Network


Latest external collaboration on country level. Dive into details by clicking on the dots.

Hotspot


Dive into the research topics where Maria Alu is active.

Publication


Featured researches published by Maria Alu.


The New England Journal of Medicine | 2016

Transcatheter or Surgical Aortic-Valve Replacement in Intermediate-Risk Patients

Martin B. Leon; Craig R. Smith; Michael J. Mack; Raj Makkar; Lars G. Svensson; Susheel Kodali; Vinod H. Thourani; E. Murat Tuzcu; D. Craig Miller; Howard C. Herrmann; Darshan Doshi; David J. Cohen; Augusto D. Pichard; Samir Kapadia; Todd M. Dewey; Vasilis Babaliaros; Wilson Y. Szeto; Mathew R. Williams; Alan Zajarias; Kevin L. Greason; Brian Whisenant; Robert W. Hodson; Jeffrey W. Moses; Alfredo Trento; David L. Brown; William F. Fearon; Philippe Pibarot; Rebecca T. Hahn; Wael A. Jaber; William N. Anderson

BACKGROUND Previous trials have shown that among high-risk patients with aortic stenosis, survival rates are similar with transcatheter aortic-valve replacement (TAVR) and surgical aortic-valve replacement. We evaluated the two procedures in a randomized trial involving intermediate-risk patients. METHODS We randomly assigned 2032 intermediate-risk patients with severe aortic stenosis, at 57 centers, to undergo either TAVR or surgical replacement. The primary end point was death from any cause or disabling stroke at 2 years. The primary hypothesis was that TAVR would not be inferior to surgical replacement. Before randomization, patients were entered into one of two cohorts on the basis of clinical and imaging findings; 76.3% of the patients were included in the transfemoral-access cohort and 23.7% in the transthoracic-access cohort. RESULTS The rate of death from any cause or disabling stroke was similar in the TAVR group and the surgery group (P=0.001 for noninferiority). At 2 years, the Kaplan-Meier event rates were 19.3% in the TAVR group and 21.1% in the surgery group (hazard ratio in the TAVR group, 0.89; 95% confidence interval [CI], 0.73 to 1.09; P=0.25). In the transfemoral-access cohort, TAVR resulted in a lower rate of death or disabling stroke than surgery (hazard ratio, 0.79; 95% CI, 0.62 to 1.00; P=0.05), whereas in the transthoracic-access cohort, outcomes were similar in the two groups. TAVR resulted in larger aortic-valve areas than did surgery and also resulted in lower rates of acute kidney injury, severe bleeding, and new-onset atrial fibrillation; surgery resulted in fewer major vascular complications and less paravalvular aortic regurgitation. CONCLUSIONS In intermediate-risk patients, TAVR was similar to surgical aortic-valve replacement with respect to the primary end point of death or disabling stroke. (Funded by Edwards Lifesciences; PARTNER 2 ClinicalTrials.gov number, NCT01314313.).


The Lancet | 2016

Transcatheter aortic valve replacement versus surgical valve replacement in intermediate-risk patients: a propensity score analysis

Vinod H. Thourani; Susheel Kodali; Raj Makkar; Howard C. Herrmann; Mathew R. Williams; Vasilis Babaliaros; Richard W. Smalling; Scott Lim; S. Chris Malaisrie; Samir Kapadia; Wilson Y. Szeto; Kevin L. Greason; Gorav Ailawadi; Brian Whisenant; Chandan Devireddy; Jonathon Leipsic; Rebecca T. Hahn; Philippe Pibarot; Neil J. Weissman; Wael A. Jaber; David Cohen; Rakesh M. Suri; E. Murat Tuzcu; Lars G. Svensson; John G. Webb; Jeffrey W. Moses; Michael J. Mack; D. Craig Miller; Craig R. Smith; Maria Alu

BACKGROUND Transcatheter aortic valve replacement (TAVR) with the SAPIEN 3 valve demonstrates good 30 day clinical outcomes in patients with severe aortic stenosis who are at intermediate risk of surgical mortality. Here we report longer-term data in intermediate-risk patients given SAPIEN 3 TAVR and compare outcomes to those of intermediate-risk patients given surgical aortic valve replacement. METHODS In the SAPIEN 3 observational study, 1077 intermediate-risk patients at 51 sites in the USA and Canada were assigned to receive TAVR with the SAPIEN 3 valve [952 [88%] via transfemoral access) between Feb 17, 2014, and Sept 3, 2014. In this population we assessed all-cause mortality and incidence of strokes, re-intervention, and aortic valve regurgitation at 1 year after implantation. Then we compared 1 year outcomes in this population with those for intermediate-risk patients treated with surgical valve replacement in the PARTNER 2A trial between Dec 23, 2011, and Nov 6, 2013, using a prespecified propensity score analysis to account for between-trial differences in baseline characteristics. The clinical events committee and echocardiographic core laboratory methods were the same for both studies. The primary endpoint was the composite of death from any cause, all strokes, and incidence of moderate or severe aortic regurgitation. We did non-inferiority (margin 7·5%) and superiority analyses in propensity score quintiles to calculate pooled weighted proportion differences for outcomes. FINDINGS At 1 year follow-up of the SAPIEN 3 observational study, 79 of 1077 patients who initiated the TAVR procedure had died (all-cause mortality 7·4%; 6·5% in the transfemoral access subgroup), and disabling strokes had occurred in 24 (2%), aortic valve re-intervention in six (1%), and moderate or severe paravalvular regurgitation in 13 (2%). In the propensity-score analysis we included 963 patients treated with SAPIEN 3 TAVR and 747 with surgical valve replacement. For the primary composite endpoint of mortality, strokes, and moderate or severe aortic regurgitation, TAVR was both non-inferior (pooled weighted proportion difference of -9·2%; 90% CI -12·4 to -6; p<0·0001) and superior (-9·2%, 95% CI -13·0 to -5·4; p<0·0001) to surgical valve replacement. INTERPRETATION TAVR with SAPIEN 3 in intermediate-risk patients with severe aortic stenosis is associated with low mortality, strokes, and regurgitation at 1 year. The propensity score analysis indicates a significant superiority for our composite outcome with TAVR compared with surgery, suggesting that TAVR might be the preferred treatment alternative in intermediate-risk patients. FUNDING None.


The Lancet | 2013

Cessation of dual antiplatelet treatment and cardiac events after percutaneous coronary intervention (PARIS): 2 year results from a prospective observational study

Roxana Mehran; Usman Baber; Philippe Gabriel Steg; Cono Ariti; Giora Weisz; Bernhard Witzenbichler; Timothy D. Henry; Annapoorna Kini; Thomas Stuckey; David J. Cohen; Peter B. Berger; Ioannis Iakovou; George Dangas; Ron Waksman; David Antoniucci; Samantha Sartori; Mitchell W. Krucoff; James B. Hermiller; Fayaz A. Shawl; C. Michael Gibson; Alaide Chieffo; Maria Alu; David J. Moliterno; Antonio Colombo; Stuart J. Pocock

BACKGROUND Dual antiplatelet therapy (DAPT) cessation increases the risk of adverse events after percutaneous coronary intervention (PCI). Whether risk changes over time, depends on the underlying reason for DAPT cessation, or both is unknown. We assessed associations between different modes of DAPT cessation and cardiovascular risk after PCI. METHODS The PARIS (patterns of non-adherence to anti-platelet regimens in stented patients) registry is a prospective observational study of patients undergoing PCI with stent implantation in 15 clinical sites in the USA and Europe between July 1, 2009, and Dec 2, 2010. Adult patients (aged 18 years or older) undergoing successful stent implantation in one or more native coronary artery and discharged on DAPT were eligible for enrolment. Patients were followed up at months 1, 6, 12, and 24 after implantation. Prespecified categories for DAPT cessation included physician-recommended discontinuation, brief interruption (for surgery), or disruption (non-compliance or because of bleeding). All adverse events and episodes of DAPT cessation were independently adjudicated. Using Cox models with time-varying covariates, we examined the effect of DAPT cessation on major adverse events (MACE [composite of cardiac death, definite or probable stent thrombosis, myocardial infarction, or target-lesion revascularisation]). Incidence rates for DAPT cessation and adverse events were calculated as Kaplan-Meier estimates of time to the first event. This study is registered with ClinicalTrials.gov, number NCT00998127. FINDINGS We enrolled 5031 patients undergoing PCI, including 5018 in the final study population. Over 2 years, the overall incidence of any DAPT cessation was 57·3%. Rate of any discontinuation was 40·8%, of interruption was 10·5%, and of disruption was 14·4%. The corresponding overall 2 year MACE rate was 11·5%, most of which (74%) occurred while patients were taking DAPT. Compared with those on DAPT, the adjusted hazard ratio (HR) for MACE due to interruption was 1·41 (95% CI 0·94-2·12; p=0·10) and to disruption was 1·50 (1·14-1.97; p=0·004). Within 7 days, 8-30 days, and more than 30 days after disruption, adjusted HRs were 7·04 (3·31-14·95), 2·17 (0·97-4·88), and 1·3 (0·97-1·76), respectively. By contrast with patients who remained on DAPT, those who discontinued had lower MACE risk (0·63 [0·46-0·86]). Results were similar after excluding patients receiving bare metal stents and using an alternative MACE definition that did not include target lesion revascularisation. INTERPRETATION In a real-world setting, for patients undergoing PCI and discharged on DAPT, cardiac events after DAPT cessation depend on the clinical circumstance and reason for cessation and attenuates over time. While most events after PCI occur in patients on DAPT, early risk for events due to disruption is substantial irrespective of stent type. FUNDING Bristol-Myers Squibb and Sanofi-Aventis.


Journal of the American College of Cardiology | 2013

Paravalvular leak after transcatheter aortic valve replacement: The new achilles' heel? A comprehensive review of the literature

Philippe Généreux; Stuart J. Head; Rebecca T. Hahn; Benoit Daneault; Susheel Kodali; Mathew R. Williams; Nicolas M. Van Mieghem; Maria Alu; Patrick W. Serruys; A. Pieter Kappetein; Martin B. Leon

Paravalvular leak (PVL) is a frequent complication of transcatheter aortic valve replacement (TAVR) and is seen at a much higher rate after TAVR than after conventional surgical aortic valve replacement. Recent reports indicating that PVL may be correlated with increased late mortality have raised concerns. However, the heterogeneity of methods for assessing and quantifying PVL, and lack of consistency in the timing of such assessments, is a hindrance to understanding its true prevalence, severity, and effect. This literature review is an effort to consolidate current knowledge in this area to better understand the prevalence, progression, and impact of post-TAVR PVL and to help direct future efforts regarding the assessment, prevention, and treatment of this troublesome complication.


American Journal of Cardiology | 2013

Relation Between Six-Minute Walk Test Performance and Outcomes After Transcatheter Aortic Valve Implantation (from the PARTNER Trial)

Philip Green; David J. Cohen; Philippe Généreux; Tom McAndrew; Suzanne V. Arnold; Maria Alu; Nirat Beohar; Charanjit S. Rihal; Michael J. Mack; Samir Kapadia; Danny Dvir; Mathew S. Maurer; Mathew R. Williams; Susheel Kodali; Martin B. Leon; Ajay J. Kirtane

Functional capacity as assessed by 6-minute walk test distance (6MWTD) has been shown to predict outcomes in selected cohorts with cardiovascular disease. To evaluate the association between 6MWTD and outcomes after transcatheter aortic valve implantation (TAVI) among participants in the Placement of AoRTic TraNscathetER valve (PARTNER) trial, TAVI recipients (n = 484) were stratified into 3 groups according to baseline 6MWTD: unable to walk (n = 218), slow walkers (n = 133), in whom 6MWTD was below the median (128.5 meters), and fast walkers (n = 133) with 6MWTD >128.5 meters. After TAVI, among fast walkers, follow-up 6MWTD decreased by 44 ± 148 meters at 12 months (p <0.02 compared with baseline). In contrast, among slow walkers, 6MWTD improved after TAVI by 58 ± 126 meters (p <0.001 compared with baseline). Similarly, among those unable to walk, 6MWTD distance increased by 66 ± 109 meters (p <0.001 compared with baseline). There were no differences in 30-day outcomes among 6MWTD groups. At 2 years, the rate of death from any cause was 42.5% in those unable to walk, 31.2% in slow walkers, and 28.8% in fast walkers (p = 0.02), driven primarily by differences in noncardiac death. In conclusion, among high-risk older adults undergoing TAVI, baseline 6MWTD does not predict procedural outcomes but does predict long-term mortality. Nonetheless, patients with poor baseline functional status exhibit the greatest improvement in 6MWTD. Additional work is required to identify those with poor functional status who stand to benefit the most from TAVI.


Heart | 2015

Transcatheter aortic valve replacement and standard therapy in inoperable patients with aortic stenosis and low EF

Jonathan Passeri; Sammy Elmariah; Ke Xu; Ignacio Inglessis; Joshua N. Baker; Maria Alu; Susheel Kodali; Martin B. Leon; Lars G. Svensson; Philippe Pibarot; William F. Fearon; Ajay J. Kirtane; Gus J. Vlahakes; Igor F. Palacios; Pamela S. Douglas

Objectives The aims of this study were to evaluate the effect of left ventricular (LV) dysfunction on clinical outcomes after transcatheter aortic valve replacement (TAVR) and standard therapy for severe aortic stenosis (AS) and to assess LV ejection fraction (LVEF) recovery and its impact on subsequent clinical outcomes. Methods Cohort B of the Placement of AoRtic TraNscathetER Valves trial randomised 342 inoperable patients with severe AS to TAVR or standard therapy. We defined LV dysfunction as an LVEF <50% and LVEF improvement as an absolute increase in LVEF ≥10% at 30 days. Results Baseline LV dysfunction did not affect survival after TAVR but was associated with increased cardiac mortality at 1 year with standard therapy (59.3% vs 45.8% with normal LVEF; HR=1.71 (95% CI 1.08 to 2.71); p=0.02). In those with LV dysfunction, LVEF improvement occurred in 48.7% and 30.4% of TAVR and standard therapy patients, respectively (p=0.08), and was independently predicted by relative wall thickness and receipt of TAVR. LVEF improvement with standard therapy portended reduced all-cause mortality at 1 year (28.6% vs 65.6% without LVEF improvement; HR=0.32 (95% CI 0.11 to 0.93); p=0.03) but not at 2 years. Conclusions In inoperable patients with severe AS, mild-to-moderate LV dysfunction is associated with higher cardiac mortality with standard therapy but not TAVR. A subset of patients undergoing standard therapy with LV dysfunction demonstrates LVEF improvement and favourable 1-year but not 2-year survival. TAVR improves survival and should be considered the standard of care for inoperable patients with AS and LVEF >20%. Trial registration number ClinicalTrials.gov Unique Identifier #NCT00530894.


JAMA Cardiology | 2017

Longitudinal Hemodynamics of Transcatheter and Surgical Aortic Valves in the PARTNER Trial

Pamela S. Douglas; Martin B. Leon; Michael J. Mack; Lars G. Svensson; John G. Webb; Rebecca T. Hahn; Philippe Pibarot; Neil J. Weissman; D. Craig Miller; Samir Kapadia; Howard C. Herrmann; Susheel Kodali; Raj Makkar; Vinod H. Thourani; Stamatios Lerakis; Ashley M. Lowry; Jeevanantham Rajeswaran; Matthew Finn; Maria Alu; Craig R. Smith; Eugene H. Blackstone

Importance Use of transcatheter aortic valve replacement (TAVR) for severe aortic stenosis is growing rapidly. However, to our knowledge, the durability of these prostheses is incompletely defined. Objective To determine the midterm hemodynamic performance of balloon-expandable transcatheter heart valves. Design, Setting, and Participants In this study, we analyzed core laboratory–generated data from echocardiograms of all patients enrolled in the Placement of Aortic Transcatheter Valves (PARTNER) 1 Trial with successful TAVR or surgical AVR (SAVR) obtained preimplantation and at 7 days, 1 and 6 months, and 1, 2, 3, 4, and 5 years postimplantation. Patients from continued access observational studies were included for comparison. Interventions Successful implantation after randomization to TAVR vs SAVR (PARTNER 1A; TAVR, n = 321; SAVR, n = 313), TAVR vs medical treatment (PARTNER 1B; TAVR, n = 165), and continued access (TAVR, n = 1996). Five-year echocardiogram data were available for 424 patients after TAVR and 49 after SAVR. Main Outcomes and Measures Death or reintervention for aortic valve structural indications, measured using aortic valve mean gradient, effective orifice area, Doppler velocity index, and evidence of hemodynamic deterioration by reintervention, adverse hemodynamics, or transvalvular regurgitation. Results Of 2795 included patients, the mean (SD) age was 84.5 (7.1) years, and 1313 (47.0%) were female. Population hemodynamic trends derived from nonlinear mixed-effects models showed small early favorable changes in the first few months post-TAVR, with a decrease of −2.9 mm Hg in aortic valve mean gradient, an increase of 0.028 in Doppler velocity index, and an increase of 0.09 cm2 in effective orifice area. There was relative stability at a median follow-up of 3.1 (maximum, 5) years. Moderate/severe transvalvular regurgitation was noted in 89 patients (3.7%) after TAVR and increased over time. Patients with SAVR showed no significant changes. In TAVR, death/reintervention was associated with lower ejection fraction, stroke volume index, and aortic valve mean gradient up to 3 years, with no association with Doppler velocity index or valve area. Reintervention occurred in 20 patients (0.8%) after TAVR and in 1 (0.3%) after SAVR and became less frequent over time. Reintervention was caused by structural deterioration of transcatheter heart valves in only 5 patients. Severely abnormal hemodynamics on echocardiograms were also infrequent and not associated with excess death or reintervention for either TAVR or SAVR. Conclusions and Relevance This large, core laboratory–based study of transcatheter heart valves revealed excellent durability of the transcatheter heart valves and SAVR. Abnormal findings in individual patients, suggestive of valve thrombosis or structural deterioration, were rare in this protocol-driven database and require further investigation. Trial Registration clinicaltrials.gov Identifier: NCT00530894


JAMA Cardiology | 2017

Association of Paravalvular Regurgitation With 1-Year Outcomes After Transcatheter Aortic Valve Replacement With the SAPIEN 3 Valve

Philippe Pibarot; Rebecca T. Hahn; Neil J. Weissman; Marie Arsenault; Jonathan Beaudoin; Mathieu Bernier; Abdellaziz Dahou; Omar K. Khalique; Federico M. Asch; Oumhani Toubal; Jonathon Leipsic; Philipp Blanke; Feifan Zhang; Rupa Parvataneni; Maria Alu; Howard C. Herrmann; Raj Makkar; Michael J. Mack; Richard W. Smalling; Martin B. Leon; Vinod H. Thourani; Susheel Kodali

Importance Moderate/severe and even mild paravalvular regurgitation (PVR) are associated with increased mortality following transcatheter aortic valve replacement (TAVR) with first and second generations of transcatheter valves. Objective To examine the incidence, evolution, and effect on 1-year outcomes of PVR following TAVR with a third-generation balloon-expandable transcatheter heart valve. Design, Setting, and Participants Prespecified analysis of PVR in the Placement of Aortic Transcatheter Valves (PARTNER) II SAPIEN 3 trial, conducted between October 1, 2013, and September 3, 2014. Multicenter, nonrandomized registry of 1661 patients at intermediate or high surgical risk undergoing TAVR with the SAPIEN 3. Patients with severe, symptomatic aortic stenosis and high/intermediate surgical risk were enrolled in the registry at 51 sites in the United States and Canada. Interventions Transcatheter aortic valve replacement with the SAPIEN 3 valve. Main Outcomes and Measures Paravalvular regurgitation was assessed in a core laboratory at 30 days and 1 year according to a 5-class scheme: 0, none or trace; 1, mild; 2, mild to moderate; 3, moderate; 4, moderate to severe; and 5, severe. We assessed the effect of PVR on 1-year mortality and heart failure rehospitalization. Results Among the 1661 included in the registry, 1592 received a SAPIEN 3 valve and had assessment of PVR. Of these patients, 55.7% had none-trace PVR, 32.6% had mild, 8.2% had mild to moderate, and 3.5% had at least moderate PVR at 30 days. At 1 year, 9.3% of patients had died and 14.2% had been rehospitalized. Only patients with at least moderate PVR had higher 1-year mortality (hazard ratio [HR], 2.40; 95% CI, 1.30-4.43; P = .005) and composite of mortality/rehospitalization (HR, 2.35; 95% CI, 1.52-3.62; P < .001). In a paired comparison including 1213 patients, 73% of the patients with at least moderate PVR at 30 days showed a reduction in PVR severity of at least 1 PVR class at 1 year. Conclusions and Relevance In this series of patients undergoing TAVR with the SAPIEN 3 valve, at least moderate PVR was rare but associated with increased risk of death and heart failure rehospitalization at 1 year. Even the upper range of the mild class in the 3-class grading scheme (ie, mild to moderate in the 5-class scheme) had no significant effect on short-term mortality or rehospitalization. Most patients with at least moderate PVR at 30 days showed a decrease of PVR severity grade at 1 year. Trial Registration clinicaltrials.gov Identifier: NCT01314313.


European Heart Journal | 2018

The incidence and prognostic implications of worsening right ventricular function after surgical or transcatheter aortic valve replacement: insights from PARTNER IIA

Paul Cremer; Yiran Zhang; Maria Alu; L. Leonardo Rodriguez; Brian R. Lindman; Alan Zajarias; Rebecca T. Hahn; Stamatios Lerakis; S. Chris Malaisrie; Pamela S. Douglas; Philippe Pibarot; Lars G. Svensson; Martin B. Leon; Wael A. Jaber

Aims In patients randomized to transcatheter or surgical aortic valve replacement (TAVR, SAVR), we sought to determine whether SAVR is associated with worsening right ventricular (RV) function and whether RV deterioration is associated with mortality. Methods and results In 1376 patients from PARTNERIIA with paired baseline and 30-day core lab echocardiograms, worsening RV function was defined as decline by at least one grade from baseline to 30 days. Our primary outcome was all-cause mortality from 30 days to 2 years. Among 744 patients with TAVR, 62 (8.3%) had worsening RV function, compared with 156 of 632 patients with SAVR (24.7%) (P < 0.0001). In a multivariable model, SAVR [odds ratio (OR) 4.05, 95% confidence interval (CI) 2.55-6.44], a dilated RV (OR 2.38, 95% CI 1.37-4.14), and more than mild tricuspid regurgitation (TR) (OR 2.58, 95% CI 1.25-5.33) were associated with worsening RV function. There were 169 deaths, and patients with worsening RV function had higher all-cause mortality [hazard ratio (HR) 1.98, 95% CI 1.40-2.79]. This association remained robust after adjusting for clinical and echocardiographic variables. Among patients with worsening RV function, there was no mortality difference between TAVR and SAVR (HR 1.16, 95% CI 0.61-2.18). The development of moderate or severe RV dysfunction from baseline normal RV function conferred the worst prognosis (HR 2.87, 95% CI 1.40-5.89). Conclusion After aortic valve replacement, worsening RV function is more common in patients with baseline RV dilation, more than mild TR, and in patients treated with SAVR. Worsening RV function and the magnitude of deterioration have important prognostic implications.


Journal of the American College of Cardiology | 2013

THE IMPACT OF SIX–MINUTE WALK TEST PERFORMANCE ON OUTCOMES AFTER TRANSCATHETER AORTIC VALVE REPLACEMENT: INSIGHTS FROM THE PARTNER TRIAL

Philip Green; Ajay J. Kirtane; Philippe Généreux; Tom McAndrew; Irene Hueter; Maria Alu; Suzanne Arnold; Nirat Beohar; Charanjit Rihal; Michael J. Mack; Samir Kapadia; Mathew S. Maurer; Mathew R. Williams; Susheel Kodali; Martin B. Leon; David J. Cohen

methods: The study population consisted of 514 TAVR pts from the PARTNER trial, who were stratiied into 3 groups according to baseline 6MWD: unable to walk (UW), slow walkers (SW) in whom 6MWD was below the median (129 m), and fast walkers (FW) with 6MWD > 129 m. The association of 6MWD group with procedural (30-day), clinical, and functional outcomes was evaluated using univariable and multivariable analyses.

Collaboration


Dive into the Maria Alu's collaboration.

Top Co-Authors

Avatar

Martin B. Leon

Columbia University Medical Center

View shared research outputs
Top Co-Authors

Avatar

Susheel Kodali

Columbia University Medical Center

View shared research outputs
Top Co-Authors

Avatar
Top Co-Authors

Avatar

Raj Makkar

Cedars-Sinai Medical Center

View shared research outputs
Top Co-Authors

Avatar
Top Co-Authors

Avatar
Top Co-Authors

Avatar

Rebecca T. Hahn

Columbia University Medical Center

View shared research outputs
Top Co-Authors

Avatar
Top Co-Authors

Avatar
Top Co-Authors

Avatar
Researchain Logo
Decentralizing Knowledge