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Biomedical subjects

T Peter

Publications and source records attributed to T Peter.

At least 19 recordsLinked to original sources
PubMed1992

Responses of the ticks Amblyomma hebraeum and A. variegatum to known or potential components of the aggregation-attachment pheromone. III. Aggregation.

Ten known or potential components of the aggregation-attachment pheromone (AAP) of the ticks Amblyomma hebraeum and A. variegatum, as well as mixtures of these components, extracts of prefed males and live prefed males, were tested as aggregation stimulants. In field assays, laboratory-reared unfed male and female ticks were released 20 cm downwind of CO2/pheromone release sites; the numbers of ticks that aggregated at the release sites were recorded after 30 min. In A. variegatum, aggregation was induced by methyl salicylate, o-nitrophenol, 2,6-dichlorophenol, phenylacetaldehyde and some mixtures containing these compounds; a strong aggregation response was induced by an extract of five prefed males A. variegatum and a weak response was induced by an extract of 50 prefed males of A. hebraeum. In A. hebraeum, aggregation was induced by phenylacetaldehyde, mixtures of compounds that included phenylacetaldehyde, extracts of 50 prefed males of A. hebraeum or A. variegatum and 50 live prefed males of A. hebraeum. In A. variegatum, aggregation was inhibited if compounds that do not occur naturally in the AAP of the species were included in mixtures. In A. hebraeum, phenylacetaldehyde appeared to act as an arrestant for ticks that had been attracted to release sites by other compounds.

Animals↗
PubMed1992

Responses of the ticks Amblyomma hebraeum and A. variegatum to known or potential components of the aggregation-attachment pheromone. IV. Attachment stimulation of nymphs.

Ten known or potential components of the aggregation-attachment pheromone (AAP) of the ticks Amblyomma hebraeum and A. variegatum, as well as a mixture of these components and extracts of prefed males of the two species, were tested as attachment stimulants for nymphs. Unfed nymphs were confined in linen bags on the ears of rabbits that had been treated with the test compounds, mixture or extracts; the numbers attached were recorded after 24 h. In A. hebraeum, attachment was induced by four compounds (2-methyl propanoic acid, methyl salicylate, o-nitrophenol and salicylaldehyde), the mixture and extracts from both species. In A. variegatum, attachment was induced by three compounds (methyl salicylate, o-nitrophenol and salicylaldehyde), the mixture and extracts from both species. Methyl salicylate and o-nitrophenol are primary components of the AAP of both A. hebraeum and A. variegatum. 2-methyl propanoic acid is a species-specific attachment stimulant for A. hebraeum. Salicylaldehyde, a phenolic compound, is not a naturally occurring AAP component. Nymphs of both species respond to fewer attachment stimulants than the adults and, as shown by their respective host ranges, are less dependent on the AAP in the regulation of attachment than the adults.

Animals↗
PubMed1992

A comparison of the attraction of nymphs and adults of the ticks Amblyomma hebraeum and A. variegatum to carbon dioxide and the male-produced aggregation-attachment pheromone.

The attraction of nymphs of the ticks Amblyomma hebraeum and A. variegatum to CO2 alone and CO2 together with the male-produced aggregation-attachment pheromone (AAP) was investigated. Matching experiments on the attraction of the adults of the two species were run for comparison. Nymphs of A. hebraeum were strongly attracted to sources of CO2 and CO2/AAP at distances of 10 and 15 m. At distances of 20 and 25 m significantly more nymphs were attracted to CO2/AAP than to CO2 alone. Adults of A. hebraeum were not attracted to CO2 alone at any distance; these ticks were attracted to CO2 and AAP together for distances of up to 25 m. The patterns of attraction of nymphs and adults of A. variegatum at 10 m were similar to those recorded in A. hebraeum.

Animals↗
PubMed1992

Olfactory responses of adult Amblyomma hebraeum and A. variegatum (Acari: Ixodidae) to attractant chemicals in laboratory tests.

Unfed adults of the African ticks, Amblyomma hebraeum Koch and A. variegatum (Fabricius), important vectors of human and animal diseases, were exposed to volatile compounds in an olfactometer in efforts to identify both tick-produced or synthetic chemicals capable of eliciting an attraction response. A formula, relative efficacy of attraction, was devised for comparison of responses between species and sexes to a particular test stimulus, or within a homogeneous population to different stimuli. Adults of both species responded strongly to known tick-pheromone constituents, nonanoic acid, methyl salicylate, 2.6-dichlorophenol and benzyl alcohol, as well as to a commercially produced antiseptic, TCP (Pfizer), and its major components, chlorinated and iodinated phenols. Benzaldehyde, a proposed tick-pheromone component, and heptadecane, not known from ticks, were markedly attractive to adults of A. hebraeum but not to those of A. variegatum. Males of the former species, but neither conspecific females not either sex of the latter species, responded significantly to salicylaldehyde (known from males of four species of ticks, including A. variegatum). o-nitrophenol, a major component of the aggregation-attachment pheromone of males of both A. variegatum and A hebraeum and a proven long-range attractant for them in the field, was only partially attractive to either species in the olfactometer. Neither species was attracted to 2-methylpropanoic acid, previously identified in volatile effluents form feeding male A. hebraeum. It is concluded that these important disease vectors respond positively to a variety of volatile chemicals, which may conceivably be used to attract them to traps, animals or acaricides in efforts to control ticks or the diseases they transmit.

Animals↗
PubMed1992

Comparison of the attachment rates of males of the ticks Amblyomma hebraeum and A. variegatum to cattle, sheep and rabbits in the absence of aggregation-attachment pheromone.

Losses in domestic ruminants caused by heartwater (Cowdria ruminantium infection) in Zimbabwe and Mozambique are greater when the vector is Amblyomma hebraeum than when the vector is A. variegatum. It has been suggested that the epidemiology of the disease may be influenced by the rates at which unfed adults of these two tick species attach to uninfested hosts (i.e. in the absence of the male-produced aggregation-attachment pheromone [AAP]). In this study we confined unfed males of A. hebraeum and A. variegatum on uninfested cattle, sheep and rabbits and recorded their attachment rates. Males of both species attached more rapidly on cattle than on sheep or rabbits. Males of A. hebraeum attached more rapidly than males of A. variegatum on all three host species. The differences in the attachment rates between the two species were much greater on sheep and rabbits than on cattle. The findings suggest that in the absence of AAP, pioneer males of both tick species may attach to cattle, and pioneer males of A. hebraeum may also attach to sheep. The differences in the attachment rates of A. hebraeum and A. variegatum provide a possible explanation for observed differences in the epidemiology of heartwater associated with these two vector species.

Analysis of Variance↗
PubMed1992

High dose oral amiodarone loading: electrophysiologic effects and clinical tolerance.

Although amiodarone is an effective drug for the treatment of life-threatening ventricular arrhythmias, no standard oral loading dose protocol has been defined, and patients often undergo prolonged hospitalization for amiodarone loading. High dose (greater than 1,800 mg/day) oral loading has usually been reserved for unstable patients with incessant ventricular tachyarrhythmias. The current study was designed to 1) examine the clinical and electrophysiologic effects of a high dose oral amiodarone loading regimen in more stable patients; and 2) ascertain its safety and tolerance, possibly allowing shortened amiodarone loading periods and potentially decreased length of hospital stay. The study group included 16 patients with a history of recurrent ventricular arrhythmias and decreased left ventricular function, who were refractory to prior antiarrhythmic drug therapy. The oral loading protocol was 50 mg/kg per day of amiodarone for 3 days, then 30 mg/kg per day for 2 days, followed by maintenance therapy of 300 to 400 mg twice daily. Electrophysiologic testing was performed at baseline, on days 1 and 5 and during week 6. Amiodarone and desethylamiodarone levels were measured and symptoms monitored. Clinically, the high dose loading protocol was well tolerated in 15 of the 16 patients. Arrhythmias were rendered noninducible by day 1 in three patients and remained noninducible throughout the study period in two of the three. The remaining patients continued to have inducible ventricular tachycardia. Ventricular tachycardia cycle length and right ventricular effective refractory period both progressively increased significantly over baseline, starting on day 1. The 15 patients who remained in the study had no significant side effects during the loading period.(ABSTRACT TRUNCATED AT 250 WORDS)

Administration, Oral↗
PubMed1992

Selection of patients for programmed ventricular stimulation: a clinical decision-making model based on multivariate analysis of clinical variables.

OBJECTIVE: This study was conducted to assess the utility of clinical variables in predicting the inducibility of sustained ventricular arrhythmias in a heterogeneous group of patients undergoing programmed ventricular stimulation. METHODS: Variables were considered in a simulated chronologic order to determine the incremental information added by the signal-averaged electrocardiogram (ECG) and left ventricular ejection fraction. All patients undergoing baseline programmed ventricular stimulation for induction of ventricular tachyarrhythmia during a 30-month period were included in the study. Fourteen historical, ECG, signal-averaged ECG and left ventricular wall motion variables were evaluated for their ability in predicting inducibility of a sustained ventricular arrhythmia, a "positive" event, at programmed ventricular stimulation. RESULTS: On univariate analysis of the clinical variables, comparison between patients with positive or negative results showed significant differences in 10 of the 14 clinical variables: major cardiac diagnosis, history of ventricular tachycardia, myocardial infarction by history or ECG, all five signal-averaged ECG variables, left ventricular ejection fraction and presence of left ventricular aneurysm. On multivariate analysis, five independent variables were determined to be important: history of ventricular tachycardia, historical or ECG evidence of myocardial infarction, history of loss of consciousness, filtered QRS duration on the signal-averaged ECG and left ventricular ejection fraction. However, with sequential multivariate analysis, a model based only on historical and conventional ECG data was found to do as well as a model that included signal-averaged ECG and left ventricular ejection fraction data. CONCLUSIONS: Routinely available noninvasive historical, ECG, signal-averaged ECG and left ventricular wall motion variables can be used to accurately predict the outcome of programmed ventricular stimulation. The majority of the predictive power was obtained with the routine model, using only historical and ECG data. The signal-averaged ECG and left ventricular wall motion analysis added no significant incremental information.

Aged↗
PubMed1991

Relation between acute ventricular arrhythmias, ventricular late potentials and mortality in acute myocardial infarction.

The relation between ventricular late potentials and the occurrence of acute (in-hospital) and hyperacute (before hospital admission) ventricular tachycardia or fibrillation was studied in 281 consecutive patients with uninterrupted acute myocardial infarction. The prevalence of late potentials was significantly higher in patients with than without ventricular tachycardia/fibrillation (65 vs 22%; p less than 0.01). These relations persisted among patients with left bundle branch block, although a different definition was used for identifying late potentials in these patients. Multivariate analysis showed that presence of late potentials and peak creatine kinase enzyme level were the only 2 independent variables associated with early ventricular tachycardia/fibrillation. Total in-hospital mortality, as well as in-hospital cardiac mortality, was significantly higher among patients with than without acute ventricular tachycardia/fibrillation. However, at 1 year, mortality rates did not differ between the 2 groups. The following conclusions were drawn from this study: (1) Late potentials are closely related to ventricular tachycardia/fibrillation in hyperacute and acute phases of infarction. (2) Presence of left bundle branch block does not mitigate against the finding of late potentials in these patients. (3) Early ventricular tachycardia/fibrillation in acute infarction is related to large infarctions and to a high in-hospital mortality rate.

Aged↗
PubMed1991

Pheromone/acaricide mixtures in the control of the tick Amblyomma hebraeum: effects of acaricides on attraction and attachment.

Unfed adults and nymphs of the bont tick Amblyomma hebraeum Koch are attracted to hosts on which fed males, emitting an aggregation-attachment pheromone (AAP), are attached. Pheromone/acaricide mixtures have the potential to selectively attract and kill these ticks. We have investigated the effects of three acaricides, amitraz (an amidine), flumethrin (a synthetic pyrethroid) and chlorfenvinphos (an organophosphate), combined with AAP, on the attraction and attachment of the unfed adults. Attraction, measured in field assays involving AAP and CO2, was not inhibited by any of the acaricides. Attachment was measured over 24 h on the ears of rabbits which had been treated with AAP and mixtures of AAP and the acaricides. None of the acaricides inhibited initial attachment. Flumethrin caused rapid and high mortality in attached and unattached ticks. Chlorfenvinphos caused little mortality in the first 24 h on the ears of the rabbits, but 75% of the exposed ticks died over the next 14 days while held in an incubator. Amitraz caused the ticks to detach after an initial period of attachment; there was little mortality in the detached ticks over the next two weeks and they could later be induced to re-attach to other rabbits. Flumethrin was considered to be the compound of choice for use in pheromone/acaricide mixtures.

Animals↗
PubMed1991

Increasing the yield of ventricular tachycardia induction: a prospective, randomized comparative study of the standard ventricular stimulation protocol to a short-to-long protocol and a new two-site protocol.

Programmed ventricular stimulation with a standard protocol that used up to three extrastimuli was compared prospectively with a short-to-long protocol and a two-site protocol in 77 consecutive patients undergoing electrophysiologic study in an attempt to increase the yield of ventricular tachycardia (VT) induction. The short-to-long protocol uses a train of eight stimuli at a short cycle length and up to two extrastimuli. The two-site protocol is similar to the standard protocol but delivers the last extrastimulus via a second spatially separated right ventricular catheter. Patients were divided into two groups based on indications for study: group 1 included 45 patients with syncope, nonsustained VT, or both, and group 2 included 32 patients with a history of sustained VT, sudden cardiac death, or both. The yield of VT induction with the short-to-long protocol was less than that with the standard protocol. In none of the patients in group 1 in whom the standard protocol results were negative did the short-to-long protocol produce sustained VT. Only two patients, both in group 2, had sustained arrhythmias induced by the short-to-long protocol when the standard protocol results were negative: one had sustained VT induced and one with long QT syndrome had ventricular fibrillation (VF) induced with the short-to-long protocol. However, the short-to-long protocol failed to induce sustained VT in seven patients in whom the standard protocol produced sustained VT. All seven of these patients required three extrastimuli with the standard protocol for induction of VT.(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗
PubMed1991

Syncope of unknown origin: clinical, noninvasive, and electrophysiologic determinants of arrhythmia induction and symptom recurrence during long-term follow-up.

Ninety-one consecutive patients with syncope of unknown origin underwent electrophysiologic studies (EPS). Univariate analysis identified the following variables: age, + signal-averaged ECG (SAECG), left ventricular ejection fraction (LVEF), history of myocardial infarction, coronary artery disease, left ventricular aneurysm, and history of sustained monomorphic ventricular tachycardia (SMVT) on Holter; multivariate analysis identified +SAECG, LVEF, and history of SMVT as risk factors for induction of SMVT at EPS. All patients were followed up for 19.0 +/- 8.3 months and 17 had recurrence of syncope. Patients were divided into empiric, EP-guided, and no therapy groups. The EP-guided therapy group included all patients with SMVT at EPS. Recurrence rates among all three groups were similar. We conclude that: (1) Patients who have inducible SMVT at EPS can be identified using certain clinical and noninvasive variables. When these patients undergo EP-guided therapy, their rate of recurrence of syncope becomes compatible with that of patients who had no arrhythmia induced at EPS. (2) Empiric therapy does not offer any benefit over no therapy in reducing the rate of recurrent of scope.

Aged↗
PubMed1990

Benefit and risks of long-term amiodarone therapy for sustained ventricular tachycardia/fibrillation: minimum of three-year follow-up in 145 patients.

Our experience with amiodarone therapy in 145 consecutively referred patients with medically refractory sustained ventricular tachycardia and/or fibrillation treated for at least 3 years was reviewed. Ninety-seven had sustained ventricular tachycardia; the remaining 48 patients were survivors of sudden cardiac death. The patients had a mean of 3.7 +/- 1.4 unsuccessful anti-arrhythmic drug trials before initiation of amiodarone. The initial doses of amiodarone averaged 845 +/- 258 mg for the first 2 weeks and 56% of all patients received a type I antiarrhythmic drug in addition to amiodarone during the initial phase of therapy. The average maintenance dose of amiodarone was 410 +/- 187 mg per day. All patients were followed for a minimum of 3 years or until death or withdrawal from therapy. The maximum follow-up was a period of 8 years. Thus, the average duration of amiodarone therapy was 39 +/- 26 months, representing 472 patient years of therapeutic time on amiodarone. The incidence of deaths either caused by a documented ventricular tachyarrhythmia or presumed to result from an arrhythmic cause was 5.5% in the first year and 3.4% in each of the second and third years of follow-up. During the entire period of follow-up, 56 patients died of all causes (38.6% of the study population). Survival over the follow-up period was influenced significantly by left ventricular function, as judged by either New York Heart Association Functional Class or objective assessment of left ventricular ejection fraction, which was available in 102 patients.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1990

[Prevalence of late potentials in acute myocardial infarction and its relation to ventricular arrhythmias in early period of acute myocardial infarction (AMI)].

The prevalence of ventricular late potentials (LP) in acute myocardial infarction (AMI) and the relationship between the presence of LP and the occurrence of spontaneous sustained ventricular tachycardia (VT) or fibrillation (VE) in the early phase (within 10 days) of AMI were studied. A total of 251 consecutive patients who had an uninterrupted natural history before special treatment formed this study. Sustained VT or VF occurred in 20 patients (8%). LP were recorded in 67 patients (27%). The incidence of LP was significantly higher among patients with VT/VF than among those without VT/VF (12 of 20, or 60%, vs 55 of 231, or 24%, P less than 0.01). The subgroup of patients whose VT/VF occurred within 1 hour of onset of AMI also showed a higher incidence of LP (5 of 9, or 56%, vs 55 of 231, or 24%, P less than 0.05). The results showed that the mechanism of VT/VF in early period including those happened within 1 hour of onset of AMI in man is due to reentry, and that LP can help to identify those high risk patients with a propensity to develop VT/VF in early period of AMI.

Electrocardiography↗
PubMed1989

Decreased incidence of ventricular late potentials after successful thrombolytic therapy for acute myocardial infarction.

In some patients with acute myocardial infarction, low-amplitude potentials that prolong the QRS complex, termed "late potentials," can be recorded on a signal-averaged electrocardiogram. The presence of these late potentials is known to be associated with an increase in the risk of ventricular tachycardia and sudden death. Because patients with acute myocardial infarction who receive thrombolytic therapy have a reduced incidence of ventricular tachyarrhythmia and sudden death, we sought to determine whether such patients also have a decreased incidence of late potentials. We studied 106 patients less than 75 years of age who were admitted with a first myocardial infarction and in whom a signal-averaged electrocardiogram was recorded within 48 hours of admission. Within four hours of the onset of chest pain, tissue plasminogen activator (t-PA) was given to 44 patients, and 62 were treated conventionally. In the t-PA group, late potentials were recorded in 2 of 44 patients (5 percent), as compared with 14 of 62 (23 percent) in the conventionally treated group (P = 0.01). Furthermore, among the patients treated with t-PA, continued occlusion of the infarct-related artery was related to the presence of late potentials. In the t-PA group, late potentials were recorded within 24 hours of angiography in 2 of the 6 patients with an occluded infarct-related artery, as compared with none of the 38 patients with a patient infarct-related artery. Our data suggest that successful thrombolytic therapy is associated with a marked reduction in the incidence of late potentials on the signal-averaged electrocardiogram. Long-term follow-up will be required to determine whether this finding predicts a reduced incidence of subsequent ventricular tachyarrhythmia and sudden death.

Cardiac Pacing, Artificial↗
PubMed1988

Utility of the signal-averaged electrocardiogram in patients presenting with sustained ventricular tachycardia or fibrillation while on an antiarrhythmic drug.

The utility of the signal-averaged electrocardiogram (SAECG) for predicting ventricular tachycardia (VT) induction in patients presenting with sustained VT or ventricular fibrillation (VF) while on an empirically chosen antiarrhythmic agent was assessed in 17 patients. At the time of presentation with a malignant arrhythmia, 12 patients were taking quinidine, three patients were taking procainamide, and two patients were taking flecainide. All patients underwent programmed ventricular stimulation when not taking antiarrhythmic drugs; 12 patients had no inducible sustained VT and five patients had inducible sustained monomorphic VT. The SAECG done in the control state without antiarrhythmic agents was negative for late potentials in 11 of 12 patients in the noninducible group and positive for late potentials in four of five patients in the inducible group (sensitivity = 80% and specificity = 92%). We conclude that in patients presenting with life-threatening ventricular arrhythmias while taking an antiarrhythmic drug, the SAECG distinguishes patients with possible proarrhythmic events from those who have the substrate for inducible sustained VT.

Adult↗
PubMed1988

Subthreshold atrial pacing in patients with a left-sided accessory pathway: an effective new method for terminating reciprocating tachycardia.

This study investigated the possibility of terminating reciprocating atrioventricular (AV) tachycardia using subthreshold atrial pacing. Ten patients with a left-sided accessory pathway and sustained AV tachycardia underwent subthreshold atrial pacing from the coronary sinus site closest to insertion of the accessory pathway. In seven of these patients, the tachycardia could be reliably terminated with subthreshold atrial overdrive pacing. When pacing at a cycle length of 80 +/- 23% of the tachycardia cycle length, the minimal subthreshold current that was effective in tachycardia termination was 64 +/- 14% of threshold current and the maximal ineffective current was 49 +/- 17% of threshold (p less than 0.05). In all cases, the tachycardia was terminated by one or two instances of atrial capture that resulted in a premature atrial impulse (20 +/- 4% advancement of the atrial cycle) that blocked the AV node limb of the tachycardia. Anterograde conduction over the accessory pathway never occurred, either during the tachycardia or during subthreshold pacing after a return to normal sinus rhythm. No instances of atrial fibrillation were provoked by subthreshold pacing. Possible explanations for the intermittent atrial capture with critically placed subthreshold impulses include supernormal atrial conduction or summation of impulses at the atrial insertion site of the accessory pathway. It is concluded that subthreshold pacing is effective in selected patients with AV tachycardia due to an accessory pathway. Furthermore, because neither atrial fibrillation nor anterograde conduction over the accessory pathway is seen with subthreshold pacing, this modality may hold significant promise for permanent antitachycardia pacing in these patients.

Adult↗
PubMed1988

Relation of monophasic action potential recorded with contact electrode to underlying transmembrane action potential properties in isolated cardiac tissues: a systematic microelectrode validation study.

Monophasic action potentials, recorded with contact non-suction electrodes, have been used both clinically and experimentally. However, to date no systematic microelectrode validation studies have been done to underlying myocardial cell populations from different myocardial regions with different transmembrane potential profiles. In the present study transmembrane action potential properties, recorded with standard microelectrodes, were compared with monophasic action potentials recorded with contact electrodes in three different (endocardium, epicardium, and free running Purkinje fibre) isolated canine preparations during pacing and during spontaneous automatic activity. The mean transmembrane durations at 50% and 90% repolarisations (APD50 and APD90) of 19-30 cells at a monophasic action potential recording site was not statistically significant from monophasic action potential duration in all three tissue preparations studied. However, in endocardial preparations, composed of superficial (1-2 cell layers) Purkinje fibres with deeper ventricular muscle cells, the APD50 (139(17) ms) and APD90 (181(26) ms) of monophasic action potentials more closely reflected (but not significantly different) the underlying deeper ventricular muscle cells (APD50 134(14) ms and APD90 167(15) ms) rather than the mean transmembrane action potential durations of the underlying most superficial Purkinje fibres (166(22) ms for APD50 and 210(30) ms for APD90) (p less than 0.025). Tetrodotoxin (TTX) at 1 x 10(-6) mol.litre-1 shortened Purkinje fibre action potential duration and slightly lengthened that of ventricular muscle. Simultaneously recorded monophasic action potential showed an intermediate change in action potential duration. Incremental pacing and applied single premature stimuli resulted in similar degrees of shortening of action potential duration for both monophasic action potential and transmembrane potential in all three preparations. In endocardial preparations, barium chloride (4 mmol.litre-1) superfusion induced early afterdepolarisations, and spontaneous phase 4 depolarisations (n = 6) in both Purkinje and ventricular muscle cells giving rise to spontaneous automatic activity. These abnormal automatic activities were accurately detected by simultaneous monophasic action potential recordings. Suppression of automaticity by verapamil (0.2-0.5 micrograms.ml-1) as confirmed by transmembrane action potential recordings were similarly detected by monophasic action potential recordings (ABSTRACT TRUNCATED AT 250 WORDS)

Action Potentials↗