N. Sherif - Academia.edu (original) (raw)

Papers by N. Sherif

Journal of Helminthology, 2003

Populations of Egyptian spiny mice (Acomys cahirinus dimidiatus) in a fragmented montane wadi sys... more Populations of Egyptian spiny mice (Acomys cahirinus dimidiatus) in a fragmented montane wadi system in the Sinai showed significant differences in the abundance of gut helminths. Differences in parasite load between populations were positively associated with measures of androgen activity but showed no significant relationship with glucocorticoid activity. Social discrimination tests with adult males from different wadis showed that those from sites with greater helminth abundance were less likely to investigate odours from other males and were less aggressive when subsequently interacting with the odour donors. Subjects showed markedly more investigation towards the odours of males from distant wadis compared with those from their own or immediately neighbouring wadi, but were less aggressive when confronted with odour donors from distant wadis. Despite this, there was a positive relationship between the amount of investigation towards distant male odour and subsequent aggression ...

Parasitology, 2004

Circulation research, 1997

We have previously shown that alpha1-adrenergic activation inhibited beta-adrenergic-stimulated L... more We have previously shown that alpha1-adrenergic activation inhibited beta-adrenergic-stimulated L-type Ca2+ current (I(Ca)). To determine the role of protein kinase C (PKC) in this regulation, the inositol trisphosphate pathway was bypassed by direct activation of PKC with 4beta-phorbol 12-myristate 13-acetate (PMA). To minimize Ca2+-induced Ca2+ inactivation, Ba2+ current (I(Ba)) was recorded through Ca2+ channels in adult rat ventricular myocytes. We found that PMA (0.1 micromol/L) consistently inhibited basal I(Ba) by 40.5+/-7.4% and isoproterenol (ISO, 0.1 micromol/L)-stimulated I(Ba) by 48.9+/-7.8%. These inhibitory effects were not observed with the inactive phorbol ester analogue alpha-phorbol 12,13-didecanoate (0.1 micromol/L). To identify the PKC isozymes that mediate these PMA effects, we intracellularly applied peptide inhibitors of a subclass of PKC isozymes, the C2-containing cPKCs. These peptides (betaC2-2 and betaC2-4) specifically inhibit the translocation and functi...

Comparative Biochemistry and Physiology Part A: Physiology, 1992

l. Bufo calamifa were exposed to tap water to solutions of urea (up to IOOOmM) and NaCl (up to 25... more l. Bufo calamifa were exposed to tap water to solutions of urea (up to IOOOmM) and NaCl (up to 250 mM).

Parasitology, 1999

We compared helminth communities in spiny mice (Acomys dimidiatus) from 4 wadis in the arid monta... more We compared helminth communities in spiny mice (Acomys dimidiatus) from 4 wadis in the arid montane region of the southern Sinai in Egypt, in a 4-week period in late summer. Total helminth species richness was 14 (8 nematodes, 5 cestodes and 1 acanthocephalan) with 94 % of mice carrying at least 1 species and an overall mean species richness of 1 . 85. The most prevalent parasites were Protospirura muricola (47 . 8%) and Dentostomella kuntzi (46 . 3%). One larval cestode, Joyeuxiella rossicum, represents a new host record. The helminth community was dominated by intestinal nematodes (88 . 7%) of which 58 . 2% were arthropod-transmitted heteroxenic species. At the component community level, 70 % of the worms were recovered from mice in just two wadis (Gharaba and Tlah) and 48 . 6 % of intestinal nematodes were from Wadi Gharaba. Although only 7 species of helminths were recorded from Wadi Gharaba, this site gave the highest Berger-Parker dominance index because of P. muricola. P. muricola was also dominant in Wadi El Arbaein whilst Syphacia minuta was the dominant species in Wadis Gebal and Tlah. At the infracommunity level, mean species richness and Brillouin's index of diversity were highest in Wadi Tlah and lowest in Wadi Gebal, and the former was age dependent. Whilst mice from different wadis differed in the nematodes that were most common, those from Wadi Gharaba carried the highest mean number of worms/mouse. The abundance of P. muricola in particular varied markedly between sites : Wadi Gharaba was distinct as the site showing the highest mean worm burden whereas mice from Wadi Gebal were uninfected. None of the directly transmitted oxyuroid nematodes showed significant variation in abundance between wadis, or host sex or age classes. Overall, the single extrinsic factor in the study, site of capture, was more important than the intrinsic factors in explaining variation in helminth communities in the region. We conclude that in the high mountains of southern Sinai, each wadi is distinct in terms of its rodent parasites, and hence we expect spatially different coevolutionary pressures on their hosts, with resultant variation in life-histories.

Pacing and Clinical Electrophysiology, 1980

A clinical evaluation of an improved Holter monitoring technique for artificial pacemaker functio... more A clinical evaluation of an improved Holter monitoring technique for artificial pacemaker function. This paper discusses shortcomings of conventional Holter monitoring in paced patients and describes a new technique which permits reliable detection of intermittent pacemaiier ma/function and counts pacemaker activity during the recording period. Evaluation of the system on 64 consecutive patients revealed i5 v^ith unsuspected episodic pacemaker dysfunction.

Pacing and Clinical Electrophysiology, 1994

CONTI, J.B., ET AL.; Catheter Entrapment in the Mitral Valve Apparatus During Radiofrequency Abla... more CONTI, J.B., ET AL.; Catheter Entrapment in the Mitral Valve Apparatus During Radiofrequency Ablation.

Journal of Zoology, 2006

Haemoparasite infections and infestations with potential arthropod vectors were assessed in spiny... more Haemoparasite infections and infestations with potential arthropod vectors were assessed in spiny mice Acomys dimidiatus from four wadis in the arid montane region of the southern Sinai in Egypt in late summer 2000. Five taxa of haemoparasites (Haemobartonella spp. 80%, Hepatozoon sp. 20.6%, Trypanosoma acomys 17.5%, Bartonella spp. 2.5% and Babesia sp. 1.9%) were recorded. Additionally, infections with two intestinal protozoa, Cryptosporidium cf. parvum and Giardia sp., were quantified, both with similar prevalence (17.0 and 17.6%, respectively). 17.9% of mice carried fleas (Parapulex chephrensis and Xenopsylla dipodilli) and 32.1% had lice (Polyplax oxyrrhyncha and Polyplax brachyrrhycha combined). Marked differences in the prevalence and abundance of infections were detected between the four wadis, particularly with respect to T. acomys, Hepatozoon sp. and fleas, which were largely aggregated in just two of the four sites (Wadis Gharaba and Tlah). In contrast, the intestinal protozoa were more common, and abundance was higher, in Wadi El Arbaein. Intrinsic factors also contributed to a variation in prevalence, with strong age-dependent increases in the prevalence and abundance of Hepatozoon sp., higher mean species richness, prevalence of Cr. cf. parvum, and abundance of Giardia sp. and Hepatozoon sp. in female mice. Haemobartonella spp. showed an age-dependent reduction in abundance and higher abundance among male mice. A weak association was found between the prevalence of T. acomys and its putative flea vector. The single extrinsic factor in the study, site of capture, was more important than the intrinsic factors in explaining variation in the prevalence and abundance of haemoparasites, intestinal protozoa and arthropod vectors. In the high mountains of southern Sinai, the parasite fauna of spiny mice is distinct in each wadi, and hence we expect the parasites to exert spatially different co-evolutionary pressures on their hosts, with a resultant variation in host life histories.

Journal of Vision, 2004

Abstract We used an event-related fMRI adaptation paradigm to investigate changes in BOLD activit... more Abstract We used an event-related fMRI adaptation paradigm to investigate changes in BOLD activity in the dorsal and ventral visual streams as a function of object identity and object orientation. On the basis of earlier work (James et al), we expected that areas in the ...

Journal of the American College of Cardiology, 1989

Journal of the American College of Cardiology, 1991

rcu.+", New Yor.4 06jutiws. This smty bwestignted pmdierion of orrhythmic e"wd.s by the sig"st-av... more rcu.+", New Yor.4 06jutiws. This smty bwestignted pmdierion of orrhythmic e"wd.s by the sig"st-avemgcd okctmrardiograln WG, and pmgralowd stimutatioo in patieos with nunisrhcmir d&ted cap dlomyopathy.

Journal of the American College of Cardiology, 1993

Journal of Electrocardiology, 2000

Journal of Electrocardiology, 1994

The predictive accuracy of time-domain (TD) late potential analysis of the signal-averaged electr... more The predictive accuracy of time-domain (TD) late potential analysis of the signal-averaged electrocardiogram in postmyocardial infarction (MI) is limited by the high incidence of false positives in inferior MI. However, frequency-domain spectral turbulence (ST) analysis suffers from a high incidence of false positives, especially in anterior MI. A prospective study was conducted of 262 patients with acute MI to investigate the hypothesis that combined TD and ST analyses of the signal-averaged electrocardiogram could improve its predictive accuracy for serious arrhythmic events in the post-MI period. Abnormal TD criteria were RMS40 less than 25/~V at 25 Hz plus RMS40 less than 16/~V at 40 Hz, and abnormal ST criteria were a turbulence score of 3 or 4. Seventeen patients had arrhythmic events during 10.5 ± 2.4 months of follow-up evaluation (13 sudden cardiac death judged to be due to arrhythmia and 4 nonfatal sustained ventricular tachycardia). The total predictive accuracy of combined TD and ST (92%) was higher than TD (87%), whereas ST had the lowest total predictive accuracy of 78 %. The negative predictive accuracy of all three analyses was high (96-97%). However, the positive predictive accuracy of TD (28%) was higher than ST (14%). Combined TD and ST significantly improved the positive predictive accuracy of the test to 35% in the total group and to 40% in patients with first anterior or inferior MI. The best results were obtained in patients with first anterior MI, where the positive predictive accuracy of combined analysis was 50%. Key words: acute myocardial infarction, sudden cardiac death, sustained ventricular tachycardia.

Journal of Cardiovascular Electrophysiology, 2001

Poly(pleo)morphic ventricular tachycardia (PVT) is a VT with continuously varying QRS morphology ... more Poly(pleo)morphic ventricular tachycardia (PVT) is a VT with continuously varying QRS morphology in any recorded ECG lead. Sometimes, simultaneous recording of more than one ECG lead is necessary to detect the changes in beat-to-beat QRS morphology. Compared with sustained monomorphic VT, PVT usually is viewed as having a more ominous prognosis. Although many prolonged episodes of fast PVT ($200 beats/min) are associated with hemodynamic collapse and usually degenerate into ventricularbrillation, a majority of episodes of PVT terminate spontaneously. 1 Torsades de pointes (TdP) is an ear-pleasing term that describes an eye-catching form of PVT. The term was rst coined by Dessertennes, 2 who described its ECG pattern of continuously changing morphology of the QRS complexes that seem to twist around an imaginary baseline. The quasi-musical term and the intriguing ECG pattern have caught the attention of electrophysiologists for years and, to some extent, have been a driving force behind the recent focused interest in the role of genetics and ion channelopathy in cardiac arrhythmias in general. More importantly, it is helping to refocus attention on the role of dispersion of ventricular repolarization in the genesis of malignant ventricular tachyarrhythmias. PVT can be seen in the presence or absence of organic heart disease. One way to classify PVT is whether it is associated with normal or prolonged QT (or QTU) segment. It has been suggested that the term TdP should be reserved for use with the long QT syndrome (LQTS). However, a minority of PVTs in patients with LQTS have a characteristic TdP con guration, and this classic con guration can be seen without a prolonged QT interval or even structural heart disease, for example, in the Brugada syndrome. There is more than one electrophysiologic mechanism for PVT, and understanding these mechanisms can be of valuable help in the proper management of individual patients. PVT can be caused by multifocal discharge, reentrant excitation, or a combination thereof. In electrophysiologic parlance, ectopic discharge can be due to normal or abnormal automaticity and early afterdepolarizations (EADs) or delayed afterdepolarizations (DADs). In a clinical report more than a quarter of a century ago, 4 a number of patients with advanced cardiac disease were described to have polymorphic rhythms and/or PVT that were explained on the basis of concurrent multifocal (parasystolic) discharge using what was fashionable at the time, i.e., deductive analysis of the ECG. The majority of those patients died of terminal heart failure; none died suddenly. Therefore, it was concluded that this type of PVT (usually , 120 beats/min) has a rather benign electrophysiologic consequence. It is possible nowadays to suggest that these rhythms are due to multifocal DAD-triggered activity, probably secondary to increased intracellular calcium of cardiac cells in the failing heart. This is essentially the same mechanism for spontaneous PVT seen in the rst 48 hours after infarction in both the experimental model and in man. On the other hand, the majority of "fast" PVT is due to reentrant excitation. To be more exact, in PVTs seen in ischemic heart disease, both the initiating and subsequent beats can all be based on reentrant excitation. The same is true for all PVTs induced by programmed electrical stimulation in the electrophysiology laboratory. 1 On the other hand, in PVT in LQTS, the initiating one or two beats are EAD-triggered beats that arise predominantly from the Purkinje network and infringe on an underlying substrate of spatial nonhomogeneous repolarization to initiate continuously varying tridimensional circulating wavefronts (scrolls). In this issue of the Journal, Dr. Andrew Wit' s group revisited the electrophysiologic mechanism of PVT that resembles TdP in the canine experimental model of myocardial infarction. 7 In an elegant study, they showed that the predominant mechanism for the change in QRS morphology was a shift in the exit point of the circulating wavefront (initially con ned to the epicardial surviving layer in this model) to activate the ventricles. Such shifts resulted from small changes in conduction velocity of the reentrant circuit, either speeding or slowing, that modi ed the length of the lines (arcs) of functional conduction block. The study nicely con rms similar conclusions reported two decades earlier using the same experimental model (see reference 5, Figs. 8 and 9).

The Journal of Arthroplasty, 1998

To evaluate the safety of autologous reinfusion of drain blood in total knee arthroplasty (TKA), ... more To evaluate the safety of autologous reinfusion of drain blood in total knee arthroplasty (TKA), eight patients were prospectively evaluated to quantify levels of methyl methacrylate (MMA) monomer in systemic blood, and in their drain blood after unilateral cemented TKA. The systemic blood was analyzed before and after reinfusion of the drain blood. The drain blood was analyzed before reinfusion, and both before and after filtration through a 40-pm filter. A separate study was performed on 10 patients to assess the effect of blood, time, and filtration on MMA levels. Levels of MMA monomer in salvage blood were low enough to allow safe reinfusion. Systemic blood showed no evidence of MMA monomer either before reinfusion of salvage blood or at 5 minutes after reinfusion. Elimination of MMA is dependent on the time that MMA is exposed to blood and is independent of filtration.

Heart, 1976

Primary ventricularfibrillation was seen in 20 of 450 consecutive patients (4 4 %) admitted withi... more Primary ventricularfibrillation was seen in 20 of 450 consecutive patients (4 4 %) admitted within 24 hours after the onset ofacute myocardial infarction. Compared withpatients withoutprimary ventricularfibrillation, they showed a lower mean age group and a higher incidence of anterior infarction. Waorning ventricular arrhythmias preceded primary ventricular fibrillation in 58 per cent of cases. However, warning arrhythmias were also present in 55 per cent ofpatients without primary ventricularfibrillation. Thefollowing mechanisms of initiation of primary ventricular fibrillation were seen. 1) In one patient, it was initiated by supraventricular premature beats showing aberrant intraventricular conduction. 2) In 2 patients, ventricular tachycardia degenerated into primary ventricular fibrillation. 3) In 17 patients, it was initiated by a ventricular premature beat; in 10 of these, the premature beat showed early coupling (RR'/QT<1-the R-on-T phnomenon). However, ventrcular premature beats showing the R-on-T phenomenon were also observed in 49 per cent of patients without pmary ventilar fibrillation. In 7, primary ventricular fibrllation was initiated by a late-coupled ventricular premature beat (RR'/QT>1); in 2, the very late coupling resulted in a ventricular fusion beat. The study suggests that waring arrhythmias and the R-on-T phenomenon are poor predictors ofprimary ventricularfibrillation in acute myocardial infarction. The observation that 41 per cent ofprimary ventricularfibrillation was initiated by a late-coupled ventricular premature beat suggests that ventricular vulnerability during acute myocardial infarction may extend throughout most of the cardiac cycle and is not necessarily confined to the QT interval. acute myocardial infarction admitted to the coronary

Critical Care Medicine, 1984

Asynchronized direct-current (DC) shock was delivered inadvertently to a 67-year-old man with ven... more Asynchronized direct-current (DC) shock was delivered inadvertently to a 67-year-old man with ventricular tachycardia. The electrical shock, which fell on the T-wave of the ECG, accelerated the tachycardia. A synchronized DC shock then converted the accelerated tachycardia to sinus rhythm. This case emphasizes the importance of synchronizing the electrical energy delivered during ventricular tachycardia.

Circulation Research, 1996

We have previously developed a canine in vivo model of the long QT syndrome (LQTS) using the neur... more We have previously developed a canine in vivo model of the long QT syndrome (LQTS) using the neurotoxin anthopleurin A (AP-A), which acts by slowing sodium channel inactivation. The recent discovery of a genetic mutation in the cardiac sodium channel in some patients with the congenital LQTS, resulting in abnormal gating behavior similar to sodium channels exposed to AP-A, provides a strong endorsement of this animal model as a valid surrogate to the clinical syndrome of LQTS. In the present study, we conducted high-resolution tridimensional isochronal mapping of both activation and repolarization patterns in puppies exposed to AP-A that developed LQTS and polymorphic ventricular tachyarrhythmias (VTs). To map repolarization, we measured activation-recovery intervals (ARIs) using multiple unipolar extracellular electrograms. We demonstrated, for the first time in vivo, the existence of spatial dispersion of repolarization in the ventricular wall and differences in regional recovery in response to cycle-length changes that were markedly exaggerated after AP-A administration. Analysis of tridimensional activation patterns showed that the initial beat of polymorphic VT consistently arose as focal activity from a subendocardial site, whereas subsequent beats were due to successive subendocardial focal activity, reentrant excitation, or a combination of both mechanisms. Reentrant excitation was due to infringement of a focal activity on the spatial dispersion of repolarization, resulting in functional conduction block and circulating wave fronts. The polymorphic QRS configuration of VT in the LQTS was due to either changing the site of origin of focal activity, resulting in varying activation patterns, or varying orientations of circulating wave fronts.

Circulation Research, 1998

Tachycardia-dependent QT/T alternans occurs in patients with the congenital or idiopathic form of... more Tachycardia-dependent QT/T alternans occurs in patients with the congenital or idiopathic form of long-QT syndrome (LQTS) and may presage the onset of polymorphic ventricular tachyarrhythmias. To examine the electrophysiological basis of arrhythmogenicity of QT/T alternans in LQTS, the tridimensional repolarization pattern of QT/T alternans was studied in the anthopleurin-A model of LQTS, a surrogate for LQT3. In 11 anesthetized mongrel puppies, tridimensional repolarization and activation patterns were analyzed from 256 to 384 unipolar electrograms. Cardiac repolarization was evaluated as the activation-recovery interval (ARI) of local electrograms. To induce QT/T alternans, the pacing cycle length (CL) was abruptly shortened in steps of 50 ms from a basic drive of 1000 ms. ARIs were calculated at epicardial (Epi), midmyocardial (Mid), and endocardial (End) sites. ARI restitution at each site was assessed by using a single premature stimulation delivered after the basic drive. ARI alternans occurred at longer CLs at Mid sites compared with End and Epi sites, and the magnitude of alternans at Mid sites was greater. Two factors contributed to the modulation of ARI during QT/T alternans: (1) differences in restitution kinetics at Mid sites, characterized by larger ⌬ARI and a slower time constant (), and (2) differences in diastolic intervals resulting in different input to restitution at the same constant CL. These 2 factors could explain not only the onset of alternans at Mid sites at longer CLs but also the critical observation that ARI dispersion between Epi and Mid sites during alternans was greater than during the slower basic CL. Marked ARI alternans could be present in local electrograms without manifest alternation of the QT/T segment in the surface ECG. The latter was seen at critically short CLs associated with reversal of the gradient of ARI between Epi and Mid sites, with a consequent reversal of polarity of the intramyocardial QT wave in alternate cycles. The arrhythmogenicity of QT/T alternans was primarily due to the greater degree of spatial dispersion of repolarization during alternans than during slower rates not associated with alternans. This could result in functional conduction block and reentrant ventricular tachyarrhythmias during the fixed drive associated with alternans. (Circ Res. 1998;83:614-628.)