The Implant-Induced Foreign Body Response Is Limited by CD13-Dependent Regulation of Ubiquitination of Fusogenic Proteins.

Implanted medical devices, from artificial heart valves and arthroscopic joints to implantable sensors, often induce a foreign body response (FBR), a form of chronic inflammation resulting from the inflammatory reaction to a persistent foreign stimulus. The FBR is characterized by a subset of multinucleated giant cells (MGCs) formed by macrophage fusion, the foreign body giant cells (FBGCs), accompanied by inflammatory cytokines, matrix deposition, and eventually deleterious fibrotic implant encapsulation. Despite efforts to improve biocompatibility, implant-induced FBR persists, compromising the utility of devices and making efforts to control the FBR imperative for long-term function. Controlling macrophage fusion in FBGC formation presents a logical target to prevent implant failure, but the actual contribution of FBGCs to FBR-induced damage is controversial. CD13 is a molecular scaffold, and in vitro induction of CD13KO bone marrow progenitors generates many more MGCs than the wild type, suggesting that CD13 regulates macrophage fusion. In the mesh implant model of FBR, CD13KO mice produced significantly more peri-implant FBGCs with enhanced TGF-ß expression and increased collagen deposition versus the wild type. Prior to fusion, increased protrusion and microprotrusion formation accompanies hyperfusion in the absence of CD13. Expression of fusogenic proteins driving cell-cell fusion was aberrantly sustained at high levels in CD13KO MGCs, which we show is due to a novel CD13 function, to our knowledge, regulating ubiquitin/proteasomal protein degradation. We propose CD13 as a physiologic brake limiting aberrant macrophage fusion and the FBR, and it may be a novel therapeutic target to improve the success of implanted medical devices. Furthermore, our data directly implicate FBGCs in the detrimental fibrosis that characterizes the FBR.

Spectral Characterization of Hierarchical Modularity in Product Architectures.

Despite the importance of the architectural modularity of products and systems, existing modularity metrics or algorithms do not account for overlapping and hierarchically embedded modules. This paper presents a graph theoretic spectral approach to characterize the degree of modular hierarchical-overlapping organization in the architecture of products and complex engineered systems. It is shown that the eigenvalues of the adjacency matrix of a product architecture graph can reveal layers of hidden modular or hierarchical modular organization that are not immediately visible in the predefined architectural description. We use the approach to analyze and discuss several design, management, and system resilience implications for complex engineered systems.

Acute type A aortic syndromes: outcomes are independent of aortic root/valve management.

Purpose: Clinical outcomes following various surgical intervention strategies for aortic root and valve pathology during repair of acute type A aortic syndromes were studied and compared. Methods: From 2004 to 2019, 634 patients underwent acute type A aortic repair. Patients were divided into 4 groups: Valve Resuspension (n = 456), Isolated Valve Replacement (AVR) (n = 24), Valve and Root Replacement (ROOT) (n = 97), and Valve Sparing Root Replacement (VSRR) (n = 57). The primary endpoint was midterm survival and multivariable risk factor analysis was performed. Results: The mean age was 55.4 ± 13 years, 424 (67%) were male, and overall early mortality was 12%. Early mortality was 13%, 8%, 11%, and 7% for the Valve Resuspension, AVR, ROOT, and VSRR groups respectively, p = 0.43. Five-year survival was 74%, 86%, 73%, and 84% for the Valve Resuspension, AVR, ROOT, and VSRR groups respectively, p = 0.46. There was no difference in late stroke, renal failure, heart block, and late bleeding (p > 0.05 for all). At late follow-up, AVR and ROOT patients had a higher mean gradient versus Valve Resuspension and VSRR patients, p < 0.0001. For the total cohort, risk factors for late mortality included preoperative peripheral vascular disease (hazard ratio (HR) 2.3, 95% confidence interval (CI) 1.2-4.4, p = 0.009) and preoperative dialysis (HR 2.8, 95% CI 1.3-6.1, p = 0.01). Conclusion: Mid-term survival following repair of acute type A aortic dissection is not independently associated with a specific type of aortic valve intervention. Native valve preservation leads to acceptable mid-term valve hemodynamics and should be the preferred therapy in this emergent clinical setting. Supplementary Information: The online version contains supplementary material available at 10.1007/s12055-023-01602-8.

Reoperative aortic root replacement for prosthetic aortic valve endocarditis: impact of aortic graft.

OBJECTIVES: Existing aortic graft complicates the surgical management of prosthetic valve endocarditis (PVE); yet, its impact has not been well studied. We compared outcomes of patients with prior aortic valve replacement (AVR) versus aortic surgery plus AVR, who underwent reoperative aortic root replacement (ARR) for PVE of the aortic valve. METHODS: All patients who underwent reoperative ARR for PVE between 2004 and 2021 from 2 aortic centres were included. Two groups were formed based on the presence/absence of aortic graft: prior aortic surgery (AO) and prior AVR (AV) alone. Inverse propensity treatment weighting matched the groups. The Kaplan-Meier method was used to analyse long-term survival, and Fine and Gray model was used to compare the cumulative incidence of reoperation. RESULTS: A total of 130 patients were included (AO n = 59; AV n = 71). After matching, AO patients had increased stroke incidence (12.4% vs 0.9%) and renal failure requiring dialysis (11.5% vs 2.5%). In-hospital mortality was comparable (21.5% AO and 18.6% AV). Survival over 5 years was 68.9% (56.6-83.8%) in AO and 62.7% (48.1-81.7%) in AV (P = 0.70). The cumulative incidence of reoperation was similar [AO 6.3% (0.0-13.2%) vs AV 6.1% (0.0-15.1%), P = 0.69]. CONCLUSIONS: Reoperative ARRs for prosthetic valve/graft endocarditis are high-risk procedures. AO patients had higher incidence of postoperative morbidity versus AV patients. For all patients surviving operative intervention, survival and reoperation rates over 5 years were comparable between groups.

Valve-sparing root replacement versus composite valve graft root replacement: Analysis of more than 1500 patients from 2 aortic centers.

OBJECTIVES: The long-term outcomes comparing valve-sparing root replacement, composite valve graft with bioprosthesis, and mechanical prosthesis have yet to be explored. We investigated the long-term survival and reintervention rates after 1 of 3 major aortic root replacements in patients with tricuspid aortic valves and patients with bicuspid aortic valves. METHODS: A total of 1507 patients underwent valve-sparing root replacement (n = 700), composite valve graft with bioprosthesis (n = 703), or composite valve graft with mechanical prosthesis (n = 104) between 2004 and 2021 in 2 aortic centers, excluding those with dissection, endocarditis, stenosis, or prior aortic valve surgery. End points included mortality over time and cumulative incidence of aortic valve/proximal aorta reintervention. Multivariable Cox regression compared adjusted 12-year survival. Fine and Gray competing risk regression compared the risk and cumulative incidence of reintervention. Propensity score-matched subgroup analysis balanced the 2 major groups (composite valve graft with bioprosthesis and valve-sparing root replacement), and landmark analysis isolated outcomes beginning 4 years postoperatively. RESULTS: On multivariable analysis, both composite valve graft with bioprosthesis (hazard ratio, 1.91, P = .001) and composite valve graft with mechanical prosthesis (hazard ratio, 2.62, P = .005) showed increased 12-year mortality risk versus valve-sparing root replacement. After propensity score matching, valve-sparing root replacement displayed improved 12-year survival versus composite valve graft with bioprosthesis (87.9% vs 78.8%, P = .033). Adjusted 12-year reintervention risk in patients receiving composite valve graft with bioprosthesis or composite valve graft with mechanical prosthesis versus valve-sparing root replacement was similar (composite valve graft with bioprosthesis subdistribution hazard ratio, 1.49, P = .170) (composite valve graft with mechanical prosthesis subdistribution hazard ratio, 0.28, P = .110), with a cumulative incidence of 7% in valve-sparing root replacement, 17% in composite valve graft with bioprosthesis, and 2% in composite valve graft with mechanical prosthesis (P = .420). Landmark analysis at 4 years showed an increased incidence of late reintervention in composite valve graft with bioprosthesis versus valve-sparing root replacement (P = .008). CONCLUSIONS: Valve-sparing root replacement, composite valve graft with mechanical prosthesis, and composite valve graft with bioprosthesis demonstrated excellent 12-year survival, with valve-sparing root replacement associated with better survival. All 3 groups have low incidence of reintervention, with valve-sparing root replacement showing decreased late postoperative need for reintervention compared with composite valve graft with bioprosthesis.

True redo-aortic root replacement versus root replacement after any previous surgery.

Objective: The impact of previous aortic root replacement (True-Redo) versus any previous operation (Any-Redo) on outcomes after reoperative aortic root replacement (redo-ROOT) is largely unknown. In this first multi-institutional study, the clinical impact True-Redo versus Any-Redo in the setting of redo-ROOT was reviewed. Methods: From 2004 to 2021, 822 patients underwent redo-ROOT at 2 major academic centers: 638 Any-Redo and 184 True-Redo. Matching based on preoperative demographics and concomitant operations resulted in 174 matched pairs. An independent risk factor analysis was performed to determine risk factors for early and late mortality. Results: Patients in the True-Redo group were younger, at 49.9 ± 15.1 versus 55.3 ± 14.7 years, P < .001. Concomitant operations were largely similar between the 2 groups, P > .05. Median cardiopulmonary bypass time (P < .001) and aortic crossclamp time (P = .03) were longer for True-Redo group. In-hospital mortality was 13% (109) and was without significant difference between groups, P = .41. Ten-year survival was 78% versus 76% for True-Redo versus Any-Redo groups respectively, P = .7. Landmark survival analysis at 4 years' postoperatively on the matched groups found that patients in the True-Redo group had improved survival outcomes (P = .046). Risk factors of in-hospital mortality consisted of older age (P < .0001), lower ejection fraction (P = .02), and male patient (P = .0003). Conclusions: Clinical outcomes following redo-ROOT are excellent. Performance of a True-Redo-ROOT does not result in worse in-hospital morbidity or mortality and has improved survival benefit at midterm follow-up when compared with patients in the Any-Redo group. The decision to perform a redo-ROOT must be taken seriously and must be individualized in a patient-specific manner for optimal outcomes.

Clinical Outcomes Using Freestyle Valve-Valsalva Graft Composite Conduit for Aortic Root Replacement.

BACKGROUND: We reviewed the clinical outcomes of a novel method of aortic root replacement using a self-constructed tissue valve conduit composed of a Freestyle subcoronary valve sewn into a Valsalva graft. METHODS: From 2005 to 2020, 523 patients had aortic root replacement operations using a self-constructed Freestyle subcoronary-Valsalva graft tissue valve conduit. Median patient age was 62 years (interquartile range [IQR] 54-70), and 430 (82%) were men. Primary outcomes were mortality and the need for reoperation. Multivariable regression analyses were performed to identify risk factors for mortality and reoperation. RESULTS: Urgent procedures comprised 48.37% of cases, and 29.26% were reoperative procedures. Concomitant ascending aorta replacement, hemiarch replacement, and total arch replacement were required in 348 (67%), 227 (44%), and 40 (8%) patients, respectively. Cardiopulmonary bypass and cross-clamp times were 189 minutes (IQR, 164-218) and 166 minutes (IQR, 145-191), respectively. Early mortality was 7.7% (40), and 5- and 10-year survival rates were 83% and 71%, respectively. At the last echocardiogram follow-up left ventricular ejection fraction, left ventricular end-diastolic diameter, degree of aortic insufficiency, and mean aortic valve gradient were significantly improved from baseline (P < .001). Increasing age, peripheral artery disease, tobacco use, increased preoperative creatinine, and prior aortic valve surgery were risk factors for both mortality and the composite outcome (P < .02). CONCLUSIONS: In a complex patient population aortic root replacement using a self-constructed composite tissue valve conduit comprising a Freestyle subcoronary valve-Valsalva graft can be performed with excellent operative and 10-year outcomes. Midterm survival was acceptable, and valve durability was outstanding with an exceedingly low incidence for valve reintervention.

Compliance with Percutaneous Tibial Nerve Stimulation at a Tertiary Academic Center versus a County Hospital.

OBJECTIVES: To compare percutaneous tibial nerve stimulation (PTNS) compliance rate at a safety-net versus tertiary academic hospital and assess the impact of social determinants on compliance. METHODS: Retrospective cohort study of 133 patients at Grady Memorial Hospital and Emory Clinic from May 2015 to March 2020 who had refractory overactive bladder (OAB) and were prescribed PTNS. RESULTS: Grady patients were younger (age 58.7±11.6 versus 70.7±13.5), predominantly male (52% versus 22%), and predominately African American (80% versus 34%). Compliance rate for PTNS was 55% at Emory and 70% at Grady. In the multivariable model including sex, race, insurance status, income level, and baseline voiding symptoms, Grady patients had 5.31 times the odds of compliance (p=.02). CONCLUSIONS: Compliance rate at a safety-net hospital was greater and was not affected by demographic and socioeconomic variables. These results support offering PTNS as standard of care to a predominantly Black population with refractory OAB.

Aortic Arch Management During Acute and Subacute Type A Aortic Syndromes.

BACKGROUND: The purpose of this study was to compare the outcomes of no arch intervention, hemiarch replacement, and total arch replacement during type A aortic syndromes in a contemporary series. METHODS: From 2004 to 2019, 634 patients have required acute type A dissection repair; these patients were divided into three groups based on type of arch intervention performed: no arch (n = 130), hemiarch (n = 397), and total arch (n = 107). The primary endpoint was mortality; a multivariable risk factor analysis was performed. Secondary endpoints were reoperation and early and late complications. RESULTS: Operative age was 55 ± 14 years for the cohort and was similar between groups (P = .34). The incidence of peripheral artery disease, heart failure, and prior coronary artery bypass graft surgery differed between the groups (P < .05). Median cardiopulmonary bypass time, aortic cross-clamp time, and length of stay were longest for the total arch group (P < .0001). Early mortality was 20%, 10%, and 10% for the no-arch, hemiarch, and total arch groups, respectively (P = .01). Ten-year survival was 54%, 66%, and 65% for the no-arch, hemiarch, and total arch groups, respectively (P = .01). There was no difference in incidence or timing of redo aortic interventions (P > .05). For the entire cohort, risk factors for late mortality included preoperative peripheral artery disease (hazard ratio 2.3; 95% confidence interval, 1.2 to 4.4; P = .009) and preoperative dialysis (hazard ratio 2.8; 95% confidence interval, 1.3 to 6.1; P = .01). CONCLUSIONS: Despite longer cardiopulmonary bypass and aortic cross-clamp times, arch intervention was not associated with worse operative or long-term outcome in this series. Patients with peripheral vascular disease and preoperative renal failure remain at highest risk for mortality after type A aortic dissection repair.

Implementation and evaluation of eight virtual surgical electives for medical students during the COVID-19 pandemic.

BACKGROUND: Eight novel virtual surgery electives (VSEs) were developed and implemented in April-May 2020 for medical students forced to continue their education remotely due to COVID-19. METHODS: Each VSE was 1-2 weeks long, contained specialty-specific course objectives, and included a variety of teaching modalities. Students completed a post-course survey to assess changes in their interest and understanding of the specialty. Quantitative methods were employed to analyze the results. RESULTS: Eighty-three students participated in the electives and 67 (80.7%) completed the post-course survey. Forty-six (68.7%) respondents reported "increased" or "greatly increased" interest in the course specialty completed. Survey respondents' post-course understanding of each specialty increased by a statistically significant amount (p-value = <0.0001). CONCLUSION: This initial effort demonstrated that VSEs can be an effective tool for increasing medical students' interest in and understanding of surgical specialties. They should be studied further with more rigorous methods in a larger population.

Postoperative Healthcare Utilization of Elderly Adults After Cochlear Implantation.

OBJECTIVE: To determine the association between geriatric age and postoperative healthcare utilization after cochlear implantation. STUDY DESIGN: Retrospective chart review. SETTING: Tertiary referral center. PATIENTS: Older adults (>59 yr) who underwent unilateral cochlear implantation from 2009 until 2016. INTERVENTION(S): Standard electrode length cochlear implantation. MAIN OUTCOME MEASURE(S): Postoperative surgical and audiological visit rate after cochlear implantation for those aged 60 to 69, 70 to 79, and 80+ years. RESULTS: Fifty-nine older adult patients were included in the study with a mean age of 71.5 ±â€Š6.9 years (range, 60-88 yr), mean duration of hearing loss of 25.4 ±â€Š19.6 years (range, 0.25-67 yr), and mean length of follow up of 37 ±â€Š24.6 months (range, 6-107 mo). There was no significant difference in the mean number of surgical and audiological visits over both the first and second postoperative years between those aged 60 to 69, 70 to 79, and 80+ years. Additionally, on one-way multivariate analysis of covariance (MANCOVA), there was no significant difference in cumulative postoperative healthcare utilization measures between each age group, when controlling for postoperative AzBio scores, estimated household income, and driving distance to the hospital. CONCLUSIONS: Older geriatric adults do not have higher rates of postoperative healthcare utilization after cochlear implantation than their younger, geriatric hearing impaired counterparts, despite presumed higher rates of frailty and comorbidity.

Development of a Risk Score to Predict New Pacemaker Implantation After Transcatheter Aortic Valve Replacement.

OBJECTIVES: The aim of this study was to define risk factors and develop a predictive risk score for new pacemaker implantation (PMI) after transcatheter aortic valve replacement (TAVR). BACKGROUND: TAVR has become an accepted treatment alternative for patients with severe aortic stenosis at elevated surgical risk. New PMI is a common occurrence after TAVR and is associated with poorer outcomes. METHODS: All patients without prior valve procedures undergoing elective TAVR with the Edwards SAPIEN 3 at a single institution (n = 1,266) were evaluated. Multivariate analysis was performed to evaluate for predictors of PMI in this population in a derivation cohort of patients with complete data (n = 778), and this model was used to develop the Emory risk score (ERS), which was tested in a validation cohort (n = 367). RESULTS: Fifty-seven patients (7.3%) in the derivation cohort required PMI. In a regression model, history of syncope (odds ratio [OR]: 2.5; p = 0.026), baseline right bundle branch block (OR: 4.3; p < 0.001), QRS duration ≥138 ms (OR: 2.5; p = 0.017), and valve oversizing >15.6% (OR: 1.9; p = 0.041) remained independent predictors of PMI and were included in the ERS. The ERS was strongly associated with PMI (per point increase OR: 2.2; p < 0.001) with an area under the receiver-operating characteristic curve of 0.778 (p < 0.001), which was similar to its performance in the derivation cohort. CONCLUSIONS: A history of syncope, right bundle branch block, longer QRS duration, and higher degree of oversizing are predictive of the need for PMI after TAVR. Additionally, the ERS for PMI was developed and validated, representing a simple bedside tool to aid in risk stratification for patients for undergoing TAVR.

Predictors and Clinical Outcomes of Next-Day Discharge After Minimalist Transfemoral Transcatheter Aortic Valve Replacement.

OBJECTIVES: This study sought to investigate predictors and safety of next-day discharge (NDD) after transcatheter aortic valve replacement (TAVR). BACKGROUND: Information about predictors and safety of NDD after TAVR is limited. METHODS: The study reviewed 663 consecutive patients who underwent elective balloon-expandable TAVR (from July 2014 to July 2016) at our institution. We first determined predictors of NDD in patients who underwent minimalist transfemoral TAVR. After excluding cases with complications, we compared 30-day and 1-year outcomes between NDD patients and those with longer hospital stay using Cox regression adjusting for the Predicted Risk of Mortality provided by the Society of Thoracic Surgeons. The primary endpoint was the composite of mortality and readmission at 1 year. RESULTS: A total of 150 patients had NDD after TAVR and 210 patients had non-NDD. Mean age and the Society of Thoracic Surgeons Predicted Risk of Mortality were 80.7 ± 8.8 years and 6.6 ± 3.7%, respectively. Predictors of NDD were male sex (odds ratio [OR]: 2.02; 95% confidence interval [CI]: 1.28 to 3.18), absence of atrial fibrillation (OR: 1.62; 95% CI: 1.02 to 2.57), serum creatinine (OR: 0.71; 95% CI: 0.55 to 0.92), and age (OR: 0.95; 95% CI: 0.93 to 0.98). As expected, 84% of patients with complications had non-NDD. After excluding cases with complications, there was no difference in hazard rates of the 30-day composite outcome between NDD and non-NDD (hazard ratio: 0.62; 95% CI: 0.20 to 1.91), but the hazard of the composite outcome at 1 year was significantly lower in the NDD group (hazard ratio: 0.47; 95% CI: 0.27 to 0.81). This difference in the composite outcome can be explained by the lower hazard of noncardiovascular related readmission in the NDD group. CONCLUSIONS: Factors predicting NDD include male sex, absence of atrial fibrillation, lower serum creatinine, and younger age. When compared with patients without complications with a longer hospital stay, NDD appears to be safe, achieving similar 30-day and superior 1-year clinical outcomes.

Comparison of Clinical and Echocardiographic Outcomes After Surgical Redo Mitral Valve Replacement and Transcatheter Mitral Valve-in-Valve Therapy.

OBJECTIVES: There are minimal data regarding clinical outcomes and echocardiographic findings after transcatheter mitral valve-in-valve replacement (TMVR) compared with redo surgical mitral valve replacement (SMVR). BACKGROUND: TMVR therapy has emerged as therapy for a degenerated bioprosthetic valve failure. METHODS: The authors retrospectively identified patients with degenerated mitral bioprostheses who underwent redo SMVR or TMVR at 3 U.S. institutions. The authors compared clinical and echocardiographic outcomes of patients who had TMVR with those of patients who underwent redo SMVR. RESULTS: Sixty-two patients underwent TMVR and 59 patients underwent SMVR during the study period. Mean age and the Society of Thoracic Surgeons Predicted Risk of Mortality (STS PROM) scores were significantly higher in patients with TMVR than in those with SMVR (age 74.9 ± 9.4 years vs. 63.7 ± 14.9 years; p < 0.001; STS PROM 12.7 ± 8.0% vs. 8.7 ± 10.1%; p < 0.0001). Total procedure time, intensive care unit hours, and post-procedure length of stay were all significantly shorter in the TMVR group. There was no difference in mortality at 1 year between the 2 groups (TMVR 11.3% vs. SMVR 11.9%; p = 0.92). Mean mitral valve pressure gradient and the grade of mitral regurgitation (MR) were similar between the TMVR group and the SMVR group (mitral valve pressure gradient 7.1 ± 2.5 mm Hg vs. 6.5 ± 2.5 mm Hg; p = 0.42; MR [≥moderate] 3.8% vs. 5.6%; p = 1.00) at 30 days. At 1 year, the mitral valve pressure gradient was higher in the TMVR group (TMVR 7.2 ± 2.7 vs. SMVR 5.5 ± 1.8; p = 0.01), although there was no difference in the grade of MR. CONCLUSIONS: Despite the higher STS PROM in TMVR patients, there was no difference in 1-year mortality between the TMVR and SMVR groups. Echocardiographic findings after TMVR were similar to SMVR at 30 days. There was a statistically significant difference in mitral gradient at 1 year, though this is likely not clinically important. TMVR may be an alternative to SMVR in patients with previous mitral bioprosthetic valves.

Outcomes After Paravalvular Leak Closure: Transcatheter Versus Surgical Approaches.

OBJECTIVES: The aim of this study was to compare outcomes of transcatheter intervention (TI) versus surgical intervention (SI) for paravalvular leak (PVL). BACKGROUND: Data comparing the treatment of PVL with TI and SI are limited. METHODS: A retrospective cohort study was conducted comparing baseline characteristics, procedural details, and 1-year survival in consecutive patients who underwent TI or SI for moderate or greater PVL from 2007 to 2016. The primary outcome was a composite of death, reintervention for PVL, or readmission for congestive heart failure-related symptoms at 1 year. RESULTS: Of 114 patients, 56 underwent TI and 58 underwent SI. PVL locations were mitral, aortic, and pulmonary in 69 (60.5%), 39 (34.2%), and 6 (5.3%) patients, respectively. At baseline, TI patients were older (age 71 vs. 62 years; p = 0.010) and had fewer cases of active endocarditis (0.0% vs. 25.9%, p < 0.001) than SI patients. The TI group had a shorter post-operative stay (4 vs. 8 days; p < 0.001), a shorter intensive care unit stay (0 vs. 3 days; p < 0.001), and fewer readmissions at 30 days (8.9% vs. 25.9%; p = 0.017). There were no differences in the primary endpoint (TI 33.9% vs. SI 39.7%; p = 0.526) or 1-year survival (TI 83.9% vs. SI 75.9%; p = 0.283) between groups. CONCLUSIONS: In this study, TI for PVL closure had comparable 1-year clinical outcomes with SI, even after adjusting for differences in baseline characteristics, with less in-hospital morbidity and 30-day rehospitalization. Although further study is needed, these findings support the increased implementation of TI for PVL closure at experienced institutions.

Community detection in graphs using singular value decomposition.

A spectral algorithm for community detection is presented. The algorithm consists of three stages: (1) matrix factorization of two matrix forms, square signless Laplacian for unipartite graphs and rectangular adjacency matrix for bipartite graphs, using singular value decompostion (SVD); (2) dimensionality reduction using an optimal linear approximation; and (3) clustering vertices using dot products in reduced dimensional space. The algorithm reveals communities in graphs without placing any restriction on the input network type or the output community type. It is applicable on unipartite or bipartite unweighted or weighted networks. It places no requirement on strict community membership and automatically reveals the number of clusters, their respective sizes and overlaps, and hierarchical modular organization. By representing vertices as vectors in real space, expressed as linear combinations of the orthogonal bases described by SVD, orthogonality becomes the metric for classifying vertices into communities. Results on several test and real world networks are presented, including cases where a mix of disjointed, overlapping, or hierarchical communities are known to exist in the network.