Toward magnetic resonance-guided electroanatomical voltage mapping for catheter ablation of scar-related ventricular tachycardia: a comparison of registration methods

Toward MR‐Guided Electroanatomical Voltage Mapping for Catheter Ablation. Introduction: Integration of preprocedural delayed enhanced magnetic resonance imaging (DE‐MRI) with electroanatomical voltage mapping (EAVM) may provide additional high‐resolution substrate information for catheter ablation of scar‐related ventricular tachycardias (VT). Accurate and fast image integration of DE‐MRI with EAVM is desirable for MR‐guided ablation. Methods and Results: Twenty‐six VT patients with large transmural scar underwent catheter ablation and preprocedural DE‐MRI. With different registration models and EAVM input, 3 image integration methods were evaluated and compared to the commercial registration module CartoMerge. The performance was evaluated both in terms of distance measure that describes surface matching, and correlation measure that describes actual scar correspondence. Compared to CartoMerge, the method that uses the translation‐and‐rotation model and high‐density EAVM input resulted in a registration error of 4.32±0.69 mm as compared to 4.84 ± 1.07 (P <0.05); the method that uses the translation model and high‐density EAVM input resulted in a registration error of 4.60 ± 0.65 mm (P = NS); and the method that uses the translation model and a single anatomical landmark input resulted in a registration error of 6.58 ± 1.63 mm (P < 0.05). No significant difference in scar correlation was observed between all 3 methods and CartoMerge (P = NS). Conclusions: During VT ablation procedures, accurate integration of EAVM and DE‐MRI can be achieved using a translation registration model and a single anatomical landmark. This model allows for image integration in minimal mapping time and is likely to reduce fluoroscopy time and increase procedure efficacy. (J Cardiovasc Electrophysiol, Vol. 23, pp. 74‐80, January 2012)     

Molecular basis for specific viral RNA recognition and 2′-O-ribose methylation by the dengue virus nonstructural protein 5 (NS5)

Dengue virus (DENV) causes several hundred million human infections and more than 20,000 deaths annually. Neither an efficacious vaccine conferring immunity against all four circulating serotypes nor specific drugs are currently available to treat this emerging global disease. Capping of the DENV RNA genome is an essential structural modification that protects the RNA from degradation by 5′ exoribonucleases, ensures efficient expression of viral proteins, and allows escape from the host innate immune response. The large flavivirus nonstructural protein 5 (NS5) (105 kDa) has RNA methyltransferase activities at its N-terminal region, which is responsible for capping the virus RNA genome. The methyl transfer reactions are thought to occur sequentially using the strictly conserved flavivirus 5′ RNA sequence as substrate (G_pppAG-RNA), leading to the formation of the 5′ RNA cap: G_0pppAG-RNA→^m7G_0pppAG-RNA (“cap-0”)→^m7G_0pppA_m2′-O-G-RNA (“cap-1”). To elucidate how viral RNA is specifically recognized and methylated, we determined the crystal structure of a ternary complex between the full-length NS5 protein from dengue virus, an octameric cap-0 viral RNA substrate bearing the authentic DENV genomic sequence (5′-^m7G_0pppA₁G₂U₃U₄G₅U₆U₇-3′), and S-adenosyl-l-homocysteine (SAH), the by-product of the methylation reaction. The structure provides for the first time, to our knowledge, a molecular basis for specific adenosine 2′-O-methylation, rationalizes mutagenesis studies targeting the K61-D146-K180-E216 enzymatic tetrad as well as residues lining the RNA binding groove, and offers previously unidentified mechanistic and evolutionary insights into cap-1 formation by NS5, which underlies innate immunity evasion by flaviviruses.Several members of the Flavivirus genus from the Flaviviridae family are major human pathogens, such as the four serotypes of dengue virus (DENV1–4), West Nile virus (WNV), Japanese encephalitis virus (JEV), and yellow fever virus (YFV). Recent large-scale DENV vaccine trials using a tetravalent formulation and three dose injections have shown only limited protection against the four DENV serotypes, and no specific antiviral drug has reached the market so far (1–3). The flavivirus genome consists of a (+)-sense single-stranded RNA of ∼11 kb with a type 1 cap structure, followed by the strictly conserved dinucleotide sequence “AG”: 5′-^m7G_pppA_m2′-O-G-3′ (4, 5). Addition of the cap moiety to the 5′ end of the viral genome is crucial for viral replication, because this structure ensures efficient production of viral polyproteins by the host translation machinery and protection against degradation by 5′-3′ exoribonucleases, and also because it conceals the triphosphorylated (or diphosphorylated) end from recognition by host cell innate immune sensors (6–9). Following (+)-strand RNA synthesis by the C-terminal RNA-dependent RNA polymerase (RdRp) domain of nonstructural protein 5 (NS5), cap formation in flaviviruses results from several sequential enzymatic reactions carried out by (i) the RNA triphosphatase activity of the NS3 protease-helicase that hydrolyzes the γ-phosphate group of the viral 5′ untranslated region (UTR), yielding a diphosphate RNA, (ii) a guanylyl-transferase activity proposed to reside in the methyltransferase (MTase) domain of NS5, which transfers a GMP molecule to the 5′-diphosphate RNA, and (iii) NS5-mediated sequential N-7- and 2′-O-methylations according to the following scheme: G_0pppAG-RNA→^m7G_0pppAG-RNA (“cap-0”)→^m7G_0pppA_m2′-O-G-RNA (“cap-1”) (5, 10–12).During flavivirus RNA replication, 5′-guanosine N-7-methylation is shown to be essential for translation of the viral polyprotein (13), whereas 2′-O-methylation on the penultimate A nucleotide conceals the viral genome from host immune sensors, notably RIG-I (14), MDA5 (15), and IFIT1 (16–18). Specifically, WNV carrying the E218A mutation in NS5 (E216A in DENV3 NS5) devoid of 2′-O (but not N-7) MTase activity was attenuated in wild-type but not Ifit1^−/− cells (16). Furthermore, the translation of JEV viral proteins was inhibited by IFIT1 through direct binding to the 5′-capped 2′-O-unmethylated mRNA (17). More recently, 2′-O-methylation at internal adenosines (but not at G, C, or U positions) by the flavivirus NS5 protein was demonstrated. The functional consequence of methylation at internal adenosines was an attenuation of viral RNA translation and replication (12). In vitro, the MTase domain of NS5 catalyzes these two enzymatic reactions with distinct requirements of RNA substrates and buffers: 5′-guanosine N-7 methyl transfer is optimal on a 211-nt segment of the 5′UTR at pH 6 and is inhibited by MgCl₂, whereas adenosine ribose 2′-O-methylation only requires a short RNA with “AG” as the first two RNA nucleotides and is maximal at pH 9–10 in the presence of Mg²⁺ ions. Thus, NS5 plays a crucial role both in virus replication and evasion of the host innate immune response, and therefore constitutes an attractive therapeutic target for antiviral drug and vaccine development (2, 19).Several crystal structures of flavivirus MTases have been reported either as free enzymes or bound to GTP (20), to the broad antiviral nucleoside analog ribavirin (21), to short cap analogs (22, 23), and to a capped-RNA octamer (24). Collectively, these structures uncovered a GTP binding site, the S-adenosyl-methionine (SAM) methyl-donor binding pocket, and a basic cleft at the protein surface that was proposed to accommodate the incoming RNA substrate. However, in the absence of a viral RNA in a catalytically meaningful position, the mechanism accounting for specific viral RNA methylation, including the structural basis for specific adenosine 2′-O-methylation, remains elusive. Moreover, the size of the RNA substrate that can be accommodated by the putative RNA binding cleft is also unknown, as well as any requirement for a specific RNA conformation. Determination of the structure of NS5 bound to a viral RNA would give valuable information to guide the design of specific NS5 inhibitors.To elucidate how the flavivirus RNA is recognized and methylated, we determined the crystal structure of a ternary complex between the full-length NS5 protein (DENV serotype 3), an authentic cap-0 viral RNA substrate (5′-^m7G_0pppA₁G₂U₃U₄G₅U₆U₇-3′), and S-adenosyl-l-homocysteine (SAH), the by-product of the methylation reaction. Together with mutagenesis data informed by the present structure, this work reveals a unique and specific interaction between the protein and viral RNA and provides the molecular basis for the methyl transfer reaction. Furthermore, despite a low sequence identity between the two proteins, the RNA recognition mode is reminiscent of how the human 2′-O-ribose methyltransferase CMTr1 binds mRNA for cap formation, suggesting that the viral methyltransferase might derive from its eukaryotic homolog.     

Hemophagocytic Lymphohistiocytosis in Intensive Care Unit: A 71-Case Strobe-Compliant Retrospective Study

Hemophagocytic lymphohistiocytosis (HLH) is a critical condition that may lead to organ failure and early death. The aim of this retrospective observational study was to describe a cohort of HLH patients admitted to intensive care unit (ICU) and investigate the risk factors of early death.A positive HLH diagnosis was defined by an HScore ≥169. Univariate and multivariate analyses were carried out to investigate hospital and 28-day mortality risk factors. Between January 2002 and July 2014, 71 HLH cases were seen at our institution.The overall 28-day mortality (start at ICU admission) and hospital mortality were 38% and 68%, respectively. The factors associated with increased 28-day mortality were the sequential organ failure assessment score at ICU admission (P < .001) and advance in age (P = 0.03). The factors associated with increased hospital mortality were a high sequential organ failure assessment score at ICU admission (P < 0.01), advance in age (P = 0.04), and the presence of lymphoma-related HLH or HLH of unknown origin (P < 0.01).Organ failure overtops the classical early-death risk factors in adult ICU-admitted HLH patients. This failure and the subsequent early death may be prevented by timely specific cytotoxic therapies and the control of the underlying disease.     

Intensive care unit mortality after cardiac arrest: the relative contribution of shock and brain injury in a large cohort

Objective

Brain injury is well established as a cause of early mortality after out-of-hospital cardiac arrest (OHCA), but postresuscitation shock also contributes to these deaths. This study aims to describe the respective incidence, risk factors, and relation to mortality of post-cardiac arrest (CA) shock and brain injury.

Design

Retrospective analysis of an observational cohort.

Setting

24-bed medical intensive care unit (ICU) in a French university hospital.

Patients

All consecutive patients admitted following OHCA were considered for analysis. Post-CA shock was defined as a need for infusion of vasoactive drugs after resuscitation. Death related to brain injury included brain death and care withdrawal for poor neurological evolution.

Intervention

None.

Measurements and main results

Between 2000 and 2009, 1,152 patients were admitted after OHCA. Post-CA shock occurred in 789 (68 %) patients. Independent factors associated with its onset were high blood lactate and creatinine levels at ICU admission. During the ICU stay, 269 (34.8 %) patients died from post-CA shock and 499 (65.2 %) from neurological injury. Age, raised blood lactate and creatinine values, and time from collapse to restoration of spontaneous circulation increased the risk of ICU mortality from both shock and brain injury, whereas a shockable rhythm was associated with reduced risk of death from these causes. Finally, bystander cardiopulmonary resuscitation (CPR) decreased the risk of death from neurological injury.

Conclusions

Brain injury accounts for the majority of deaths, but post-CA shock affects more than two-thirds of OHCA patients. Mortality from post-CA shock and brain injury share similar risk factors, which are related to the quality of the rescue process.     

Validation of a new standardized cystatin C turbidimetric assay: Evaluation of the three novel CKD-EPI equations in hypertensive patients

Objectives

Analytical and clinical performances of the new standardized cystatin C particle-enhanced turbidimetric immunoassay (PETIA) using DiaSys reagents on Olympus AU2700® analyzer were evaluated.

Design and methods

We have studied imprecision, linearity, limit of detection and limit of quantification of this new immunoassay. Method comparison was assessed in relation to results generated by the standardized Siemens-particle-enhanced nephelometric immunoassay (PENIA). In order to evaluate the clinical relevance of this assay, estimated glomerular filtration rate (GFR) was calculated using MDRD, CKD-EPI creatinine, CKD-EPI cystatin C 2012 and CKD-EPI creatinine–cystatin C 2012 equations and compared to GFR measured using urinary clearance of ^99mTc-DTPA in 100 hypertensive patients.

Results

Cystatin C measurements using DiaSys reagents have reliable analytical performances and are comparable to the standardized Siemens-PENIA method (bias of 0.01 mg/L). The mean measured GFR was 90.0 ± 29.7 mL/min/1.73 m². Bias and accuracy of the three CKD-EPI equations were better than the MDRD. Both CKD-EPI creatinine-based and cystatin C-based formulae had similar bias, precision and accuracy. The combined creatinine–cystatin C equation was significantly more accurate and precise than the CKD-EPI creatinine equation in patients with GFR above 60 mL/min/1.73 m².

Conclusions

The use of cystatin C in a combined equation with creatinine could improve the accuracy of eGFR in the reference interval.     

Life stress and the long-term treatment course of recurrent depression: III. Nonsevere life events predict recurrence for medicated patients over 3 years

Research has consistently documented the significance of severe life events for onset of major depression. Theory, however, suggests other forms of stress are relevant for depression's recurrence. Nonsevere life events were tested in relation to depression for 126 patients with recurrent depression in a 3-year randomized maintenance protocol. Life stress was assessed every 12 weeks and rated along dimensions of severity, focus, and independence. A significant interaction between specific types of nonsevere life events and medication was found. For medicated patients, subject-focused independent nonsevere life events predicted recurrence; for unmedicated patients, these events predicted fewer recurrences. Other nonsevere life events did not predict recurrence. The findings underscore the potential importance of specific stressors for triggering recurrences of depression.