Use of HeartWare Ventricular Assist System for Systemic Ventricular Support of a Pediatric Patient After Mustard Procedure

Background:

The HeartWare Ventricular Assist System is indicated to provide mechanical circulatory support of patients with intractable heart failure as a bridge to cardiac transplantation. We describe the use of this device to support the systemic right ventricle (RV) of a pediatric patient with New York Heart Association class IIIC congestive heart failure who had undergone Mustard procedure for D-transposition of the great vessels as an infant.

Case report:

A HeartWare ventricular assist device was implanted in the left chest of a 16-year-old female patient (body surface area 1.43 m2) who presented with edema and later deteriorated, developing acute kidney injury, dysrhythmia, and pulmonary edema.

Results:

The patient’s edema and acute kidney injury resolved after device placement. She was discharged home and successfully underwent device removal with heart transplant five months later.

Conclusion:

The HeartWare device may be used for extended support as a systemic RV in a pediatric patient. It is feasible to consider using the device in this patient population.

Technique of Aortic Root Reconstruction Using a New Model of Dacron Graft with Prefabricated Coronary Branches

Aortic root reconstruction is a demanding surgical procedure still associated with a significant morbidity. Arguably, the most demanding aspect of the operation is reestablishing continuity between the prosthetic graft replacing the aortic root and the coronary arteries. With the objective of simplifying the possible challenges of coronary reimplantation, we designed a new model of aortic root graft with prefabricated coronary branches. We used this technique in 8 patients (6 males, 2 females; mean age, 54 years). There were 6 modified Bentall procedures and 2 valve-sparing root replacements with the “reimplantation” technique. There was no mortality or morbidity related to the use of this new prosthetic graft. Our purpose was to report in detail the technique of aortic root reconstruction using this new graft with prefabricated coronary branches. The use of this graft may simplify the procedure and offer a valuable tool for aortic root reconstruction in cases where the reimplantation of the coronary buttons may represent a technical challenge.

Mycotic aneurysm in a child with history of coarctation of the aorta repair

A mycotic aneurysm is a rare condition occasionally seen in patients with a history of prior cardiac or vascular surgery. Here we report the presentation of a mycotic aneurysm in a pediatric patient at the site of prior aortic coarctation repair. This patient's initial presentation suggested rheumatologic or oncologic disease, and after diagnosis he continued to show evidence of splenic, renal and vascular injury distal to the mycotic aneurysm site while being treated with antibiotics. We discuss the diagnosis, treatment and management of this condition.

Normothermic Cardiopulmonary Bypass with Beating Heart for Management of Renal Cell Carcinoma with Atrial Tumor Thrombus

Renal cell carcinoma is occasionally complicated by the formation of a neoplastic thrombus invading the inferior vena cava. Rarely, the thrombus extends into the vena cava, reaching the right atrium. In these situations, despite the advanced tumor stage, surgical resection continues to offer the best chance for effective treatment. The operation requires a complex surgical approach with mobilization of the liver and use, in most cases, of extracorporeal circulation, which allows removal of the tumor thrombus from the right atrium. Traditionally, the intervention is performed using deep hypo-thermic circulatory arrest or, less frequently, using moderate hypothermia, aortic cross clamping, and cardioplegic cardiac arrest. These strategies have the downside of causing increased blood loss, coagulopathy, and long operative time and can potentially have a negative impact on survival. We report a different operative approach using normothermic cardiopulmonary bypass, with the expectation of lowering the rate of blood product transfusions, hospital length of stay, and overall incidence of complications.

Outcomes before and after implementation of a pediatric rapid-response extracorporeal membrane oxygenation program

BACKGROUND

Rapid-response extracorporeal membrane oxygenation (RR-ECMO) has been implemented at select centers to expedite cannulation for patients placed on ECMO during extracorporeal cardiopulmonary resuscitation (ECPR). In 2008, we established such a program and used it for all pediatric venoarterial ECMO initiations. This study was designed to compare outcomes before and after program implementation.

METHODS

Between 2003 and 2011, 144 pediatric patients were placed on venoarterial ECMO. Records of patients placed on ECMO before (17 ECPR and 62 non-ECPR) or after (14 ECPR and 51 non-ECPR) RR-ECMO program implementation were retrospectively compared.

RESULTS

The peak performance of the ECMO team was assessed by measuring ECMO initiation times for the ECPR patient subgroup (n = 31). There was a shift toward more ECPR initiations achieved in less than 40 minutes (24% pre-RR-ECMO versus 43% RR-ECMO; p = 0.25) and fewer requiring more than 60 minutes (47% pre-RR-ECMO versus 21% RR-ECMO; p = 0.14) after program implementation, although these changes did not reach statistical significance. After multivariable risk adjustment, RR-ECMO was associated with a 52% reduction in neurologic complications for all patients (adjusted odds ratio, 0.48; 95% confidence interval, 0.23 to 0.98; p = 0.04), but the risk of in-hospital death remained unchanged (adjusted odds ratio, 0.99; 95% confidence interval, 0.50 to 1.99; p = 0.99).

CONCLUSIONS

Implementation of a pediatric RR-ECMO program for venoarterial ECMO initiation was associated with reduced neurologic complications but not improved survival during the first 3 years of program implementation. These data suggest that development of a coordinated system for rapid ECMO deployment may benefit both ECPR and non-ECPR patients, but further efforts are required to improve survival.

Anomalous Aortic Origin of a Coronary Artery: Preoperative Diagnosis and Surgical Planning

Background: Anomalous aortic origin of a coronary artery (AAOCA), the anomalous coronary artery arises from an inappropriate coronary sinus and travels between the aorta and pulmonary artery. Proper surgical management depends upon correct diagnosis and accurate characterization of the origin and course of the coronary artery. Transthoracic echocardiography (TTE) has been the mainstay for diagnosis, but magnetic resonance imaging (MRI) and computed tomographic angiography (CTA) have been increasingly utilized. In this study, we report the largest series of surgically repaired AAOCA and accuracy of preoperative diagnostic studies. Methods: A review of 53 consecutive patients (mean age 13.9 years, range 4-65 years) undergoing repair of an AAOCA from 1995 to 2009 was performed. In all, 40 patients were identified with an anomalous right coronary artery (ARCA) from the left sinus of Valsalva, 13 patients had an anomalous left coronary artery (ALCA) arising from the opposite sinus. Symptoms of angina or syncope were present in 58% and 46% of cases with ARCA and ALCA, respectively. Results of preoperative diagnostic testing were compared to actual surgical findings to determine the accuracy of the tests. Results: Lack of an intramural course was observed intraoperatively in 7 cases (5 ARCA and 2 ALCA). Preoperative TTE accurately predicted whether the AAOCA was intramural or extramural in 49 (92.5%) of 53 cases. Magnetic resonance imaging was predictive in 5 (83.3%) of 6 patients and CTA in 11 (64.7%) of 17. Survival was 100%. Complications occurred in 4 (7.5%) of 53 patients (mean follow-up 29 months). Patency was confirmed in 97.7% with TTE, and 23 (95.8%) of 24 patients had a negative postoperative functional study. Conclusions: Transthoracic echocardiography was found to be very accurate at defining the presence or absence of an intramural course in AAOCA. Both MRI and CTA can provide additional information but may not be as accurate as TTE.

Differential Mapping of the Amino Acids Mediating Agonist and Antagonist Coordination with the Human Thromboxane A2 Receptor Protein

Despite the well documented involvement of thromboxane A(2) receptor (TPR) signaling in the pathogenesis of thrombotic diseases, there are currently no rationally designed antagonists available for clinical use. To a large extent, this derives from a lack of knowledge regarding the topography of the TPR ligand binding pocket. On this basis, the purpose of the current study was to identify the specific amino acid residues in the TPR protein that regulate ligand coordination and binding. The sites selected for mutation reside within or in close proximity to a region we previously defined as a TPR ligand binding region (i.e. the C terminus of the second extracellular loop and the leading edge of the fifth transmembrane domain). Mutation of these residues caused varying effects on the TPR-ligand coordination process. Specifically, the D193A, D193Q, and D193R mutants lost SQ29,548 (antagonist) binding and exhibited a dramatically reduced calcium response, which could not be restored by elevated U46619 (agonist) doses. The F184Y mutant lost SQ29,548 binding and exhibited a reduced calcium response (which could be restored by elevated U46619); and the T186A and S191T mutants lost SQ29,548 binding and retained a normal U46619-induced calcium response. Furthermore, these last three mutants also revealed a divergence in the binding of two structurally different antagonists, SQ29,548 and BM13.505. Two separate mutants that exhibited SQ29,548 binding yielded either a normal (F196Y) or reduced (S201T) U46619 response. Finally, mutation of other residues directly adjacent to those described above (e.g. E190A and F200A) produced no detectable effects on either SQ29,548 binding or the U46619-induced response. In summary, these results identify key amino acids (in particular Asp(193)) involved in TPR ligand coordination. These findings also demonstrate that TPR-specific ligands interact with different residues in the ligand-binding pocket.

Histopathology and transmurality of acute microwave lesions on the beating human atrium

Microwave energy allows thoracoscopic beating-heart ablation for the treatment of atrial fibrillation. However, there is a paucity of data on the histologic effects of microwave energy on the beating human heart. This study aims to histopathologically characterize microwave lesions on the beating human atrium. Microwave energy was applied prior to cardiectomy on the beating native right atrium in eight patients undergoing heart transplantation and as a circumferential left atrial 'box' lesion in one patient undergoing heart-lung transplantation. Lesions were applied following heparinization and cannulation, but before initiation of cardiopulmonary bypass. Following cardiectomy, specimens were resected, fixed and subjected to histologic preparation. Grossly, all atrial lesions were 'comma-shaped' with an area of maximum injury on the surface. Microscopically, myocyte injury manifested as acute coagulation necrosis with hypereosinophilic myocytes with both nuclear loss and pyknosis. Contraction bands were noted at the periphery of lesions. The injury was transmural in all right atrial lesions. The left atrial sample contained a circumferential lesion ranging from 0.1 to 0.8 cm in width. The cut edge demonstrated lesion depths of 0.2-0.6 cm, maximum (transmural) in the inferior margin. Microwave ablation represents an acceptable energy source to create characteristic lesions on the beating human atrium.

Mapping of a ligand-binding site for the human thromboxane A2 receptor protein

The human thromboxane A(2) (TP) receptor, a member of the G protein-coupled receptor superfamily, consists of seven transmembrane segments. Attempts to elucidate the specific segment(s) that define the receptor ligand-binding pocket have produced less than definitive and sometimes conflicting results. On this basis, the present work identified an amino acid sequence of the TP receptor that is directly involved in ligand binding. Mapping of this domain was confirmed by two separate approaches: photoaffinity labeling and site-specific antibodies. The newly synthesized, biotinylated photoaffinity probe, SQBAzide, was first shown to specifically label TP receptor protein. Sequential digestion of this protein with CNBr/trypsin revealed photolabeling of a 2.9-kDa peptide. Using anti-peptide antibodies directed against different regions of the receptor protein, it was established that this peptide represents the predicted cleavage product for CNBr/trypsin and corresponds to amino acids Arg(174)-Met(202) of the receptor protein. Furthermore, antibody screening revealed that inhibition of the amino acid region Cys(183)-Asp(193) was critical for radioligand binding and platelet aggregation, whereas inhibition of Gly(172)-Cys(183) was not. Collectively these findings provide evidence that ligands interact with amino acids contained within the C-terminal portion of the third extracellular domain (ED3) of the receptor protein. This information should be of significant value in the study of TP receptor structure and signaling.

Synthesis and biological characterization of sqbazide, a novel biotinylated photoaffinity probe for the study of the human platelet thromboxane A2 receptor

SQBAzide, a biotinylated, azido derivative of the TXA2 receptor antagonist, SQ31,491, was synthesized and characterized. The compound specifically inhibited human platelet aggregation mediated by TXA2 receptor activation and irreversibly labeled platelet TXA2 receptors upon exposure to ultraviolet light. This probe should prove to be of significant value for the study of the receptor-ligand binding domain.

A sensitive technique for the detection of the alpha 7 neuronal nicotinic acetylcholine receptor antagonist, methyllycaconitine, in rat plasma and brain

Methyllycaconitine (MLA) is the most potent and selective antagonist of the alpha-bungarotoxin sensitive neuronal nicotinic acetylcholine receptor (nAChR). In the present study, an accurate and reproducible technique for the extraction and analysis of MLA from rat plasma and brain is described. This study further sought to determine whether pharmacologically relevant concentrations of MLA could be achieved in brain following peripheral administration. The detection limits for MLA were 0.5 ng/ml for plasma samples and 1.0 ng/g for brain samples. The pharmacokinetic properties of MLA in rat are characterized by a short elimination half-life (19 min) following intravenous (i.v.) administration and poor bioavailability following oral (p.o.) administration. Remarkably, the elimination half-life is significantly longer following p.o. administration (408 min). To assess the extent to which MLA can penetrate into brain, brain and plasma levels of MLA were determined at different time points following intraperitoneal (i.p.) administration of a dose of MLA that produced no observable side effects. Maximal plasma and brain levels were 694 +/- 106 ng/ml and 32 +/- 3 ng/g, respectively. These concentrations are within a range previously reported to selectively block alpha 7 nAChR mediated responses in vitro. Peripherally administered MLA may therefore be a useful tool to further probe the central nervous system functions of the alpha 7 nAChR subunit in vivo.