The effect on bioadhesive polymers either freely in solution or covalently attached to a support on human macrophages

Cell surface adhesion receptors interact with a family of adhesion molecules known as integrins. It is assumed that the cells recognize and bind a specific amino acid sequence. It is likely that the host inflammatory response may be mediated via the recognition of the inflammatory cells with the specific integrin molecules. The mechanism of such behavior has not been fully elucidated. This investigation was designed to provide more insight regarding the cellular response associated with incubation of macrophages with polymers either freely in solution or adhered to surfaces. Peripheral macrophages were seeded at a density of 4 x 10(6) cells on supports coated with either amino-acid heteropolymers of RGE, RGD, or amino-acid homopolymer Poly-L-lysine. Cells were also seeded at the same density in 24 well plates and the wells were treated with RGD, RGE or Poly-L-lysine. The cells were examined morphologically and biochemically at 24, 48, and 72 hours. The results showed cells growing on supports coated with RGD had significantly (p < 0.05) higher numbers of cells adhering and remaining viable, in comparison to cells growing on Poly-L-lysine or RGE supports. Cells growing on supports coated with RGE appeared irregularly (elongated and spindle) shaped and unevenly spaced. The cells growing on Poly-L-Lysine coated supports showed cellular disruption and lysis, whereas cells growing on the RGD appeared intact, regularly spaced and began fusing into giant cells. Lactate dehydrogenase activity was used as a measure of membrane integrity, and cells grown on coated supports with Poly-L lysine showed a two-fold increase in activity over control and peptide treated groups. On the other hand, cells growing in media containing the free RGE, RGD and Poly-L-lysine showed no statistical differences in cell number, and did not show increased activity of LDH for the entire duration of the experiment. The data suggests that the RGD, RGE and Poly-L-lysine dissolved in solution are highly biocompatible to the macrophages. However, when they are attached to a support they can affect cellular adherence as well as cellular activation.

The effect of polymer coating biomaterials individually and incombination on the behavior of transformed RAW macrophage cells

The use of homopolymers as coatings for biomaterials has received much attention in the last decade. However, the modifications and alterations induced by using such materials towards inflammatory cells have not been fully investigated. The specific objectives of this study were to investigate the role of hetero and homopolymers of amino acids on cell proliferation, and to determine the biochemical behavior associated with the incubation of RAW cells with various polymers. The RAW macrophage cell line was obtained from the American Type Culture Collection (Rockville, MD) and maintained in sterile media (RPMI) supplemented with 10% fetal bovine serum and 1% antibiotics and antimycotics. The cells were plated at a density of 1 x 10(6) cells/ml onto 24 well plates. The plates were divided into four groups of six wells per group per phase (24, 48, and 72 hours). Cells in the first group were treated with RGD, cells in group II were treated with poly-L-lysine, group III cells were treated with RGD + poly-L-lysine, and cells in group IV were treated with media alone, and served as controls. Cell number, as well as, protein, MDA, lactate dehydrogenase (LDH), and cytochrome C (cyto C) were determined at the end of 24, 48 and 72 hours. Data obtained from this investigation revealed that: (I) there were no significant difference in total cell counts between all experimental groups and control at the end of the 48 hour phase. However, at 24 hours there were fewer cells in the poly-L-lysine treated wells in comparison to control group (p < 0.05), (II) RGD and poly-L-lysine treatments did not cause changes in MDA or protein concentrations for the entire duration of the experiment, and (III) RGD treatment for 48 and 72 hours did not cause a reduction in the LDH activity compared to control and poly-L-lysine treated groups. Data obtained from this investigation could provide more insight regarding the design and development for safe and biocompatible orthopedic, dental and drug delivery devices.

Permanent explantation of implantable cardioverter defibrillators

Although ICD therapy is seen as an irrevocable mode of therapy in most patients, a small number of patients do have their devices permanently explanted. The long-term outcome in these patients has not been described. The purpose of this single center study was to evaluate the long-term outcome of patients whose ICD was explanted and not replaced and to propose clinical variables that can be considered when making the decision to discontinue therapy. Ten of 323 (3.1%) patients in our ICD registry had their devices permanently explanted or turned off between 1986 and December 1998. The devices had been in place for 39 +/- 31 months preexplant. No patient had received appropriate therapy prior to surgery, which was indicated for infection or lead fracture. All patients are alive and well 75 +/- 30 months postexplant with 1 (10%) patient requiring late reimplantation. We reviewed the English language literature describing ICD explanation without replacement. A total of 151 patients were reported in eight studies and were followed for up to 30 months postexplant. Excluding patients with terminal illness or heart transplantation 57.6% survived without reimplantation. In selected patients, after not using an ICD for a long period and when clinical circumstances justify, device therapy may be discontinued with some degree of safety.

Can antiarrhythmic agents be selected based on mechanism of action?

When selecting an antiarrhythmic agent the clinician needs to be able to accurately predict the probability that a particular drug will serve its intended purpose in a given patient. This is difficult because of the complexity of variables which govern the relationship between drug administration and clinical outcome. The efficacy of a drug may potentially be predicted from its mechanism of action. At least two classifications of antiarrhythmic agents based on mechanism of action have been proposed. The Vaughan Williams classification is based on the predominant electrophysiological effects of a drug on the action potential. In the Sicilian Gambit approach, a number of potential targets ('vulnerable parameters') for drug action are identified and antiarrhythmic drugs or substances that affect cardiac electrophysiology are characterised by their actions on each of these. The usefulness of these classification systems in predicting antiarrhythmic drug efficacy are limited. Furthermore, in the Vaughan Williams classification not all drugs in the same class have identical effects, whereas some drugs in different classes have overlapping actions. The Sicilian Gambit requires in-depth knowledge regarding cellular and molecular targets of antiarrhythmic agents which may make it intimidating or simply impractical for regular clinical use. Surrogate measures such as 24-hour Holter monitoring and programmed electrical stimulation have been used to predict anti-arrhythmic drug efficacy. However, studies such the Cardiac Arrhythmia Suppression Trial (CAST) have shown that suppression of ventricular ectopy on Holter monitoring does not necessarily correlate with improved survival and may in fact be dangerous. Conversely, studies using programmed electrical stimulation to assess drug effect on variables such as tachycardia inducibility, refractory period and ventricular tachycardia cycle length show that suppression of tachycardia inducibility, prolongation of refractory period and prolongation of ventricular tachycardia cycle length, are all associated with reduced recurrence of tachycardia and possibly improved survival. The most practical use of the current classification systems applied to antiarrhythmic agents may be in their ability to predict with reasonable accuracy, the risk and type of proarrhythmia based on the mechanism of action of an agent.

Oligomeric structure of bAE3 protein

The "brain" form of the anion exchanger protein 3 (bAE3) has been purified to homogeneity from the rabbit kidney by differential centrifugation and immunoaffinity chromatography. A single protein band of approximately 165 kDa was detected by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and Western blotting. Monomers, dimers (a major component), and a higher oligomeric form (apparently tetramers) were found after oxidative cross-linking of purified bAE3. The largest form of bAE3 was separated from dimers and monomers by sucrose gradient centrifugation and was studied by transmission electron microscopy to confirm a tetrameric structure. Two main types of bAE3 images were detected, round (approximately 11-14 nm) and square-shaped (approximately 12 x 12 nm). Image analysis revealed fourfold rotational symmetry of both the round and square-shaped images, indicating that bAE3 consists of multiples of 4 subunits. We conclude that bAE3 in Triton X-100 solution is predominantly a mixture of dimers and tetramers with a smaller amount of monomers.

Misconceptions about STD-protective behavior. Project RESPECT Study Group

CONTEXT

Misconceptions about STD-protective behaviors have not been studied before and after STD counseling. Further, to the best of our knowledge, the relationship of these misconceptions to condom use and STD incidence has not previously been described in published reports.

OBJECTIVES

The main purpose of the study was to determine the prevalence of misconceptions about STD prevention among STD clinic attendees (N=3498) in five large cities, as well as whether misconceptions decreased after STD diagnosis, STD counseling, or both. The study also identified predictors of persistent misconceptions and determined the relationship of STD incidence and unprotected sex to persistent misconceptions.

METHODS

Data from a randomized controlled trial evaluating HIV/STD counseling interventions (Project RESPECT) were used for the present analyses. Participants completed an interview upon study enrollment and every 3 months following enrollment for a 1-year period. A portion of the interview assessed participants' misconceptions about STD-protective behaviors.

RESULTS

At baseline, 16.3% believed that washing the genitals after sex protected from STDs. Likewise, urinating after sex (38.7%), douching (45.7%), and use of oral contraceptives (19. 9%) were believed to prevent STDs. Prevalence of misconceptions was significantly diminished at a 3-month follow-up (p<.001). Those continuing to have misconceptions were more likely to be aged > or = 24 and African American. Those continuing to have these misconceptions did not have higher STD incidence.

CONCLUSIONS

Misconceptions about STD-protective behaviors are common, and the event of an STD or STD counseling or both generally reduces these misconceptions. Although these misconceptions may not directly translate into risky behavior, they may preclude movement toward safer sex.

Rate dependence of the effect of antiarrhythmic drugs delaying cardiac repolarization: an overview

Prolongation of the cardiac action potential and refractoriness (class III effect) is a potentially beneficial electrophysiological mechanism of action. However, this effect may be diminished or eliminated at rapid heart rates, so-called 'reverse rate dependence' of prolongation of repolarization. Action potential duration normally shortens as heart rate increases, due to increases in outward repolarizing currents, and/or decreases in inward depolarizing currents. The assessment of the effect of drugs on action potential duration is complicated by inter-species differences in ionic currents mediating repolarization, heterogeneity within the heart in repolarizing currents, and differential effect of drugs in different species, during differing experimental conditions, and at different rates of stimulation. In general, most drugs which predominantly block the IKr repolarizing current exhibit reverse rate-dependent effects on cardiac repolarization. Drugs or combinations of drugs which produce multiple ionic channel blocks and possibly those which block the IKs current, may be less prone to this potentially undesirable effect.

Role of gender and personality on quality-of-life impairment in intermittent atrial fibrillation

Patients with atrial fibrillation (AF) report impaired health-related quality of life (QOL). Differences between men and women with AF have not been described and personality attributes such as somatization (tendency to amplify benign bodily sensations) may mediate potential gender differences in QOL. Patients with AF (n = 264, 59% men) who participated in the Canadian Trial of Atrial Fibrillation (n = 403) completed validated QOL questionnaires at baseline, 3 months, and 12 months after antiarrhythmic drug treatment. Women were significantly older than men and a greater proportion had hypertension, but other cardiac variables did not differ between women and men. At baseline, after controlling for significant clinical and demographic factors, women reported worse physical health (p = 0.002) and functional capacity (p < 0.001), but not mental health or general well-being. Women also had more frequent and severe cardiac symptoms than men (both p < 0.001). Physical health improved significantly from baseline to 3 months for women (p = 0.002), but not for men (p = 0.066). Conversely, mental health improved for men (p = 0.007), but not for women. Cardiac symptom frequency and severity improved over time for women and men (all p < 0.001). Tendency to somatize predicted poor QOL, and women had higher scores than men (p = 0.023). However, after controlling for somatization, women still had worse physical function, functional capacity, and symptom burden than men. Independent of cardiac disease severity and age, women with AF had significantly more impaired QOL than men, specifically on domains related to physical rather than emotional functioning. Personality attributes may have a role in influencing QOL outcomes.

The impairment of health-related quality of life in patients with intermittent atrial fibrillation: implications for the assessment of investigational therapy

OBJECTIVES

We sought to assess the impact of intermittent atrial fibrillation (AF) on health-related quality of life (QoL).

BACKGROUND

Intermittent AF is a common condition with little data on health-related QoL questionnaires to guide investigational therapies.

METHODS

Outpatients from four centers, with documented AF (n = 152), completed validated QoL questionnaires (Medical Outcomes Study Short Form 36 [SF-36], Specific Activity, Symptom Checklist, Illness Intrusiveness and University of Toronto AF Severity Scales). Comparison groups were made up of healthy individuals (n = 47) and four cardiac control groups: published (n = 78) and created for study (n = 69) percutaneous transluminal coronary angioplasty (PTCA); published heart failure (n = 216) and published postmyocardial infarction (MI) (n = 107).

RESULTS

Across all domains of the SF-36, AF patients reported substantially worse QoL than healthy controls (1.3 to 2.0 standard deviation units), with scores of 24%, 23%, 16% and 30% lower than healthy individuals on measures of physical and social functioning, mental and general health, respectively (all p < 0.001). Patients with AF were either significantly worse (p < 0.05, published controls) or as impaired (study controls) as either PTCA or post-MI patients on all domains of the SF-36 and the same as heart failure controls on SF-36 psychological subscales. Patients with AF were as impaired or worse than study PTCA controls on measures of illness intrusiveness, activity limitations and symptoms. Associations between objective disease indexes and subjective QoL measures had poor correlations and accounted for <6% of the total variability in QoL scores.

CONCLUSIONS

Quality of life is as impaired in patients with intermittent AF as in patients with significant structural heart disease. Patients' perception of QoL is not dependent on the objective measures of disease severity that are usually employed.

Cloning, characterization and chromosomal assignment of NBC4, a new member of the sodium bicarbonate cotransporter family

We report the cloning, characterization and chromosomal assignment of a new member of the sodium bicarbonate cotransporter (NBC) family, NBC4, from human heart. NBC4 maps to chromosome 2p13 and is a new candidate gene for Alstrom syndrome. NBC4 encodes a 1074-residue polypeptide with 12 putative membrane-spanning domains. Unlike other members of the NBC family, NBC4 has a unique glycine-rich region (amino acids 438-485). In addition, NBC4 lacks the lysine-rich C-terminus of NBC1 with which it is most homologous. The first of two putative stilbene binding motifs (K(M/L)(X)K) is lacking in NBC4 (amino acids 655-658). The approximately 6 kb NBC4 transcript is moderately expressed in heart, with the highest expression in liver, testes and spleen.

Randomized crossover comparison of DDDR versus VDD pacing after atrioventricular junction ablation for prevention of atrial fibrillation. The atrial pacing peri-ablation for paroxysmal atrial fibrillation (PA (3)) study investigators

BACKGROUND

Some clinical data suggest that atrial-based pacing prevents paroxysmal atrial fibrillation (AF). This study tested the hypothesis that DDDR pacing compared with VDD pacing prevents AF after atrioventricular (AV) junction ablation.

METHODS AND RESULTS

Patients were randomized to DDDR pacing (n=33) or to VDD pacing (n=34) after AV junction ablation and followed every 2 months for 6 months. Patients then crossed over to the alternate pacing mode and were followed for an additional 6 months. Primary analysis included the time to first recurrence of sustained AF (duration >5 minutes), total AF burden, and the development of permanent AF. The time to first episode of AF was similar in the DDDR group (0.37 days, 95% CI 0.1 to 1.3 days) and the VDD pacing group (0.5 days, 95% CI 0.2 to 1.7 days, P=NS). AF burden increased over time in both groups (P<0.01). At the 6-month follow-up, AF burden was 6.93 h/d (95% CI 4. 37 to 10.96 h/d) in the DDDR group and 6.30 h/d (95% CI 3.99 to 9.94 h/d) in the VDD group (P=NS). Twelve (35%) patients in the DDDR group and 11 (32%) patients in the VDD group had permanent AF within 6 months of ablation. Within 1 year of follow-up, 43% of patients had permanent AF.

CONCLUSIONS

DDDR pacing compared with VDD pacing does not prevent paroxysmal AF over the long term in patients in the absence of antiarrhythmic drug therapy after total AV junction ablation. Many patients have permanent AF within the first year after ablation.

A genetic linkage map of the baboon (Papio hamadryas) genome based on human microsatellite polymorphisms

A first-generation genetic linkage map of the baboon (Papio hamadryas) genome was developed for use in biomedical and evolutionary genetics. Pedigreed baboons (n = 694) were selected from the breeding colony maintained by the Southwest Foundation for Biomedical Research. To facilitate comparison with the human genome, the baboon linkage map consists primarily of human microsatellite loci amplified using published human PCR primers. Genotypes for 325 human microsatellites and 6 novel baboon microsatellites were used in linkage analyses performed with the MultiMap expert system. The resulting sex-averaged meiotic recombination map covers all 20 baboon autosomes, with average spacing among loci of 7.2 cM. Direct comparison among homologous (orthologous) loci reveals that, for 7 human autosomes, locus order is conserved between humans and baboons. For the other 15 autosomes, one or more rearrangements distinguish the two genomes. The total centimorgan distances among homologous markers are 28.0% longer in the human genome than in the baboon, suggesting that rates of recombination may be higher in humans. This baboon linkage map is the first reported for any nonhuman primate species and creates opportunities for mapping quantitative trait loci in baboons, as well as for comparative evolutionary analyses of genome structure.

Two C-terminal variants of NBC4, a new member of the sodium bicarbonate cotransporter family: cloning, characterization, and localization

We report the cloning, characterization, and chromosomal assignment of a new member of the sodium bicarbonate cotransporter (NBC) family, NBC4. The NBC4 gene was mapped to chromosome 2p13 and is a new candidate gene for Alstrom syndrome. Two variants of the transporter have been isolated from human testis and heart, which differ in their C termini. NBC4a encodes a 1137-residue polypeptide and is widely expressed in various tissues, including liver, testis, and spleen. NBC4b is identical to NBC4a except that it has a 16-nucleotide insert, creating a C-terminal frame shift. NBC4b encodes a 1074-residue polypeptide and is highly expressed in heart. Amino acids 1-1046 are common to both NBC4 variants. NBC4a has two protein-interacting domains that are lacking in NBC4b: a proline-rich sequence, PPPSVIKIP (amino acids 1102-1110), and a consensus PDZ-interacting domain, SYSL (1134-1137). NBC4b lacks the stretch of charged residues present in the C terminus of NBC4a and other members of the NBC family. Unlike other members of the NBC family, both NBC4a and NBC4b have a unique glycine-rich region (amino acids 440-469). In comparison with other members of the bicarbonate transport superfamily, NBC4a and NBC4b are most similar structurally to the electrogenic sodium bicarbonate cotransporters (NBC1).

October 18, 2000 8:30-8:45. Problem Solving with FDG Positron Emission Mammography

Purpose: To examine one potential clinical application of dedicated devices for positron emission mammography.Background: Dedicated devices for breast imaging with FDG have technical specifications that appear well-suited for detecting small breast cancers, including registration with x-rays, high count sensitivity, and spatial resolution in the 2-3 mm range.Methods: In IRB-approved clinical trials, patients who were scheduled for biopsy for suspicious findings on x-ray mammograms were injected with 10-20 mCi FDG intravenously one to two hours prior to x-ray guided core biopsy or lumpectomy. Positron emission mammograms using a dedicated device were performed just before biopsy, and results compared to final histopathology.Results: Three patients whose cancers were missed on initial x-ray mammograms or whose mammograms contained subtle abnormalities that were not strongly suspicious for cancer, were shown to have very suspicious hot spots on positron emission mammograms. These patients were later confirmed to have cancer.Discussion: The role for dedicated devices for positron emission mammography is evolving. Finding cancers that are either mammographically occult or have low indices of suspicion is a potential application for this technique. Further clinical and technical work will be needed to better define the strengths and weaknesses of the device in this application.

Is electrical storm in ICD patients the sign of a dying heart? Outcome of patients with clusters of ventricular tachyarrhythmias

BACKGROUND

Electrical storm in patients with implanted cardioverter defibrillators (ICDs) is purported to carry an ominous prognosis.

METHODS AND RESULTS

We retrospectively compared 40 patients with electrical storm (defined as three or more episodes of ventricular arrhythmia requiring ICD therapy in a 24 h period) with those only having isolated appropriate ICD therapy (n=57) and with patients having no or only inappropriate ICD therapy (n=125). All patients received ICDs for documented sustained VT or VF. There was no significant difference in age, sex, ejection fraction, total follow-up time, or underlying heart disease between any of the three groups. Patients who had electrical storm received their first appropriate ICD therapy 275 +/- 369 days post-implant (35% had storm as their first event) with storm occurring an average of 599 +/- 710 days post-implant. Patients had 1.5 +/- 1.0 storms in total (median= 1), with 55 +/- 91 episodes per storm. There were no significant differences in actuarial survival at 5-year follow-up between the three groups. Eighty percent of storm patients were alive 5 years post-implant.

CONCLUSION

Storm is a common occurrence in ICD patients, can occur at any time during the follow-up period, and does not independently confer increased mortality.

Structural organization of the human NBC1 gene: kNBC1 is transcribed from an alternative promoter in intron 3

Several electrogenic sodium bicarbonate cotransporters have been cloned from different human organs. In the renal proximal tubule, the electrogenic sodium bicarbonate cotransporter kNBC1 (1035aa) mediates the majority of basolateral sodium bicarbonate absorption. In pancreatic ducts, the electrogenic sodium bicarbonate cotransporter pNBC1 (1079aa) mediates basolateral sodium bicarbonate influx. hNBC1 (hhNBC), cloned from human heart, is identical to pNBC1 at the amino acid level. We have demonstrated that kNBC1 and pNBC1 are highly homologous proteins that have different N-termini. In kNBC1, 41 amino acids replace the initial 85 amino acids of pNBC1. Whether these proteins are coded by one or more genes is unknown. In order to determine the genetic basis for these transcripts, we first characterized the genomic organization of the NBC1 gene (SLC4A4). NBC1 spans approximately 450 kilobases containing 26 exons that are flanked by typical splice donor and acceptor sequences at the intron-exon boundaries. Exon 1 is specific for the pNBC1 transcript. The first alternative exon of the hNBC1 transcript, containing the 5'-untranslated region, is derived from the last 43 nucleotides of intron 1 in the NBC1 gene coupled to exon 2. kNBC1 is transcribed from an alternative promoter in intron 3. In the first alternative exon of kNBC1, the last 313 nucleotides of intron 3 are coupled to exon 4, which is common to pNBC1 and hNBC1. The major transcription initiation site in kNBC1 is located 192 nucleotides upstream from the translation initiation codon. A minor start site is located 182 nucleotides upstream from the translation initiation codon. Structural analysis of the proximal kNBC1 promoter revealed an atypical TATA sequence (-33) and several potentially important transcription factor binding sites. Functional studies showed that the 5'-flanking region of the alternative kNBC1 promoter (-159 to+43) is sufficient for promoter activity. This work is the first demonstration that the three N-terminal transcripts of the human electrogenic sodium bicarbonate cotransporter NBC1 are encoded by the SLC4A4 gene. Furthermore, knowledge of the genomic organization and alternative promoter usage in the NBC1 gene provides a molecular basis for understanding disorders involving electrogenic sodium bicarbonate cotransporters and facilitates the elucidation of transcriptional control of NBC1 expression.

Inappropriate therapy from atrial fibrillation and sinus tachycardia in automated implantable cardioverter defibrillators

BACKGROUND

Inappropriate therapy from supraventricular tachyarrhythmias (atrial fibrillation [AF] and sinus tachycardia [ST]) in patients with implanted cardioverter defibrillators is a major challenge. We tested the performance of stability algorithms from 3 manufacturers for episodes of inappropriate therapy delivered because of AF and an onset algorithm for all episodes of inappropriate therapy caused by ST.

METHODS

Therapy was classified as caused by ventricular tachycardia (VT), ST, or AF from review of stored intracardiac electrograms, history, clinical information, and R-R data before study inception. By using 30 to 60 R-R intervals before therapy, sensitivity and specificity for a family of stability values and percentage of onset values were calculated for each manufacturer and receiver operating characteristic curves generated.

RESULTS

Of the 217 patients monitored, 62 (29%) received inappropriate therapy, and 40 had complete R-R information available. Of the 40 patients, 21 patients received therapy for AF, 19 for ST, and 1 patient for noise; 15 (38%) also received appropriate therapy for VT. We analyzed 83 episodes of VT from 18 patients, 94 episodes of AF from 21 patients, and 56 episodes of ST from 19 patients. Specificity, in the clinically relevant sensitivity range of >/=95%, was comparable across manufacturers at about 40%. An onset value of 80% was associated with 91% sensitivity and 95% specificity for the specific algorithm tested.

CONCLUSIONS

Inappropriate therapy is a common problem in implantable cardiac defibrillators. The performance of the stability algorithms used to differentiate AF from VT was less than ideal, though comparable across manufacturers. The onset algorithm accurately differentiates ST from VT.

Effect of physiological mechanical perturbations on intact human myocardial repolarization

OBJECTIVE

The objective of this study was to investigate the relationship between acute decreases in right ventricular volume during Valsalva strain (with resultant changes in autonomic neural tone) and measures of local endocardial repolarization time independent of heart rate and autonomic neural tone.

METHODS

Patients implanted with a stimulus to T wave (Stim-T) sensing pacemaker specially adapted to output a validate measure of beat to beat local repolarization (n = 9) performed Valsalva manoeuvers (40 mmHg for 15 s) while paced at a cycle length of 500 ms. Stim-T intervals were measured before and after autonomic blockade (Block: 0.03 mg/kg i.v. atropine +/- 0.15 mg/kg propranolol). Right ventricular end diastolic volume was estimated by simultaneous 2D-echocardiography.

RESULTS

Without autonomic blockade, compared to baseline, repolarization significantly prolonged during Valsalva strain (1.1 +/- 0.7%) and shortened during release (-1.4 +/- 1.0%). After block, strain related repolarization prolongation was also observed (1.0 +/- 0.6%), with significantly less release related repolarization shortening (-0.8 +/- 0.8%) compared to pre-block (P < 0.05). Right ventricular end diastolic volume decreased during strain by 11 +/- 10 and 9 +/- 16% from baseline, pre- and post-block respectively (P < 0.05).

CONCLUSION

In a chronically instrumented human model, an acute physiologic volume reduction modestly prolongs right ventricular repolarization independent of changes in rate or autonomic tone.

Genome-wide screen for atopy susceptibility alleles in the Hutterites

A genome-wide screen for loci influencing positive skin prick tests (SPT) to airborne allergens was conducted in the Hutterites, a founder population of European ancestry. Positive SPT to 14 standardized allergens was measured in 370 subjects in our primary sample and 324 subjects in a replication sample. Evidence for linkage to positive SPT was assessed using the transmission disequilibrium test (TDT) with 337 autosomal markers (average spacing 9.13 cM, SD = 7.8 cM). Three loci showed the strongest overall evidence of linkage to atopy, with at least one allele-specific and a locus-specific p< 1 x 10(-4). This study provides evidence for at least three atopy-susceptibility loci in the Hutterites on chromosomes 1, 6 and 16.

The class III effect of azimilide is not associated with reverse use-dependence in open-chest dogs

Certain class III antiarrhythmic agents manifest loss of effect at short cycle lengths (CLs). This effect may limit their efficacy in the presence of tachycardia. We studied the frequency-dependent effect of azimilide (NE-10064), a new class III agent, on the right ventricular monophasic action potential (APD90) in 12 open-chest dogs. The monophasic action-potential duration at different pacing CLs (140-400 ms), during sinus rhythm, and ventricular fibrillation CL (VFCL) from left epicardial electrograms were recorded before and after increasing doses of intravenous azimilide. At pacing CL of 400 ms, APD90 was significantly prolonged after 7, 17, and 30 mg/kg of azimilide by 5.4, 7.7, and 10.7%, respectively. The extent of APD90 prolongation was independent of rate. Azimilide increased the APD90 by similar amounts at CL of 400 ms and at the fastest possible stimulation rate maintaining 1:1 capture (mean, 171 +/- 23 ms): by 2.6 +/- 8.6% and 5.6 +/- 5.9% at 2 mg/kg, 5.4 +/- 4.8% and 4.8 +/- 4.7% at 7 mg/kg, 7.7 +/- 5.6% and 9.9 +/-4.5% at 17 mg/kg, and 10.7 +/- 2.6% and 19.3 +/- 11.9% at 30 mg/kg, respectively. Azimilide caused no changes in arterial blood pressure or heart rate. Azimilide prolongs APD90 even at very short CLs. The absence of reverse use-dependence of effect on APD90 may have clinical importance.

Early switch from intravenous to oral antibiotics and early hospital discharge: a prospective observational study of 200 consecutive patients with community-acquired pneumonia

To determine the proportion of patients who can be treated with early switch to oral antibiotics and early discharge, to evaluate clinical outcome and patient satisfaction for patients treated with early switch and early discharge, and to define the factors that interfere with early discharge for some of the patients who underwent early switch to oral antibiotic therapy.

DESIGN

Prospective study.

PARTICIPANTS

Two hundred consecutive hospitalized patients with community-acquired pneumonia.

MAIN OUTCOME MEASURES

Number of days needed to switch to oral therapy and length of hospital stay. Clinical outcome and satisfaction with care were evaluated for those patients treated with early switch and early discharge.

RESULTS

Early switch to oral antibiotics (within the first 3 days of hospitalization) was performed in 133 patients (67%). Clinical failure was documented in 1 patient. Early switch and early discharge was performed in 88 patients (44%). The mean length of hospital stay for this group was 3.4 days. The most common reason for prolonged hospitalization after the switch to oral antibiotics was the need for diagnostic workup. More than 95% of patients were satisfied with the care they had received.

CONCLUSIONS

Using simple clinical and laboratory criteria, a significant proportion of hospitalized patients with community-acquired pneumonia (44%) can be treated with early switch and early discharge. This model did not affect patient outcome, decreased the length of hospitalization, and was associated with a high level of patient satisfaction.

Validation of a noninvasive measure of local myocardial repolarization in a conscious human model: adaptation of repolarization to changes in rate

INTRODUCTION

A commercial pacemaker sensor measure of the unipolar endocardial stimulus to T wave interval may accurately reflect changes in the monophasic action potential duration at 90% repolarization (APD90). This sensor system was used to study the kinetics of adaptation of repolarization duration to changes in heart rate in humans.

METHODS AND RESULTS

Patients were studied using an external pacemaker capable of displaying all stimulus to T wave intervals for each paced beat. Right ventricular stimulation was delivered via the pacemaker and compared simultaneously to APD90. Steady-state pacing was simulated by 60 seconds of pacing at cycle lengths (CLs) 350 to 700 msec. Adaptation to a new ventricular rate was analyzed with a sudden 200-msec decrease in CL. The relation between repolarization measure and steady-state CL (n = 16) was linear with a slope of 0.16 and 0.19 for APD90 and stimulus to T wave interval, respectively (P = NS). The adaptation of both repolarization measures to a sudden change in rate were best modeled by a biexponential function. Stimulus to T wave interval exhibited a parallel course to APD90, and an analysis of normalized differences between APD90 and stimulus to T wave interval followed an approximately normal distribution, with 93.5% of the paired differences within 2 SD of the mean.

CONCLUSION

A pacemaker sensor measure of stimulus to T wave interval accurately parallels APD90 during both steady-state and sudden changes in rate. Repolarization in human endocardium follows a linear relation to steady-state CL and adapts to a new rate with a biexponential function. This model represents a novel method for studying human cardiac repolarization.