Study of Pacemaker and Implantable Cardioverter Defibrillator Triggering by Electronic Article Surveillance Devices (SPICED TEAS)

The magnetic fields emitted by electronic article surveillance (EAS) systems (shoplifting gates) are a source of interference for implanted medical devices. In the Study of Pacemaker and Implantable Cardioverter Defibrillator Triggering by Electronic Article Surveillance Devices (SPICED TEAS), 25 adult volunteers with ICDs and 50 with pacemakers were exposed to the fields of six different EAS systems. These EAS systems used three modes of operation: magnetic audio frequency, swept radiofrequency, and acoustomagnetic technology. No ICD exhibited interference mimicking sensing of tachyarrhythmias with any EAS system. Pacemakers interacted variably, depending on the type of EAS system. Swept radiofrequency systems produced no interaction with any implanted medical device. One magnetic audio frequency system interacted with 2 of 50 pacemakers. The acoustomagnetic system interacted with 48 of 50 pacemakers. Interactions included asynchronous pacing, atrial oversensing (producing "EAS induced tachycardia" in the ventricle), ventricular oversensing (with pacemaker inhibition), and paced beats resulting from the direct induction of current in the pacemaker ("EAS induced pacing"). These interactions produced symptoms in some patients (palpitations, presyncope) only while patients were in the EAS field. No pacemaker was reprogrammed. We conclude that high energy, pulsed low frequency EAS systems such as acoustomagnetic systems interfere with most pacemakers. Pacemaker patients should be advised to minimize exposure to the fields of such systems to prevent the possibility of serious clinical events.

Antigenic and immunogenic properties of synthetic peptide-based T-cell determinant polymers.

Presentation of T-cell determinants to the immune system in multimeric form has clear advantages and the production of synthetic peptide-based polymers using the solubilisable KS resin described by Goddard et al. [1] provides a method of assembling such polymers and also offers the means for making heteropolymers. The present study investigates the potential of polymeric synthetic peptide constructs in eliciting proliferative T-cell responses to determinants of the influenza virus hemagglutinin. The induction of vigorous CD4+ T-cell immunity was achieved with a polymeric construct containing two different T-cell determinants. The data presented here also highlight the fact that distancing the determinant from the support backbone with appropriate amino acid residues is an important consideration for the success of these polymeric immunogens. This approach may be readily applied in other systems where induction of helper T-cell responses are required.

N,O-bisFmoc derivatives of N-(2-hydroxy-4-methoxybenzyl)-amino acids: useful intermediates in peptide synthesis.

2-Hydroxy-4-methoxybenzyl-amino acid residues inhibit interchain association in solid phase peptide synthesis. They are easily introduced through their N,O-bisFmoc derivatives. Preparation of a range of these derivatives is described.

Some 'difficult sequences' made easy. A study of interchain association in solid-phase peptide synthesis.

Case studies of the solid-phase synthesis of some 'difficult sequences' using continuous-flow Fmoc-polyamide techniques are presented. Solvent change and peptide side chain and backbone modification procedures recently found to reduce association effects are applied, and the results compared to syntheses under standard conditions.

Upper rate lockout: an unexpected feature of rate adaptive atrioventricular delay.

We present a case in which use of rate adaptive AV delay resulted in unexpected pacemaker 2:1 AV block when the patient's atrial rate exceeded the pacemaker maximum tracking rate but was below the predicted multiblock rate. "Lockout" of normal upper rate behavior was accompanied with the requirement of a slower atrial rate for reassociation than loss of atrial tracking, a form of upper rate hysteresis. The mechanism of upper rate lockout is discussed, along with potential ways to avoid the problem. The use of software based pacemakers with an extended range of programmable options allows the most flexibility in optimizing pacemaker performance in an individual patient.

Doppler echocardiographic assessment of the hemodynamic benefits of rate adaptive AV delay during exercise in paced patients with complete heart block.

To determine if rate adaptation of the atrioventricular (AV) delay (i.e., linearly decreasing the AV interval for increasing sinus rate) improves exercise left ventricular systolic hemodynamics, we performed paired maximal semi-upright bicycle exercise tests (EXTs) on 14 chronotropically competent patients with dual chamber pacemakers. Nine patients with complete AV block (CAVB) and total ventricular pacing dependence during exercise comprised the experimental group. Pacemakers in these patients were programmed randomly to rate adaptive AV delay (AVDR) for one EXT and fixed AV delay (AVDF) for the other EXT. AVDF was 156 msec; AVDR decreased linearly from 156-63 msec from rates of 78-142 beats/min. The other five patients had intact AV conduction and comprised the control group who were exercised in identical fashion while their pacemakers were inhibited throughout exercise to assure reproducibility of hemodynamic measurements between EXTs. Cardiac hemodynamics were calculated using measured Doppler echocardiographic systolic aortic valve flows recorded suprasternally with an independent 2-MHz Doppler transducer during a graded ramp exercise protocol. For analysis, exercise was divided into four phases to compare Doppler measurements at submaximal and maximal levels of exercise: rest, early exercise (1st stage), late exercise (stage preceding peak), and peak. Patients achieved statistically similar heart rates between EXTs at each phase of exercise. Although at lower levels of exercise cardiac hemodynamics did not differ, experimental patients (with CAVB) showed a statistically significant benefit to cardiac output at peak exercise with heart rates of 129 +/- 13 beats/min (AVDR: 9.4 +/- 2.8 L/min; AVDF: 8.2 +/- 2.6 L/min, P = 0.002), stroke volume (AVDR: 74.1 +/- 25.6 mL; AVDF: 64.3 +/- 24.4 mL, P = 0.0003), and aortic ejection time (AVDR: 253.3 +/- 35.7 msec; AVDF: 226.7 +/- 35.0 msec, P = 0.002). Duration of exercise, peak rate pressure product, peak aortic flow velocities, and acceleration times did not differ. In contrast, control group patients (intact AV conduction throughout exercise) showed no statistical differences between any hemodynamic parameters measured at any phase of exercise from the first to second exercise test. These data demonstrate that systolic cardiac hemodynamics measured echocardiographically at the high heart rates achieved with peak exercise are improved with AVDR compared to AVDF in chronotropically competent patients with complete AV block. This is due primarily to improved stroke volume and a longer systolic ejection time with AV delay rate adaptation.

Comparison of epicardial and endocardial programmed stimulation in patients at risk for ventricular arrhythmias after cardiac surgery.

Programmed ventricular stimulation was performed on 36 patients after recent cardiac surgery using implanted right ventricular epicardial temporary wires and with catheters positioned percutaneously at two right ventricular endocardial sites. Patients were followed for a mean of 18.5 months (range 3 to 36 months). Epicardial wires were nonfunctional in 10 patients (28%) due to excessively high pacing thresholds. Overall, 22 patients (61%) had inducible sustained ventricular tachycardia; epicardial wires were functional in 15 (68%) of these patients. Six patients without inducible ventricular tachycardia with epicardial stimulation were inducible using endocardial stimulation. Of the 24 patients in whom epicardial and endocardial ventricular stimulation could be performed, concordant results were obtained in only 17 (71%), despite similar epicardial and endocardial ventricular effective and functional refractory periods. A total of 14 arrhythmic events occurred during the follow-up period. Of the 22 patients with an inducible sustained ventricular tachycardia, 12 (64%) had subsequent arrhythmic events. Only 2 of the 14 noninducible patients had follow-up arrhythmic events, one of which was caused by medication proarrhythmia. Endocardial ventricular stimulation had a superior sensitivity (83% versus 30%, P < 0.0001) and an improved negative predictive value (86% versus 61%, P < 0.05) compared with epicardial ventricular stimulation. These results indicate that noninducibility using epicardial programmed ventricular stimulation does not reliably portend a low risk for recurrent ventricular tachyarrhythmias. Epicardial programmed stimulation, used alone, may be inadequate for postoperative electrophysiological evaluation of patients at risk for ventricular arrhythmias.

Amino acid structure and "difficult sequences" in solid phase peptide synthesis.

Deprotection peak profiles have been determined as a measure of internal aggregation during Fmoc-polyamide continuous flow solid phase synthesis. The results have been correlated with amino-acid structure and discussed in terms of minimising aggregation during synthesis.

Production and characterization of an anti-peptide antibody specific for the growth-associated protein, GAP-43.

In an attempt to raise specific anti-GAP-43 antibodies, a C-terminal tetradecapeptide was synthesized based on the predicted rat GAP-43 amino acid sequence using the F-moc polyamide solid phase procedure. The synthesized carboxy-terminal peptide was purified by reverse phase HPLC, conjugated to bovine serum albumin (BSA) and used as an immunogen. Polyclonal antipeptide antibodies raised in rabbits were affinity purified and their specificity for GAP-43 tested by Western blotting. Brain and spinal cord homogenates and GAP-43 enriched synaptosomal membrane fractions were analysed either by SDS-PAGE or reverse phase HPLC. The anti-GAP-43 antibodies detected a major immunoreactive band at 43 kDa (B-50), and a minor immunoreactive band at 38 kDa (B-60) together with an additional protein-band at 68 kDa, which was related to the peptide carrier, BSA. Immunohistochemical studies using these carboxy-terminal antipeptide antibodies revealed a widespread distribution of GAP-43 immunoreactivity throughout the adult rat brain and spinal cord, in a pattern generally consistent with earlier histochemical studies. It is concluded that the C-terminal GAP-43 specific tetradecapeptide is a potent immunogen and provides a convenient tool for the production of sequence specific anti-GAP-43 antibodies.

An acquired interatrial fistula secondary to para-aortic abscess documented by transesophageal echocardiography.

Para-aortic ring abscess and resulting fistulous communication between adjacent structures frequently occur in prosthetic aortic valve endocarditis but are rarely diagnosed preoperatively. We report a patient who had an abscess involving the aortic-mitral intervalvular fibrosa that eroded into the interatrial septum, causing an interatrial communication with a left-to-right shunt. The abscess was detected by transthoracic echocardiography, but the fistula was only seen by the subsequent transesophageal echocardiogram. To our knowledge, this is the first report of an interatrial fistula secondary to a para-aortic valve abscess and its diagnosis preoperatively. Transesophageal echocardiography should be performed in any patient suspected to have complicated aortic endocarditis.

DBU as an N alpha-deprotecting reagent for the fluorenylmethoxycarbonyl group in continuous flow solid-phase peptide synthesis.

The versatility and efficiency of the N alpha-fluorenylmethoxycarbonyl method of solid-phase peptide synthesis have been further enhanced by recent and continuing refinements in side-chain protecting group, linker and amino acid-coupling technology. In contrast, comparatively little work has been carried out on studying and further improving the N alpha-deprotection step. This report demonstrates that, in low concentrations, the non-nucleophilic amidine 1,8-diazabicyclo[5.4.0]undec-7-ene is a preferred alternative to the more commonly employed piperidine for the rapid and efficient cleavage of the N alpha-fluorenylmethoxycarbonyl group in the continuous flow method of solid-phase peptide synthesis. In the cases studied, use of this base did not cause cyclization of Asp(OBut)-Gly or Asn-Gly sequence to succinimide derivatives. At the recommended concentration of 2% 1,8-diazabicyclo[5.4.0]undec-7-ene in dimethylformamide, racemization of resin-bound C-terminal S-trityl cysteine was substantially reduced compared with standard piperidine-mediated deprotection conditions. Additionally, use of the base appears to reduce the extent of broadening of ultraviolet fluorenylmethoxycarbonyl-deprotection peaks occasionally observed when piperidine is employed, indicating that its reaction kinetics and mode of action are different.

Conotoxin GI: disulfide bridges, synthesis, and preparation of iodinated derivatives.

The 13 amino acid toxic peptide from the marine snail Conus geographus, conotoxin GI, blocks the acetylcholine receptor at the neuromuscular junction. In this report, we describe a method for analyzing disulfide bonding in nanomole amounts of small cystine-rich peptides. The procedure involves partial reduction and a double-label alkylation of cysteine residues. Using this method, we show that the natural conotoxin GI has a (2-7, 3-13) disulfide configuration. The structure of conotoxin GI has been confirmed by chemical synthesis. The preparation and purification of molecularly homogeneous, iodinated derivatives of this toxin are also described. All derivatives, including the [diiodohistidine,diiodotyrosine]conotoxin GI, retained at least half of the biological activity of unmodified toxin. Since the tetraiodinated toxin, which is greater than 25% by weight iodine, retains considerable toxicity, unmodified histidine and tyrosine residues in conotoxin GI are not crucial for biological activity.

Successful use of oligopeptides as immunogens in the preparation of antisera to immediate-early gene products of herpes simplex virus type 1.

Antisera to two herpes simplex virus-type 1 (HSV-1) immediate-early gene products ( IE12 and IE175 ) have been produced using oligopeptides, constructed on the basis of proposed DNA coding sequences, as immunogens. In both cases the synthetic peptides were linked to bovine serum albumin via an N-terminal tyrosine prior to immunization. Both the IE12 and the IE175 antisera reacted with their respective HSV-1 antigens and with antigens produced by the HSV-1 immediate-early mutant tsK but not with functionally equivalent antigens induced by HSV-2. IE12 induced by tsK was found to have an altered mobility with respect to the wild-type IE12 and its precipitation was accompanied by a second, minor, component of lower mobility. Revertants of tsK gave similar results. Labelling IE12 with a variety of amino acids indicated that the first of three possible initiation codons was used in its translation from mRNA. The results imply that the other initiation codons were not used. Wildtype IE12 is produced for at least 3 h after release of cycloheximide block and appears to be turned over rapidly.

4-Chloromethylphenoxyacetyl polystyrene and polyamide supports for solid-phase peptide synthesis.

Two functionalised supports for the solid-phase synthesis of peptides under mild reaction conditions were prepared: 4-chloromethylphenoxyacetamidomethyl-copoly (styrene-1%-divinylbenzene) and 4-chloromethylphenoxyacetyl-norleucyl-poly (dimethylacrylamide). They were devised in order to avoid the danger of racemization which exists during base-catalyzed esterification of the first protected amino acid to the 4-alkoxybenzyl alcohol resins formerly employed in combination with N alpha-9-fluorenylmethoxycarbonyl and tert.-butyl side-chain protecting groups. Esterification of N alpha-protected amino acids to the new resins can be achieved easily and without significant levels of racemization by means of their caesium salts, while cleavage from the supports is possible by treatment with trifluoroacetic acid. The 4-chloromethylphenoxyacetyl polystyrene resin was tested by the synthesis of Leu-enkephalin which was cleaved, at the end of the synthesis, from the solid support in 91% yield by 60% trifluoroacetic acid in methylene chloride, and was shown to be more than 99% pure by ion-exchange chromatography and reverse phase high pressure liquid chromatography.

A correlative neurobehavioral-morphological model of acrylamide neuropathy.

Sprague-Dawley rats were intoxicated with 50 mg/kg/day of acrylamide monomer given by daily intraperitoneal injections. The progression of disease was studied in intoxicated animals and unintoxicated controls using a functionally-oriented behavioral battery focusing on sensory-motor behaviors. Correlative morphological examination focused on neuronal cell bodies and nerve fibers at early time points. The results were compared with previous results from animals intoxicated with another prototype neurotoxin, 2,5-hexanedione (2,5-HD), and studied with the identical behavioral battery. With both toxins behavioral changes slightly preceded observed structural damage at the sites examined. Broadly similar behavioral patterns occurred with both toxins, i.e., more-complex functions showed the earliest deficits; hindlimb functions deteriorated before forelimb functions; grasp reflex deteriorated before place reflex. This pattern correlates with the established pattern of selective vulnerability of long and large axons. Although the patterns of behavioral toxicities were broadly similar, the functionally-oriented battery succeeded in detecting differences which corresponded with established neuropathological subtleties in the two dying-back processes. We discuss potential difficulties in correlating behavioral/clinical results with morphological data but stress the importance of such correlations.

Autonomic-cardiovascular dysfunction accompanies sensory-motor impairment during acrylamide intoxication.

We investigated the effects of acrylamide monomer on autonomic-cardiovascular functions and simple sensory-motor behaviors. Rats were intoxicated by ip injections of acrylamide at a dose of 50 mg/kg/day for 10 days; control animals received an equivalent volume of saline. Heart rate (HR) and systolic arterial blood pressure (BP) were measured using the method of indirect tail plethysmography. Intoxicated animals showed fluctuating but significant increases in HR and BP after the first dose of acrylamide, during the course of the intoxication, and two days after the last dose. Deficits in sensory-motor behaviors appeared after the first dose of acrylamide and progressed steadily throughout the exposure period, remaining two days after the last dose. More complex sensory-motor behaviors were affected earliest; hindlimb functions were affected before forelimb functions, characteristic of dying-back axonopathy. These results demonstrate that acrylamide alters common measures of autonomic-cardiovascular functioning in addition to simple sensory-motor behaviors.

Acid-labile resin linkage agents for use in solid phase peptide synthesis.

Details are given of the preparation of two acid-labile peptide-resin linkage agents for use in solid phase peptide synthesis, viz. 4-hydroxymethylphenoxy-acetic acid and 3-methoxy-4-hydroxymethylphenoxyacetic acid. The latter is suitable for the preparation of peptide fragments bearing t-butyl-based side chain protecting groups.