Harvard Medical School

Background: In the study of coronary artery disease, the mechanisms underlying atherosclerosis initiation and progression or regression remain incompletely understood. Our research conceptualized the cardiovascular system as an integrated network of pumps and pipes, advocating for a paradigm shift from static imaging of coronary stenosis to dynamic assessments of coronary flow. Further review of fluid mechanics highlighted the water hammer phenomenon as a compelling analog for processes in coronary arteries. Methods: In this review, the analytical methodology employed a comprehensive, multifaceted approach that incorporated a review of fluid mechanics principles, in vitro acoustic experimentation, frame-by-frame visual angiographic assessments of in vivo coronary flow, and an artificial intelligence (AI) protocol designed to analyze the water hammer phenomenon within an acoustic framework. In the analysis of coronary flow, the angiograms were selected from patients with unstable angina if they had previously undergone one or more coronary angiograms, allowing for a longitudinal comparison of dynamic flow and phenomena. Results: The acoustic investigations pinpointed pockets of contrast concentrations, which might correspond to compression and rarefaction zones. Compression antinodes were correlated to severe stenosis, due to rapid shifts from low-pressure diastolic flow to high-pressure systolic surges, resulting in intimal injury. Rarefaction antinodes were correlated with milder lesions, due to de-escalating transitions from high systolic pressure to lower diastolic pressure. The areas of nodes remained without lesions. Based on the locations of antinodes and nodes, a coronary acoustic action map was constructed, enabling the identification of existing lesions, forecasting the progression of current lesions, and predicting the development of future lesions. Conclusions: The results suggested that intimal injury was likely induced by acoustic retrograde pressure waves from the water hammer phenomenon and developed new lesions at specifically exact locations.

In the study of coronary artery disease (CAD), the mechanism of plaque formation and development is still an important subject for investigation. A limitation of current coronary angiography (CAG) is that it can only show static images of the narrowing of arterial channels without identifying the mechanism of the disease or predicting its progression or regression. To address this limitation, the CAG technique has been modified. The new approach emphasizes identifying and analyzing blood flow patterns, employing methodologies akin to those used by hydraulic engineers for fluid or gas movement through domestic or industrial pipes and pumps. With the new technique, various flow patterns and arterial phenomena—such as laminar, turbulent, antegrade, retrograde, and recirculating flow and potentially water hammer shock and vortex formation—are identified, recorded, and classified. These phenomena are then correlated with the presence of lesions at different locations within the coronary vasculature. The formation and growth of these lesions are explained from the perspective of fluid mechanics. As the pathophysiology of CAD and other cardiovascular conditions becomes clearer, new medical, surgical, and interventional treatments could be developed to reverse abnormal coronary flow dynamics and restore laminar flow, leading to improved clinical outcomes.

Background: In the research of coronary artery disease, the precise initial injury that starts the atherosclerotic cascade remains unidentified. Moreover, the mechanisms governing the progression or regression of coronary plaque are not yet fully understood. Based on the concept that the cardiovascular system is a network of pumps and pipes, could fluid mechanics principles and practices elucidate the question of atherosclerosis using flow dynamics images from a novel angiographic technique, focusing on antegrade and retrograde flows and their collisions in iliac and coronary arteries?

Methods: From January 2023 to May 2024, coronary angiograms of all hemodynamically stable patients with stable or unstable angina were screened. The angiograms displaying either no lesions (normal) or mild-to-moderate lesions were selected. Each patient underwent an evaluation of flow dynamics and arterial phenomena in both iliac and right coronary arteries. For each artery, data were categorized based on the following parameters: laminar versus non-laminar flow, presence versus absence of collisions, and presence versus absence of retrograde flow. Additionally, in two sub-studies, we analyzed the relationship between retrograde flow and blood pressure, and artificial intelligence algorithms were used to detect the retrograde flow in the right coronary artery.

Results: A total of 95 patients were screened, and 51 were included in this study. The results comprised quantitative data (prevalence of laminar flows, collisions, and retrograde flows) and qualitative data (morphological characteristics of antegrade laminar flow, retrograde contrast flow, and instances of flow collision). The results showed that in the iliac artery, laminar flow was observed in 47.06% (24/51) of cases, with collisions noted in 23.53% (12/51). Retrograde flow was present in 47.06% (24/51) of cases, and notably, 75% (18/24) of these cases were associated with uncontrolled diastolic blood pressure (DBP) above 80 mmHg (p < 0.001). Conversely, in the RCA, laminar flow was observed in 54.9% (28/51) of cases, with collisions noted in only 3.92% (2/51). Retrograde flow was identified in 7.84% (4/51) of cases, and all these cases (100%, 4/4) were associated with uncontrolled systolic blood pressure (SBP) above 120 mmHg, though statistical significance was not reached due to the small sample size (p > 0.05).

Conclusions: Based on the concept that the cardiovascular system is a network of pumps and pipes, this research methodology provides intriguing insights into arterial flow behaviors by integrating fluid mechanics practices with novel angiographic observations. The preliminary results of this study identified laminar flow as the predominant pattern, with retrograde flow and collisions occurring infrequently. The implications of vortex, collision, and disorganized flow highlight potential mechanisms for endothelial damage and atherosclerosis initiation. Moreover, the correlation with blood pressure underscores the critical role of hypertension management in preventing adverse hemodynamic events. Future directions include refining imaging techniques and further exploring the mechanistic links between flow dynamics and vascular pathophysiology to enhance diagnostic and therapeutic strategies for cardiovascular diseases.

ABSTRACT 1: Accuracy of Tachypnea to Predict Mortality in Young Infants: A Systematic Review and Meta-analysis

Context: Tachypnea in young infants is commonly used in clinical assessment to identify high-risk infants, however the optimal respiratory rate threshold is unclear. Objective: To systematically review the evidence on the accuracy of different thresholds of tachypnea to predict mortality in infants 0-59 days. Data Sources: MEDLINE, Embase, CINAHL, Global Index Medicus, and CENTRAL. Study Selection: Studies reporting the accuracy of tachypnea (≥60, ≥70, or ≥80 breaths per minute (bpm)) to predict mortality in infants 0-59 days. Data Extraction: We followed Cochrane methods for study screening, data extraction, and quality assessment using the Newcastle-Ottawa and QUAPAS scales. Results: Of 7641 studies identified, 8 were included. Tachypnea with threshold of ≥60 bpm had an overall sensitivity of 57% (95% CI: 23%-86%) and specificity of 54% (95% CI: 28%-79%) for predicting future mortality in infants by 59 days of age (6 studies, N = 3819 infants). The pooled odds ratio for the association between tachypnea ≥60 bpm and mortality was 2.00 (95% CI: 1.39-2.87, 7 studies, N = 7122 infants). Tachypnea ≥70 bpm had a 4.6-fold higher odds of mortality (95% CI: 1.60-13.00, 1 study, N = 6924 infants). There was limited data on other thresholds and timing of mortality (early versus late neonatal periods). Limitations: Heterogeneity and the low number of studies limited the evidence. Conclusions: Tachypnea was associated with significantly higher odds of mortality in young infants. Overall sensitivity and specificity were low. Further research is needed to determine the optimal threshold and the accuracy for different postnatal ages.

ABSTRACT 2: Accuracy of Infant Clinical Signs to Predict Neonatal Mortality in Rural Bangladesh Background: Clinical signs provide early warning of illness in neonates at high risk of dying in community settings in low- and middle- income countries (LMICs). There is limited validation of current clinical signs and/or algorithms to predict neonatal mortality in LMICs. Objectives: 1) To examine the diagnostic accuracy of existing clinical sign algorithms to predict neonatal mortality, and 2) To determine the association of individual clinical signs with neonatal mortality and their diagnostic accuracy in predicting neonatal death. Methods: We conducted a secondary analysis of a birth cohort in Sylhet, Bangladesh (NCT01572532). Of 7788 live births, 6251 newborns had a clinical examination during a community health worker home visit within 3 days of birth, and 5289 were followed up until 28 days of age with available vital status. We validated existing newborn clinical sign algorithms identified from our prior systematic review (Shafiq 2024), including four Integrated Management of Childhood Illness (IMCI)-like checklist algorithms and the Score of Essential Neonatal Symptoms and Signs (SENSS). We also estimated the odds ratios (ORs) for neonatal mortality associated with individual clinical signs exploring optimal thresholds using univariable logistic regression; and calculated sensitivity and specificity of individual clinical signs for identifying neonatal death. Results: The WHO Young Infant Study 7-sign modification Z checklist algorithm had the sensitivity of 66.7% (95% CI: 56.6% to 75.7%) and specificity of 68.6% (95% CI: 67.3% to 69.9%) for predicting future mortality. The SENSS algorithm had an Area Under the Curve (AUC) of 75.9% (95% CI: 69.9% to 82.0%), calibration intercept of -1.21 (95% CI: -1.69 to -0.72), and calibration slope of 0.94 (95% CI: 0.78 to 1.11). Among individual clinical signs at birth, fast breathing ≥80 breaths per minute (bpm), fever ≥38.5˚C, and hypothermia .5˚C showed the strongest association with neonatal death, with ORs were 44.4 (95% CI: 13.8 to 142.6) for fast breathing ≥80 bpm, 39.3 (95% CI: 3.5 to 441.3) for fever ≥38.5˚C, and 30.3 (95% CI: 17.1 to 53.9) for hypothermia .5˚C. Conclusions: Four IMCI-like checklist algorithms had low sensitivity and high specificity to predict neonatal mortality. The Score of Essential Neonatal Symptoms and Signs (SENSS) algorithm reported fair discrimination to identifying neonates at high risk of dying. Further research is needed to optimize clinical sign algorithms to identify high-risk infants in different age groups and settings.

ABSTRACT Objective To examine the relationship between a primary open-angle glaucoma (POAG) polygenic risk score (PRS) and laser trabeculoplasty (LTP) outcomes. Design Retrospective observational follow-up study in a Biobank-linked clinical sample and three case groups identified from population-based cohorts. Participants We included data from patients aged 40 and above with POAG who underwent LTP in the Mass General Biobank, the Nurses’ Health Study, Nurses’ Health Study 2, and the Health Professionals Follow-up Study. Methods A PRS was calculated using prior genome-wide association study (GWAS) summary statistics, and participants with LTP were categorized into either a high- (top 10%) or low-score (remaining 90%) category. Statistical analyses included Kaplan-Meier survival analysis to assess time to LTP failure, Cox proportional hazards models to evaluate the impact of PRS on failure risk, and Area Under the Curve (AUC) to measure predictive accuracy. Main outcome measure LTP failure, defined as less than a 20% reduction in intraocular pressure (IOP) from baseline or the need for additional glaucoma surgical or laser procedures, assessed six weeks after LTP and within two years of follow-up. Results The study included 109 participants, grouped into low PRS (bottom 90th percentile; 72 participants) and high PRS (top 10th percentile; 37 participants). The median time to LTP failure was significantly longer for low PRS patients (12 months, 95%CI: 8.94–16.79) than in those with high PRS (6 months, 95%CI: 5.62–7.36, p.0001). Participants in the high PRS group had a 2.03 times higher risk of LTP failure (95%CI: 1.25–3.32, p=0.004) after adjusting for age, sex, genetic ancestry, LTP type, baseline IOP, IOP-lowering medication number, and visual field mean deviation (MD). A model incorporating PRS in addition to clinical characteristics had higher predictive accuracy over time (AUC = 0.73 vs. 0.66, p=0.03 at 18 months after LTP). Conclusions A higher PRS was significantly associated with increased risk of LTP failure in this sample of POAG patients. These findings suggest PRS may help identify patients at higher risk for LTP failure, but further research with a prospective, population-based sample is needed to confirm this association.

ABSTRACT Objective: To compare three unsupervised clustering algorithms: k-means, Fuzzy c-means (FCM), and hierarchical clustering analysis (HCA) for primary open-angle glaucoma (POAG) phenotyping and to identify clinical POAG subtypes using multimodal structural and functional data from Electronic Health Records.

Design: Retrospective cohort study.

Participants: 4,274 eyes from patients with POAG seen between 2016 and 2023 at a tertiary ophthalmology center.

Methods: We extracted 21 continuous clinical features per eye, including baseline and longitudinal visual field indices, intraocular pressure (IOP) parameters, OCT-derived retinal nerve fiber layer (RNFL) metrics, and optic nerve morphology. Dimensionality reduction was performed using Sparse Principal Component Analysis (Sparse PCA), retaining seven components. The optimal number of clusters (K=5) was determined based on silhouette score and HCA dendrogram inspection. We then compared agreement between methods and evaluated cluster performance. Post hoc comparisons across clusters used Kruskal-Wallis and chi-square tests.

Main Outcome Measures: Clustering performance was assessed using internal validation metrics (Calinski-Harabasz index, Davies-Bouldin index, Dunn index, and silhouette score) and cluster stability metrics (mean Jaccard similarity for k-means and HCA; fuzzy partition coefficient for FCM). Agreement across methods was quantified using unweighted Cohen’s kappa. Distinct POAG phenotypes were characterized based on demographic, clinical, and treatment features.

Results: HCA showed the weakest internal validity (Calinski-Harabasz index = 308.5; Dunn index = 0.02; silhouette score = 0.102) and the lowest cluster stability (mean Jaccard similarity = 0.27). K-means and FCM achieved higher validity (Calinski-Harabasz = 731; Dunn index = 0.013; silhouette scores = 0.133 and 0.132, respectively). FCM yielded the highest overall stability (fuzzy partition coefficient = 0.89). Agreement between FCM and k-means was excellent (Cohen’s kappa = 0.97). Based on FCM-derived clustering, we identified five phenotypes: (1) Small-disc with minimal progression, (2) Early-stage with stable structure-function, (3) RNFL-thinned with preserved function, (4) Rapidly progressing with high IOP variability, and (5) End-stage with apparent functional plateau.   Conclusions: In this large real-world cohort of POAG patients, FCM and k-means outperformed HCA in both internal validity and cluster stability. FCM yielded the highest fuzzy partition coefficient and excellent agreement with k-means, supporting its use for POAG phenotypic segmentation. The five derived POAG subtypes exhibited distinct structural-functional profiles and IOP dynamics. Future work will incorporate archetypal analysis to model spatial patterns of visual field loss and further refine individualized disease trajectories.

Abstract
Title: Mitochondrial Transplantation as a Novel Therapeutic Strategy for Retinal Ischemia-Reperfusion Injury Authors: Fernando Rubio-Mijangos1,2, Aybuke Çelik1, Maria Loscertales2, Alexander Bigger-Allen3, Sitaram Emani1, Pedro del Nido1, Demetrios Vavvas2*, James D. McCully1* 1Department of Cardiac Surgery, Boston Children’s Hospital, Department of Surgery, Harvard Medical School, Boston, MA, 02215, USA 2Department of Ophthalmology, Retina Service, Massachusetts Eye and Ear, Harvard Medical School, Boston, MA 02114, USA 3Urological Diseases Research Center, Boston Children’s Hospital, Harvard Medical School, Boston, MA 02114, USA *Co-last authors Keywords: Mitochondrial transplantation; Retinal ischemia-reperfusion injury; Oxidative stress; Mitochondrial dysfunction; Cellular bioenergetics; ARPE-19; Inflammation; Apoptosis; Background Mitochondria are central to cellular homeostasis, providing ATP through oxidative phosphorylation while also regulating oxidative stress, apoptosis, and immune responses. Retinal ischemia-reperfusion injury (RIRI) disrupts mitochondrial function, triggering oxidative stress, inflammation, and neurovascular degeneration. Given the critical role of mitochondria in retinal cell survival, mitochondrial transplantation (MT) has emerged as a promising therapeutic strategy to restore mitochondrial integrity and bioenergetics in ischemic tissues. This study evaluates the potential of MT in rescuing oxidative stress-induced mitochondrial dysfunction in an in vitro model of RIRI. Methods ARPE-19 cells were differentiated into a mature retinal pigment epithelium-like phenotype and subjected to oxidative stress using hydrogen peroxide (H₂O₂). Mitochondria were isolated from ARPE-19 cells and characterized for viability and function. Transplantation was performed at optimized doses, and mitochondrial uptake, ATP production, oxidative stress resilience, and cell survival were assessed. Bulk RNA sequencing was conducted to analyze transcriptional responses following MT, identifying differentially expressed genes and enriched biological pathways involved in cellular stress adaptation. Results Transplanted mitochondria were efficiently internalized by ARPE-19 cells and integrated into the host mitochondrial network, restoring ATP levels in a dose-dependent manner. MT significantly improved cell survival and reduced oxidative stress-induced apoptosis at 0.25-0.5 mM H₂O₂ concentrations. RNA sequencing revealed that MT downregulated inflammatory and apoptotic pathways, including IL-17, VEGF, and CASP9 signaling, while upregulating stress-adaptive pathways such as TNF, NF-κB, SGK1, and efferocytosis. Notably, MT reduced IL6 and IL6R expression, potentially mitigating inflammation-driven mitochondrial dysfunction. Conclusion MT demonstrates significant potential in restoring mitochondrial function and modulating stress-responsive transcriptional programs in RIRI models. By mitigating oxidative stress, preserving ATP levels, and reprogramming inflammatory responses, MT presents a promising therapeutic approach for retinal ischemic diseases. Future Directions Further investigations are required to validate these findings in vivo, refine transplantation protocols, and assess the long-term efficacy and safety of MT. Proteomic and metabolomic analyses could provide deeper insights into mitochondrial integration and functional recovery, advancing MT as a viable intervention for retinal ischemia.

Background: Patients with sarcopenia and elevated body mass index (BMI) are at high risk of platinum-associated adverse events (AEs). This study examines the association between sarcopenia, BMI, and AEs in patients with non-small cell lung cancer (NSCLC). Methods: Retrospective cohort study including adult patients with NSCLC who started cisplatin or carboplatin between 2015-2022. Sarcopenia was defined on computed tomography (CT) using sex-specific cutoffs for skeletal muscle index. We determined the association between CT-defined sarcopenia in patients with normal BMI ( 25 kg/m2) and elevated BMI (≥ 25 kg/m2) and ≥ grade 2 AEs (including anemia, thrombocytopenia, neutropenia, and creatinine increased), chemotherapy discontinuation and mortality within 90 days using a Fine-Gray subdistribution hazard model. The association between receiving an excess carboplatin dose and AEs was evaluated. Results: Of 604 included patients, mean age was 66±10 years, 307 were female (51%), and 167 (28%) had sarcopenia. Sarcopenia and elevated BMI (N = 67) was associated with an increased risk of grade ≥ 2 anemia (subdistribution hazard ratio [sHR] 1.64, 95% confidence interval [CI] 1.17-2.29, P = 0.004), thrombocytopenia (sHR 2.25, 95%CI 1.16-4.36, P = 0.016), and creatinine increased (sHR 2.72, 95%CI 1.45-5.13, P = 0.002). Sensitivity analyses demonstrated that patients whose Cockcroft-Gault based glomerular filtration rate (GFR) dictated a carboplatin dose ≥ 25mg higher than CKD-EPI GFR were at significantly higher risk of grade ≥ 2 AEs and chemotherapy discontinuation. Conclusions: Combined CT-defined sarcopenia with elevated BMI is associated with an increased risk of platinum-associated AEs in patients with NSCLC; this may be due to GFR misestimation in patients with low muscle mass and elevated BMI.

Fracture healing is a highly regulated process dependent on angiogenesis and osteogenesis, both of which are modulated by vascular endothelial growth factor (VEGF). While VEGF is crucial for vascular invasion and bone regeneration, its rapid degradation in vivo limits its therapeutic potential. This study investigates the efficacy of PR1P, a novel peptide that binds to and stabilizes endogenous VEGF, in enhancing fracture repair. Using a murine femoral fracture model, PR1P was administered intraperitoneally every other day for either 5 or 14 days post-injury. Healing was assessed at days 5, 14, and 28 using micro-CT, RT-qPCR, histology, and immunohistochemistry. Results demonstrated that short-term PR1P treatment enhanced early angiogenesis and chondrogenesis, while prolonged administration promoted angiogenic maturation, osteogenic gene expression, and normalization of bone remodeling by day 28. Notably, extended PR1P exposure mitigated the decline in bone mineralization seen with shorter dosing and supported more coordinated transition from repair to remodeling phases. These findings position PR1P as a promising VEGF-stabilizing therapeutic that can enhance bone regeneration by extending endogenous VEGF signaling during critical phases of fracture healing.

This thesis investigates the risks and benefits of hormone replacement therapy (HRT) in high-risk populations, particularly in women who have undergone prophylactic risk-reducing surgeries (PRRS) to prevent familial ovarian cancer and women with chronic kidney disease. It comprises two manuscripts that address the effects of HRT on breast cancer and chronic kidney disease (CKD) progression.

Manuscript 1 focuses on the association between breast cancer risk and HRT use after PRRS in women at increased risk of familial ovarian cancer. A systematic review and meta-analysis were conducted, synthesizing data from 8 studies involving 2,689 participants. The analysis revealed no significant increase in breast cancer risk for women using HRT post-PRRS, suggesting that HRT may be a safe option for managing menopause symptoms in this high-risk population. Despite previous concerns over estrogen’s potential to elevate breast cancer risk, the results indicated that estrogen-only HRT did not increase the risk compared to non-users.

Manuscript 2 explores the association of exogenous estrogen use with CKD progression and adverse cardiovascular outcomes in women with CKD, using data from the Chronic Renal Insufficiency Cohort (CRIC). The study demonstrated that estrogen use was associated with a 47% lower risk of CKD progression, although it did not show a reduction in adverse cardiovascular events or all-cause mortality. This finding provides some reassurance for the use of estrogen in women with CKD, particularly for those at risk of kidney decline.

In both manuscripts, the results emphasize the need for personalized treatment strategies and further prospective studies to validate these findings. This research contributes to understanding the role of HRT in managing risks related to ovarian cancer, breast cancer, and CKD in high-risk women.

Background: Pediatric Hospital Medicine (PHM) is one of the newest pediatric subspecialties, and the number of PHM fellowship programs continues to grow rapidly. Many PHM attendings have limited experience supervising fellows. Currently, the PHM fellowship program at Boston Children’s Hospital lacks a structured curriculum to prepare attendings for clinical supervision. This study aims to conduct an organizational needs assessment among PHM attendings and fellows to identify faculty development needs related to fellow supervision. This assessment represents the second step in Kern’s six-step approach to curriculum development, as incorporating faculty and fellow input is essential for designing a curriculum that meets attendings’ needs. Methods: This cross-sectional study utilized three surveys targeting: (1) attendings at the main academic site (BCH), (2) attendings at the community site (SSH), and (3) current and graduated PHM fellows. The attending surveys assessed overall preparedness for fellow supervision, key topics to include in a curriculum, and overall interest in a curriculum. Fellow surveys explored their experiences working with attendings. Surveys were distributed anonymously via Qualtrics. Data analysis included descriptive statistics and a modified qualitative analysis using the framework method for free-response questions. Results: Results from BCH and SSH surveys varied given the inherent differences in training environments. The academic site (BCH) had a survey completion rate of 71.1% (32/45). Attendings expressed a need for more training on supervising both residents and fellows while tailoring teaching to the fellow’s level. Additionally, the majority of attendings at both sites shared interest in participating in a curriculum on fellow supervision. At the community site, the completion rate was 53.8% (7/13), with attendings identifying teaching to the fellow’s level and providing feedback as key training needs. The fellow survey had a completion rate of 78.6% (11/14). Fellows identified promoting fellow autonomy as a critical topic at both training sites. Qualitative responses highlighted the need to educate community site faculty on the overall goals of fellowship training. Across all groups, the preferred curriculum delivery method was a shared document or resource folder. Conclusion: Our organizational needs assessment highlights the need for enhanced attending training on PHM fellow supervision from the perspectives of both attendings and fellows. While training priorities may differ between the academic and community sites due to the inherent differences in training environment, ongoing faculty development is essential for effectively preparing the next generation of PHM fellows.