients using 22- to 25-gauge needles. Ten patients had fiberoptic bronchoscopic (FOB) examination with brushings and biopsies. Mediastinoscopy (n = 8) or thoracotomy (n = 6) was performed in patients where either FNAB or FOB was not diagnostic or where lymphoma was suspected clinically. The rates of true-positive diagnoses were 20%, 66%, 75%, and 100% for FOB, FNAB, mediastinoscopy, and thoracotomy, respectively. The rate of false-negative for FNAB was 34%. Only one patient developed nonsignificant pneumothorax after FNAB. These findings suggest that CT-guided FNAB is a useful and safe procedure and should be considered in the initial evaluation of patients suspected of having mediastinal tuberculosis.

Adolescent↗
PubMed1994

Late recurrence of Wegener's granulomatosis presenting as tracheal stenosis in a renal transplant patient.

An unusual case of a 46-year-old man who had end-stage renal disease due to crescentic glomerulonephritis that was treated by a cadaveric renal allograft is presented. About 18 months post-Tx, the patient developed severe tracheal stenosis which, on biopsy, revealed granulation tissue and chronic inflammation. After another 18 months he developed necrotizing glomerulonephritis involving the renal allograft and an inflammatory retro-orbital pseudotumor. The latter, on biopsy, revealed granulomatous vasculitis characteristic of Wegener's granulomatosis. This diagnosis was further confirmed by strongly positive anti-neutrophil antibodies with diffuse granular cytoplasmic immunofluorescence (C-ANCA). The patient was treated successfully with cyclophosphamide therapy.

Antibodies, Antineutrophil Cytoplasmic↗
PubMed1993

Bundle branch reentry: a mechanism of ventricular tachycardia in the absence of myocardial or valvular dysfunction.

OBJECTIVES: The aim of this study was to present bundle branch reentry as the mechanism of sustained ventricular tachycardia in the absence of myocardial or valvular dysfunction. BACKGROUND: Previous reports have documented the relation between structural heart disease and bundle branch reentrant ventricular tachycardia. Myocardial or valvular dysfunction has thus far been recognized as the only anatomic substrate for the development of this tachycardia. METHODS: Three patients with a wide QRS complex tachycardia underwent noninvasive and invasive cardiac evaluation and electrophysiologic studies to identify the substrate and mechanism of tachycardia. Catheter ablation of the right bundle branch using radiofrequency current was performed in each patient. RESULTS: The patients were all men (aged 54, 34 and 72 years) who presented with presyncope, palpitation and cardiac arrest, respectively. Electrocardiography during sinus rhythm revealed nonspecific intraventricular conduction delay in all three patients. Cardiac evaluation revealed no evidence of myocardial or valvular dysfunction in any patient. The baseline HV interval was prolonged in each patient (90, 100 and 75 ms, respectively). Programmed right ventricular stimulation initiated bundle branch reentrant tachycardia with typical left (three patients) and right (one patient) bundle branch block pattern. Catheter ablation of the right bundle branch using radiofrequency current abolished bundle branch reentry in all three patients. After 26-, 13- and 8-month follow-up periods, complete right bundle branch block persisted, and all three patients remained asymptomatic without antiarrhythmic drugs. CONCLUSIONS: Sustained bundle branch reentry can be a clinical arrhythmia in patients with no identifiable myocardial or valvular dysfunction except for isolated conduction abnormalities in the His-Purkinje system. This mechanism of tachycardia should be recognized during electrophysiologic evaluation, given the seriousness of this arrhythmia and the availability of the effective treatment.

Adult↗
PubMed1993

Outcome with implantable cardioverter-defibrillator therapy for survivors of ventricular fibrillation secondary to idiopathic dilated cardiomyopathy or coronary artery disease without myocardial infarction.

Patients with idiopathic dilated cardiomyopathy (IDC) constitute a minority among implantable cardioverter-defibrillator (ICD) recipients; how these patients fare versus those with coronary artery disease (CAD) is not well defined, nor is the mechanism of cardiac arrest recurrence, which may involve a more significant role of bradyarrhythmias. A retrospective multicenter study regarding outcome of ICD therapy was conducted in 224 patients with either IDC (n = 69; 31%) or CAD (n = 155; 69%) presenting exclusively with ventricular fibrillation (VF) unassociated with acute myocardial infarction. Patients with IDC were significantly younger (mean age 57 vs 61 years in patients with CAD, p < 0.04) and less male predominant (64 vs 79% in patients with CAD, p < 0.02). There was no significant difference in mean left ventricular ejection fraction (0.27 in IDC patients vs 0.29 in CAD patients), but sustained ventricular tachycardia was induced less often in patients with IDC (21 vs 58% in CAD patients, p < 0.001). Bradycardia pacing, either by an ICD with bradycardia pacing ability or a separate bradycardia pacemaker, was available in only 15% of ICD implantees. During a median follow-up duration of 1.7 years for patients with IDC and 1.9 years for patients with CAD, estimated cumulative event rates were similar for any type shock (2-year incidence of 74% in IDC patients, 69% in CAD patients) as well as for appropriate shock (2-year incidence of 46% in IDC patients, 40% in CAD patients).(ABSTRACT TRUNCATED AT 250 WORDS)

Cardiomyopathy, Dilated↗
PubMed1993

Cooperativity during multiple phosphorylations catalyzed by rhodopsin kinase: supporting evidence using synthetic phosphopeptides.

Rhodopsin kinase is a key component in the shutdown of visual transduction. The phosphorylation of rhodopsin's C-terminus was evaluated using synthetic peptides derived from the last 12 amino acids (337-348) as substrates and their phosphorylated counterparts as inhibitors. It was found that synthetic peptides were phosphorylated at the serine residue corresponding to Ser-343 in the primary sequence of bovine rhodopsin. The phosphopeptides were prepared by incorporating into the peptide chain a trityl-protected serine derivative at the site destined to contain the phosphoryl group. The trityl group was selectively released with 20% (v/v) dichloroacetic acid; the free hydroxyl group was then phosphitylated with di-tert-butyl N,N-diethylphosphoramidite, and the resulting phosphite derivative was oxidized with m-chloroperoxybenzoic acid. The phosphopeptides were found to have a greater affinity for the kinase compared with their nonphosphorylated counterparts; for the peptides corresponding to residues 337-348 of rhodopsin the affinity increased in the order VSKTETSQVAPA < VSKTETS[PO3H2]QVAPA < VS[PO3H2]KTETS[PO3H2]QVAPA. The results are interpreted to support the cooperativity hypotheses proposed previously [Wilden, U., & Kühn, H. (1982) Biochemistry 21, 3014-3022; Aton, B. R., Litman, B. J., & Jackson, M. L. (1984) Biochemistry 23, 1737-1741].

Amino Acid Sequence↗
PubMed1993

Comparison of cardiac pacing with drug therapy in the treatment of neurocardiogenic (vasovagal) syncope with bradycardia or asystole.

BACKGROUND: The efficacy of permanent cardiac pacing in patients with neurocardiogenic (or vasovagal) syncope associated with bradycardia or asystole is not clear. We compared the efficacy of cardiac pacing with that of oral drug therapy in the prevention of hypotension and syncope during head-up tilt testing. METHODS: Among 70 patients with a history of syncope in whom hypotension and syncope could be provoked during head-up tilt testing, 22 had bradycardia (a heart rate < 60 beats per minute, with a decline in the rate by at least 20 beats per minute) or asystole along with hypotension during testing. There were 9 men and 13 women, with a mean (+/- SD) age of 41 +/- 17 years. Head-up tilt testing was repeated during atrioventricular sequential pacing (in 20 patients with sinus rhythm) or ventricular pacing (in 2 patients with atrial fibrillation). Regardless of the results obtained during artificial pacing, all the patients subsequently had upright-tilt testing repeated during therapy with oral metoprolol, theophylline, or disopyramide. RESULTS: During the initial tilt test, 6 patients had asystole and 16 had bradycardia along with hypotension. Despite artificial pacing, the mean arterial pressure during head-up tilt testing still fell significantly, from 97 +/- 19 to 57 +/- 19 mm Hg (P < 0.001); 5 patients had syncope, and 15 had presyncope. By contrast, 19 patients who later received only medical therapy (metoprolol in 10, theophylline in 3, and disopyramide in 6), 2 patients who received both metoprolol and atrioventricular sequential pacing, and 1 patient who received only atrioventricular sequential pacing had negative head-up tilt tests. After a median follow-up of 16 months, 18 of the 19 patients who were treated with drugs alone (94 percent) remained free of recurrent syncope or presyncope, whereas the patient treated only with permanent dual-chamber pacemaker had recurrent syncope. CONCLUSIONS: In patients with neurocardiogenic syncope associated with bradycardia or asystole, drug therapy is often effective in preventing syncope, whereas artificial pacing is not.

Adolescent↗
PubMed1993

Phosphorylation of solubilised dark-adapted rhodopsin. Insights into the activation of rhodopsin kinase.

A protocol for the separation of phosphorhodopsin from phospho-opsin has been developed. The method takes advantage of the finding that, while 0.5% N,N-dimethyldodecylamine-N-oxide completely solubilises membrane-embedded phosphorhodopsin, at this concentration of detergent, phospho-opsin is only sparingly soluble. Phosphorhodopsin solubilised in this manner may be freed from contaminant phospho-opsin by chromatography on hydroxyapatite. Using this method, the rhodopsin-kinase-catalysed phosphorylation of photoexcited rhodopsin and native rhodopsin was studied in rod outer-segment membranes at different levels of bleaching. Prior to analysis of the phosphorylation mixture, the phosphorylated form of photoexcited rhodopsin was converted into phospho-opsin by treatment with NH2OH. It was found that, while at a 5% bleach level the amount of phosphorhodopsin produced was 15% that of phospho-opsin, at 60% bleaching the phosphorhodopsin was less than 1% of phospho-opsin. The phosphorylation reaction under different bleaching conditions was also studied in a completely soluble system (using 2% dodecyl maltoside) and the pattern of phosphate incorporation into rhodopsin versus opsin was identical to that in the membrane system. We have previously proposed that rhodopsin kinase normally exists in an inactive form and is only activated following interaction with photoexcited rhodopsin. The present work strengthens this conclusion and also shows that, following activation, the kinase preferentially phosphorylates photoexcited rhodopsin but can also act upon unbleached rhodopsin. Two possible mechanisms for the activation of the kinase are considered. From the distribution of phosphorhodopsin and phospho-opsin at different bleaching levels, the relative rates of the phosphorylation of photoexcited rhodopsin (kR*) and rhodopsin (kR) were calculated. kR*/kR values for the membrane system of 71 +/- 20 and, for the solubilised system, of 80 +/- 19 were obtained. The algebraic equation used to obtain these values highlights the fact that the ratio of the concentrations of the two substrates, photoexcited rhodopsin and rhodopsin, in a sample, determines the final distribution of phosphate between bleached and unbleached rhodopsin. This conclusion may contribute to the understanding of 'high-gain' phosphorylation observed previously.

Animals↗
PubMed1993

Fanconi's syndrome with hepatorenal glycogenosis associated with phosphorylase b kinase deficiency.

OBJECTIVE: To describe two patients with Fanconi's nephropathy secondary to glycogen storage disease and speculate on the possible etiology. DESIGN: Convenience sample. SETTING: Tertiary care, referral center. PATIENTS: Two related children referred for failure to thrive, rickets, and hepatomegaly. INTERVENTION: Dietary and therapeutic measures for rickets and renal tubular acidosis. MEASUREMENTS AND RESULTS: The main laboratory findings were fasting hypoglycemia and massive glucosuria, with evidence of multiple renal tubular dysfunction characteristic of the Fanconi syndrome. Liver and kidney biopsy specimens were consistent with glycogen storage disease. Enzymatic assay of liver homogenates revealed marked deficiency of phosphorylase b kinase in one patient and absent activity in the other. CONCLUSION: Phosphorylase b kinase deficiency may be causally related to hepatorenal glycogenosis with the Fanconi syndrome. More patients with this syndrome need to be studied before a definitive causal role is implicated.

Biopsy↗
PubMed1993

Ventricular tachycardia due to sustained bundle branch reentry: diagnostic and therapeutic considerations.

We have identified bundle-branch reentry (BBR) as the mechanism of ventricular tachycardia (VT) during electrophysiologic studies in 48 patients at our institution. All but three patients had significant structural heart disease, that is, dilated ischemic or idiopathic cardiomyopathy, the most common of anatomic substrates. Syncope and sudden death were the modes of presentation in up to 70% of these patients. The critical prerequisite for the development of this arrhythmia is conduction delay in the His-Purkinje system, which was present in all patients and manifests as a nonspecific conduction delay or a left bundle-branch block (LBBB) in the surface electrocardiogram (ECG) and a prolonged HV interval in the intracardiac recordings. VT with an LBBB morphology is the most common form of BBR, present in 98% of patients. Transcatheter ablation of the right bundle branch (RBB) with the use of radiofrequency current is the treatment of choice, as it effectively eliminates BBR. During long-term follow-up, recurrent tachycardia due to BBR was not documented in any patient; however, congestive heart failure was a common cause of death in this population.

Bundle of His↗
PubMed1993

Fine-needle aspiration biopsy of Langerhans histiocytosis (histiocytosis-X).

A series of 14 fine-needle aspiration biopsies (FNAB) from histologically proven cases of histiocytosis-x (Hx) were reviewed. The smears revealed a variable mixture of Langerhans cells, eosinophils, macrophages, polymorphonuclear cells, and giant cells. Based on the predominant cells present, the cases were further categorized as Langerhans cell predominant (nine cases), eosinophil predominant (two cases), and macrophage predominant (three cases). Langerhans cells were usually polygonal without significant evidence of phagocytosis and frequently contained indented nuclei. In three cases, several Langerhans cells showed prominent dendritic processes. Electron microscopy in 10 cases revealed Langerhans cells with varying degrees of morphologic differentiation. All cases studied revealed Birbeck granules. These findings indicate that FNAB may be an effective technique for diagnosing Hx.

Adolescent↗
PubMed1993

Physics and engineering of transcatheter cardiac tissue ablation.

Ablation of arrhythmogenic cardiac tissues has emerged as one of the most important advances in cardiac electrophysiology. With the introduction of transcatheter ablation, the treatment of ventricular tachycardia, Wolff-Parkinson-White syndrome and other cardiac arrhythmias has progressed from an expensive and painful surgical therapy accompanied by a long recovery period to the less expensive, less traumatic transcatheter approach. The feasibility of cardiac ablation, along with the increasing number of physicians using the technique, requires understanding of the anatomic and electrophysiologic bases of transcatheter ablation as well as the different technologies, their limitations and complications. This report provides an overview of the physical, scientific and technical aspects of cardiac ablation performed with the methods currently available and a summary of the limitations of each method and expected future technologic developments in this growing field. Emphasis is placed on radiofrequency and direct current energies, the primary methods now used. Methods such as cryoablation and laser, and microwave and chemical ablation are discussed with less detail because the method of delivering energy for these ablative procedures has not been fully developed.

Animals↗