Changes in Donor Utilization and Outcomes for Patients Bridged With Durable Left Ventricular Assist Device

We studied the impact of the 2018 heart allocation policy change on donor characteristics and posttransplant outcomes of left ventricular assist device (LVAD)-bridged heart transplant (HT) recipients. Left ventricular assist device-bridged adult HT recipients from October 2014 to October 2022 in the United Network for Organ Sharing database were categorized into old allocation policy (OAP) and new allocation policy (NAP) cohorts. Baseline characteristics, posttransplant outcomes, and subgroup analyses of unstable and stable LVAD-bridged recipients were assessed. The study included 7,384 HT recipients; 4,345 (58.8%) were transplanted in the OAP era and 3,039 (41.2%) in the NAP era. Old allocation policy recipients were most frequently status 1A at transplantation (71.1%), whereas NAP recipients were most frequently status 3 (40.0%), and status 4 (31.9%). Median donor sequence number (DSN) was higher in the NAP versus OAP era (9 vs. 3, p < 0.001). On multivariable analysis, NAP recipients had 20% higher 1 year mortality compared to OAP (adjusted hazard ratio [aHR] = 1.20 [95% confidence interval {CI}: 1.04-1.40], p = 0.01). Status 1 or 2 recipients had 28% higher 1 year mortality compared to status 1A (aHR = 1.28 [95% CI: 1.01-1.63], p = 0.04). Status 1 and 2 LVAD-supported recipients had higher mortality following the 2018 allocation change, indicating the need for closer surveillance of LVAD-bridged patients who may decompensate on the waitlist.

Impact of Extracorporeal Membrane Oxygenation Bridging Duration on Lung Transplant Outcomes

BACKGROUND

We sought to characterize the association between venovenous extracorporeal membrane oxygenation (VV-ECMO) bridging duration and outcomes in patients listed for lung transplantation.

METHODS

A retrospective observational study was conducted using the Organ Procurement and Transplantation Network (OPTN) database to identify adults (≥18 years old) who were listed for lung transplantation between 2016-2020 and who were bridged with VV-ECMO. Patients were then stratified into groups, determined by risk inflection points, depending on the amount of time spent on pre-transplant ECMO: Group 1 (≤5 days), Group 2 (6-10 days), Group 3 (11-20 days), and Group 4 (>20 days). Waitlist survival between groups was analyzed using Fine-Gray competing risk models. Post-transplant survival was compared using Cox regression.

RESULTS

Of 566 eligible VV-ECMO bridge-to-lung-transplant patients (median age=54, 49% male), 174 (31%), 124 (22%), 130 (23%), and 138 (24%) were categorized as Groups 1, 2, 3, and 4, respectively. Overall, median duration of VV-ECMO was 10 days (range=1-211) and 178 patients (31%) died on the waitlist. In the Fine-Gray model, compared to Group 1, patients bridged with longer ECMO durations in Groups 2 (SHR=2.95, 95%CI: 1.63-5.35), 3 (SHR=3.96, 95%CI: 2.36-6.63), and 4 (SHR=4.33, 95%CI: 2.59-7.22, all p<0.001), were more likely to die on the waitlist. Of 388 patients receiving a transplant, pre-transplant ECMO duration was not associated with one-year survival in Cox regression.

CONCLUSIONS

Prolonged ECMO bridging duration was associated with worse waitlist mortality but did not impact post-lung transplant survival. Prioritization of very early transplantation may improve waitlist outcomes in this population.

Bigger pies, bigger slices: Increased hospitalization costs for lung transplantation recipients in the non-donation service area allocation era

OBJECTIVE

On November 24, 2017, lung transplant allocation switched from donation service area to a 250-nautical mile radius policy to improve equity in access to lung transplantation. Given the growing consideration of healthcare costs, we evaluated changes in hospitalization costs after this policy change.

METHODS

Lung transplant hospitalizations were identified within the National Inpatient Sample from 2005 to 2020. Recipients were categorized as donation service area era (August 2015 to October 2017) or non-donation service area era (December 2017 to February 2020). Median total hospitalization costs (inflation adjusted) were compared by era nationally and regionally. Multivariable generalized linear regression was performed to determine if the removal of the donation service area was associated with total hospitalization costs. The model was adjusted for recipient demographics, Charlson Comorbidity Index, hospitalization region, transplant type (single, double), and use of extracorporeal membrane oxygenation, ex vivo lung perfusion, and mechanical ventilation.

RESULTS

We analyzed 12,985 lung transplant recipients (median age of 61 years, 66% were male): 7070 in the donation service area era and 5915 in the non-donation service area era. Demographics were not different between recipients in both eras. Non-donation service area era recipients had greater extracorporeal membrane oxygenation use, mechanical ventilation (<24 hours), and longer length of stay than donation service area era recipients. Median total hospitalization costs for non-donation service area versus donation service area era recipients increased by $24,198 ($157,964 vs $182,162, percentage change = 15.32%, P < .001). Median costs increased in East North Central ($42,281) and Mountain ($35,521) regions (both P < .01). After adjustment, median costs for non-donation service area versus donation service area era recipients still increased ($19,168, 95% CI, 145-38,191, P = .048).

CONCLUSIONS

Hospitalization costs for lung transplant hospitalizations have increased from 2015 to 2020. The transition from donation service area-based allocation to the non-donation service area system may have contributed to this increase after 2017 by increasing access to transplant for sicker recipients.

Special Considerations for Advanced Heart Failure Surgeries: Durable Left Ventricular Devices and Heart Transplantation

Heart transplantation and durable left ventricular assist devices (LVADs) represent two definitive therapies for end-stage heart failure in the modern era. Despite technological advances, both treatment modalities continue to experience unique risks that impact surgical and perioperative decision-making. Here, we review special populations and factors that impact risk in LVAD and heart transplant surgery and examine critical decisions in the management of these patients. As both heart transplantation and the use of durable LVADs as destination therapy continue to increase, these considerations will be of increasing relevance in managing advanced heart failure and improving outcomes.

Debunking the July Effect in lung transplantation recipients

Objective

The "July Effect" is a theory that the influx of trainees from July to September negatively impacts patient outcomes. We aimed to study this theoretical phenomenon in lung transplant recipients given the highly technical nature of thoracic procedures.

Methods

Adult lung transplant hospitalizations were identified within the National Inpatient Sample (2005-2020). Recipients were categorized as academic Q1 (July to September) or Q2-Q4 (October to June). In-hospital mortality, operator-driven complications (pneumothorax, dehiscence including wound dehiscence, bronchial anastomosis, and others, and vocal cord/diaphragm paralysis, all 3 treated as a composite outcome), length of stay, and inflation-adjusted hospitalization charges were compared between both groups. Multivariable logistic regression was performed to assess the association between academic quarter and in-hospital mortality and operator-driven complications. The models were adjusted for recipient demographics and transplant characteristics. Subgroup analysis was performed between academic and nonacademic hospitals.

Results

Of 30,788 lung transplants, 7838 occurred in Q1 and 22,950 occurred in Q2-Q4. Recipient demographic and clinical characteristics were similar between groups. Dehiscence (n = 922, 4% vs n = 236, 3%), post-transplant cardiac arrest (n = 532, 2% vs n = 113, 1%), and pulmonary embolism (n = 712, 3% vs n = 164, 2%) were more common in Q2-Q4 versus Q1 recipients (all P < .05). Other operator-driven complications, in-hospital mortality, and resource use were similar between groups (P > .05). These inferences remained unchanged in adjusted analyses and on subgroup analyses of academic versus nonacademic hospitals.

Conclusions

The "July Effect" is not evident in US lung transplantation recipient outcomes during the transplant hospitalization. This suggests that current institutional monitoring systems for trainees across multiple specialties, including surgery, anesthesia, critical care, nursing, and others, are robust.

Outcomes of Lung Transplant Candidates Aged ≥70 Years During the Lung Allocation Score Era

BACKGROUND

With the increasing age of lung transplant candidates, we studied waitlist and posttransplantation outcomes of candidates ≥70 years during the Lung Allocation Score era.

METHODS

Adult lung transplant candidates from 2005 to 2020 in the United Network for Organ Sharing database were included and stratified on the basis of age at listing into 18 to 59 years old, 60 to 69 years old, and ≥70 years old. Baseline characteristics, waitlist outcomes, and posttransplantation outcomes were assessed.

RESULTS

A total of 37,623 candidates were included (52.3% aged 18-59 years, 40.6% aged 60-69 years, 7.1% aged ≥70 years). Candidates ≥70 years were more likely than younger candidates to receive a transplant (81.9% vs 72.7% [aged 60-69 years] vs 61.6% [aged 18-59 years]) and less likely to die or to deteriorate on the waitlist within 1 year (9.1% vs 10.1% [aged 60-69 years] vs 12.2% [aged 18-59 years]; P < .001). Donors for older recipients were more likely to be extended criteria (75.7% vs 70.1% [aged 60-69 years] vs 65.7% [aged 18-59 years]; P < .001). Recipients ≥70 years were found to have lower rates of acute rejection (6.7% vs 7.4% [aged 60-69 years] vs 9.2% [aged 18-59 years]; P < .001) and prolonged intubation (21.7% vs 27.4% [aged 60-69 years] vs 34.5% [aged 18-59 years]; P < .001). Recipients aged ≥70 years had increased 1-year (adjusted hazard ratio [aHR], 1.19 [95% CI, 1.06-1.33]; P < .001), 3-year (aHR, 1.28 [95% CI, 1.18-1.39]; P < .001), and 5-year mortality (aHR, 1.29 [95% CI, 1.21-1.38]; P < .001) compared with recipients aged 60 to 69 years.

CONCLUSIONS

Candidates ≥70 years had favorable waitlist and perioperative outcomes despite increased use of extended criteria donors. Careful selection of candidates and postoperative surveillance may improve posttransplantation survival in this population.

Unusual presentation and delayed diagnosis of cardiac angiosarcoma

BACKGROUND

Primary cardiac angiosarcomas are very rare and present aggressively with high rates of metastasis. Given the poor prognosis, particularly once disease has spread, early diagnosis and multidisciplinary treatment is essential.

CASE PRESENTATION

We present the case of a 46-year-old male who presented with chest pain, intermittent fevers, and dyspnea. Workup with computed tomography scan and transesophageal echocardiography demonstrated a right atrial pseudoaneurysm. Given the concern for rupture, the patient was taken to the operating room, where resection of the pseudoaneurysm and repair using a bovine pericardial patch was performed. Histopathology report initially demonstrated perivascular lymphocyte infiltrate. Six weeks later, the patient represented with chest pain and new word finding difficulty. Workup revealed multiple solid lung, pericardial, brain, and bone nodules. Eventual biopsy of a cardiophrenic nodule demonstrated angiosarcoma, and rereview of the original pathology slides confirmed the diagnosis of primary cardiac angiosarcoma.

CONCLUSIONS

Primary cardiac angiosarcomas are often misdiagnosed given the rarity of these tumors, but early diagnosis and initiation of treatment is essential. The unique presentation of our case demonstrates that clinical suspicion for cardiac angiosarcoma should be maintained for spontaneous pseudoaneurysm originating from the right atrium.

Outcomes following concomitant multiorgan heart transplantation from circulatory death donors: The United States experience

BACKGROUND

Donation after circulatory death (DCD) has reemerged as a method of expanding the donor heart pool. Given the high waitlist mortality of multiorgan heart candidates, we evaluated waitlist outcomes associated with willingness to consider DCD offers and post-transplant outcomes following DCD transplant for these candidates.

METHODS

We identified adult multiorgan heart candidates and recipients between January 1, 2020 and March 31, 2023 nationally. Among candidates that met inclusion criteria, we compared the cumulative incidence of transplant, with waitlist death/deterioration as a competing risk, by willingness to consider DCD offers. Among recipients of DCD versus brain death (DBD) transplants, we compared perioperative outcomes and post-transplant survival.

RESULTS

Of 1,802 heart-kidney, 266 heart-liver, and 440 heart-lung candidates, 15.8%, 12.4%, and 31.1%, respectively, were willing to consider DCD offers. On adjusted analysis, willingness to consider DCD offers was associated with higher likelihood of transplant for all multiorgan heart candidates and decreased likelihood of waitlist deterioration for heart-lung candidates. Of 1,100 heart-kidney, 173 heart-liver, and 159 heart-lung recipients, 5.4%, 2.3%, and 2.5%, respectively, received DCD organs. Recipients of DCD and DBD heart-kidney transplants had a similar likelihood of perioperative outcomes and 1-year survival. All other DCD multiorgan heart recipients have survived to the last follow-up.

CONCLUSIONS

Multiorgan heart candidates who were willing to consider DCD offers had favorable waitlist outcomes, and heart-kidney recipients of DCD transplants had similar post-transplant outcomes to recipients of DBD transplants. We recommend the use of DCD organs to increase the donor pool for these high-risk candidates.

Outcomes of Recipients Aged 65 Years and Older Bridged to Lung Transplant With Extracorporeal Membrane Oxygenation

Extracorporeal membrane oxygenation (ECMO) as a bridge to lung transplant (BTT) has been used for critically ill candidates with excellent outcomes, but data on this strategy in older recipients remain limited. We compared outcomes of no BTT, mechanical ventilation (MV)-only BTT, and ECMO BTT in recipients of greater than or equal to 65 years. Lung-only recipients of greater than or equal to 65 years in the United Network for Organ Sharing database between 2008 and 2022 were included and stratified by bridging strategy. Of the 9,936 transplants included, 226 (2.3%) were MV-only BTT and 159 (1.6%) were ECMO BTT. Extracorporeal membrane oxygenation BTT recipients were more likely to have restrictive disease pathology, had higher median lung allocation score, and spent fewer days on the waitlist (all p < 0.001). Compared to no-BTT recipients, ECMO BTT recipients were more likely to be intubated or on ECMO at 72 hours posttransplant and had longer hospital lengths of stay (all p < 0.001). Extracorporeal membrane oxygenation BTT recipients had increased risk of 3 years mortality compared to both no-BTT (adjusted hazard ratio [aHR] = 1.48 [95% confidence interval {CI}: 1.14-1.91], p = 0.003) and MV-only recipients (aHR = 1.50 [95% CI: 1.08-2.07], p = 0.02). Overall, we found that ECMO BTT in older recipients is associated with inferior posttransplant outcomes compared to MV-only or no BTT, but over half of recipients remained alive at 3 years posttransplant.

Kidney Donation After Circulatory Death Using Thoracoabdominal Normothermic Regional Perfusion: The Largest Report of the United States Experience

BACKGROUND

Thoracoabdominal normothermic regional perfusion (TA-NRP) has been increasingly used for donation after circulatory death (DCD) procurements in the United States. We present the largest report of outcomes of kidney transplants performed using DCD donor grafts perfused with TA-NRP.

METHODS

Adult DCD kidney transplants between 2020 and 2022 in the United Network for Organ Sharing database were included. Donors with ≥50 min between asystole and aortic cross-clamp time in which the heart was also transplanted were considered TA-NRP donors. All other donors were considered direct recovery donors. Multivariable regressions were used to assess delayed graft function, as well as posttransplant survival and all-cause graft failure at 30, 90, and 180 d. A propensity-matched analysis of cohorts matched on donor Kidney Donor Profile Index was performed.

RESULTS

Of the 16 140 total DCD kidney transplants performed during the study period, 306 (1.9%) used TA-NRP. TA-NRP donors were younger ( P  < 0.001) and had lower Kidney Donor Profile Index ( P  < 0.001) compared with direct recovery donors. Recipients receiving grafts recovered using TA-NRP were younger ( P  < 0.001) and more likely to be blood group O ( P  < 0.001). Transplants using TA-NRP had lower likelihood of delayed graft function (adjusted odds ratio 0.22 [95% confidence interval, 0.15-0.31], P  < 0.001) but similar 180-d survival ( P  = 0.8) and all-cause graft failure ( P  = 0.3) as transplants using direct recovery grafts. These inferences were unchanged on propensity-matched analysis.

CONCLUSIONS

Our results demonstrate that kidney transplants using TA-NRP DCD allografts have positive short-term mortality and graft survival outcomes, with significantly decreased rates of delayed graft function compared with direct recovery DCD grafts.

Uptake and 1-year outcomes of lung transplantation for COVID-19

OBJECTIVE

End-stage lung disease from severe COVID-19 infection is an increasingly common indication for lung transplantation (LT), but there are limited data on outcomes. We evaluated 1-year COVID-19 LT outcomes.

METHODS

We identified all adult US LT recipients January 2020 to October 2022 in the Scientific Registry for Transplant Recipients, using diagnosis codes to identify recipients transplanted for COVID-19. We used multivariable regression to compare in-hospital acute rejection, prolonged ventilator support, tracheostomy, dialysis, and 1-year mortality between COVID-19 and non-COVID-19 recipients, adjusting for donor, recipient, and transplant characteristics.

RESULTS

LT for COVID-19 increased from 0.8% to 10.7% of total LT volume during 2020 to 2021. The number of centers performing LT for COVID-19 increased from 12 to 50. Recipients transplanted for COVID-19 were younger; were more likely to be male and Hispanic; were more likely to be on a ventilator, extracorporeal membrane oxygenation support, and dialysis pre-LT; were more likely to receive bilateral LT; and had higher lung allocation score and shorter waitlist time than other recipients (all P values < .001). COVID-19 LT had higher risk of prolonged ventilator support (adjusted odds ratio, 2.28; P < .001), tracheostomy (adjusted odds ratio 5.3; P < .001), and longer length of stay (median, 27 vs 19 days; P < .001). Risk of in-hospital acute rejection (adjusted odds ratio, 0.99; P = .95) and 1-year mortality (adjusted hazard ratio, 0.73; P = .12) were similar for COVID-19 LTs and LTs for other indications, even accounting for center-level differences.

CONCLUSIONS

COVID-19 LT is associated with higher risk of immediate postoperative complications but similar risk of 1-year mortality despite more severe pre-LT illness. These encouraging results support the ongoing use of LT for COVID-19-related lung disease.

The effect of allograft ischemic time on outcomes following bilateral, single, and reoperative lung transplantation

OBJECTIVE

To determine whether allograft ischemic times affect outcomes following bilateral, single, and redo lung transplantation.

METHODS

A nationwide cohort of lung transplant recipients from 2005 through 2020 was examined using the Organ Procurement and Transplantation Network registry. The effects of standard (<6 hours) and extended (≥6 hours) ischemic times on outcomes following primary bilateral (n = 19,624), primary single (n = 688), redo bilateral (n = 8461), and redo single (n = 449) lung transplantation were analyzed. A priori subgroup analysis was performed in the primary and redo bilateral-lung transplant cohorts by further stratifying the extended ischemic time group into mild (≥6 and <8 hours), moderate (≥8 and <10 hours), and long (≥10 hours) subgroups. Primary outcomes included 30-day mortality, 1-year mortality, intubation at 72 hours' posttransplant, extracorporeal membrane oxygenation (ECMO) support at 72 hours' posttransplant, and a composite variable of intubation or ECMO at 72 hours' posttransplant. Secondary outcomes included acute rejection, postoperative dialysis, and hospital length of stay.

RESULTS

Recipients of allografts with ischemic times ≥6 hours experienced increased 30-day and 1-year mortality following primary bilateral-lung transplantation, but increased mortality was not observed following primary single, redo bilateral, or redo single-lung transplants. Extended ischemic times correlated with prolonged intubation or increased postoperative ECMO support in the primary bilateral, primary single, and redo bilateral-lung transplant cohorts but did not affect these outcomes following redo single-lung transplantation.

CONCLUSIONS

Since prolonged allograft ischemia correlates with worse transplant outcomes, the decision to use donor lungs with extended ischemic times must consider the specific benefits and risks associated with individual recipient factors and institutional expertise.

National utilization, trends, and lung transplant outcomes of static versus portable ex vivo lung perfusion platforms

BACKGROUND

This study compared utilization and outcomes of the 2 widely utilized ex vivo lung perfusion (EVLP) platforms in the United States: a static platform and a portable platform.

METHODS

Adult (age 18 years or older) bilateral lung-only transplants utilizing EVLP between February 28, 2018, and December 31, 2022, in the United Network for Organ Sharing database were included. Predischarge acute rejection, intubation at 72 hours posttransplant, extracorporeal membrane oxygenation at 72 hours posttransplant, primary graft dysfunction grade 3 at 72 hours posttransplant, 30-day mortality, and 1-year mortality were evaluated using multivariable regressions.

RESULTS

Overall, 607 (6.3%) lung transplants during the study period used EVLP (51.2% static, 48.8% portable). Static EVLP was primarily utilized in the eastern United States, whereas portable EVLP was primarily utilized in the western United States. Static EVLP donors were more likely to be donation after circulatory death (33.4% vs 26.0%; P = .005), have a >20 pack-year smoking history (13.5% vs 6.5%; P = .005), and be extended criteria donors (92.3% vs 85.0%; P = .013), whereas portable EVLP donors were more likely to be older than age 55 years (14.2% vs 8.0%; P = .02). Transplants utilizing the static and portable platforms had similar risk of acute rejection, intubation at 72 hours, extracorporeal membrane oxygenation at 72 hours, primary graft dysfunction grade 3 at 72 hours, and posttransplant mortality at 30 days and 1 year (all P values > .05).

CONCLUSIONS

The static and portable platforms had significant differences in donor characteristics and geographic distributions of utilization. Despite this, posttransplant survival was similar between the 2 EVLP platforms.

Costs and Readmissions Associated with Type A Aortic Dissections at High- and Low-Volume Centers

BACKGROUND

Costs and readmissions associated with type A aortic dissection repairs are not well understood. We investigated statewide readmissions, costs, and outcomes associated with the surgical management of type A aortic dissection repairs at low- and high-volume centers.

METHODS

We identified all adult type A aortic dissection patients who underwent operative repair in the Maryland Health Services Cost Review Commission's database (2012-2020). Hospitals were stratified into high- (top quartile of total repairs) or low-volume centers.

RESULTS

Of the 249 patients included, 193 (77.5%) were treated at a high-volume center. Patients treated at high- and low-volume centers had no differences in age, sex, race, primary payer, or severity (all p > 0.5). High- compared to low-volume centers had a greater proportion of patients transferred in (71.5% vs. 17.9%, p < 0.001). High-volume centers also had longer lengths of stay (12 vs. 8 days, p < 0.001), similar inpatient mortality (13.0% vs. 16.1%, p = 0.6), and similar proportion of patients readmitted (54.9% vs. 51.8%, p = 0.7). High-volume centers had greater index admission costs ($114,859 vs. $72,090, p < 0.001) and similar readmission costs ($48,367 vs. $42,204, p = 0.5). At high-volume centers, transferred patients compared to direct admissions had greater severity of illness (p = 0.05), similar mortality (p = 0.53), and greater lengths of stay (p = 0.05).

CONCLUSIONS

High-volume centers had a greater number of patients transferred from other institutions compared to low-volume centers. High-volume centers were associated with increased index admission resource utilization, with transfer patients having higher illness severity and greater resource utilization, yet similar mortality, compared to direct admission patients.

Current status and future potential of ex vivo lung perfusion in clinical lung transplantation

Lung transplantation is accepted as a well-established and effective treatment for patients with end-stage lung disease. While the number of candidates added to the waitlist continues to rise, the number of transplants performed remains limited by the number of suitable organ donors. Ex vivo lung perfusion (EVLP) emerged as a method of addressing the organ shortage by allowing the evaluation and potential reconditioning of marginal donor lungs or minimizing risks of prolonged ischemic time due to logistical challenges. The currently available FDA-approved EVLP systems have demonstrated excellent outcomes in clinical trials, and retrospective studies have demonstrated similar post-transplant survival between recipients who received marginal donor lungs perfused using EVLP and recipients who received standard criteria lungs stored using conventional methods. Despite this, widespread utilization has plateaued in the last few years, likely due to the significant costs associated with initiating EVLP programs. Centralized, dedicated EVLP perfusion centers are currently being investigated as a potential method of further expanding utilization of this technology. In the preclinical setting, potential applications of EVLP that are currently being studied include prolongation of organ preservation, reconditioning of unsuitable lungs, and further enhancement of already suitable lungs. As adoption of EVLP technology becomes more widespread, we may begin to see future implementation of these potential applications into the clinical setting.

Expanding the Criteria for Heart Transplantation Donors: A Review of DCD, Increased Ischemic Times, HCV, HIV, and Extended Criteria Donors

With the demand for heart transplantation continuing to outpace the available donor organs, previously underutilized donors are now being reconsidered. We sought to describe the emerging techniques and outcomes of expanded criteria heart transplantation. A comprehensive review of the recent literature concerning expanded donor selection in heart transplantation was performed using the PubMed MEDLINE database. To characterize trends in transplant practice, the United Network for Organ Sharing (UNOS/OPTN) registry was queried for all adult isolated heart transplants since 2010, and data regarding transplant parameters was collected. Donation after cardiac death (DCD), DCD with normothermic regional perfusion, increased ischemic time, hepatitis C positive donor organs, HIV-positive donor organs, and extended criteria donors were identified as promising avenues currently being explored to expand the number of donor organs. The utilization of various expanded criteria for heart transplantation was summarized since 2010 and showed an increasing use of these donor organs, contributing to the overall increasing frequency of heart transplantation. Utilization of expanded criteria for donor selection in heart transplantation has the potential to increase the supply of donor organs with comparable outcomes in selected recipients.

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.

Serial lung mass volume ratios as prognostic indicators of neonatal respiratory morbidity in fetal pulmonary malformations

BACKGROUND

Several studies have shown that the congenital pulmonary airway malformation volume ratio is a useful prognosticator of neonatal outcome in prenatally diagnosed lung lesions. However, there remains a lack of consensus on which congenital pulmonary airway malformation volume ratio values have the best predictive value because of operator dependence, inherent changes in lung lesion size throughout gestation, and the widespread use of maternal steroids.

OBJECTIVE

This study sought to determine the association between serial congenital pulmonary airway malformation volume ratio measurements and neonatal outcomes among fetuses with lung malformations.

STUDY DESIGN

This was a retrospective cohort study of fetuses with a prenatally diagnosed lung malformation managed at 2 major fetal centers from January 2010 to December 2021. Prenatal variables, including prospectively measured congenital pulmonary airway malformation volume ratio measurements (initial, maximum, and final), were analyzed. The results were correlated with 3 outcome measures, namely surgical resection before 30 days of life, a need for supplemental O2 at birth, and endotracheal intubation at birth. Statistical analyses were performed using receiver operating characteristic curve analyses, Welch 2 sample t tests, and multivariable logistic regressions (P<.05).

RESULTS

There were 123 fetuses with isolated lung lesions identified. Eight (6.5%) had hydrops. The mean initial congenital pulmonary airway malformation volume ratio was 0.67±0.61 cm2 at 22.9±3.9 weeks' gestation. The mean maximum congenital pulmonary airway malformation volume ratio was 1.08 ± 0.94 cm2 at 27.0 ± 4.0 weeks' gestation. The mean final congenital pulmonary airway malformation volume ratio was 0.58±0.60 cm2 at 33.2±4.1 weeks' gestation. At a mean gestational age at delivery of 38.3±2.6 weeks, 15 (12.2%) underwent neonatal lung resection for symptomatic disease. In a multivariable regression, all 3 congenital pulmonary airway malformation volume ratio measurements showed a significant correlation with neonatal lung resection (P<.001). Optimal congenital pulmonary airway malformation volume ratio cutoffs were established based on an initial congenital pulmonary airway malformation volume ratio of ≥0.8 cm2, maximum congenital pulmonary airway malformation volume ratio of ≥1.5 cm2, and a final congenital pulmonary airway malformation volume ratio of ≥1.3 cm2 with associated areas under the curve of 0.89, 0.97, and 0.93, respectively. The final congenital pulmonary airway malformation volume ratio had the highest specificity for predicting surgical lung resection in the early postnatal period.

CONCLUSION

Measuring congenital pulmonary airway malformation volume ratios throughout pregnancy in fetuses with pulmonary malformations has clinical value for prenatal counseling and planning care transition after delivery. Fetuses with a final congenital pulmonary airway malformation volume ratio of more than 1.3 cm2 are likely to require neonatal surgery and therefore should be delivered at tertiary care centers with a neonatal intensive care unit and pediatric surgical expertise.

Cost-Effectiveness of Drug-Coated Balloon Angioplasty versus Plain Old Balloon Angioplasty for Arteriovenous Fistula Stenosis

OBJECTIVE

To compare the cost-effectiveness of drug-coated balloon angioplasty (DCB) versus plain old balloon angioplasty (POBA) for treatment of arteriovenous fistula (AVF) stenosis.

METHODS

A Markov model was created to compare DCB versus POBA for AVF stenosis over a 2-year time horizon from a United States payer's perspective. Probabilities related to complications, restenosis, retreatment, and all-cause mortality were obtained from published literature. Costs were calculated using Medicare reimbursement rates and data from published cost analyses, inflation-adjusted to 2021. Health outcomes were measured with quality-adjusted life years (QALY). Probabilistic and deterministic sensitivity analyses were performed with a willingness-to-pay threshold of $100,000/QALY.

RESULTS

Base case calculation showed better quality-of-life outcomes but increased cost with POBA compared to DCB, with an incremental cost-effectiveness ratio of $27,413/QALY, making POBA the more cost-effective strategy in the base case model. Sensitivity analyses showed that DCB becomes cost-effective if the 24-month mortality rate after DCB is no more than 3.4% higher than that after POBA. In secondary analyses where mortality rates were equalized, DCB was more cost-effective than POBA until its additional cost reached more than $4213 per intervention.

CONCLUSION

When modeled from a payer's perspective over 2 years, the cost utility of DCB versus POBA varies with mortality outcomes. POBA is cost-effective if 2-year all-cause mortality after DCB is greater than 3.4% higher than after POBA. If 2-year mortality after DCB is less than 3.4% higher than after POBA, DCB is cost-effective until its additional cost per procedure exceeds $4213 more than POBA.

LEVEL OF EVIDENCE IV

HISTORICALLY CONTROLLED STUDY.: This journal requires that authors assign a level of evidence to each article. For a full description of these Evidence-Based Medicine ratings, please refer to the Table of Contents or the online Instructions to Authors www.springer.com/00266 .

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.

Prenatal Sonography in Suspected Proximal Gastrointestinal Obstructions: Diagnostic Accuracy and Neonatal Outcomes

BACKGROUND

The purpose of this study was to assess diagnostic accuracy and neonatal outcomes in fetuses with a suspected proximal gastrointestinal obstruction (GIO).

METHODS

After IRB approval, a retrospective chart review was conducted on prenatally suspected and/or postnatally confirmed cases of proximal GIO at a tertiary care facility (2012-2022). Maternal-fetal records were queried for presence of a double bubble ± polyhydramnios, and neonatal outcomes were assessed to calculate the diagnostic accuracy of fetal sonography.

RESULTS

Among 56 confirmed cases, the median birthweight and gestational age at birth were 2550 g [interquartile range (IQR) 2028-3012] and 37 weeks (IQR 34-38), respectively. There was one (2%) false-positive and three (6%) false-negatives by ultrasound. Double bubble had a sensitivity, specificity, positive predictive value, and negative predictive value for proximal GIO of 85%, 98%, 98%, and 83%, respectively. Pathologies included 49 (88%) with duodenal obstruction/annular pancreas, three (5%) with malrotation, and three (5%) with jejunal atresia. The median postoperative length of stay was 27 days (IQR 19-42). Cardiac anomalies were associated with significantly higher complications (45% vs 17%, p = 0.030).

CONCLUSIONS

In this contemporary series, fetal sonography has high diagnostic accuracy for detecting proximal gastrointestinal obstruction. These data are informative for pediatric surgeons in prenatal counseling and preoperative discussions with families.

LEVEL OF EVIDENCE

Diagnostic Study, Level III.

Trends in use and three-year outcomes of hepatitis C virus-viremic donor lung transplants for hepatitis C virus-seronegative recipients

OBJECTIVE

The feasibility and 6-month outcome safety of lung transplants (LTs) from hepatitis C virus (HCV)-viremic donors for HCV-seronegative recipients (R-) were established in 2019, but longer-term safety and uptake of this practice nationally remain unknown.

METHODS

We identified HCV-seronegative LT recipients (R-) 2015-2020 using the Scientific Registry of Transplant Recipients. We classified donors as seronegative (D-) or viremic (D+). We used χ2 testing, rank-sum testing, and Cox regression to compare posttransplant outcomes between HCV D+/R- and D-/R- LT recipients.

RESULTS

HCV D+/R- LT increased from 2 to 97/year; centers performing HCV D+/R- LT increased from 1 to 25. HCV D+/R- versus HCV D-/R- LT recipients had more obstructive disease (35.7% vs 23.3%, P < .001), lower lung allocation score (36.5 vs 41.1, P < .001), and longer waitlist time (P = .002). HCV D+/R- LT had similar risk of acute rejection (adjusted odds ratio [aOR], 0.87; P = .58), extracorporeal membranous oxygenation (aOR, 1.94; P = .10), and tracheostomy (aOR, 0.42; P = .16); similar median hospital stay (P = .07); and lower risk of ventilator > 48 hours (aOR, 0.68; P = .006). Adjusting for donor, recipient, and transplant characteristics, risk of all-cause graft failure and mortality were similar at 30 days, 1 year, and 3 years for HCV D+/R- versus HCV D-/R- LT (all P > .1), as well as for high- (≥20/year) versus low-volume LT centers and high- (≥5/year) versus low-volume HCV D+/R- LT centers (all P > .5).

CONCLUSIONS

HCV D+/R- and HCV D-/R- LT have similar outcomes at 3 years posttransplant. These results underscore the safety of HCV D+/R- LT and the potential benefit of expanding this practice further.

Trends and three-year outcomes of hepatitis C virus-viremic donor heart transplant for hepatitis C virus-seronegative recipients

Objective

Heart transplants (HTs) from hepatitis C virus (HCV)-viremic donors to HCV-seronegative recipients (HCV D+/R-) have good 6-month outcomes, but practice uptake and long-term outcomes overall and among candidates on mechanical circulatory support (MCS) have yet to be established.

Methods

Using the Scientific Registry of Transplant Recipients, we identified US adult HCV-seronegative HT recipients (R-) from 2015 to 2021. We classified donors as HCV-seronegative (D-) or HCV-viremic (D+). We used multivariable regression to compare post-HT extracorporeal membranous oxygenation, dialysis, pacemaker, acute rejection, and risk of post-HT mortality between HCV D+/R- and HCV D-/R-. Models were adjusted for donor, recipient, and transplant characteristics and center HT volume. We performed subgroup analyses of recipients bridged with MCS.

Results

From 2015 to 2021, the number of HCV D+/R- HT increased from 1 to 181 and the number of centers performing HCV D+/R- HT increased from 1 to 60. Compared with HCV D-/R- recipients, HCV D+/R- versus D-/R- recipients overall and among patients bridged with MCS had similar odds of post-HT extracorporeal membranous oxygenation, dialysis, pacemaker, and acute rejection; and mortality risk at 30 days, 1 year, and 3 years (all P > .05). High center HT volume but not HCV D+/R- volume (<5 vs >5 in any year) was associated with lower mortality for HCV D+/R- HT.

Conclusions

HCV D+/R- and D-/R- HT have similar outcomes at 3 years' posttransplant. These results underscore the opportunity provided by HCV D+/R- HT, including among the growing population bridged with MCS, and the potential benefit of further expanding use of HCV+ allografts.

Outcomes after heart transplantation in patients who have undergone a bridge-to-bridge strategy

Objectives

We compared posttransplant outcomes between patients bridged from temporary mechanical circulatory support to durable left ventricular assist device before transplant (bridge-to-bridge [BTB] strategy) and patients bridged from temporary mechanical circulatory support directly to transplant (bridge-to-transplant [BTT] strategy).

Methods

We identified adult heart transplant recipients in the Organ Procurement and Transplantation Network database between 2005 and 2020 who were supported with extracorporeal membrane oxygenation, intra-aortic balloon pump, or temporary ventricular assist device as a BTB or BTT strategy. Kaplan-Meier survival analysis and Cox regressions were used to assess 1-year, 5-year, and 10-year survival. Posttransplant length of stay and complications were compared as secondary outcomes.

Results

In total, 201 extracorporeal membrane oxygenation (61 BTB, 140 BTT), 1385 intra-aortic balloon pump (460 BTB, 925 BTT), and 234 temporary ventricular assist device (75 BTB, 159 BTT) patients were identified. For patients supported with extracorporeal membrane oxygenation, intra-aortic balloon pump, or temporary ventricular assist device, there were no differences in survival between BTB and BTT at 1 and 5 years posttransplant, as well as 10 years posttransplant even after adjusting for baseline characteristics. The extracorporeal membrane oxygenation BTB group had greater rates of acute rejection (32.8% vs 13.6%; P = .002) and lower rates of dialysis (1.6% vs 21.4%; P < .001). For intra-aortic balloon pump and temporary ventricular assist device patients, there were no differences in posttransplant length of stay, acute rejection, airway compromise, stroke, dialysis, or pacemaker insertion between BTB and BTT recipients.

Conclusions

BTB patients have similar short- and midterm posttransplant survival as BTT patients. Future studies should continue to investigate the tradeoff between prolonged temporary mechanical circulatory support versus transitioning to durable mechanical circulatory support.

Massive left atrial thrombus evades multimodality imaging as a myxoma in a bicaval heart transplant recipient

Intracardiac masses are an extremely rare and poorly described complication following a bicaval heart transplantation. We describe the case of an asymptomatic 62-year-old male with a large left atrial mass found incidentally on transthoracic echocardiography 6 years post-transplant. A battery of additional imaging tests was ordered including transesophageal echocardiography, ¹⁸ F-fluorodeoxyglucose positron emission tomography/computed tomography, and T1 and T2 magnetic resonance imaging. Although imaging biomarkers were generally nonspecific, the mass was most consistent with a cardiac myxoma. However, intraoperative findings confirmed by pathology revealed a massive organizing thrombus. The patient had an uneventful recovery after surgical removal of the mass. Our case highlights a very rare phenomenon in heart transplant recipients which remains a unique diagnostic challenge even with current advances in imaging.

Caseous necrosis of the mitral annulus masquerading as an intracardiac mass

Caseous necrosis of the mitral annulus is a rare condition which typically involves the posterior leaflet or annulus. We report the case of a 71-year-old female with extensive comorbidities, presenting with dyspnea and angina, who had an incidental echocardiographic finding of a mass on or near the mitral valve. The mass increased in size over the course of three years and was associated with severe mitral regurgitation. The mass was initially thought to be a myxoma, however, surgical exploration revealed caseous necrosis of the posterior mitral annulus. Following removal of the necrotic tissue and distorted mitral leaflet, a bioprosthetic mitral valve was implanted and the patient recovered uneventfully.

Pulmonary artery transection for resection of a middle mediastinal paraganglioma

We report the case of a 65‐year‐old male patient who presented with chest pain and was found to have a mediastinal paraganglioma between the left atrium and main pulmonary artery. This is the first reported case of a mediastinal paraganglioma resection utilization transection of the main pulmonary artery.

Bridge to transplantation from mechanical circulatory support: a narrative review

Objective

To highlight recent developments in the utilization of mechanical circulatory support (MCS) devices as bridge-to-transplant strategies and to discuss trends in MCS use following the changes to the United Network for Organ Sharing (UNOS) heart allocation system.

Background

MCS devices have played an increasingly important role in the treatment of heart failure patients. Over the past several years, technological advancements have led to new developments in MCS devices and expanding indications for MCS use. In October of 2018, the UNOS heart allocation policy was revised to prioritize higher-urgency patients, including those supported with temporary MCS devices. Since then, changes in trends of MCS utilization have been observed.

Methods

Articles from the PubMed database regarding the use of MCS devices as bridge-to-transplant strategies were reviewed.

Conclusions

Over the past decade, utilization of temporary MCS devices, which include the intra-aortic balloon pump (IABP), percutaneous ventricular assist devices (pVADs), and extracorporeal membrane oxygenation (ECMO), has become increasingly common. Recent advancements in MCS include the development of pVADs that can fully unload the left ventricle (LV) as well as devices designed to provide right-sided support. Technological advancements in durable left ventricular assist devices (LVADs) have also led to improved outcomes both on the device and following heart transplantation. Following the 2018 UNOS heart allocation policy revision, the utilization of temporary MCS in advanced heart failure patients has further increased and the proportion of patients bridged directly from a temporary MCS device has exponentially risen. However, following the start of the COVID-19 pandemic, the trends have reversed, with a decrease in the percentage of patients bridged from a temporary MCS device. As long-term data following the allocation policy revision becomes available, future studies should investigate how trends in MCS use for patients with advanced heart failure continue to evolve.

Milk polar lipids modulate lipid metabolism, gut permeability, and systemic inflammation in high-fat-fed C57BL/6J ob/ob mice, a model of severe obesity

Dynamic interactions between lipid metabolism, gut permeability, and systemic inflammation remain unclear in the context of obesity. Milk polar lipids, lipids derived from the milk fat globule membrane, could positively affect the aforementioned obesity-related endpoints. This study aimed to test the hypotheses that milk polar lipids will reduce gut permeability, systemic inflammation, and liver lipid levels, and differentially affect the hepatic expression of genes associated with fatty acid synthesis and cholesterol regulation in preexisting obesity. We fed 3 groups of C57BL/6J ob/ob mice (n = 6 per group) for 2 wk: (1) a modified AIN-93G diet (CO) with 34% fat by energy; (2) CO with milk gangliosides (GG) at 0.2 g/kg of diet; and (3) CO with milk phospholipids (PL) at 10 g/kg of diet. The GG and PL were provided as semi-purified concentrates and replaced 2.0% and 7.2% of dietary fat by energy. The GG and PL did not affect total food intake, weight gain, fasting glucose, or gut permeability. The PL decreased liver mass and the mesenteric fat depot compared with the CO. The GG increased tight junction protein occludin in colon mucosa compared with the CO. The GG and PL decreased tight junction protein zonula occludens-1 in jejunum mucosa compared with the CO. Plasma endotoxin increased during the study but was unaffected by the treatments. Compared with the CO and GG, the PL increased plasma sphingomyelin and plasma IL-6. The GG and PL differentially regulated genes associated with lipid metabolism in the liver compared with the CO. Regarding general effects on lipid metabolism, the GG and PL decreased lipid levels in the liver and the mesenteric depot, and increased lipid levels in the plasma. Diet consumption decreased significantly when the ob/ob mice were kept in metabolic cages, which were not big enough and resulted in unwanted animal deaths. Future studies may keep this in mind and use better metabolic equipment for ob/ob mice. In conclusion, dietary milk polar lipids may have limited beneficial effects on gut barrier integrity, systemic inflammation, and lipid metabolism in the context of severe obesity.

Growth of arterioles precedes that of capillaries in stretch-induced angiogenesis in skeletal muscle

Arteriolar growth accompanying capillary angiogenesis has been linked with hemodynamic factors resulting from increased blood flow. Here we describe the growth of arterioles occurring in rat skeletal muscles stretched by an overload due to the removal of agonist muscles, where blood flow was not increased, and we provide morphological evidence for the type of cells involved in this growth. Rat extensor digitorum longus (EDL) and extensor hallucis proprius (EHP) were overloaded by unilateral extirpation of their agonist, tibialis anterior. EDL muscles were taken for immunohistochemistry in cryostat sections to mark endothelial cells (Griffonia simplicifolia I, GSI lectin), smooth muscle cells and pericytes (alpha smooth muscle actin, alphaSMA), and "mature" arterioles (smooth muscle myosin heavy chains). EHP muscles were used for corresponding evaluation by confocal and electron microscopy. The number of capillaries surrounding muscle fibers was not significantly different after 1 week of stretch but was higher after 2 weeks (5.15 +/- 0.2 vs 4.3 +/- 0.2 in controls, P < 0.05). Similarly, capillary density (CD) and capillary/fiber ratio (C/F) gradually increased (CD 778 +/- 86 at 2 weeks vs 593 +/- 35 mm(-2) in controls, C/F 2.07 +/- 0.13 vs 1.38 +/- 0.06, respectively). In contrast, the number of alphaSMA-positive vessels around fibers increased after 1 week (2.16 +/- 0.09 vs 0.25 +/- 0.02 in controls) and was lower after 2 weeks (1.42 +/- 0.24, P < 0.05, vs 1 week). Arteriolar density was higher at 1 (110.9 +/- 7.5 mm(-2)) and 2 weeks (70.7 +/- 12.1) with respect to controls (31.0 +/- 1.6 mm(-2)). The increased density was greater in alphaSMA-positive vessels <10 microm in diameter (controls 18.0 +/- 1.04, 1 week 77.2 +/- 4.5, 2 wk 42.2 +/- 9.0 mm(-2)) than in vessels >10 microm (13.0 +/- 0.8, 33.7 +/- 4.0, 29.5 +/- 4.7 mm(-2)). Electron microscopy showed "activated" (TEM fine structure) and proliferating (immunogold labeling for BrdU) fibroblasts in the vicinity of capillaries, some of which were embedded in the capillary basement membrane, consistent with a transformation into pericytes and possibly later smooth muscle cells. Confocal microscopy indicated that some mesenchymal cells became GSI positive and formed extended processes which contacted capillaries via tapered endings. Growth of arterioles in stretched muscles appears to involve proliferation of fibroblasts, which may migrate toward capillaries and precedes any apparent increase in capillarization.

The role of pericytes in controlling angiogenesis in vivo

In order to evaluate the interaction between endothelial cells and the perivascular pericytes during physiological angiogenesis, stereological analysis of fine structure was performed on samples of rat skeletal muscle where capillary growth was induced to a similar extent by three different interventions (indirect electrical stimulation, vasodilatation by alpha 1-blockade, stretch due to synergist extirpation). There was a significant reduction in the relative area of contact between pericytes and the capillary abluminal surface with stimulation, and withdrawal of pericyte processes coincided with an increase in anatomical capillary supply. These data indicate that pericytes may play an anti-angiogenic role in vivo in normal adult tissue similar to that proposed for in vitro models of angiogenesis, with their retraction during increased muscle activity possibly releasing endothelial cells from their contact inhibition. However, following long-term peripheral vasodilatation expansion of the capillary bed was accompanied by a co-ordinated increase in pericytes, such that coverage of capillaries was similar to that in control muscles. In addition, growth of capillaries following prolonged stretch resulted in a slightly greater increase in the pericyte population, suggesting they may be permissive for endothelial cell migration. Thus, the role of pericytes in controlling physiological angiogenesis is dependent on the nature of the initial stimulus, suggesting that in vitro data have to be interpreted with caution when discussing the mechanism of capillary growth in vivo.

Unorthodox angiogenesis in skeletal muscle

OBJECTIVE

The morphological pattern of angiogenesis occurring in mature, differentiated skeletal muscle in response to chronically increased muscle blood flow, muscle stretch or repetitious muscle contractions was examined to determine (a) whether capillary neoformation follows the generally accepted temporal paradigm, and (b) how the growth pattern is influenced by mechanical stimuli.

METHODS

Adult rats were treated for a maximum of 14 days either with the vasodilator prazosin, to elevate skeletal muscle blood flow, or underwent surgical removal of one ankle flexor, to induce compensatory overload in the remaining muscles, or had muscles chronically stimulated by implanted electrodes. Extensor digitorum longus and/or extensor hallucis proprius muscles were removed at intervals and processed for electron microscopy. A systematic examination of capillaries and their ultrastructure characterised the sequence of morphological changes indicative of angiogenesis, i.e., basement membrane disruption, endothelial cell (EC) sprouting and proliferation [immunogold labelling after bromodeoxyuridine (BrdU) incorporation].

RESULTS

Capillary growth in response to increased blood flow occurred by luminal division without sprouting or basement membrane (BM) breakage. In stretched muscles, EC proliferation and abluminal sprouting gave rise to new capillaries, with BM loss only at sprout tips. These distinct mechanisms appear to be additive as in chronically stimulated muscles (increased blood flow with repetitive stretch and shortening during muscle contractions) both forms of capillary growth occurred. Endothelial cell numbers per capillary profile, mitotic EC nuclei, and BrdU labelling confirmed cell proliferation prior to overt angiogenesis.

CONCLUSIONS

Physiological angiogenesis within adult skeletal muscle progresses by mechanisms that do not readily conform to the consensus view of capillary growth, derived mainly from observations made during development, pathological vessel growth, or from in vitro systems. The temporal and spatial pattern of growth is determined by the polarity of the mechanical stimulus, i.e., by intra-luminal (increased shear stress) or abluminal (external stretch) stimuli.

Matrix metalloproteinase activity is required for activity-induced angiogenesis in rat skeletal muscle

Proteolysis of the capillary basement membrane is a hallmark of inflammation-mediated angiogenesis, but it is undetermined whether proteolysis plays a critical role in the process of activity-induced angiogenesis. Matrix metalloproteinases (MMPs) constitute the major class of proteases responsible for degradation of basement membrane proteins. We observed significant elevations of mRNA and protein levels of both MMP-2 and membrane type 1 (MT1)-MMP (2.9 +/- 0.7- and 1.5 +/- 0.1-fold above control, respectively) after 3 days of chronic electrical stimulation of rat skeletal muscle. Inhibition of MMP activity via the inhibitor GM-6001 prevented the growth of new capillaries as assessed by the capillary-to-fiber ratio (1.34 +/- 0.08 in GM-6001-treated muscles compared with 1.69 +/- 0.03 in control 7-day-stimulated muscles). This inhibition correlated with a significant reduction in the number of capillaries with observable breaks in the basement membrane, as assessed by electron microscopy (0.27 +/- 0.27% in GM-6001-treated muscles compared with 3.72 +/- 0.65% in control stimulated muscles). Proliferation of capillary-associated cells was significantly elevated by 2 days and remained elevated throughout 14 days of stimulation. Capillary-associated cell proliferation during muscle stimulation was not affected by MMP inhibition (80.3 +/- 9.3 nuclei in control and 63.5 +/- 8.5 nuclei in GM-6001-treated animals). We conclude that MMP proteolysis of capillary basement membrane proteins is a critical component of physiological angiogenesis, and we postulate that capillary-associated proliferation precedes and occurs independently of endothelial cell sprout formation.

Capillary growth in overloaded, hypertrophic adult rat skeletal muscle: an ultrastructural study

We examined the early stages of angiogenesis in overloaded m. extensor digitorum longus following extirpation of the agonist m. tibialis anterior. Capillary-to-fibre ratio increased after 1 week (1.54+/-0.02) vs. control (1.38+/0.06; P < 0.01) and resulted in a greater tortuosity of the capillary bed at 2 weeks, indicating the presence of lateral sprouts or anastomoses. Capillary endothelial cells (ECs) showed ultrastructural signs of activation, were thickened, and had irregular luminal and abluminal surfaces. The proportion of ECs with abluminal processes increased after overload (13.5+/-0.6% vs. 2.0+/-1.5%, 1 week vs. contralateral, P < 0.01; 12.5+/-2.6% vs. 3.5+/-0.6%, 2 weeks vs. contralateral, P < 0.01), whereas there was no significant change in proportion of luminal processes. Abluminal processes occurred in approximately 13% of capillaries in overloaded muscles (P < 0.01 v. control and contralateral), and most were associated with focal breakage of the basement membrane (BM). Small sprouts (<3 microm in diameter) comprised of one or two ECs sometimes lacked a lumen, and others had a slitlike or vacuolelike lumen between adjacent ECs or vacuolelike lumen formed by fusion of vesicles within a single EC. Endothelial mitosis was occasionally seen in nonsprouting capillaries with intact BM, increasing the average number of ECs per capillary from approximately 1.7 in control muscles to 2.1 after 1 week of overload (P < 0.05) when bromodeoxyuridine incorporation was also higher (P < 0.001). We conclude that muscle overload induces capillary growth by sprouting of existing capillaries, probably due to mechanical stretch acting from the abluminal side of the vessels.

Appearance of the capillary endothelial glycocalyx in chronically stimulated rat skeletal muscles in relation to angiogenesis

The endothelial glycocalyx layer of capillaries was stained with Ruthenium Red and examined by transmission electron microscopy in rat extensor hallucis proprius muscles after 2 or 4 days of indirect electrical stimulation via implanted electrodes. The layer appeared continuous on the luminal surface of 63% capillaries in control muscles and absent 13%. This situation was reversed in muscles stimulated for 2 or 4 days, with a continuous layer in 12 and 10% of capillaries and no glycocalyx in 44 and 58%, respectively. The greater disruption of the endothelial luminal glycocalyx in capillaries from stimulated muscles suggests that flow-related shear forces on endothelial cells could be important signals for initiation of angiogenesis in actively contracting skeletal muscle.

Viral infection at the blood-brain barrier in multiple sclerosis:--an ultrastructural study of tissues from a UK Regional Brain Bank

Although viral infections are often invoked as environmental factors in the aetiology and pathogenesis of multiple sclerosis (MS) it is only recently that a specific, indirect, cytokine-mediated mechanism for triggering of relapses during viral infections has been demonstrated. It is not yet clear however whether this indirect mechanism can account for all reported viral associations with the aetiopathogenesis of MS. A direct causal role of central nervous system (CNS) viral infection in MS has largely been discounted following repeated failures to demonstrate virus within the oligodendrocyte-myelin unit. In the light of increasing evidence of blood-brain barrier (BBB) dysfunction in MS and to further explore the issue of possible viral involvement in MS, an ultrastructural search for viruses was undertaken in the CNS microvasculature, in autopsy and biopsy tissue from human CNS primary demyelinating diseases, including MS (20 cases), idiopathic monophasic CNS demyelinating disease (Mdemy, four cases) and metabolic or immunopathological demyelinating disease (two cases). For comparison, tissues from CNS viral disease in which demyelination is a major feature (nine cases) were examined in the same way. Control CNS tissues (nine cases) from a range of other neurological and non-neurological diseases were also examined. Outside the MS and Mdemy groups, morphological evidence of virus associations with the BBB were found only in the acute and subacute viral encephalitides (three cases subacute sclerosing panencephalitis, one case of Herpes encephalitis) and in one case of disseminated Cytomegalovirus infection. In a small proportion of MS and Mdemy cases, particles resembling either adenovirus (one case of MS) or paramyxovirus (one case of MS, one case of Mdemy) were found in the vicinity of microvessels. In each case a different cell type or extracellular compartment was involved and an exact correlation between the virus particles and the demyelinating lesions could not be demonstrated. Furthermore, corroborative clinical or laboratory evidence of current CNS infection in these primary demyelinating disease cases was available only from the single positive Mdemy case and not from the two cases of MS. This and other previously published evidence from MS (which implicated a Coronavirus) and other diseases highlights the potential vulnerability to viral infection of cells associated with the BBB. Furthermore it is concluded that the detection rate of such infections in pathological tissue could underestimate their true frequency. A possible role of transient virus-BBB interactions in triggering focal inflammation, BBB breakdown and demyelination in some cases of MS and parainfectious demyelinating disease cannot be discounted.

Measles virus infection of cells in perivascular infiltrates in the brain in subacute sclerosing panencephalitis: confirmation by non-radioactive in situ hybridization, immunocytochemistry and electron microscopy

As part of continuing multidisciplinary studies on the neuropathogenesis of subacute sclerosing panencephalitis (SSPE), in situ hybridisation, immunocytochemistry and electron microscopy were used to detect measles virus nucleic acid, protein and nucleocapsids in brain perivascular infiltrates of three cases. Perivascular cuffing cells which contained measles virus nucleic acid and antigens were found in all cases. Infected cuffs occurred predominantly in areas of general parenchymal cell infection and in many of these a high proportion of the infiltrating cells were infected. Other cuffs in these areas were either uninfected or contained only a few infected cells. Occasional infected cells were also seen in cuffs in non-infected areas. In contrast, no specific immunocytochemical reactions or in situ hybridisation for measles virus was observed in brain tissue from a patient with herpes encephalitis. By electron microscopy viral nucleocapsid, consistent with measles virus, was found within the cytoplasm of plasma cells in the inflammatory cuffs in SSPE brain tissue. Possible explanations for our results are that infiltrates become infected on arrival in the CNS or alternatively, that the infected infiltrates reflect a generalised infection of the reticuloendothelial system. The frequent presence of uninfected cuffs favours the former explanation.

Cerebral endothelial cell infection by measles virus in subacute sclerosing panencephalitis: ultrastructural and in situ hybridization evidence

Infection of vascular endothelium plays a central role in the pathogenesis of acute measles virus infection outside the central nervous system (CNS) but has not been described in the human CNS. An ultrastructural survey was made of blood vessels in five cases of subacute sclerosing panencephalitis (SSPE) to determine whether or not infection of cerebral vascular endothelium occurred in this persistent fatal CNS disease caused by measles virus. Morbillivirus nucleocapsids were found in a few endothelial cells in three necropsy cases but not in the limited tissue available from two biopsies. In a severe parenchymal lesion in one necropsied case, endothelial cells hybridized in situ with a biotinylated probe specific for the N genomic RNA of measles virus. It is concluded that human cerebral endothelium is susceptible to measles virus infection.