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Biomedical subjects

M Akhtar

Publications and source records attributed to M Akhtar.

At least 325 records · Page 18Linked to original sources
PubMed1986

Incidence and clinical significance of ventricular fibrillation induced with single and double ventricular extrastimuli.

Of 718 patients evaluated for suspected or documented ventricular tachyarrhythmias, ventricular fibrillation (VF) was induced in 28 (incidence 3.9%) by single and double extrastimuli. Nine of the 28 patients had suspected but no clinically documented ventricular tachycardia (VT) or VF (group 1), 11 had documented VT (group 2) and 8 had out of hospital VF (group 3). In group 1, electropharmacologic control was achieved in 8 patients with the initial agent tested; however, symptoms recurred in 6 patients. In 4 patients the drug was discontinued. After a follow-up of 26 +/- 11 months in group 1, no patient had died. In only 2 of 19 patients in groups 2 and 3 were arrhythmias controlled with the initial agent; 15 patients had VT and 2 VF. Control with class I agents was achieved in 9 of 19 patients and none died until the drug regimen was changed empirically in 3 of these 9. Ten patients, all from groups 2 and 3, were treated empirically with amiodarone; 3 died. All patients died either suddenly or in VT. The mortality rate in groups 2 and 3 after a mean follow-up of 24 +/- 9 months was 32% (p less than 0.05). Continued symptoms and no deaths in group 1 suggests a nonclinical nature of induced VF. Control of induced VF on serial drug testing in group 2 and 3 also indicates a false-negative drug efficacy response, as pharmacologic control of emergent VT on subsequent studies appeared essential to their survival despite control of induced VF. Thus, even with single or double premature stimuli, induction of VF can be a nonclinical response, especially in patients without clinical VF.

Adult↗
PubMed1986

Aspiration cytology of neuroblastoma. Light and electron microscopic correlations.

Fine-needle aspiration biopsy (FNAB) smears from 16 cases of neuroblastoma are reviewed, and various cytomorphologic features helpful in diagnosing this tumor are described. Cytoplasmic processes were present in ten cases, and pseudorosettes in three cases. Electron microscopic study of FNAB samples revealed that all diagnostically important features, such as cell processes, neurosecretory granules, and synaptic cell junctions, could be recognized. These findings indicate that FNAB studied by light and electron microscopy is an effective method for diagnosing neuroblastoma.

Biopsy, Needle↗
PubMed1986

Sequence and interspecies transfer of an aminoglycoside phosphotransferase gene (APH) of Bacillus circulans. Self-defence mechanism in antibiotic-producing organisms.

The APH gene of a butirosin-producing Bacillus circulans was cloned and shown to be expressed in Escherichia coli and Streptomyces lividans. The gene was sequenced and a possible developmentally regulated promoter identified. When the deduced protein sequence was compared with those from transposon Tn5, transposon Tn903, Streptomyces fradiae, Staphylococcus aureus and Streptococcus faecalis, significant homology was found, indicating that the genes may have a common origin.

Bacillus↗
PubMed1986

The synthesis and use of oligodeoxynucleotides in plasmid DNA sequencing.

A convenient procedure for the synthesis and purification of oligonucleotides is described. 16-base long primers synthesised by this method were used to investigate DNA sequencing using plasmid DNA as a template. This allowed the further analysis of the E. coli glt A sequence coding for citrate synthase and enabled determination of the 5'-non-coding regulatory region of the aminoglycoside phosphotransferase gene.

Base Sequence↗
PubMed1986

Functional characteristics of human macro-reentry: a study of "pre-excited" circuits by extrastimulus method.

The effect of improved conduction in areas of delay was tested during macro-reentry within the His-Purkinje system, in an attempt to separate the role of conduction delay from that of prematurity of the extrastimulus as the key determinant of reentry. Using the right ventricular extrastimulus technique (S1S2 method), both the critical His-Purkinje system delays and the zone of S1S2 intervals causing His-Purkinje system reentry were determined. Then, using a previously described technique of atrioventricular (AV) sequential pacing during the basic drive, the potential site of His-Purkinje system conduction delay was (anterogradely) excited earlier (pre-excitation), as compared with the control S1S2 method. This produced a decrease in retrograde His-Purkinje system delay (S2H2), as compared with the same S1S2 interval during the control method. Changing the degree of pre-excitation at each S1S2 interval allowed for determination of the critical (or shortest) S2H2 delay necessary for His-Purkinje system reentry at each coupling interval. Of importance was the observation that the critical delay was not specific for each case but varied with the prematurity of S2. For example, the critical S2H2 delay required for reentry was actually less at shorter S1S2 intervals as compared with longer S1S2 intervals (from 206 +/- 25 to 187 +/- 20 ms, p less than 0.01). These data suggest that manifestation of reentry is a complex interplay between degree of prematurity and conduction delay. The so-called critical conduction delay can be readily modified by altering the site of block, which in turn may be dependent on prematurity of the extrastimulus.

Bundle of His↗
PubMed1986

An improved technic for processing aspiration biopsy for electron microscopy.

This article describes a technic for processing aspiration biopsy samples for electron microscopy. Red blood cells present in these samples were separated from the tissue fragments with the use of a nylon sieve. The tissue fragments were pelleted and processed for electron microscopy in a routine manner. An analysis of 19 cases processed in this manner revealed that this separation technic is highly effective and results in a significant improvement in cellular yield.

Biopsy, Needle↗
PubMed1986

Evaluation of radioimmunoassay performance for staphylococcal enterotoxin in foods: application of external quality assessment survey.

An external quality assessment survey for staphylococcal enterotoxin A, B, and C2 determinations was performed in the collaborative study. Three analysts in two laboratories took part. Three types of food, cheese, salami, and pasta, were artificially contaminated with either one toxin only or all three toxins. A total of 378 analyses were performed. The group mean of the analytical values corresponded fairly well to the given enterotoxin concentrations. However, a considerable interlaboratory imprecision was found despite analyses being performed with the same reagents and methodology.

Cheese↗
PubMed1986

Effect of sudden rate acceleration on the human His-Purkinje system: adaptation of refractoriness in a dampened oscillatory pattern.

Although the refractoriness of the human His-Purkinje system (HPS) during constant-cycle length pacing appears to be closely related to the cycle length of the stimulation, the mode of adaptation of this refractoriness with sudden rate acceleration is not well understood. A systematic evaluation of this adaptation was performed in 14 patients with normal QRS durations and HV intervals referred for electrophysiologic evaluation. The relative refractory period of the HPS (HPS-RRP) was evaluated by the extrastimulus (S2) method during a constant ventricular drive (S1) having a cycle length as close to sinus rhythm as possible. An accelerated train of 6 ventricular beats (S1') was then added to the constant drive and the HPS-RRP of each successive beat of this train was similarly determined. Mean S1 cycle length was 750 +/- 164 msec (range 600 to 1000). Mean S1' cycle length was 475 +/- 55 msec (range 400 to 600). The HPS-RRP of each successive beat of the accelerated train was significantly shorter than that during the S1 drive and behaved in a dampened oscillatory fashion alternating from a lower value on the odd-numbered beats to a higher value on the even-numbered beats. In contrast, the effective and relative refractory periods of the ventricular myocardium during the accelerated train behaved in a cumulative manner, decreasing progressively with the first 2 beats of the train before reaching a plateau value. In conclusion, the data reported here present a new and intriguing picture of the mode of adaptation of the HPS refractoriness to sudden rate acceleration. At least in the range of the cycle lengths used in this study, the refractoriness of the HPS behaves in a dampened oscillatory manner that is radically different from the behavior of the ventricular myocardial refractoriness.

Adaptation, Physiological↗
PubMed1986

Normal electrophysiologic responses of the human heart.

A thorough understanding of physiologic behavior of the human conduction system is essential to define the abnormalities. This article deals with normal responses of the cardiac conduction system to both antegrade and retrograde direction. Responses to electrical as well as mechanical stimulation are discussed.

Electrophysiology↗
PubMed1985

Aspiration cytology of Ewing's sarcoma. Light and electron microscopic correlations.

Fine-needle aspiration biopsy specimens from 15 histologically proven cases of Ewing's sarcoma of the bone were studied by both light and electron microscopy. Large glycogen deposits in the Ewing's sarcoma cells could be easily recognized in smears stained routinely with Diff-Quik (American Scientific Product, McGraw Park, IL). These deposits appeared as punched-out clear spaces in the cytoplasm. Ultrastructurally the tumor cells could be divided into chief cells and dark cells. The chief cells were further categorized based on their nuclear morphologic features into cleaved, noncleaved, and intermediate cells. The dominant cell was noncleaved in eight, cleaved in three, and intermediate in four cases. All five tumors with abundant glycogen were composed predominantly of noncleaved cells. The tumor cells in aspiration material appeared to be irregular in shape, and some had cytoplasmic processes. In one tumor these processes were quite prominent; this caused some difficulty in differentiation from neuroblastoma.

Adolescent↗
PubMed1985

The mechanism of the C-13(3) esterification step in the biosynthesis of bacteriochlorophyll a.

5-Aminolaevulinate labelled with 18O at its C-1 carboxy oxygen atoms was prepared and incorporated into bacteriochlorophyll aphytyl of Rhodopseudomonas sphaeroides and bacteriochlorophyll ageranylgeranyl of Rhodospirillum rubrum. The biosynthetic samples of the bacteriochlorophylls were separately processed to obtain their isoprenyl alcohol components from the C-17(3) ester linkages and methanol from the C-13(3) methoxycarbonyl group. Methods were developed for the quantification of the isotopic composition of the various alcohols (methanol, phytol, geranylgeraniol). It was shown that the hydroxyl oxygen atoms of all the three alcohols originated from one of the C-1 oxygen atoms of the precursor 5-aminolaevulinate. In the light of these results the in vivo mechanism for the O-methylation reaction at C-13(3) during the biosynthesis of the two species of bacteriochlorophylls is discussed.

Aminolevulinic Acid↗
PubMed1985

Fine-needle aspiration biopsy diagnosis of round cell malignant tumors of childhood. A combined light and electron microscopic approach.

A series of fine-needle aspiration biopsies (FNAB) from 76 children with round cell malignant tumors was studied by both light and electron microscopy. In 14 cases the material submitted for electron microscopy was inadequate, whereas in the remaining 62 biopsies a definitive diagnosis could be made. These included 29 malignant lymphomas, 8 neuroblastomas, 12 Ewing's sarcomas, 3 metastatic retinoblastomas, 3 Wilms' tumors, 3 rhabdomyosarcomas, and 4 unclassified tumors. The results from this study indicate that FNAB studied by light and electron microscopy can be effective in diagnosing small cell tumors in children.

Biopsy, Needle↗
PubMed1985

Value of preexisting bundle branch block in the electrocardiographic differentiation of supraventricular from ventricular origin of wide QRS tachycardia.

The relation between the morphologic configuration of QRS complexes during wide QRS tachycardia induced during electrophysiologic studies and sinus rhythm was examined in 18 patients who had preexisting left or right bundle branch block. Representative QRS complexes during sinus rhythm and during tachycardia were isolated from each patient and juxtaposed for comparison. The QRS complexes that constituted each pair were judged by 4 observers as being identical, different or, if the decision was equivocal, similar. Nine patients had supraventricular tachycardia (SVT). In 8 of the 9 patients, all 4 observers found the QRS complexes during sinus rhythm and SVT identical in morphologic configuration. In the other patient, 2 observers found the QRS complexes identical and 2 found them similar. In 12 patients ventricular tachycardia (VT) was induced. In 11 of these 12, all 4 observers found the QRS complexes during VT different from their respective sinus beats. In the other patient, 3 observers found the QRS complexes different, whereas the fourth found them similar. During SVT, the QRS duration was unchanged from the corresponding value during sinus rhythm, whereas in patients with VT, QRS width increased by a mean of 56 +/- 20 ms (p less than 0.001). The results of our study suggest that the electrocardiographic differentiation of wide QRS tachycardia in patients with preexisting bundle branch block can be accomplished easily and accurately by comparing the QRS complexes during tachycardia with those during sinus rhythm: If the complexes are identical, the tachycardia is supraventricular, but if they are different, the arrhythmia is ventricular in origin.

Atrioventricular Node↗
PubMed1985

Primary cranial and intracranial chondrosarcoma. A survey.

Fifty cases of intracranial and cranial chondrosarcoma were reviewed in the world literature including two of our own. These were analyzed relevant to their histological subgroup, site of origin, age and sex incidence, calcification and vascularity, recurrence, and metastases. The analysis was done in order to clarify points in the diagnosis, management, and prognosis of this rare tumour. The mesenchymal subtype is a more malignant form with a higher tendency for recurrence, metastasis, and increased vascularity.

Adult↗