Three-year chronic follow-up from the pilot study of a substernal extravascular implantable cardioverter defibrillator

Funding Acknowledgements

Type of funding sources: Private grant(s) and/or Sponsorship. Main funding source(s): Medtronic

Background

The investigational Extravascular Implantable Cardioverter-Defibrillator (EV ICD) uses a substernal lead and delivers defibrillation and pacing therapies, including antitachycardia pacing (ATP).

Objective

To characterize EV ICD system performance through 3 years.

Methods

The prospective, first-in-human EV ICD Pilot study was conducted at 4 sites in Australia and New Zealand. ICD-indicated patients were enrolled July-December of 2018. Defibrillation testing was conducted for all patients at implant, and chronically per physician discretion. Electrical testing was conducted at pre-hospital discharge, 2 weeks, 4-6 weeks and 3 months post-implant, and every 6 months thereafter. Posture effects on pacing and sensing were evaluated through 3 months.

Results

Of 26 patients enrolled, 21 underwent the EV ICD implant procedure. There were no intraprocedural complications. After successful implantation and testing, 17 of 21 patients entered chronic follow-up. 14 patients continue follow up, representing 523 patient-months. Eight elective chronic defibrillation tests converted 7 of 7 patients with ≤ 40 J (maximum energy). Five episodes of spontaneous ventricular tachycardia (VT) were detected in 1 patient and either self-terminated or successfully defibrillated with appropriate shock.

Over the total course of follow-up, 3 patients received an inappropriate shock due to; lead tip displacement with subsequent P-wave oversensing; Electromagnetic interference (EMI) in a ungrounded hot-tub; and EMI while doing plumbing work on unearthed electrical pipes, resulting in an annualized inappropriate shock rate of 6.9%.

Pacing capture thresholds remained stable across time (5.1 ± 2.0 V at implant and 5.5 ± 2.7 V at 3 years); similarly, R-wave amplitudes were stable across time (3.4 ±2.0 mV at implant and 4.2 ± 2.7 mV at 3 years). Pacing thresholds tended to be lowest with the patient lying on the right side and pacing threshold often increased relative to supine position for left-side, prone or bending postures. R-wave amplitude tended to be greater when bending forward.

There were 10 system or procedure-related adverse events in 8 patients through 3 years, including 3 elective system removals for: a single inappropriate shock (1), chronic defibrillation testing showing no safety margin in a patient with arrhythmogenic right ventricular dysplasia (1), intolerance to ATP (1 - high pacing threshold and frequent VT). Other than the lead tip displacement within the first 3 months, no additional clinically significant lead displacements have been observed through 3 years.

Conclusion

The EV ICD is a novel platform for delivering high-voltage therapy. There were no procedure and system related complications observed after the first year post-implant. Lead position and chronic system performance have generally remained stable through 3 years with a low rate of adverse events.

Long-term outcomes of 265,737 patients hospitalised with atrial fibrillation and atrial flutter from 2008 to 2015

Background

Atrial fibrillation/atrial flutter (AF/AFL) hospitalisations are common, however, little is known about the long-term outcomes of these episodes.

Objective

To examine the incidence of mortality, all-cause and cause-specific re-hospitalisations at up to 8 years after a hospitalisation for AF/AFL.

Methods

Unique patients hospitalised with a primary diagnosis of AF/AFL from 2008–2015 were identified using nation-wide hospitalisation data from Australia and New Zealand. All-cause mortality was the primary outcome. Secondary endpoints included all-cause and cause-specific re-hospitalisations. Results were reported as incident rate per 100 patient-years.

Results

We included 265,737 patients (mean age 69.9±13.9y, female 45.2%, elective 28.7%). The median length of stay was 1 day (Interquartile range [IQR] 0–4 days) and the median CHA2DS2-VASc score was 2 (IQR 1–2). During the index hospitalisation, 9,837 (3.7%) patients underwent catheter or surgical ablation and 52,634 (19.8%) underwent cardioversion. During the median follow-up time of 3.4 years (range 0–8.0 years), 53,669 patients died (incident rate of 5.7/100 patient-years) with a survival probability gradually decreasing from 92.8% (95% CI 92.7–92.9%) at 1-year to 65.4% (95% CI 64.9–65.8%) at 8-years post-discharge (Table 1 and Figure 1). All-cause re-hospitalisations occurred in 210,118 patients (incident rate of 22.2/100 patient-years) with a rehospitalisation-free survival probability of 7.1% (95% CI 6.9—7.3%) at the end of follow-up. Unplanned re-hospitalisations occurred more frequently than planned episodes (incident rate of 17.2 vs. 16.6/100 patient-years respectively). AF/AFL accounted for 25.1% of all-cause re-hospitalisations (incident rate of 8.9/100 patient-years) and the probability of freedom from re-hospitalisations for AF/AFL was 55.4% (95% CI 55.0–55.8%) at 8-years. Incident rates of re-hospitalisations for catheter ablation (1.5/100 patient-years), stroke (1.6/100 patient-years), heart failure (2.7/100 patient-years), and acute myocardial infarction (1.0/100 patient-years) were low. In subgroup analyses, worse survival was observed in female patients, older age groups, patients with comorbid heart failure, hypertension, diabetes, and those who did not undergo ablation during the index hospitalisation.

Conclusion

Nearly two-thirds of patients were surviving by 8-years following an AF/AFL hospitalisation with a low rate of re-hospitalisations for stroke, heart failure, and myocardial infarction. However, re-hospitalisations for recurrent atrial arrhythmia were common. Efforts to reduce re-hospitalisations, especially unplanned encounters, are required to improve patient outcomes.

Funding Acknowledgement

Type of funding sources: Foundation. Main funding source(s): National Heart Foundation of Australia

The prevalence of obesity among forensic intellectual disability inpatients

Background

Inpatient mental health settings have been described as “obesogenic” environments, due to factors including psychotropic medication, high calorie food, restricted physical activity and sedentary lifestyles. No research has investigated obesity among forensic intellectual disability inpatients, despite this populations’ increased risk. Therefore, this paper aims to evaluate the prevalence and correlates of overweight and obesity on, and during admission.

Method

The weight and body mass index data of 46 inpatients (15 women and 31 men) within a specialist intellectual disability forensic service was examined for the study.

Results

Only six patients (13%) were a normal weight at admission, whereas 40 (87%) were overweight or obese. During their admission, 28 (61%) gained weight (average 11.8 kg), and one (2%) maintained. However, 17 patients (37%) lost weight (average 6.2 kg), though 16 remained in overweight/obese categories. There was no correlation between length of stay and weight/BMI.

Conclusions

The majority of patients were overweight or obese on admission, and approximately 60% gained weight during their admission. Women appeared at greater risk of obesity. There was no relationship between length of stay and weight. This is potentially due to the high prevalence of obesity on admission and the impact of previous admissions on weight. The results highlight the need for effective weight management interventions with this population.

Disclosure of interest

The authors have not supplied their declaration of competing interest.

Reduction of histone cytotoxicity by the Alzheimer beta-amyloid peptide precursor

In a search for Alzheimer beta-amyloid peptide precursor ligands, Potempska et al. (Arch. Biochem. Biophys. (1993) 304, 448) found that histones bind with high affinity and specificity to the secreted precursor. Because exogenous histones can be cytotoxic, we compared the effects of histones on the viability of cells which produce little beta-amyloid peptide precursor (U-937) to those on cells that produce twenty times as much precursor (COS-7). Addition of purified histones caused necrosis of U-937 cells (histone H4, LD50 = 1.5 microM). Extracellular A beta precursor in the submicromolar range prevented histone-induced U-937 cell necrosis. Cell-surface precursor also reduced histone toxicity: COS-7 cells were less sensitive to the toxic effects of histone H4 (LD50 = 5.4 microM). COS-7 cells in which the expression of an APP mRNA-directed ribozyme reduced the synthesis of the protein by up to 80% were more sensitive to histone H4 (LD50 = 3.2 microM) than cells that expressed the vector alone. Histone H4 binds to cell-associated A beta precursor. Cells expressing the A beta precursor-directed ribozyme bound less 125I-labeled histone H4 than those expressing the vector alone. In the limited extracellular space of tissues in vivo, both secreted and cell-surface A beta precursor protein may play significant roles in trapping chromatin or histones and removing them from the extracellular milieu.

Multiple proteins interact at a unique cis-element in the 3'-untranslated region of amyloid precursor protein mRNA

Growing evidence suggests that Alzheimer's disease results from dysregulated production and deposition of beta-amyloid in the central nervous system. beta-Amyloid is derived from proteolytic processing of one of multiple amyloid precursor protein (APP) isoforms. The production of APP in many somatic tissues and tumor cell lines provides a more accessible model to study the regulation of APP gene expression. Recent data suggest that APP mRNAs accumulate in activated lymphocytes and neuronal tumor lines. We are interested in defining the contribution of alterations in stability to changes in steady-state APP mRNA levels in these model systems. Herein we demonstrate by mobility shift assay that the 3'-untranslated region of APP RNAs which contain a contiguous 29-base region interacts in vitro with multiple mRNA-binding proteins found in cytosolic lysates prepared from normal and transformed human cells. UV cross-linking of radiolabeled APP RNAs to cytosolic protein extracts followed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis identified six distinct RNA-protein complexes of 42, 47, 65, 73, 84, and 104 kDa. Competition assays with APP, AU-rich, or irrelevant RNAs demonstrated that binding was specific and in some cases preferential for AU- or U-rich sequences by which we tentatively place the binding site of the proteins along the 29-base region. APP mRNA-binding proteins were constitutively active in all tumor lines examined as well as at diminished levels in whole human brain cytosolic lysates. The core element is AU-rich and highly conserved between human and some murine APP mRNAs. In the accompanying paper (Zaidi, S. H. E. and Malter, J. S. (1994) J. Biol. Chem. 269, 24007-24013) we show that this 29-base element in the 3'-untranslated region regulates the stability of APP mRNA. Cumulatively these data suggest that steady-state APP mRNA levels are modulated by cytosolic protein-RNA interactions.

Novel cleavage of a hammerhead ribozyme targeted to beta-amyloid peptide precursor mRNA

A trans-acting hammerhead ribozyme (D0) was designed to cleave at the first GUC decreases X target sequence in Alzheimer amyloid precursor (beta APP) mRNA. A synthetic 26-base substrate analog of beta APP mRNA, labeled with either [alpha-32P]CTP or [alpha-35S]CTP underwent Mg(+2)-dependent, site-specific cleavage in vitro. Cleavage was found to occur at two sites. The major product of the reaction, a 13-base oligonucleotide, resulted from cleavage at the consensus cut site of hammerhead ribozymes. A minor 12-base product was formed by cleavage one base 5' to this site. When the beta APP substrate analog was labeled with [alpha-35S]ATP (Rp isomer) another cleavage site, amounting to 25-30% of the total product formed, was also activated. A series of ribozyme deletion mutants delimited the new cleavage site to the phosphate linkage 5' to the G residue of the hammerhead consensus cut site, GUC decreases X. We conclude that small changes in RNA conformation can dramatically alter ribozyme specificity in vitro. This may have implications for targeting hammerhead ribozymes in vivo.

Distribution and activity of alternatively spliced Alzheimer amyloid peptide precursor and scrapie PrP mRNAs on rat brain polysomes

Mammalian brains contain low levels of the Alzheimer amyloid precursor variants (AAPPs) and the normal form of the scrapie agent protease-resistant protein (PrPc); however, their mRNAs are readily detectable. To understand these discrepancies we have investigated some aspects of the translational regulation of these mRNAs. An accurate blot-hybridization procedure was developed to measure absolute amounts of mRNA. Rat brain contains the following mRNA levels (ng/g tissue) AAPP(695), 170; AAPP(751/770), 63; PrPc, 144; actin, 615; glyceraldehyde-3-phosphate dehydrogenase (G3PDH), 359; ferritin, 148. The method was also used to determine the distribution of mRNAs between translationally active polysomes and translationally inactive ribonucleoprotein protein particles (mRNPs). More than 90% of G3PDH and actin mRNAs were associated with polysomal RNA; whereas, ferritin light chain mRNA was predominantly (90%) in mRNP RNA. The degree of cross-contamination of mRNPs with polysomes was less than 10%. Probes specific for the scrapie PrP protein and the AAPP(695) splice junction revealed that 70% of these mRNAs were associated with polysomes. One-half of AAPP(751/770) mRNAs (which comprise 20-30% of all AAPP mRNA in brain) were found in polysomes. We conclude therefore that both scrapie and AAPP mRNAs are subject to translational regulation in rat brain. Evidence from in vitro translational experiments confirm the message distribution determined by blot hybridization and corroborate the hypothesis that AAPP is subject to partial post-transcriptional regulation. Nevertheless, the low tissue levels of AAPP and PrPc must result primarily from their relatively rapid turnover.

Effect of point mutations in the decoding site (C1400) region of 16S ribosomal RNA on the ability of ribosomes to carry out individual steps of protein synthesis

In order to probe the relationship between structure and function of the ribosome, an in vitro system [Denman et al. (1988) Biochemistry (preceding paper in this issue)] was used to make a series of base changes around C1400, a residue known to be at the decoding site. Replacement of C1400 by U, A, or G, deletion of single bases at and to either side of C1400, and insertion of C or U next to C1400 were done. In a separate study, a mutant with seven extra nucleotides at the 3' end was constructed. The activity of these 11 mutants in A and P site binding and in initiation-dependent and initiation-independent peptide synthesis was analyzed. None of the base substitutions of C1400 were markedly inhibitory despite the almost complete conservation of this residue in ribosomal RNAs from a wide range of species. The insertions and deletions completely blocked initiation-dependent peptide synthesis but markedly stimulated the initiation-independent reaction. The effects on tRNA binding were variable. The extra stem and loop at the 3' end blocked initiation-dependent peptide synthesis but did not influence the other assays. The only modification to block all ribosomal function was the deletion of G1401. It appears that while the conserved and cross-linkable C1400 is not essential for function, the adjacent conserved G1401 is.

In vitro assembly of 30S and 70S bacterial ribosomes from 16S RNA containing single base substitutions, insertions, and deletions around the decoding site (C1400)

An in vitro system developed for the site-specific mutagenesis of 16S RNA of Escherichia coli ribosomes [Krzyzosiak et al. (1987) Biochemistry 26, 2353-2364] was used to make 10 single base changes around C1400, a residue known to be at the decoding site. C1400 was replaced by U, A, or G, five single base deletions at and to either side of C1400 were made, and C or U was inserted next to C1400. Another mutant possessed seven additional nucleotides at the 3' end of the 16S RNA such that a stem and loop involving the anti-Shine-Dalgarno sequence could form. Each of the mutant RNAs was reconstituted with a complete mixture of 30S proteins to yield 30S ribosomes. Modified in vitro reconstitution conditions were required to obtain assembly of all of the synthetic ribosomes. Quantitative HPLC analysis of the protein content of each mutant showed that all of the proteins were present. The ability of synthetic 30S to form 70S particles under functional assay conditions was about 75% that of natural 30S and was unchanged by any of the mutations except for the deletion of G1401, which decreased the association activity under the standard conditions to 35-40% of synthetic 30S. That part of the ribosomal P site which interacts with the anticodon loop of tRNA was investigated by near-UV (greater than 300 nm) induced cross-linking of AcVal-tRNA. Cross-linking depended on both 30S subunits and the correct codon. The cross-linking yield of all mutants with a pyrimidine at position 1400 was equal to control isolated 30S, and the first-order rate constants for cross-linking of those mutants tested were like reconstituted natural 30S. The site of cross-linking for mutants with a C or U insertion between C1400 and G1401 was shifted to the inserted residue. Cross-linking to the base 5' to G1401 rather than to the residue 3' to C1399 indicates that G1401 is an important structural determinant of the P site.

An efficiently mutagenizable recombinant plasmid for in vitro transcription of the Escherichia coli 16 S RNA gene

The portion of the rrnB operon coding for 16 S RNA was modified to permit efficient in vitro transcription by T7 RNA polymerase of full-length, correctly terminated, biologically active 16 S RNA (W. Krzyzosiak et al., 1987, Biochemistry 26, 2353-2364). The 5'-end of the gene was fused to the class III T7 promoter and the 3'-end was modified so that cleavage with MstII would generate correctly terminated RNA upon runoff transcription. The modified gene was placed in pUC19 by a four-way ligation reaction involving linearized pUC19, a 1490-bp fragment of 16 S rDNA, and two synthetic oligodeoxynucleotides. Because of the cohesive end design, phosphorylation of the synthetic oligomers was not necessary. Single and tandem cassette insertions were used to generate single base changes in the C-1400 region of 16 S RNA. Three examples are described. This method is generally applicable to the 16 S RNA molecule as suitable singlecleavage restriction sites allow all regions to be mutated by this approach.

The role of 16S RNA in ribosome function: single base alterations and their effect on in vitro protein synthesis

An in vitro system developed for the site-specific mutagenesis of 16S RNA of Escherichia coli ribosomes (Krzyzosiak et al., Biochemistry 26, 2353-2364, 1987) was used to make 10 single base changes around C1400, the residue known to be at the decoding site. C1400 was replaced by U, A, or G, 5 single base deletions at and to either side of C1400 were made, and C or U was inserted next to C1400. Another mutant possessed 7 additional nucleotides at the 3' end of the 16S RNA such that a stem and loop involving the anti-Shine-Dalgarno sequence could form. Another series of 8 mutants tested hypothetical base-pairing between C1404, G1405 and C1496, G1497. The activity of these 19 mutants in A and P site binding, and in initiation-dependent and initiation-independent peptide synthesis was determined. None of the base substitutions of C1400 were strongly inhibitory. The insertions and deletions completely blocked initiation-dependent peptide synthesis but markedly stimulated the initiation-independent reaction. The effects of tRNA binding were variable. The only alteration to block all ribosomal function was the deletion of G1401. The extra stem and loop at the 3'-end blocked initiation-dependent peptide synthesis, but all other assays were normal. The mutants which break and reform the hypothetical base-pairs had a functional pattern that suggest the contiguous base-pairs do exist and are functionally important.

Crosslinking of the anticodon of P site bound tRNA to C-1400 of E.coli 16S RNA does not require the participation of the 50S subunit

Crosslinking of the 5'-anticodon base of ribosomal P site bound AcVal-tRNA to residue C-1400 of 16S RNA or to its equivalent in 18S RNA has been shown to occur on 70S or 80S ribosomes of both prokaryotes and eukaryotes [Ciesiolka, J., Nurse, K., Klein, J. and Ofengand, J. (1985) Biochemistry 24, 3233-3239]. In the present work, we show that the crosslinking rate, crosslinking yield, and site of crosslinking are all unchanged when the 50S subunit is omitted. Therefore, all of the positional features of tRNA-ribosome complexes which allow crosslinking to occur are entirely contained in the 30S subunit. Blockage of reverse transcription by crosslink formation was used to determine the site of crosslinking. This analysis revealed that RNA modifications which do not directly block base-pairing ligands sometimes allow the modified base to be transcribed, leading to doublet band formation even when there is only a single crosslink site.