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Biomedical subjects

M Akhtar

Publications and source records attributed to M Akhtar.

At least 199 records · Page 11Linked to original sources
PubMed1993

Ventricular fibrillation in patients without significant structural heart disease: a multicenter experience with implantable cardioverter-defibrillator therapy.

OBJECTIVES: This study was undertaken to characterize the outcome of survivors of ventricular fibrillation with no or minimal structural heart disease who received an implantable cardioverter-defibrillator. BACKGROUND: The prognosis among survivors of ventricular fibrillation with minimal or no structural cardiac abnormalities remains unclear. Since the advent of implantable cardioverter-defibrillators, this question takes on added importance. METHODS: This 10-center retrospective study provided information on 28 survivors of ventricular fibrillation (mean age 42 years) with minimal or no structural abnormalities who were treated with an implantable cardioverter-defibrillator. RESULTS: Ventricular tachyarrhythmias (polymorphic in all but one patient) were induced during baseline programmed stimulation in 39% of patients. During a median 30.6-month follow-up period after implantable cardioverter-defibrillator implantation, there were no cardiac deaths and two noncardiac deaths. Sixteen patients experienced 36 shock episodes (total 88 shocks). The majority of shocks were classified as "indeterminate"; one patient received 47 "spurious" shocks during one shock episode and each of four patients received one "appropriate" shock. Ventricular arrhythmias were not inducible in any of these latter four patients. CONCLUSIONS: Survivors of ventricular fibrillation with minimal or no structural cardiac abnormalities receiving an implantable cardioverter-defibrillator have an excellent 3-year survival rate. The occurrence, albeit infrequent, of appropriate implantable cardioverter-defibrillator shocks in this group suggests that these patients have a potential risk of recurrent cardiac arrest whose fatal outcome may be avoided by implantable cardioverter-defibrillator therapy.

Actuarial Analysis↗
PubMed1993

Mechanistic studies on aromatase and related C-C bond cleaving P-450 enzymes.

Some P-450 systems, notably aromatase and 14 alpha-demethylase catalyse not only the hydroxylate reaction but also the oxidation of an alcohol into a carbonyl compound as well as a C-C bond cleavage process. All these reactions occur at the same active site. A somewhat analogous situation is noted with 17 alpha-hydroxylase-17,20-lyase that participates in hydroxylation as well as C-C bond cleavage process. The C-C bond cleavage reactions catalysed by the above enzymes conform to the general equation: [formula: see text] It is argued that all three types of reaction catalyzed by these enzymes may be viewed as variations on a common theme. In P-450 dependent hydroxylation the initially formed FeIII-O-O. species is converted into FeIII-O-OH and the heterolysis of the oxygen-oxygen bond of the latter then gives the oxo-derivative for which a number of canonical structures are possible; for example FeV = O<==>(+.)FeIV = O<==>FeIV-O.. One of these, FeIV-O. behaves like an alkoxyl radical and participates in hydrogen abstraction from C-H bond to produce FeIV-OH and carbon radical. The latter is then quenched by the delivery of hydroxyl radical from FeIV-OH. The latter species may thus be regarded as a carrier of hydroxyl radical. We have proposed that the C-C bond cleavage reaction occurs through the participation of the FeIII-O-OH species that is trapped by the electrophilic property of the carbonyl compound giving a peroxide adduct that fragments to produce an acyl-carbon cleavage. Scientific developments leading up to this conclusion are considered. In the first author's views, "The study of mechanisms is not a scientific but a cultural activity. Mechanisms do not aim at an absolute truth but are intended to be a "running" commentary on the status of knowledge in a field. As the structural knowledge in a field advances Mechanisms evolve to take note of the new findings. Just as a constructive "running" commentary provides the stimulus for higher standards of performance, so Mechanisms call for better and firmer structural information from their practitioners".

Animals↗
PubMed1993

Cardioversion, defibrillation, and overdrive pacing of ventricular arrhythmias: the effect of moricizine in dogs with sustained monomorphic ventricular tachycardia.

The purpose of this investigation is to define whether the antiarrhythmic drug moricizine has beneficial or adverse effects on currently used antitachycardia and antifibrillatory devices. These studies were performed in a dog model of sustained monomorphic ventricular tachycardia (VT). In 11 dogs, the left anterior descending artery and all surrounding epicardial collateral feeder vessels were ligated. Defibrillator patches were implanted and the dogs were allowed to recover. After a 7-day recovery period, effective refractory period (ERP), end diastolic threshold (EDT), VT induction, and VT and ventricular fibrillation (VF) termination data were collected before and after moricizine infusion (2 mg/kg). In this experimental model, moricizine caused the following electrophysiological changes: a prolongation of the ERP from 173 +/- 14 to 182 +/- 15 (P < 0.02) with no significant effect on the EDT for pacing; a prolongation of the VT cycle length from 175 +/- 18 to 201 +/- 23 msec (P < 0.003); an increased cycle length required for overdrive pacing from 136 +/- 20 to 157 +/- 22 msec (P < 0.01); no effect on the energy required to cardiovert VT; an increase in the defibrillation threshold from 7.5 +/- 4 to 9.4 +/- 4 joules (P < 0.006) and; in 5 of the 8 dogs with VT, the VT could be initiated with somewhat less aggressive stimulation. Significant beneficial electrophysiological physiological effects were noted on the VT cycle length, including a proportionately prolonged overdrive pacing cycle length for VT termination.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

Implantable cardioverter defibrillator for prevention of sudden cardiac death in patients with ventricular tachycardia and ventricular fibrillation: ICD therapy in sudden cardiac death.

Among the various therapy options for survivors of ventricular tachycardia-ventricular fibrillation (VT-VF), the implantable cardioverter defibrillator (ICD) seems most promising. It reliably terminates VT-VF and thus significantly impacts sudden cardiac death (SCD) survival. It is more effective than any of the known antiarrhythmic drugs in prevention of SCD, particularly among survivors of cardiac arrest. Compared to VT surgery, the ICD therapy can be offered to a larger pool of patients and can be placed at a lower surgical risk. With proper patient selection, ICD therapy is of major benefits to its recipients since it markedly reduces the chances of VT-VF related mortality; the main cause of premature death in this population. The ICD therapy is cost effective when compared to other medical interventions and could be more so if the implant is carried out early in the course of VT-VF management.

Death, Sudden, Cardiac↗
PubMed1993

Electrophysiological behavior of atrioventricular node after selective fast or slow pathway ablation in patients with atrioventricular nodal reentrant tachycardia.

One hundred twenty consecutive patients with symptomatic atrioventricular nodal reentrant tachycardia (AVNRT) underwent catheter ablation using radiofrequency energy. Fast pathway ablation was attempted in the first 16 consecutive patients by application of radiofrequency current in the anterior and superior aspect of the tricuspid annulus. Successful results were accomplished in 13 patients, complete atrioventricular (AV) block occurred in three. One hundred four patients underwent ablation of the slow pathway in the posterior and inferior aspect of the tricuspid annulus, which was successful in 98 patients. The remaining six patients subsequently underwent a fast pathway ablation with successful results in four and AV block in two. Therefore, 102 (98%) of the last 104 patients became free of AVNRT while maintaining intact AV conduction. This study characterizes the electrophysiological properties of the residual AV node following a selective fast or slow pathway ablation.

Atrioventricular Node↗
PubMed1993

Electrophysiologic spectrum of atrioventricular nodal behavior in patients with atrioventricular nodal reentrant tachycardia undergoing selective fast or slow pathway ablation.

INTRODUCTION: The objective of this report is to delineate the atrioventricular (AV) nodal electrophysiologic behavior in patients undergoing fast or slow pathway ablation for control of their AV nodal reentrant tachycardia (AVNRT). METHODS AND RESULTS: One hundred sixteen consecutive patients with symptomatic AVNRT were included. Twenty-two patients underwent fast pathway ablation with complete abolition of AVNRT in all and development of complete AV block in five patients. Of 17 patients with intact AV conduction postablation, 12 had demonstrated antegrade dual pathway physiology during baseline study, which was maintained in three and lost in nine patients postablation. Two patients with successful fast pathway ablation developed uncommon AVNRT necessitating a slow pathway ablation. Twenty-one patients demonstrated both common and uncommon forms of AV nodal reentry during baseline study. The earliest site of atrial activation was close to the His-bundle recording site (anterior interatrial septum) during common variety and the coronary sinus ostium (posterior interatrial septum) during the uncommon AV nodal reentry in all 21 patients. Ninety-six patients underwent successful slow pathway ablation. Among these, the antegrade dual pathway physiology demonstrable during baseline study (60 patients) was maintained in 25 and lost in 35 patients postablation. CONCLUSION: These data suggest that: (1) dual pathway physiology may persist after successful ablation, which might be a reflection of multiple reentrant pathways in patients with AVNRT; and (2) the retrograde pathways during common and uncommon AVNRT have anatomically separate atrial breakthroughs. These findings have important electrophysiologic implications regarding the prevailing concept of the AV nodal physiology in patients with AVNRT.

Adolescent↗
PubMed1993

Bundle branch reentrant ventricular tachycardia: cumulative experience in 48 patients.

INTRODUCTION: The clinical, electrophysiologic features and follow-up of 48 patients with inducible bundle branch reentrant (BBR) tachycardia are presented. METHODS AND RESULTS: Forty-eight patients were identified in whom a diagnosis of BBR tachycardia was made during electrophysiologic evaluation. The clinical presentation was syncope or sudden death in 38 patients, and sustained palpitations during wide QRS complex tachycardia in 5 patients. Electrophysiologic studies were performed in 5 additional patients for various other reasons. Structural heart disease was present in 45 patients. Idiopathic dilated cardiomyopathy and coronary artery disease were the anatomical substrates in 19 (39%) and 24 (50%) patients, respectively, severe aortic regurgitation was present in 2 patients, and no organic heart disease was identified in 3. All 48 patients had evidence of His-Purkinje system disease. BBR tachycardia with left and right bundle branch block morphologies was induced in 46 and 5 patients, respectively, and interfascicular BBR tachycardia was initiated in 2 patients. Ventricular tachycardia of a myocardial origin was induced in 11 patients. Management of BBR tachycardia included transcatheter bundle branch ablation in 28 patients, and antiarrhythmic drug therapy in 16 patients. Four patients were treated with implantable defibrillators. After a mean follow-up of 15.8 months in 42 patients, there were 13 deaths due to congestive heart failure, 4 sudden cardiac deaths, 3 nonsudden cardiac deaths, and 3 noncardiac related deaths. CONCLUSION: Sustained BBR, a form of monomorphic ventricular tachycardia, is a highly malignant arrhythmia usually seen in patients with structural heart disease. Three different types of BBR tachycardia are described. If distinguished from ventricular tachycardia of a myocardial origin, catheter ablation of the right bundle branch can be easily performed and effectively eliminates BBR. During follow-up, congestive heart failure is the most common cause of death in this population.

Adult↗
PubMed1993

Retrograde (transseptal) activation of right bundle branch during sinus rhythm.

A 40-year-old man undergoing electrophysiologic study for recurrent palpitations was found to have a right bundle branch block during sinus rhythm and right bundle potentials occurring after ventricular activation. The sequence of activation of the proximal and distal right bundle potentials was suggestive of a retrograde invasion of the right bundle during sinus rhythm. This transseptal activation of the right bundle via the left bundle exhibited decremental conduction characteristics during atrial as well as ventricular stimulation. Observations made in this case may provide some important information concerning the electrophysiologic behavior of transseptal impulses.

Adult↗
PubMed1993

Simple solutions to false-positive staphylococcal enterotoxin assays with seafood tested with an enzyme-linked immunosorbent assay kit (TECRA).

The TECRA kit, a commercial staphylococcal enterotoxin visual immunoassay kit, is an enzyme-linked immunosorbent assay system which utilizes polyvalent antisera against staphylococcal enterotoxin types A to E. The test is simple and rapid to perform (4 h) and has therefore been widely used for screening purposes. In this study, the TECRA kit produced a number of false-positive reactions with seafood; 25% of 218 samples of seven types of seafood gave false-positive results, particularly shellfish such as mussels (85%), clams (32%), oysters (23%), winkles (20%), and squid (13%). Some nonshellfish samples also gave false-positive results with the TECRA kit (smelt [20%] and trout [10%]). The substance contributing to the false-positive results differed from true staphylococcal enterotoxins in that it was: (i) heat labile, being completely inactivated by heating for 3 min at 70 degrees C, compared with 5% inactivation of true staphylococcal enterotoxins by the same heat treatment, (ii) in a selective reaction with normal rabbit or calf serum (nonspecific reactions were completely abolished by these sera, whereas staphylococcal enterotoxins were not affected), and (iii) incapable of binding to a copper-chelate Sepharose gel (all of the substance remained in the unbound wash fraction, whereas staphylococcal enterotoxins were quantitatively bound to the gel). The false-positive reactions occurring with seafood were not associated with substances produced by microorganisms, since the bacterial isolates from the samples did not give positive results with the TECRA kit.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

Atrioventricular nodal reentry. Clinical, electrophysiological, and therapeutic considerations.

BACKGROUND: Atrioventricular (AV) nodal reentry is a relatively common cause of regular, narrow QRS tachycardia. The underlying basis for this arrhythmia is functional (and anatomic) duality of pathways in the region of the AV node, although the exact boundaries of the reentrant circuit have not been convincingly defined. During the more common type of AV nodal reentry (seen in approximately 90% of cases), a slow conducting pathway is used in the anterograde direction, and a fast pathway is operative in the retrograde direction. In the uncommon form, the direction of impulse propagation within the reentrant circuit is reversed. In this article, the clinical, ECG, and electrophysiological features of AV nodal reentry as well as approaches to therapy are discussed. METHODS AND RESULTS: Clinical diagnosis may be made from the surface ECG. In the common type of AV nodal reentry, the P wave is obscured by the QRS or may be present in its terminal portion. The P wave in the uncommon form occurs late (i.e., in or after the T wave), producing a pattern of long RP and short PR. Both forms of AV nodal reentry are controllable with various therapeutic modalities. For acute termination, adenosine is probably the ideal agent. Prevention of recurrences can be achieved with several pharmacological agents, including beta-blockers, calcium channel blockers, and class Ia, Ic, and III antiarrhythmic agents. Curative therapy is now available with a variety of nonpharmacological methods. However, the most promising therapy at the present time is catheter modification of the AV node by ablation of either the fast or slow pathway, using radiofrequency energy. Ablation of the fast pathway carries a higher risk of second- or third-degree AV block. Slow pathway ablation, by providing a high rate of success and minimal risk of AV block, seems to be a more acceptable initial approach. CONCLUSIONS: AV nodal reentry is a common cause of paroxysmal supraventricular tachycardia, and a precise diagnosis can be made with intracardiac electrophysiological evaluation. Although the arrhythmia responds to a variety of antiarrhythmic agents, curative therapy can now be offered with catheter modification of the AV node using radiofrequency energy. At the time of this writing, it seems that catheter modification of the AV node is rapidly becoming the therapy of initial choice in patients with symptomatic AV nodal reentrant tachycardia requiring treatment.

Adult↗
PubMed1993

Gonadal dysgerminoma-seminoma associated with severe hypercalcemia.

A case is reported, of a 25-year-old phenotypic female, karyotypic male patient with metastatic gonadal dysgerminoma-seminoma and severe hypercalcemic paraneoplastic syndrome. Patient manifested normal female external genitalia, vagina, uterus, and fallopian tubes but with 46 XY karyotype. Adnexal gonads were calcified. External beam radiation therapy resolved the hypercalcemic state. Exploratory laparotomy after irradiation revealed gonadoblastoma originating from dysgenetic gonads.

Adult↗
PubMed1993

Polymyositis--a review and follow up study of 24 cases.

Twenty-four cases of polymyositis, 3 (12.5%) of them Dermatomyositis, have been treated and followed up for over 12 years. Majority (75%) were males. Inflammatory lesion was the cause in 18 (75%), collagen disease in 4 (16.7%) and malignancy in 2 (8.35%). Presenting features were fever (100%), proximal muscle weakness (95.8%) and tenderness (54.2%), facial and respiratory muscle weakness (4.2%). Raised CPK and transaminases, electromyogram abnormality and positive muscle biopsy were recorded in all. All were treated with steroids. Complication/associations noted were arthalgia (25%), dysphagia (20.6%), peripheral neuritis (8.35%), diabetes mellitus (4.2%), pulmonary fibrosis (4.2%) and malabsorption (4.2%). Fourteen cases (58%), all of inflammatory aetiology, recovered completely. Seven cases (29.2%) developed permanent atrophy of affected muscles. Cases with collagen disease and malignancy fared worse and deteriorated because of the primary disease.

Adult↗
PubMed1993

Control of supraventricular tachycardia with transcatheter ablative technique using radio frequency as the energy source.

Supraventricular tachycardia constitutes a significant clinical problem, frequently requiring medical intervention. We analyzed data in 413 consecutive patients with supraventricular tachycardia treated at our center with the catheter ablative technique and found the following outcome. Among 272 patients who had regular narrow QRS tachycardia without ventricular pre-excitation during sinus rhythm (Group I), control was achieved in all but one case (success rate 99.6%). Patients in Group II had ventricular pre-excitation during sinus rhythm and narrow or wide QRS tachycardia. Elimination of ventricular pre-excitation and control of the tachycardia was achieved in 104 of the 106 cases in this group (a success rate of 98%). Group III patients had atrial flutter-fibrillation as the predominate arrhythmia and control of rapid ventricular response was successfully achieved with atrioventricular junctional ablation in all 35 cases. Serious complications were related to anticoagulation and were seen in less than 2% of the cases. There were no instances of thromboembolic phenomena or death related to these procedures. It is concluded that the catheter ablative technique with radio frequency as the energy source is a highly effective means for control of supraventricular tachycardia with minimal associated risk of serious complications.

Adult↗
PubMed1993

Complications in 1000 consecutive treadmill tests.

Complication in 1000 consecutive Tread Mill Tests (TMT) done at the Cardiology Centre of Command Hospital (SC) Pune are reported. The tests were done following Bruce Protocol and analysed based on Selzer's criteria. Complications were noted in 18 cases (1.8%) which included ventricular fibrillation, ventricular tachycardia, atrial fibrillation, malignant VPBs, conduction disturbances, asystole following hyperventilation (HV), complete SA block following HV, atrial flutter following HV, hypotension and severe angina requiring ICCU care. No acute myocardial infarctions or deaths were noted. Coronary arteriography (CART) was done in 50 (5.0%) selected cases including 10 with complications. It is concluded that TMT is a safe procedure if carried out after proper patient selection and under supervision of an experienced and efficient team.

Adolescent↗
PubMed1993

Atrioventricular nodal reentrant tachycardia. Electrophysiologic characteristics, therapeutic interventions, and specific reference to anatomic boundary of the reentrant circuit.

Over the past several decades there has been enormous progress in the understanding of many electrophysiologic characteristics of the AVNRT circuit. Although a great number of questions have been resolved, several pertinent issues require further investigation. Medical treatment remains the most widely used therapeutic intervention for acute or short-term management of patients with recurrent AVNRT. However, nonpharmacologic approaches, particularly transcatheter modification of the AV node, have increasingly become popular for long-term management. Radiofrequency energy has been safe and effective for transcatheter ablative techniques. It seems highly likely that in the next several years, selective transcatheter ablation of the AV nodal (slow or fast) pathway, by providing permanent cure, will become the modality of choice in symptomatic patients with AVNRT.

Diagnosis, Differential↗