Medium-term patency and anatomic changes after direct bronchial artery revascularization in lung and heart-lung transplantation with the internal thoracic artery conduit

Complement-mediated microvascular injury leads to chronic rejection

Microvascular loss may be an unappreciated root cause of chronic rejection for all solid organ transplants. As the only solid organ transplant that does not undergo primary systemic arterial revascularization at the time of surgery, lung transplants rely on the establishment of a microcirculation and are especially vulnerable to the effects of microvascular loss. Microangiopathy, with its attendant ischemia, can lead to tissue infarction and airway fibrosis. Maintaining healthy vasculature in lung allografts may be critical for preventing terminal airway fibrosis, also known as the bronchiolitis obliterans syndrome (BOS). BOS is the major obstacle to lung transplant success and affects up to 60% of patients surviving 5 years. The role of complement in causing acute microvascular loss and ischemia during rejection has recently been examined using the mouse orthotopic tracheal transplantation; this is an ideal model for parsing the role of airway vasculature in rejection. Prior to the development of airway fibrosis in rejecting tracheal allografts, C3 deposits on the vascular endothelium just as tissue hypoxia is first detected. With the eventual destruction of vessels, microvascular blood flow to the graft stops altogether for several days. Complement deficiency and complement inhibition lead to markedly improved tissue oxygenation in transplants, diminished airway remodeling, and accelerated vascular repair. CD4+ T cells and antibody-dependent complement activity independently mediate vascular destruction and sustained tissue ischemia during acute rejection. Consequently, interceding against complement-mediated microvascular injury with adjunctive therapy during acute rejection episodes, in addition to standard immunosuppression which targets CD4+ T cells, may help prevent the subsequent development of chronic rejection.

Bronchial blood supply after lung transplantation without bronchial artery revascularization

PURPOSE OF REVIEW

This review discusses how the bronchial artery circulation is interrupted following lung transplantation and what may be the long-term complications of compromising systemic blood flow to allograft airways.

RECENT FINDINGS

Preclinical and clinical studies have shown that the loss of airway microcirculations is highly associated with the development of airway hypoxia and an increased susceptibility to chronic rejection.

SUMMARY

The bronchial artery circulation has been highly conserved through evolution. Current evidence suggests that the failure to routinely perform bronchial artery revascularization at the time of lung transplantation may predispose patients to develop the bronchiolitis obliterans syndrome.

Lung transplant airway hypoxia: a diathesis to fibrosis?

RATIONALE

Chronic rejection, manifested pathologically as airway fibrosis, is the major problem limiting long-term survival in lung transplant recipients. Airway hypoxia and ischemia, resulting from a failure to restore the bronchial artery (BA) circulation at the time of transplantation, may predispose patients to chronic rejection. To address this possibility, clinical information is needed describing the status of lung perfusion and airway oxygenation after transplantation.

OBJECTIVES

To determine the relative pulmonary arterial blood flow, airway tissue oxygenation and BA anatomy in the transplanted lung was compared with the contralateral native lung in lung allograft recipients.

METHODS

Routine perfusion scans were evaluated at 3 and 12 months after transplantation in 15 single transplant recipients. Next, airway tissue oximetry was performed in 12 patients during surveillance bronchoscopies in the first year after transplant and in 4 control subjects. Finally, computed tomography (CT)-angiography studies on 11 recipients were reconstructed to evaluate the post-transplant anatomy of the BAs.

MEASUREMENTS AND MAIN RESULTS

By 3 months after transplantation, deoxygenated pulmonary arterial blood is shunted away from the native lung to the transplanted lung. In the first year, healthy lung transplant recipients exhibit significant airway hypoxia distal to the graft anastomosis. CT-angiography studies demonstrate that BAs are abbreviated, generally stopping at or before the anastomosis, in transplant airways.

CONCLUSIONS

Despite pulmonary artery blood being shunted to transplanted lungs after transplantation, grafts are hypoxic compared with both native (diseased) and control airways. Airway hypoxia may be due to the lack of radiologically demonstrable BAs after lung transplantation.

Microvascular destruction identifies murine allografts that cannot be rescued from airway fibrosis

Small airway fibrosis (bronchiolitis obliterans syndrome) is the primary obstacle to long-term survival following lung transplantation. Here, we show the importance of functional microvasculature in the prevention of epithelial loss and fibrosis due to rejection and for the first time, relate allograft microvascular injury and loss of tissue perfusion to immunotherapy-resistant rejection. To explore the role of alloimmune rejection and airway ischemia in the development of fibroproliferation, we used a murine orthotopic tracheal transplant model. We determined that transplants were reperfused by connection of recipient vessels to donor vessels at the surgical anastomosis site. Microcirculation through the newly formed vascular anastomoses appeared partially dependent on VEGFR2 and CXCR2 pathways. In the absence of immunosuppression, the microvasculature in rejecting allografts exhibited vascular complement deposition, diminished endothelial CD31 expression, and absent perfusion prior to the onset of fibroproliferation. Rejecting grafts with extensive endothelial cell injury were refractory to immunotherapy. After early microvascular loss, neovascularization was eventually observed in the membranous trachea, indicating a reestablishment of graft perfusion in established fibrosis. One implication of this study is that bronchial artery revascularization at the time of lung transplantation may decrease the risk of subsequent airway fibrosis.

Revascularization of trachea in lung and tracheal transplantation

Ischemia is the primary risk factor for airway complications in double lung transplantation using tracheal anastomosis and in tracheal transplantation. Many treatment options as to revascularization for the trachea were herein described and reviewed. They include direct revascularization (using a conduit such as artery or vein), revascularization with tissue wrapping (using omentum, muscle, internal thoracic artery pedicle, pleura, or pericardial fat pad), and with drug administration (using corticosteroid hormone, prostaglandin, or angiogenic factor). As there are few organized reports including new information on revascularization for the trachea these days, this review article would help thoracic surgeons who get engaged transplantation.

The Copenhagen National Lung Transplant Group: survival after single lung, double lung, and heart-lung transplantation

OBJECTIVE

To review the 13-year clinical experience of a single center's adult lung transplantation program.

METHODS

From January 1992 to December 2003, 369 lung transplantations were performed on 362 patients. Single lung transplantation was performed in 234 cases, double lung transplantation in 113 cases (comprising en-bloc double lung transplantation in 44 cases and bilateral sequential lung transplantation in 69 cases), heart-lung transplantation in 21 cases, and lobe of lung transplantation in 1 case. Recipient diagnoses included chronic obstructive pulmonary disease (COPD) (n = 175), alpha1 antitrypsin (alpha1AT) deficiency (n = 86), cystic fibrosis (n = 36), pulmonary fibrosis (n = 20), Eisenmenger syndrome and secondary pulmonary hypertension (n = 24), primary pulmonary hypertension (n = 8), sarcoidosis (n = 7), silicosis (n = 4), bronchiectasis (n = 1), and graft-vs-host disease (n = 1).

RESULTS

For patients surviving to discharge, the median duration of the intensive care unit stay was 3 days (1-67), and the median duration of the post-operative hospital stay was 37 days (16-144). Mortality for the entire series was 6% at 30 days and 10% at 90 days. The main causes of post-operative inpatient death were primary graft failure (41%), sepsis (29%), cardiac (15%), and hemorrhage (9%). The 1-, 3-, 5-, and 10-year actuarial survival rates for the entire series was 81%, 68%, 63%, and 36%, respectively. There were no significant differences in survival between types of transplant. No significant differences in survival were seen between alpha(1)AT deficiency and COPD patients after stratifying for age. Cox regression analysis demonstrated that age 60 years or older, donor age 50 years or older, and a recipient pre-operative body mass index of 25 or higher were independent predictors of poor survival.

CONCLUSIONS

This center has 1-, 3-, and 5-year survival rates comparable to other high volume centers. Recipient age, pre-operative body mass index, and donor age significantly influence outcome after lung transplantation.

Heterotopic en bloc tracheobronchial transplantation with direct revascularization in pigs

OBJECTIVE

This article describes the application of a novel aortic tube technique for directly revascularized tracheobronchial transplantation with dual blood supply in pigs.

METHODS

Eleven adult Large White pigs underwent heterotopic tracheal transplantation with a dual revascularization technique (inferior thyroid artery and bronchial artery). Seven tracheobronchial grafts were perfused ex vivo, and hemodynamic data were collected.

RESULTS

At the last evaluation, 6 pigs had normally epithelialized mucus-producing allografts with correct morphologic conformation and cartilage viability. The histopathologic examination revealed homogeneous tissue regardless of biopsy site (trachea, carina, or bronchi), demonstrating the efficacy of the revascularization procedure. Four animals had early ischemic necrosis develop, 2 from acute rejection and 2 from technical mishap. One additional pig had acute rejection starting on the 14th postoperative day. The CD4(+)/CD8(+) ratio was maintained close to or above 0.8 in the subgroup with rejection and below 0.6 in the animals that were correctly immunosuppressed. Pressure-flow curves in 7 ex vivo tracheobronchial grafts showed a nonsignificant difference (P <.12) in vascular resistance between the bronchial artery territory (lower resistance) and the inferior thyroid artery territory.

CONCLUSIONS

For the first time, a transplantation technique encompassing the entire trachea, carina, and stem bronchi has been made possible. By means of the dual inferior thyroid and bronchial artery axis, we were able to obtain a structurally healthy and functional graft to replace the main airway.

Human bronchial artery blood flow after lung Tx with direct bronchial artery revascularization

The inaccuracy of measuring human bronchial artery blood flow has previously been considerable. En bloc double-lung transplantation with bronchial artery revascularization (BAR) using a single conduit offers the unique opportunity of direct measurement of the total bronchial artery blood flow. In eight en bloc double-lung-transplanted patients with complete BAR, the basal blood flow was measured by using a 0.014-in. Doppler guide wire and arteriography. The average peak velocity in the conduit was 12-73 cm/s [+/-2.1 (SD) cm/s], and the conduit diameter was 1.7-3.1 mm [+/-0.10 (SD) mm], giving individual basal flow values between 19 and 67 ml/min [+/-5 (SD) ml/min], or 0.2-1.9% of estimated cardiac output. In three patients basal measurements were followed by injection of nitroglycerin and verapamil into the conduit. This increased the bronchial artery flow to 121-262% of basal values (31-89 ml/min). The measured values appear more physiologically plausible than previous bronchial artery blood flow measurements in humans.

Does bronchial artery revascularization influence results concerning bronchiolitis obliterans syndrome and/or obliterative bronchiolitis after lung transplantation?

OBJECTIVE

To study the frequency of histological obliterative bronchiolitis and clinical bronchiolitis obliterans syndrome after en bloc double lung transplantation with bronchial artery revascularization and bilateral lung transplantation without bronchial artery revascularization.

METHODS

Primary en bloc double lung transplantation with bronchial artery revascularization using the internal mammary artery as conduit was performed in 62 patients. The frequencies of obliterative bronchiolitis and bronchiolitis obliterans syndrome have been established from transbronchial biopsies and lung function measurements. Results have been analyzed in relation to the arteriographic success of bronchial artery revascularization and have been compared to results from Stanford University, obtained through personal communications.

RESULTS

Survival after 1, 2, 3, 4 and 5 years was 85, 81, 69, 69, and 69%, respectively. Fifteen patients developed bronchiolitis obliterans syndrome while seven developed obliterative bronchiolitis. Survival was superior for patients with bronchial artery revascularization classified as complete or incomplete bilateral versus incomplete hemilateral, incomplete poor or failed (P = 0.016, log-rank test). For patients surviving > or = 3 months post-transplant, the post-operative baseline FEV1 was lower for patients who later developed bronchiolitis obliterans syndrome compared to patients who did not (P = 0.007). The development of bronchiolitis obliterans syndrome and obliterative bronchiolitis were both correlated to observation time post-transplant but not to the number of rejections or infections when corrected for observation time.

CONCLUSIONS

In a subgroup of lung transplant patients, a process in the transplanted lungs, eventually leading to bronchiolitis obliterans syndrome diagnosis, seems to start in the donor during the transplantation and/or in the early post-operative cause. A comparison with results after bilateral lung transplantation without bronchial artery revascularization suggests that good direct bronchial artery revascularization may postpone the onset of bronchiolitis obliterans syndrome and obliterative bronchiolitis. The positive trend motivates further use of direct bronchial artery revascularization in lung transplantation.