Emergent Applications of Machine Learning for Diagnosing and Managing Appendicitis: A State-of-the-Art Review

Background: Appendicitis is an inflammatory condition that requires timely and effective intervention. Despite being one of the most common surgically treated diseases, the condition is difficult to diagnose because of atypical presentations. Ultrasound and computed tomography (CT) imaging improve the sensitivity and specificity of diagnoses, yet these tools bear the drawbacks of high operator dependency and radiation exposure, respectively. However, new artificial intelligence tools (such as machine learning) may be able to address these shortcomings. Methods: We conducted a state-of-the-art review to delineate the various use cases of emerging machine learning algorithms for diagnosing and managing appendicitis in recent literature. The query ("Appendectomy" OR "Appendicitis") AND ("Machine Learning" OR "Artificial Intelligence") was searched across three databases for publications ranging from 2012 to 2022. Upon filtering for duplicates and based on our predefined inclusion criteria, 39 relevant studies were identified. Results: The algorithms used in these studies performed with an average accuracy of 86% (18/39), a sensitivity of 81% (16/39), a specificity of 75% (16/39), and area under the receiver operating characteristic curves (AUROCs) of 0.82 (15/39) where reported. Based on accuracy alone, the optimal model was logistic regression in 18% of studies, an artificial neural network in 15%, a random forest in 13%, and a support vector machine in 10%. Conclusions: The identified studies suggest that machine learning may provide a novel solution for diagnosing appendicitis and preparing for patient-specific post-operative complications. However, further studies are warranted to assess the feasibility and advisability of implementing machine learning-based tools in clinical practice.

Causal determinants of postoperative length of stay in cardiac surgery using causal graphical learning

OBJECTIVE

We aimed to learn the causal determinants of postoperative length of stay in cardiac surgery patients undergoing isolated coronary artery bypass grafting or aortic valve replacement surgery.

METHODS

For patients undergoing isolated coronary artery bypass grafting or isolated aortic valve replacement surgeries between 2011 and 2016, we used causal graphical modeling on electronic health record data. The Fast Causal Inference (FCI) algorithm from the Tetrad software was used on data to estimate a Partial Ancestral Graph (PAG) depicting direct and indirect causes of postoperative length of stay, given background clinical knowledge. Then, we used the latent variable intervention-calculus when the directed acyclic graph is absent (LV-IDA) algorithm to estimate strengths of causal effects of interest. Finally, we ran a linear regression for postoperative length of stay to contrast statistical associations with what was learned by our causal analysis.

RESULTS

In our cohort of 2610 patients, the mean postoperative length of stay was 219 hours compared with the Society of Thoracic Surgeons 2016 national mean postoperative length of stay of approximately 168 hours. Most variables that clinicians believe to be predictors of postoperative length of stay were found to be causes, but some were direct (eg, age, diabetes, hematocrit, total operating time, and postoperative complications), and others were indirect (including gender, race, and operating surgeon). The strongest average causal effects on postoperative length of stay were exhibited by preoperative dialysis (209 hours); neuro-, pulmonary-, and infection-related postoperative complications (315 hours, 89 hours, and 131 hours, respectively); reintubation (61 hours); extubation in operating room (-47 hours); and total operating room duration (48 hours). Linear regression coefficients diverged from causal effects in magnitude (eg, dialysis) and direction (eg, crossclamp time).

CONCLUSIONS

By using retrospective electronic health record data and background clinical knowledge, causal graphical modeling retrieved direct and indirect causes of postoperative length of stay and their relative strengths. These insights will be useful in designing clinical protocols and targeting improvements in patient management.

Impact of intraoperative blood products, fluid administration, and persistent hypothermia on bleeding leading to reexploration after cardiac surgery

OBJECTIVE

Risk factors for severe postoperative bleeding after cardiac surgery remain multiple and incompletely elucidated. We evaluated the impact of intraoperative blood product transfusions, intravenous fluid administration, and persistently low core body temperature (CBT) at intensive care unit arrival on risk of perioperative bleeding leading to reexploration.

METHODS

We retrospectively queried our tertiary care center's Society of Thoracic Surgeons Institutional Database for all index, on-pump, adult cardiac surgery patients between July 2016 and September 2022. Intraoperative fluid (crystalloid and colloid) and blood product administrations, as well as perioperative CBT data, were harvested from electronic medical records. Linear and nonlinear mixed models, treating surgeon as a random effect to account for inter-surgeon practice differences, were used to assess the association between above factors and reexploration for bleeding.

RESULTS

Of 4037 patients, 151 (3.7%) underwent reexploration for bleeding. Reexplored patients experienced remarkably greater postoperative morbidity (23% vs 6%, P < .001) and 30-day mortality (14% vs 2%, P < .001). In linear models, progressively increasing IV crystalloid administration (adjusted odds ratio, 1.11, 95% confidence interval, 1.03-1.19) and decreasing CBT on intensive care unit arrival (adjusted odds ratio, 1.20; 95% confidence interval, 1.05-1.37) were associated with greater risk of bleeding leading to reexploration. Nonlinear analysis revealed increasing risk after ∼6 L of crystalloid administration and a U-shaped relationship between CBT and reexploration risk. Intraoperative blood product transfusion of any kind was not associated with reexploration.

CONCLUSIONS

We found evidence of both dilution- and hypothermia-related effects associated with perioperative bleeding leading to reexploration in cardiac surgery. Interventions targeting modification of such risk factors may decrease the rate this complication.

Effect of concurrent mitral valve surgery for secondary mitral regurgitation upon mortality after aortic valve replacement or coronary artery bypass surgery

Objectives

It is uncertain whether concurrent mitral valve repair or replacement for moderate or greater secondary mitral regurgitation at the time of coronary artery bypass graft or aortic valve replacement surgery improves long-term survival.

Methods

Patients undergoing coronary artery bypass graft and/or aortic valve replacement surgery with moderate or greater secondary mitral regurgitation were reviewed. The effect of concurrent mitral valve repair or replacement upon long-term mortality was assessed while accounting for patient and operative characteristics and mitral regurgitation severity.

Results

Of 1,515 patients, 938 underwent coronary artery bypass graft or aortic valve replacement surgery alone and 577 underwent concurrent mitral valve repair or replacement. Concurrent mitral valve repair or replacement did not alter the risk of postoperative mortality for patients with moderate mitral regurgitation (hazard ratio = 0.93; 0.75-1.17) or more-than-moderate mitral regurgitation (hazard ratio = 1.09; 0.74-1.60) in multivariable regression. Patients with more-than-moderate mitral regurgitation undergoing coronary artery bypass graft-only surgery had a survival advantage from concurrent mitral valve repair or replacement in the first two postoperative years (P = 0.028) that did not persist beyond that time. Patients who underwent concurrent mitral valve repair or replacement had a higher rate of later mitral valve operation or reoperation over the five subsequent years (1.9% vs. 0.2%; P = 0.0014) than those who did not.

Conclusions

These observations suggest that mitral valve repair or replacement for more-than-moderate mitral regurgitation at the time of coronary artery bypass grafting may be reasonable in a suitably selected coronary artery bypass graft population but not for aortic valve replacement, with or without coronary artery bypass grafting. Our findings are supportive of 2021 European guidelines that severe secondary mitral regurgitation "should" or be "reasonabl[y]" intervened upon at the time of coronary artery bypass grafting but do not support 2020 American guidelines for performing mitral valve repair or replacement concurrent with aortic valve replacement, with or without coronary artery bypass grafting.

Historical Accounts of Congenital Heart Surgery

We present historical accounts of congenital heart surgery since the early 1900s, as our specialty evolved from individual heroic efforts into an established and sophisticated surgical specialty with consistent and excellent results. We highlight colleagues and intrepid pioneers who have strived to solve seemingly insurmountable problems during this remarkable journey and celebrate continued success into the 21st century with surgical advances that have resulted in innovative operations, database inquiries, quality measures, new techniques of medical illustration, and the establishment of the Congenital Heart Surgeons' Society, which has become the leading organization dedicated to congenital heart surgery in North America.

Recruited macrophages elicit atrial fibrillation

Atrial fibrillation disrupts contraction of the atria, leading to stroke and heart failure. We deciphered how immune and stromal cells contribute to atrial fibrillation. Single-cell transcriptomes from human atria documented inflammatory monocyte and SPP1+ macrophage expansion in atrial fibrillation. Combining hypertension, obesity, and mitral valve regurgitation (HOMER) in mice elicited enlarged, fibrosed, and fibrillation-prone atria. Single-cell transcriptomes from HOMER mouse atria recapitulated cell composition and transcriptome changes observed in patients. Inhibiting monocyte migration reduced arrhythmia in Ccr2-∕- HOMER mice. Cell-cell interaction analysis identified SPP1 as a pleiotropic signal that promotes atrial fibrillation through cross-talk with local immune and stromal cells. Deleting Spp1 reduced atrial fibrillation in HOMER mice. These results identify SPP1+ macrophages as targets for immunotherapy in atrial fibrillation.

The impact of a statewide payment reform on transcatheter aortic valve replacement (TAVR) utilization and readmissions

BACKGROUND

Transcatheter aortic valve replacement (TAVR) is an increasingly used but relatively expensive procedure with substantial associated readmission rates. It is unknown how cost-constrictive payment reform measures, such as Maryland's All Payer Model, impact TAVR utilization given its relative expense. This study investigated the impact of Maryland's All Payer Model on TAVR utilization and readmissions among Maryland Medicare beneficiaries.

METHODS

This was a quasi-experimental investigation of Maryland Medicare patients undergoing TAVR between 2012 and 2018. New Jersey data were used for comparison. Longitudinal interrupted time series analyses were used to study TAVR utilization and difference-in-differences analyses were used to investigate post-TAVR readmissions.

RESULTS

During the first year of payment reform (2014), TAVR utilization among Maryland Medicare beneficiaries dropped by 8% (95% confidence interval [CI]: -9.2% to -7.1%; p < 0.001), with no concomitant change in TAVR utilization in New Jersey (0.2%, 95% CI: 0%-1%, p = 0.09). Longitudinally, however, the All Payer Model did not impact TAVR utilization in Maryland compared to New Jersey. Difference-in-differences analyses demonstrated that implementation of the All Payer Model was not associated with significantly greater declines in 30-day post-TAVR readmissions in Maryland versus New Jersey (-2.1%; 95% CI: -5.2% to 0.9%; p =0.1).

CONCLUSIONS

Maryland's All Payer Model resulted in an immediate decline in TAVR utilization, likely a result of hospitals adjusting to global budgeting. However, beyond this transition period, this cost-constrictive reform measure did not limit Maryland TAVR utilization. In addition, the All Payer Model did not reduce post-TAVR 30-day readmissions. These findings may help inform expansion of globally budgeted healthcare payment structures.

Arterial oxygen and carbon dioxide tension and acute brain injury in extracorporeal cardiopulmonary resuscitation patients: Analysis of the extracorporeal life support organization registry

BACKGROUND

Acute brain injury (ABI) remains common after extracorporeal cardiopulmonary resuscitation (ECPR). Using a large international multicenter cohort, we investigated the impact of peri-cannulation arterial oxygen (PaO2) and carbon dioxide (PaCO2) on ABI occurrence.

METHODS

We retrospectively analyzed adult (≥18 years old) ECPR patients in the Extracorporeal Life Support Organization registry from 1/2009 through 12/2020. Composite ABI included ischemic stroke, intracranial hemorrhage (ICH), seizures, and brain death. The registry collects 2 blood gas data pre- (6 hours) and post- (24 hours) cannulation. Blood gas parameters were classified as: hypoxia (<60mm Hg), normoxia (60-119mm Hg), and mild (120-199mm Hg), moderate (200-299mm Hg), and severe hyperoxia (≥300mm Hg); hypocarbia (<35mm Hg), normocarbia (35-44mm Hg), mild (45-54mm Hg) and severe hypercarbia (≥55mm Hg). Missing values were handled using multiple imputation. Multivariable logistic regression analysis was used to assess the relationship of PaO2 and PaCO2 with ABI.

RESULTS

Of 3,125 patients with ECPR intervention (median age=58, 69% male), 488 (16%) experienced ABI (7% ischemic stroke; 3% ICH). In multivariable analysis, on-ECMO moderate (aOR=1.42, 95%CI: 1.02-1.97) and severe hyperoxia (aOR=1.59, 95%CI: 1.20-2.10) were associated with composite ABI. Additionally, severe hyperoxia was associated with ischemic stroke (aOR=1.63, 95%CI: 1.11-2.40), ICH (aOR=1.92, 95%CI: 1.08-3.40), and in-hospital mortality (aOR=1.58, 95%CI: 1.21-2.06). Mild hypercarbia pre-ECMO was protective of composite ABI (aOR=0.61, 95%CI: 0.44-0.84) and ischemic stroke (aOR=0.56, 95%CI: 0.35-0.89).

CONCLUSIONS

Early severe hyperoxia (≥300mm Hg) on ECMO was a significant risk factor for ABI and mortality. Careful consideration should be given in early oxygen delivery in ECPR patients who are at risk of reperfusion injury.

Prediction of operative mortality for patients undergoing cardiac surgical procedures without established risk scores

OBJECTIVE

Current cardiac surgery risk models do not address a substantial fraction of procedures. We sought to create models to predict the risk of operative mortality for an expanded set of cases.

METHODS

Four supervised machine learning models were trained using preoperative variables present in the Society of Thoracic Surgeons (STS) data set of the Massachusetts General Hospital to predict and classify operative mortality in procedures without STS risk scores. A total of 424 (5.5%) mortality events occurred out of 7745 cases. Models included logistic regression with elastic net regularization (LogReg), support vector machine, random forest (RF), and extreme gradient boosted trees (XGBoost). Model discrimination was assessed via area under the receiver operating characteristic curve (AUC), and calibration was assessed via calibration slope and expected-to-observed event ratio. External validation was performed using STS data sets from Brigham and Women's Hospital (BWH) and the Johns Hopkins Hospital (JHH).

RESULTS

Models performed comparably with the highest mean AUC of 0.83 (RF) and expected-to-observed event ratio of 1.00. On external validation, the AUC was 0.81 in BWH (RF) and 0.79 in JHH (LogReg/RF). Models trained and applied on the same institution's data achieved AUCs of 0.81 (BWH: LogReg/RF/XGBoost) and 0.82 (JHH: LogReg/RF/XGBoost).

CONCLUSIONS

Machine learning models trained on preoperative patient data can predict operative mortality at a high level of accuracy for cardiac surgical procedures without established risk scores. Such procedures comprise 23% of all cardiac surgical procedures nationwide. This work also highlights the value of using local institutional data to train new prediction models that account for institution-specific practices.

Early Reexploration for Bleeding Is Associated With Improved Outcome in Cardiac Surgery

BACKGROUND

Reexploration after cardiac surgery, most frequently for bleeding, is a quality metric used to assess surgical performance. This may cause surgeons to delay return to the operating room in favor of attempting nonoperative management. This study investigated the impact of the timing of reexploration on morbidity and mortality.

METHODS

This study was a single-institution retrospective review of all adult cardiac surgery patients from July 2010 to June 2020. Time to reexploration was assessed, and outcomes were compared across increasing time intervals. Reported bleeding sites were classified into 5 groups, and bleeding rate (chest tube output) was compared across bleeding sites. Univariable analysis was performed using the Fisher exact and Kruskal-Wallis tests. Multivariable logistic regression models were used for risk-adjusted analyses.

RESULTS

Of 10 070 eligible patients, 251 (2.5%) required reexploration for postoperative bleeding. The most common site of bleeding was "any suture line" (n = 70; 28%). Interestingly, in 30% of cases (n = 75) "no active bleeding" site was reported. The highest rate of bleeding (mL/h) was observed in the "any mediastinal structure" group (median, 450; interquartile range [IQR], 185, 8878), and the lowest rate was noted in the "no active bleeding" group (median, 151.2; IQR, 102, 270). Both morbidity rates (0-4 hours, 12.3% vs 25-48 hours, 37.5%; P = .001) and mortality rates (0-4 hours, 3.1% vs 25-48 hours, 43.8%; P = .001) escalated significantly with increasing time to reexploration.

CONCLUSIONS

Delayed reexploration for bleeding after cardiac surgery is associated with increased risk for morbidity and mortality. Early surgical intervention, particularly within 4 hours, may improve outcomes. Implications from using reoperation as a performance metric may lead to unnecessary delay and patient harm.

Deep Learning to Predict Mortality After Cardiothoracic Surgery Using Preoperative Chest Radiographs

BACKGROUND

The Society of Thoracic Surgeons Predicted Risk of Mortality (STS-PROM) estimates mortality risk only for certain common procedures (eg, coronary artery bypass or valve surgery) and is cumbersome, requiring greater than 60 inputs. We hypothesized that deep learning can estimate postoperative mortality risk based on a preoperative chest radiograph for cardiac surgeries in which STS-PROM scores were available (STS index procedures) or unavailable (non-STS index procedures).

METHODS

We developed a deep learning model (CXR-CTSurgery) to predict postoperative mortality based on preoperative chest radiographs in 9283 patients at Massachusetts General Hospital (MGH) having cardiac surgery before April 8, 2014. CXR-CTSurgery was tested on 3615 different MGH patients and externally tested on 2840 patients from Brigham and Women's Hospital (BWH) having surgery after April 8, 2014. Discrimination for mortality was compared with the STS-PROM using the C-statistic. Calibration was assessed using the observed-to-expected ratio (O/E ratio).

RESULTS

For STS index procedures, CXR-CTSurgery had a C-statistic similar to STS-PROM at MGH (CXR-CTSurgery: 0.83 vs STS-PROM: 0.88; P = .20) and BWH (0.74 vs 0.80; P = .14) testing cohorts. The CXR-CTSurgery C-statistic for non-STS index procedures was similar to STS index procedures in the MGH (0.87 vs 0.83) and BWH (0.73 vs 0.74) testing cohorts. For STS index procedures, CXR-CTSurgery had better calibration than the STS-PROM in the MGH (O/E ratio: 0.74 vs 0.52) and BWH (O/E ratio: 0.91 vs 0.73) testing cohorts.

CONCLUSIONS

CXR-CTSurgery predicts postoperative mortality based on a preoperative CXR with similar discrimination and better calibration than the STS-PROM. This may be useful when the STS-PROM cannot be calculated or for non-STS index procedures.

Resting Energy Expenditure of Patients on Venovenous Extracorporeal Membrane Oxygenation for Adult Respiratory Distress Syndrome: A Pilot Study

OBJECTIVES

The objectives of this study were to 1) in patients without pulmonary function, determine resting energy expenditure (REE) in venovenous extracorporeal membrane oxygenation (ECMO) acute respiratory distress syndrome (ARDS) patients by paralysis status and 2) determine the threshold tidal volume (TV) associated with meaningful gas exchange as determined by measurable end-tidal carbon dioxide elimination (etV̇co₂).

DESIGN

Retrospective observational study.

SETTING

A tertiary high ECMO volume academic institution.

PATIENTS/SUBJECTS

Ten adult ARDS patients on venovenous ECMO.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

The modified Weir equation, Fick principle, Henderson-Hasselbalch equation, ECMO flow, hemoglobin, and pre and post oxygenator blood gases were used to determine ECMO carbon dioxide production (V̇co₂), ECMO oxygen consumption, and REE. REE values were matched to patients' paralysis status based on medication flowsheets and compared using a paired t test. Linear regression was performed to determine the threshold TV normalized to ideal body weight (IBW) associated with measurable ventilator etV̇co₂, above which meaningful ventilation occurs. When lungs were not functioning, patients had significantly lower mean REE when paralyzed (23.4 ± 2.8 kcal/kg/d) than when not paralyzed (29.2 ± 5.8 kcal/kg/d) (p = 0.02). Furthermore, mean REE was not similar between patients and varied as much as 1.7 times between patients when paralyzed and as much as 1.4 times when not paralyzed. Linear regression showed that ventilator V̇co₂ was measurable and increased linearly when TV was greater than or equal to 0.7 mL/kg.

CONCLUSIONS

REE is patient-specific and varies significantly with and without patient paralysis. When TV exceeds 0.7 mL/kg IBW, ventilator V̇co₂ increases measurably and must be considered in determining total REE.

Extruded poly (glycerol sebacate) and polyglycolic acid vascular graft forms a neoartery

In the ongoing search for the optimal biomaterial for tissue engineered vascular grafts (TEVGs), poly (glycerol sebacate) (PGS) has emerged as a new potential candidate. We have utilized a novel method to create unique, pore-free, extruded PGS grafts with and without a supportive exterior layer of polyglycolic acid (PGA). The 1 mm diameter by 5 mm length TEVGs were implanted in a rat model of infrarenal abdominal aorta interposition grafting. Three months after implantation, TEVGs comprised of extruded PGS with an external PGA braid demonstrated a patency rate of 9/10 (90%) with no signs of dilatation, dehiscence, or rupture. The PGS/PGA graft was remodeled into a neoartery with complete endothelialization of the neoartery lumen and formation of smooth muscle actinin multilayers as demonstrated via immunohistochemistry. Formation and maturation of extracellular matrix material were also observed, with amounts of elastin and collagen comparable to native rat aorta. No significant host inflammatory response was observed. These findings suggest the combination of an extruded PGS tube with an external reinforcing PGA braid is a promising material for small diameter TEVGs.

Leveraging Machine Learning to Predict 30-Day Hospital Readmission after Cardiac Surgery

BACKGROUND

Hospital readmission within 30 days of discharge is a well-studied outcome. Predicting readmission after cardiac surgery, however, is notoriously challenging; the best-performing models in the literature have AUCs around .65. A reliable predictive model would enable clinicians to identify patients at-risk for readmission and develop prevention strategies.

METHODS

We analyzed our institution's STS Adult Cardiac Surgery Database (STS), augmented with electronic medical record (EMR) data. Predictors included demographics, pre-operative comorbidities, proxies for intra-operative risk, indicators of post-operative complications, and timeseries-derived variables. We trained several machine learning models, evaluating each on a held-out test set.

RESULTS

Our analysis cohort consisted of 4,924 cases from 2011-2016. 723 (14.7%) were readmitted within 30 days of discharge. Our models included 141 STS-derived and 24 EMR-derived variables. A random forest model performed best, with test AUC .76 (95% CI: (.73, .79)). Using exclusively pre-operative variables, as in STS calculated risk scores, degraded the AUC: .64 (95% CI: .60, .68). Key predictors included length of stay (12.5x more important than the average variable) and whether the patient was discharged to a rehab facility (11.2x).

CONCLUSIONS

Our approach, augmenting STS variables with EMR data and employing flexible machine learning modeling, yielded state-of-the-art performance for predicting 30-day readmission. Separately, the importance of variables not directly related to in-patient care, such as discharge location, amplifies questions about the efficacy of assessing care quality via readmissions.

Neuromonitoring detects brain injury in patients receiving extracorporeal membrane oxygenation support

OBJECTIVE

There is limited evidence on standardized protocols for optimal neurological monitoring methods in patients receiving extracorporeal membrane oxygenation (ECMO). We previously introduced protocolized noninvasive multimodal neuromonitoring using serial neurological examinations, electroencephalography, transcranial Doppler ultrasound, and somatosensory evoked potentials. The purpose of this study was to examine if standardized neuromonitoring is associated with detection of acute brain injury (ABI) and improved patient outcomes.

METHODS

A retrospective analysis of ECMO patients who received neurocritical care consultation was performed and outcomes were reviewed. The cohort was stratified according to those who did not receive standardized neuromonitoring (era 1: 2016-2017) and those who received standardized neuromonitoring (era 2: 2017-2020). Multivariable logistic regression was used to evaluate the association between standardized neuromonitoring and ABI.

RESULTS

A total of 215 patients (mean age, 54 years; 60% male) underwent ECMO (71% venoarterial-ECMO) in our institution, 70 in era 1 and 145 in era 2. The proportion of patients diagnosed with ABI were 23% in era 1 and 33% in era 2 (P = .12). In multivariable logistic regression, standardized neuromonitoring (odds ratio, 2.24; 95% CI, 1.12-4.48; P = .02) and pre-ECMO cardiac arrest (odds ratio, 2.17; 95% CI, 1.14-4.14; P = .02) were independently associated with ABI. There was a greater proportion of patients with good neurological outcomes when discharged alive in era 2 (54% vs 30%; P = .04).

CONCLUSIONS

Standardized neuromonitoring was associated with increased ABIs in ECMO patients. Although neuromonitoring does not prevent ABI from occurring, it might prevent worsening with timely interventions (eg, anticoagulation management, optimizing oxygen delivery and blood pressure), leading to improved neurological outcomes at discharge.

Late onset atrial fibrillation in patients undergoing surgical aortic valve replacement

OBJECTIVE

Aortic valve disease is a risk factor for atrial fibrillation (AF), and AF is associated with increased late mortality and morbidity after cardiac surgery. The evolution of alternative approaches to AF prophylaxis, including less invasive technologies and medical therapies, has altered the balance between risk and potential benefit for prophylactic intervention at the time of surgical aortic valve replacement (SAVR). Such interventions impose incremental risk, however, making an understanding of predictors of new onset AF that persists beyond the perioperative episode relevant.

METHODS

We conducted a retrospective single-institution cohort analysis of patients undergoing SAVR with no history of preoperative AF (n = 1014). These patients were cross-referenced against an institutional electrocardiogram (ECG) database to identify those with ECGs 3-12 months after surgery. Logistic regression was used to identify predictors of late AF.

RESULTS

Among the 401 patients (40%), who had ECGs in our institution 3-12 months after surgery, 16 (4%) had late AF. Patients with late AF were older than patients without late AF (73 vs. 65, p = .025), and underwent procedures that were more urgent/emergent (38% vs. 15%, p = .015), with higher predicted risk of mortality (2.2% vs. 1.3%, p = .012). Predictors associated with the development of late AF were advanced age, higher preoperative creatinine level and urgent/emergent surgery.

CONCLUSIONS

The incidence of late AF 3-12 months after SAVR, is low. Prophylactic AF interventions at the time of SAVR may not be warranted.

846 Dysphagia Rates in Single- And Multiple-Level Anterior Cervical Discectomy and Fusion Surgery: A Meta-Analysis

Aim

To conduct a meta-analysis to assess dysphagia complicating single-level and multiple-level (≥2) anterior cervical discectomy and fusion (ACDF) surgery.

Method

Electronic searches were performed using four electronic databases from their inception to December 2017. Relevant studies reporting the rate of dysphagia as an endpoint for patients undergoing ACDF for degenerative disease, myelopathy, cervical canal stenosis or ossification of the posterior longitudinal ligament were identified according to prior inclusion and exclusion criteria. Statistical analysis was performed using a fixed effect model. P-scores were used to rank the levels of ACDF based on the rate of dysphagia. I2 was used to explore heterogeneity.

Results

Ten studies were identified and included in the systematic review and meta-analysis, with a total of 4,018 patients identified; 2,362 patients underwent single-level ACDF, while 1,656 underwent multiple level (≥2 ACDF). The mean age ranged from 49.45 to 57.77 years. Mean follow-up time ranged from 2 days to 27.3 months. Overall, meta-analysis demonstrated a statistically significant higher dysphagia rate for multiple-level ACDF (6.6%) than for single-level ACDF (4%) (P heterogeneity =0.151, OR = 1.42, 95% CI: 1.05–1.91, I2=32%).

Conclusions

Dysphagia is a relatively common complication in the early postoperative period following ACDF and may cause patients significant discomfort and distress. This meta-analysis demonstrates a higher rate of dysphagia with multiple-level ACDF than with single-level ACDF at a period of 12–24 months.

843 Annular Closure Device for Disc Herniation: Meta-Analysis of Clinical Outcome and Complications

Aim

To assist surgeons to determine a potential approach to reduce incidences of recurrent lumbar disc herniation and assess the current devices regarding their outcomes and complications.

Method

Four electronic full-text databases were systematically searched through September 2017. All results were pooled utilising meta-analysis with weighted mean difference and odds ratio as summary statistics.

Results

Four studies met inclusion criteria. Three studies reported the use of Barricaid (ACD) while one study reported the use of Anulex (AR). A total of 24 symptomatic reherniation were reported among 811 discectomies with ACD/AR as compared to 51 out of 645 in the control group (OR: 0.34; 95% CI: 0.20,0.56; I2 = 0%; P &lt; 0.0001). Durotomies were lower among the ACD/AR patients with only 3 reported cases compared to 7 in the control group (OR: 0.54; 95% CI: 0.13, 2.23; I2 = 11%; P = 0.39). Similar outcomes for post-operative Oswestry Disability Index and visual analogue scale were obtained when both groups were compared.

Conclusions

Early results showed the use of Barricaid and Anulex devices are beneficial for short term outcomes demonstrating a reduction in symptomatic disc reherniation with low post-operative complication rates. Long-term studies are required to further investigate the efficacy of such devices.

Joint preoperative transthoracic and intraoperative transoesophageal echocardiographic assessment of functional mitral regurgitation severity provides better association with long-term mortality

OBJECTIVES

Functional mitral regurgitation (MR) is observed with ischaemic heart disease or aortic valve disease. Assessing the value of mitral valve repair or replacement (MVR/P) is complicated by frequent discordance between preoperative transthoracic echocardiographic (pTTE) and intraoperative transoesophageal echocardiographic (iTOE) assessment of MR severity. We examined the association of pTTE and iTOE with postoperative mortality in patients with or without MR, at the time of coronary artery bypass grafting (CABG) and/or aortic valve replacement without MVR/P.

METHODS

Medical records of 6629 patients undergoing CABG and/or aortic valve replacement surgery with or without functional MR and who did not undergo MVR/P were reviewed. MR severity assessed by pTTE and iTOE were examined for association with postoperative mortality using proportional hazards regression while accounting for patient and operative characteristics.

RESULTS

In 72% of 709 patients with clinically significant (moderate or greater) functional MR detected by pTTE, iTOE performed after induction of anaesthesia demonstrated a reduction in MR severity, while 2% of patients had increased severity of MR by iTOE. iTOE assessment of MR was better associated with long-term postoperative mortality than pTTE in patients with moderate MR [hazard ratio (HR) 1.31 (1.11-1.55) vs 1.02 (0.89-1.17), P-value for comparison of HR 0.025] but was not different for more than moderate MR [1.43 (0.96-2.14) vs 1.27 (0.80-2.02)].

CONCLUSIONS

In patients undergoing CABG and/or aortic valve replacement without MVR/P, these findings support intraoperative reassessment of MR severity by iTOE as an adjunct to pTTE in the prediction of mortality. Alone, these findings do not yet provide evidence for an operative strategy.

Early Vascular Cells Improve Microvascularization Within 3D Cardiac Spheroids

Introduction: A key obstacle in the creation of engineered cardiac tissues of clinically relevant sizes is limited diffusion of oxygen and nutrients. Thus, there is a need for organized vascularization within a three-dimensional (3D) tissue environment. Human induced pluripotent stem cell (hiPSC)-derived early vascular cells (EVCs) have shown to improve organization of vascular networks within hydrogels. We hypothesize that introduction of EVCs into 3D microtissue spheroids will lead to increased microvascular formation and improve spheroid formation. Methods: HiPSC-derived cardiomyocytes (CMs) were cocultured with human adult ventricular cardiac fibroblasts (FB) and either human umbilical vein endothelial cells (HUVECs) or hiPSC-derived EVCs for 72 h to form mixed cell spheroids. Three different groups of cell ratios were tested: Group 1 (control) consisted of CM:FB:HUVEC 70:15:15, Group 2 consisted of CM:FB:EVC 70:15:15, and Group 3 consisted of CM:FB:EVC 40:15:45. Vascularization, cell distribution, and cardiac function were investigated. Results: Improved microvasculature was found in EVC spheroids with new morphologies of endothelial organization not found in Group 1 spheroids. CMs were found in a core-shell type distribution in Group 1 spheroids, but more uniformly distributed in EVC spheroids. Contraction rate increased into Group 2 spheroids compared to Group 1 spheroids. Conclusion: The triculture of CM, FB, and EVC within a multicellular cardiac spheroid promotes microvascular formation and cardiac spheroid contraction.

Red blood cell storage duration and peri-operative outcomes in paediatric cardiac surgery

BACKGROUND

Prior research on red blood cell (RBC) storage duration and clinical outcomes in paediatric cardiac surgery has shown conflicting results. The purpose of this study was to evaluate whether blood stored for a longer duration is harmful in these patients.

METHODS

We performed a retrospective cohort study of paediatric patients undergoing cardiac surgery at our institution between January 2011 and June 2015. Patients were stratified based on whether they were transfused RBCs stored for ≤15 days (fresher blood) or >15 days (older blood). The primary outcome was composite morbidity, with prolonged length of stay (LOS) as a secondary outcome. Subgroup analyses were performed after stratification by RBC transfusion volume (≤2 vs. >2 RBC units). Multivariable logistic regression models were used to assess the impact of RBC storage duration on composite morbidity and prolonged LOS.

RESULTS

Of 461 patients, 122 (26·5%) received fresher blood and 339 (73·5%) received older blood. The overall rate of composite morbidity was 18·0% (n = 22) for patients receiving fresher blood and 13·6% (n = 46) for patients receiving older blood (P = 0·24). In the risk-adjusted model, patients receiving older blood did not exhibit an increased risk of composite morbidity (OR: 0·74, 95% CI: 0·37-1·47, P = 0·40) or prolonged LOS (OR: 0·72, 95% CI: 0·38-1·35, P = 0·30) compared to patients receiving fresher blood. Similar results were seen after stratification by RBC transfusion volume.

CONCLUSIONS

Transfusing RBCs stored for a longer duration was not associated with an increased risk of morbidity or prolonged LOS in paediatric cardiac surgery patients.

Fast-degrading TEVGs Lead to Increased ECM Cross-linking Enzymes Expression

Tissue-engineered vascular grafts (TEVGs) require adequate extracellular matrix (ECM) to withstand arterial pressure. Tissue transglutaminase (TG2) and lysyl oxidase (LOX) are enzymes that cross-link ECM proteins and play a pivotal role in the development of vascular stiffness associated with aging. The purpose of this study is to investigate the expression of ECM cross-linking enzymes and mechanisms of scaffold degeneration leading to vascular stiffness in TEVG remodeling. Fast- and slow-degrading electrospun TEVGs were fabricated using polydioxanone (PDO) and poly(L-lactide-co-caprolactone) (PLCL) copolymer, with a PDO/PLCL ratio of 9:1 for fast-degrading and 1:1 for slow-degrading graft. These grafts were implanted in rats (n=5/group) as abdominal aortic interposition conduits. The grafts were harvested at one month to evaluate patency, mechanical properties, vascular neotissue formation and the expression of ECM cross-linking enzymes. All TEVGs were patent without any aneurysmal formation at one month. ECM area, TG2 positive area and LOX positive area were significantly greater in fast-degrading TEVGs compared to slow-degrading TEVGs, with significantly less remaining scaffold. The mechanical properties of fast-degrading TEVGs were similar to that of native aorta, as demonstrated by strain-stress curve. In conclusion, at one month, fast-degrading TEVGs had rapid and well-organized ECM with greater TG2 and LOX expression and native-like mechanical properties, compared to slow-degrading TEVGs.

Factors Related to Survival in Low-Glomerular Filtration Rate Cohorts Undergoing Lung Transplant

BACKGROUND

Historically, a glomerular filtration rate (GFR) of less than 50 mL/min per 1.73 m² has been considered a contraindication to lung transplantation. Combined or sequential lung-kidney transplantation is an option for those with a GFR less than 30 mL/min per 1.73 m². Patients with a GFR of 30 to 50 mL/min per 1.73 m² are provided with no options for transplantation. This study explores factors associated with improved survival in patients who undergo isolated lung transplantation with a GFR of 30 to 50 mL/min per 1.73 m².

METHODS

The United Network for Organ Sharing database was queried for adult patients undergoing primary isolated lung transplantation between January 2007 and March 2018. Regression models were used to identify factors associated with improved survival in lung recipients with a preoperative GFR of 30 to 50 mL/min per 1.73 m². The propensity score method was used to match highly performing patients (outpatient recipients aged less than 60 years) with a GFR of 30 to 50 mL/min per 1.73 m² with patients who had a GFR greater than 50 mL/min per 1.73 m². Kaplan-Meier, Cox, and logistic regression analyses compared outcomes in matched populations.

RESULTS

A total of 21,282 lung transplantations were performed during the study period. Compared with patients with a GFR greater than 50 mL/min per 1.73 m², survival was significantly worse for patients with a GFR of 30 to 50 mL/min per 1.73 m². Multivariate analysis of patients with a GFR of 30 to 50 mL/min per 1.73 m² demonstrated outpatient status and age less than 60 years to be predictive of superior survival. After propensity matching, survival of this highly performing subset with a GFR of 30 to 50 mL/min per 1.73 m² was no different from that of patients with a normal GFR.

CONCLUSIONS

Outpatient recipients aged less than 60 years represent an optimal subset of patients with a GFR of 30 to 50 mL/min per 1.73 m². Lung transplant listing should not be declined based only on a GFR less than 50 mL/min per 1.73 m².

Association of Heparin Dose, Route, Timing, and Duration With Heparin-Induced Thrombocytopenia

BACKGROUND

The prevalence of heparin-induced thrombocytopenia (HIT) varies by population and the type and duration of heparinoid exposure; however, the association with unfractionated heparin (UFH) dose, route, timing, and duration has not been evaluated in cardiac surgery patients.

METHODS

A retrospective case-control study matched HIT-positive adult cardiac surgery patients (positive platelet factor 4 immunoglobulin G and serotonin release assays) 1:1 with HIT-negative controls. Total UFH dose, route, timing, and duration were compared between groups.

RESULTS

The study included 124 patients, 92 male (74%), with mean age of 65 ± 11 years. Significantly more HIT-positive patients received intravenous UFH preoperatively or postoperatively compared with patients without HIT (55 [88.7%] vs 23 [37.1%]; P < .001). There were no significant differences regarding intraoperative or subcutaneous UFH dose or duration. When controlling for obesity and cardiopulmonary bypass duration using multivariable conditional logistic regression, the odds of HIT were increased 10-fold in patients who received preoperative or postoperative intravenous UFH continuous infusion (odds ratio 10.2, 95% confidence interval, 3.1 to 33.7; P < .001). Receiver-operating characteristic curves demonstrated that receiving preoperative or postoperative intravenous UFH infusion total dose greater than 32,000 units (sensitivity 82%, specificity 74%, area under the curve 0.78) or longer than 7 hours (sensitivity 87%, specificity 68%, area under the curve 0.77) was associated with HIT.

CONCLUSIONS

Odds of HIT were increased 10-fold in adult cardiac surgery patients receiving preoperative or postoperative intravenous UFH infusion. Intraoperative UFH dose and subcutaneous route were not associated with HIT. Future study should evaluate incorporation of intravenous UFH administration, dose, and duration in HIT scoring tools for cardiac surgery patients.

Pulmonary Venoatrial Connection Using a Ringed Tube Graft to Repair Partial Anomalous Pulmonary Venous Return

Left-sided partial anomalous pulmonary venous return (left pulmonary veins to left vertical vein) was repaired in a 70-year-old patient by ligation of the vertical vein and connection of the pulmonary veins to the left atrial appendage using a ringed polytetrafluoroethylene tube graft. The graft made the connection technically easier and facilitated a torque-free and tension-free anastomosis that was "stented" open by the rings.

Nutrition Support After Cardiac Surgery: Lessons Learned From a Prospective Study

The importance of postoperative nutrition support (NS) has been poorly recognized in cardiac surgery. In this population, we aim to describe the delivery of NS, factors affecting calorie/protein delivery and NS-associated morbidity. From January 2015 to January 2017, we prospectively observed all cardiac surgery patients at a single institution who could not take nutrition orally, requiring postoperative NS, either enteral or parenteral, for the duration of NS up to 14 days. We compared outcomes to patients without NS and examined NS indications, factors affecting its delivery and its associated complications. Nine percent of patients (232/2603) required NS for a total of 1938 NS-days. The most common indication was mechanical ventilation. NS met 69% of daily caloric needs. On days when tube feeds (TFs) were held (mean of 13 hours), this decreased to 43%, compared to 96% when TFs were not held (P < 0.001). The most common reason for holding TFs was procedures. When TFs were supplemented with parenteral nutrition (TFs + PN), 86% of daily caloric needs were met. Even on days when TFs were held, this only dropped to 77% (TFs + PN), compared to 36% (TFs-only). By multivariable logistic regression, elemental and semielemental formulas, TF volume, and postpyloric feeds increased the risk of diarrhea, occurring in 28% of patients and 18% of TF-days. In cardiac surgery patients given postoperative NS, mortality and morbidity were an order of magnitude higher than those able to be fed orally. Enteral feeding delivered approximately two-thirds of needs, but PN supplementation dramatically improved this. Diarrhea was common, associated with the postpyloric route, increasing TF volume, and nonintact formula.

Corrugated nanofiber tissue-engineered vascular graft to prevent kinking for arteriovenous shunts in an ovine model

Objective

Prosthetic grafts are often needed in open vascular procedures. However, the smaller diameter prosthetic grafts (<6 mm) have low patency and often result in complications from infection. Tissue-engineered vascular grafts (TEVGs) are a promising replacement for small diameter prosthetic grafts. TEVGs start as a biodegradable scaffold to promote autologous cell proliferation and functional neotissue regeneration. Owing to the limitations of graft materials; however, most TEVGs are rigid and easily kinked when implanted in limited spaces, which precludes clinical application. We have developed a novel corrugated nanofiber graft to prevent kinking.

Methods

TEVGs with corrugated walls (5-mm internal diameter by 10 cm length) were created by electrospinning a blend of poly-ε-caprolactone and poly(L-lactide-co-caprolactone). The biodegradable grafts were then implanted between the carotid artery and the external jugular vein in a U-shape using an ovine model. TEVGs were implanted on both the left and right side of a sheep (n = 4, grafts = 8). The grafts were explanted 1 month after implantation and inspected with mechanical and histologic analyses. Graft patency was confirmed by measuring graft diameter and blood flow velocity using ultrasound, which was performed on day 4 and every following week after implantation.

Results

All sheep survived postoperatively except for one sheep that died of acute heart failure 2 weeks after implantation. The graft patency rate was 87.5% (seven grafts out of eight) with one graft becoming occluded in the early phase after implantation. There was no significant kinking of the grafts. Overall, endothelial cells were observed in the grafts 1 month after the surgeries without graft rupture, calcification, or aneurysmal change.

Conclusions

Our novel corrugated nanofiber vascular graft displayed neotissue formation without kinking in large animal model.

This basic science research article reported tissue-engineered vascular grafts for arteriovenous shunt procedures. Nanofibrous grafts were electrospun with polyglycolic acid and poly-ε-caprolactone with a corrugated wall design to prevent graft kinking. The tissue-engineered vascular grafts were then implanted in U-shape between the carotid artery and the external jugular vein of an ovine model. This graft had 87.5% patency rate and did not display significant kinking. Overall, re-endothelialization was observed in the grafts one month after the surgeries without graft rupture, calcification or aneurysmal change. This graft is a promising alternative to small diameter prosthetic grafts.

Different degradation rates of nanofiber vascular grafts in small and large animal models

Nanofiber vascular grafts have been shown to create neovessels made of autologous tissue, by in vivo scaffold biodegradation over time. However, many studies on graft materials and biodegradation have been conducted in vitro or in small animal models, instead of large animal models, which demonstrate different degradation profiles. In this study, we compared the degradation profiles of nanofiber vascular grafts in a rat model and a sheep model, while controlling for the type of graft material, the duration of implantation, fabrication method, type of circulation (arterial/venous), and type of surgery (interposition graft). We found that there was significantly less remaining scaffold (i.e., faster degradation) in nanofiber vascular grafts implanted in the sheep model compared with the rat model, in both the arterial and the venous circulations, at 6 months postimplantation. In addition, there was more extracellular matrix deposition, more elastin formation, more mature collagen, and no calcification in the sheep model compared with the rat model. In conclusion, studies comparing degradation of vascular grafts in large and small animal models remain limited. For clinical translation of nanofiber vascular grafts, it is important to understand these differences.

Principles of Spheroid Preparation for Creation of 3D Cardiac Tissue Using Biomaterial-Free Bioprinting

Biomaterial-free three-dimensional (3D) bioprinting is a relatively new field within 3D bioprinting, where 3D tissues are created from the fusion of 3D multicellular spheroids, without requiring biomaterial. This is in contrast to traditional 3D bioprinting, which requires biomaterials to carry the cells to be bioprinted, such as a hydrogel or decellularized extracellular matrix. Here, we discuss principles of spheroid preparation for biomaterial-free 3D bioprinting of cardiac tissue. In addition, we discuss principles of using spheroids as building blocks in biomaterial-free 3D bioprinting, including spheroid dislodgement, spheroid transfer, and spheroid fusion. These principles are important considerations, to create the next generation of biomaterial-free spheroid-based 3D bioprinters.

Cardiac regeneration using human-induced pluripotent stem cell-derived biomaterial-free 3D-bioprinted cardiac patch in vivo

One of the leading causes of death worldwide is heart failure. Despite advances in the treatment and prevention of heart failure, the number of affected patients continues to increase. We have recently developed 3D-bioprinted biomaterial-free cardiac tissue that has the potential to improve cardiac function. This study aims to evaluate the in vivo regenerative potential of these 3D-bioprinted cardiac patches. The cardiac patches were generated using 3D-bioprinting technology in conjunction with cellular spheroids created from a coculture of human-induced pluripotent stem cell-derived cardiomyocytes, fibroblasts, and endothelial cells. Once printed and cultured, the cardiac patches were implanted into a rat myocardial infarction model (n = 6). A control group (n = 6) without the implantation of cardiac tissue patches was used for comparison. The potential for regeneration was measured 4 weeks after the surgery with histology and echocardiography. 4 weeks after surgery, the survival rates were 100% and 83% in the experimental and the control group, respectively. In the cardiac patch group, the average vessel counts within the infarcted area were higher than those within the control group. The scar area in the cardiac patch group was significantly smaller than that in the control group. (Figure S1) Echocardiography showed a trend of improvement of cardiac function for the experimental group, and this trend correlated with increased patch production of extracellular vesicles. 3D-bioprinted cardiac patches have the potential to improve the regeneration of cardiac tissue and promote angiogenesis in the infarcted tissues and reduce the scar tissue formation.

A Century of Heparin

The year 2018 was the centennial of the naming of heparin by Emmett Holt and William Howell and the 102nd anniversary of Jay McLean's discovery of an anticoagulant heparphosphatide at Johns Hopkins Hospital in Baltimore. This article discusses recently discovered historical artifacts that shed new light on heparin's christening, including McLean's unpublished letter written in 1950 that represents one of the most complete accounts of heparin's discovery before his untimely death. In addition, the article describes the finding of a plaque dedicated to McLean and explores the circumstances of its removal from public display, as learned from interviews with present and former staff members.

Trends and Updates on Cardiopulmonary Bypass Setup in Pediatric Cardiac Surgery

Perfusion strategies for cardiopulmonary bypass have direct consequences on pediatric cardiac surgery outcomes. However, inconsistent study results and a lack of uniform evidence-based guidelines for pediatric cardiopulmonary bypass management have led to considerable variability in perfusion practices among, and even within, institutions. Important aspects of cardiopulmonary bypass that can be optimized to improve clinical outcomes of pediatric patients undergoing cardiac surgery include extracorporeal circuit components, priming solutions, and additives. This review summarizes the current literature on circuit components and priming solution composition with an emphasis on crystalloid, colloid, and blood-based primes, as well as mannitol, bicarbonate, and calcium.

Formation of Neoarteries with Optimal Remodeling Using Rapidly Degrading Textile Vascular Grafts

IMPACT STATEMENT

We utilized innovative textile technology to create tissue-engineered vascular grafts (TEVGs) comprised exclusively of rapidly degrading material poly(glycolic acid). Our new technology led to robust neotissue formation in the TEVGs, especially extracellular matrix formation, such as elastin. In addition, the rapid degradation of the polymer significantly reduced complications, such as stenosis or calcification, as seen with the use of slow degrading polymers in the majority of previous studies for aortic small diameter TEVGs.

A Review of Goal-Directed Cardiopulmonary Bypass Management in Pediatric Cardiac Surgery

Cardiopulmonary bypass perfusion management significantly affects postoperative outcomes. In recent years, the principles of goal-directed therapy have been applied to the field of cardiothoracic surgery to improve patient outcomes. Goal-directed therapy involves continuous peri- and postoperative monitoring of vital clinical parameters to tailor perfusion to each patient's specific needs. Closely measured parameters include fibrinogen, platelet count, lactate, venous oxygen saturation, central venous oxygen saturation, mean arterial pressure, perfusion flow rate, and perfusion pulsatility. These parameters have been shown to influence postoperative fresh frozen plasma transfusion rate, coagulation state, end-organ perfusion, and mortality. In this review, we discuss the recent paradigm shift in pediatric perfusion management toward goal-directed perfusion.