Isosorbide DiNitrate Effect on Hemodynamic Profile, Liver Stiffness, and Exercise Tolerance in Fontan Circulation (The NEET Clinical Trial)

After Fontan operation, decreased venous capacitance and venoconstriction are adaptive mechanisms to maintain venous return and cardiac output. The consequent higher venous pressure may adversely impact end-organ function, exercise capacity and result in worse clinical outcomes. This pilot study evaluated the safety and effect of isosorbide dinitrate (ISDN), a venodilator, on exercise capacity, peripheral venous pressure (PVP), and liver stiffness in patients with Fontan circulation. In this prospective single-arm trial, 15 individuals with Fontan circulation were evaluated at baseline and after 4 weeks of therapeutic treatment with ISDN. Primary aims were to assess the safety of ISDN and the effect on maximal exercise. We also aimed to evaluate the effect of ISDN on ultrasound-assessed liver stiffness, markers of submaximal exercise, and PVP at rest and peak exercise. Repeated measures t-tests were used to assess change in variables of interest in response to ISDN. Mean age was 23.5 ± 9.2 years (range 11.2-39.0 years), and 10/15 (67%) were male. There was no statistically significant change in peak VO₂ (1401 ± 428 to 1428 ± 436 mL/min, p = 0.128), but VO₂ at the anaerobic threshold increased (1087 ± 313 to 1115 ± 302 mL/min, p = 0.03). ISDN was also associated with a lower peak exercise PVP (22.5 ± 4.5 to 20.6 ± 3.0 mmHg, p = 0.015). Liver stiffness was lower with ISDN, though the difference was not statistically significant (2.3 ± 0.4 to 2.1 ± 0.5 m/s, p = 0.079). Of the patients completing the trial, mild headache was common (67%), but there were no major adverse events. Treatment with ISDN for 4 weeks is well-tolerated in patients with a Fontan circulation. ISDN is associated with an increase in VO₂ at anaerobic threshold, lower peak PVP, and a trend toward lower liver stiffness. Larger, longer duration studies will be necessary to define the impact of ISDN on clinical outcomes in the Fontan circulation.Clinical Trial Registration: URL: https://clinicaltrials.gov . Unique identifier: NCT04297241.

Overly Selective Offer Acceptance is Associated With High Waitlist Mortality for the Most Ill Lung Transplant Candidates

The demand for organs for lung transplantation (LTx) continues to outweigh supply. However, nearly 75% of donor lungs are never transplanted. LTx offer acceptance practices and the effects on waitlist/post-transplant outcomes by candidate clinical acuity are understudied. UNOS was used to identify all LTx candidates, donors, and offers from 2005 to 2019. Candidates were grouped by Lung Allocation Score (LAS; applicable post-2005, ages ≥12 years): LAS<40, 40-60, 61-80, and >80. Offer acceptance patterns, waitlist death/decompensation, and post-transplant survival (PTS) were compared. "Acceptable organ offers" were those from donors whose organs were accepted for transplantation. Approximately 3 million offers to 34,531 candidates were reviewed. Median waitlist durations were: 9 days-(LAS>80), 17 days-(LAS 61-80), 42 days-(LAS 40-60), 125 days-(LAS<40) (P < 0.001 between all). Per waitlist-day, offer rates were: total offers - 0.8/day-(LAS>80), 0.7/day-(LAS 61-80), 0.6/day-(LAS 40-60), 0.4/day-(LAS<40); acceptable offers - 0.34/day-(LAS>80), 0.32/day-(LAS 61-80), 0.24/day-(LAS 40-60), 0.15/day-(LAS<40) (both P < 0.001 between all LAS). Among patients who experienced waitlist mortality/decompensation, ≥1 acceptable offer was declined in 92% (3939/4270) of patients - 78% for LAS >80, 88% for LAS 61-80, 93% for LAS 40-60, and 96% for LAS <40. Thirty-day waitlist mortality/decompensation rates were: 46%-(LAS>80), 24%-(LAS 61-80), 5%-(LAS 40-60), <1%-(LAS<40) (P < 0.001 between all). PTS was equivalent between patients for whom the first/second offer vs later offers were accepted (all LAS P > 0.4). The first offers that LTx candidates receive (including acceptable organs) are declined for nearly all candidates. Healthier candidates can afford offer selectivity but more ill patients (LAS>60) cannot, experiencing exceedingly high 30-day waitlist mortality.

Mini right axillary thoracotomy for congenital heart defect repair can become a safe surgical routine

OBJECTIVE

Owing to its obvious cosmetic appeal, minimal invasive repair of congenital heart defects (CHDs) through the mini right axillary thoracotomy is becoming routine in many centres. Besides cosmesis, and before becoming a new norm, it is important to establish its outcomes as safe compared to repairs through traditional median sternotomy.

METHODS

Between 2013 and 2021, 116 consecutive patients underwent defect repairs through mini right axillary thoracotomy. Patient, operative data, and hospital outcomes were compared to contemporary mini right axillary thoracotomy and sternotomy series.

RESULTS

There was no mortality or need for approach conversion (mean age 4.3 years, range 0.17-17, mean weight 18.6 kg, range 4.8-74.4) in 118 repairs for atrial septal defect, ventricular septal defect, partial anomalous pulmonary venous return, partial atrioventricular canal with mitral cleft, scimitar syndrome, double-chambered right ventricle, cor triatriatum, and tricuspid valve repair. Protocol included on-table extubation, achieved in 97 children, with 23 outliers leading to 0.7 average hours of mechanical ventilation (range 0-66 hours), indwelling chest drain time of 2.6 days (range 1-9 days), intensive care stay of 1.8 days (range 1-10 days), and hospital stay of 3.9 days (range 2-18 days). Late revisions were required in one patient after scimitar repair for scimitar vein stenosis at 2 weeks, and in another for repair of superior caval vein stenosis after a Warden operation at 2 months; reoperations (5/116 = 4.3%) were successfully performed through the same mini right axillary incision.

CONCLUSIONS

While providing obvious cosmetic advantages, the minimally invasive right axillary thoracotomy approach for the surgical repair of common CHDs yields excellent results and is safe compared to the benchmark median sternotomy approach.

Risk of Pediatric Cardiac Surgery Increased in Patients Undergoing Tracheal Surgery During the Same Hospitalization

BACKGROUND

The impact of complex tracheal surgery (TS) on outcomes of children undergoing cardiac surgery has rarely been investigated in large national databases and could impact anticipated outcomes in those patients.

METHODS

The Pediatric Health Information System database was reviewed from January 1, 2005 to December 31, 2014, for pediatric (<18 years) patients undergoing select cardiac surgical procedures using International Classification of Disease-9 procedural coding. Patients were divided based upon having TS (excluding tracheostomy) during the same hospitalization. Patients with tracheal and cardiac surgeries (CHS + TS) were propensity matched in a 1 : 2 fashion to patients undergoing isolated cardiac surgeries without TS (CHS) based upon cardiac procedure(s), age at surgery, gender, and discharge year. Hospital mortality and other outcomes were compared between the 2 matched groups.

RESULTS

The 283 CHS + TS patients were similar to the 566 CHS patients in gender, race, age, cardiac procedures, and presence of chromosomal abnormalities, all P > .05. Hospital mortality was 13.8% (n = 39) for CHS + TS and 5.8% (n = 33) for CHS patients with an unadjusted 2.58 hazard ratio of death (95% confidence interval: 1.59-4.20; P < .001). CHS + TS was also associated with a greater length of stay (63 days vs 12 days), a higher cost per hospitalization ($322 402 vs $80 273), and more readmissions (64.3% [n = 182] vs 41.8% [n = 243]), all P < .001.

CONCLUSIONS

Patients undergoing cardiac and TS in the same hospitalization are at greater risk of in-hospital mortality than patients undergoing similar cardiac surgeries alone and incur higher resource utilization thereafter. The increased risk of mortality is currently underappreciated, but it is important to recognize when discussing expectations with families and providers.

Transplantation for Congenital Heart Disease: Focus on the Impact of Functionally Univentricular Versus Biventricular Circulation

BACKGROUND

Varying single center data exist regarding the posttransplant outcomes of patients with single ventricle circulation, particularly following the Fontan operation. We sought to better elucidate these results in patients with congenital heart disease (CHD) through combining two national databases.

METHODS

The United Network for Organ Sharing (UNOS) transplantation database was merged with the Pediatric Health Information System (PHIS), an administrative database with 71% of UNOS patients matched. Patients undergoing transplantation at a PHIS hospital from 2006 to 2017 were categorized as single ventricle or biventricular strategy based on their diagnoses and procedures in 90% of patients. When known, single ventricle patients were further analyzed by their palliative stage post-Glenn or post-Fontan (known in 31%).

RESULTS

A total of 1,517 CHD transplantations were identified, 67% with single ventricle strategy (1,016). Single ventricle, biventricular, and indeterminate patients had similar survival (log-rank P > .1). Risk factors for mortality in patients with CHD were extracorporeal membrane oxygenation (ECMO) support at transplant (hazard: 2.27), ABO blood type incompatibility (hazard: 1.61), African American recipient (hazard 1.42), and liver dysfunction (hazard 1.29). A total of 130 confirmed Fontan and 185 confirmed bidirectional Glenn patients underwent transplantation, each with survival equivalent to biventricular patients (log-rank P > .500). For Fontan patients, renal dysfunction (hazard: 5.40) and transplant <1 year after Fontan (hazard 2.82) were found to be associated with mortality.

CONCLUSIONS

Single ventricle patients, as a group, experience similar outcomes as biventricular patients with CHD undergoing transplantation, and this extends to Fontan patients. Risk factors for mortality correlate with end-organ dysfunction as well as race and ABO blood type incompatibility in the CHD population.

Tracheal surgery for airway anomalies associated with increased mortality in pediatric patients undergoing heart surgery: Society of Thoracic Surgeons Database analysis

OBJECTIVES

Airway anomalies are common in children with cardiac disease but with an unquantified impact on outcomes. We sought to define the association between airway anomalies and tracheal surgery with cardiac surgery outcomes using the Society of Thoracic Surgery Congenital Heart Surgery Database.

METHODS

Index cardiac operations in children aged less than 18 years (January 2010 to September 2018) were identified from the Society of Thoracic Surgery Congenital Heart Surgery Database. Patients were divided on the basis of reported diagnosis of an airway anomaly and subdivided on the basis of tracheal lesion and tracheal surgery. Multivariable analysis evaluated associations between airway disease and outcomes controlling for covariates from the Society of Thoracic Surgery Congenital Heart Surgery Database Mortality Risk Model.

RESULTS

Of 198,674 index cardiovascular operations, 6861 (3.4%) were performed in patients with airway anomalies, including 428 patients (0.2%) who also underwent tracheal operations during the same hospitalization. Patients with airway anomalies underwent more complex cardiac operations (45% vs 36% Society of Thoracic Surgeons/European Association for Cardiothoracic Surgery Congenital Heart Surgery Mortality category ≥3 procedures) and had a higher prevalence of preoperative risk factors (73% vs 39%; both P < .001). In multivariable analysis, patients with airway anomalies had increased odds of major morbidity and tracheostomy (P < .001). Operative mortality was also increased in patients with airway anomalies, except those with malacia. Tracheal surgery within the same hospitalization increased the odds of operative mortality (adjusted odds ratio, 3.9; P < .0001), major morbidity (adjusted odds ratio, 3.7; P < .0001), and tracheostomy (adjusted odds ratio, 16.7; P < .0001).

CONCLUSIONS

Patients undergoing cardiac surgery and tracheal surgery are at significantly higher risk of morbidity and mortality than patients receiving cardiac surgery alone. Most of those with unoperated airway anomalies have higher morbidity and mortality, which makes it an important preoperative consideration.

Cardiomyocyte cell cycling, maturation, and growth by multinucleation in postnatal swine

BACKGROUND

Rodent cardiomyocytes (CM) undergo mitotic arrest and decline of mononucleated-diploid population post-birth, which are implicated in neonatal loss of heart regenerative potential. However, the dynamics of postnatal CM maturation are largely unknown in swine, despite a similar neonatal cardiac regenerative capacity as rodents. Here, we provide a comprehensive analysis of postnatal cardiac maturation in swine, including CM cell cycling, multinucleation and hypertrophic growth, as well as non-CM cardiac factors such as extracellular matrix (ECM), immune cells, capillaries, and neurons. Our study reveals discordance in postnatal pig heart maturational events compared to rodents.

METHODS AND RESULTS

Left-ventricular myocardium from White Yorkshire-Landrace pigs at postnatal day (P)0 to 6 months (6mo) was analyzed. Mature cardiac sarcomeric characteristics, such as fetal TNNI1 repression and Cx43 co-localization to cell junctions, were not evident until P30 in pigs. In CMs, appreciable binucleation is observed by P7, with extensive multinucleation (4-16 nuclei per CM) beyond P15. Individual CM nuclei remain predominantly diploid at all ages. CM mononucleation at ~50% incidence is observed at P7-P15, and CM mitotic activity is measurable up to 2mo. CM cross-sectional area does not increase until 2mo-6mo in pigs, though longitudinal CM growth proportional to multinucleation occurs after P15. RNAseq analysis of neonatal pig left ventricles showed increased expression of ECM maturation, immune signaling, neuronal remodeling, and reactive oxygen species response genes, highlighting significance of the non-CM milieu in postnatal mammalian heart maturation.

CONCLUSIONS

CM maturational events such as decline of mononucleation and cell cycle arrest occur over a 2-month postnatal period in pigs, despite reported loss of heart regenerative potential by P3. Moreover, CMs grow primarily by multinucleation and longitudinal hypertrophy in older pig CMs, distinct from mice and humans. These differences are important to consider for preclinical testing of cardiovascular therapies using swine, and may offer opportunities to study aspects of heart regeneration unavailable in other models.

Norwood With Obstructed Total Anomalous Pulmonary Venous Connection and Tracheoesophageal Fistula Repair: Operating Room Delivery

A baby boy with prenatally diagnosed hypoplastic left heart syndrome variant with obstructed veins was born in the operating room (OR) and underwent emergent Norwood operation and repair of obstructed infra-diaphragmatic total anomalous pulmonary venous connection. Post-operatively, esophageal atresia with tracheoesophageal fistula was identified and repaired on day of life 11. The patient is thriving at 22 months of age. (Level of Difficulty: Advanced.)

Pediatric heart-lung transplantation: A contemporary analysis of outcomes

BACKGROUND

Pediatric heart-lung transplantation (HLT) is rare, and no report has analyzed patient outcomes since time of listing. We analyzed pediatric HLTs to understand risk factors for waitlist and post-HLT mortality.

METHODS

All pediatric (<18 year old) HLT candidates were identified within the UNOS database (n = 573) and grouped by age, era, and by diagnosis. Logistical regression and Cox proportional hazard modeling identified risk factors for 6-month WL and overall post-transplant mortality.

RESULTS

209/573 (37%) HLT candidates were transplanted, 7% recovered, 42% died waiting, and 15% were removed for another/unknown reason. Diagnoses were primary pulmonary hypertension(n = 130), congenital heart disease(CHD) without Eisenmenger's syndrome (ES) (n = 65), CHD with ES (n = 73), and other (n = 305). Patients with a diagnosis other than CHD with ES (OR: 7.55, P = .001), on IV inotropic support (OR: 2.79, P < .001), and infants (OR: 2.20, P = .004) were associated with waitlist mortality. There has been a 56% reduction in HLTs across eras (Era 1:10.8/yr vs Era 2:4.7/yr). Risk factors for post-transplant mortality were ECMO (HR: 4.1, P = .016), and being infant (HR: 2.2, P = .04) or 1-11 years old (HR: 1.78, P = .015). ECMO patients have an 87% 2-year mortality rate with a median post-transplant survival of 64 days. Overall, post-transplant survival was unchanged (log-rank P = .067) between eras. Excluding ECMO patients, in the recent era 29 non-infant patients with primary pulmonary hypertension had 93% 1-year survival and 67% 5-year survival.

CONCLUSIONS

Nearly 600 pediatric patients have been listed for HLT in UNOS, although numbers are decreasing in the current era. HLT for a patient on ECMO appears to be an ineffective strategy; however, in well-selected cohorts, HLT can provide considerable post-transplant survival.

Expanding the donor pool for congenital heart disease transplant candidates by implementing 3D imaging-derived total cardiac volumes

BACKGROUND

Heart transplant waitlist mortality remains high in infants <1 year of age and among those with CHD. Currently, the median accepted donor-to-recipient weight percentage is approximately 130% of the recipient's weight. We hypothesized that patients with CHD may accept a larger organ using novel 3D-derived imaging data to estimate donor and recipient TCV.

METHODS

A single-center, retrospective study was performed using CT data for 13 patients with CHD and 94 control patients. 3D visualization software was used to create digital 3D heart models that provide an estimate of TCV. In addition, echocardiograms obtained prior to cross-sectional imaging were reviewed for presence of ventricular chamber dilation.

RESULTS

Sixty-two percent (8/13) of patients with CHD had 3D-derived TCV resulting in a weight that was >130% larger than their actual weight. This was seen in single-ventricle patients following Blalock-Taussig shunt and Fontan palliation, and patients with biventricular repair. Of those, 75% (6/8) had reported moderate-to-severe ventricular chamber dilation by echocardiogram or cardiac magnetic resonance imaging.

CONCLUSIONS

In a large portion of patients with CHD, 3D-derived TCV place the recipient at a higher listing weight than their actual weight. We propose obtaining cross-sectional imaging to better assess TCV in a recipient, which may increase the donor range for CHD recipients and improve organ utilization in pediatrics.

Scar Formation with Decreased Cardiac Function Following Ischemia/Reperfusion Injury in 1 Month Old Swine

Studies in mice show a brief neonatal period of cardiac regeneration with minimal scar formation, but less is known about reparative mechanisms in large mammals. A transient cardiac injury approach (ischemia/reperfusion, IR) was used in weaned postnatal day (P)30 pigs to assess regenerative repair in young large mammals at a stage when cardiomyocyte (CM) mitotic activity is still detected. Female and male P30 pigs were subjected to cardiac ischemia (1 h) by occlusion of the left anterior descending artery followed by reperfusion, or to a sham operation. Following IR, myocardial damage occurred, with cardiac ejection fraction significantly decreased 2 h post-ischemia. No improvement or worsening of cardiac function to the 4 week study end-point was observed. Histology demonstrated CM cell cycling, detectable by phospho-histone H3 staining, at 2 months of age in multinucleated CMs in both sham-operated and IR pigs. Inflammation and regional scar formation in the epicardial region proximal to injury were observed 4 weeks post-IR. Thus, pigs subjected to cardiac IR at P30 show myocardial damage with a prolonged decrease in cardiac function, formation of a regional scar, and increased inflammation, but do not regenerate myocardium even in the presence of CM mitotic activity.

How Small Is Too Small? Decision-Making and Management of the Small Aortic Root in the Setting of Interrupted Aortic Arch

Interrupted aortic arch is commonly associated with a posterior malalignment ventricular septal defect (VSD) and left ventricular outflow tract (LVOT) hypoplasia. Standard repair is carried out in the neonatal period and includes re-establishing arc continuity and VSD closure. Reintervention on the LVOT for obstruction is a common and an ongoing source of morbidity and mortality. A variety of preoperative echocardiographic measurements have been identified to identify patients at risk for developing LVOT obstruction but an aortic valve annulus dimension (mm) < patient's weight (kg) + 1 mm is a reasonable threshold to identify a patient at increased risk for future LVOT reintervention. Prophylactic direct approaches to prevent future LVOT obstruction include myectomy/myotomy and left-sided placement of the VSD patch but do not reliably prevent late LVOT obstruction. Patients amendable to a biventricular repair but with important LVOT hypoplasia are probably best served with a Yasui operation, either as a primary operation or staged with a Norwood procedure. In the case of complex redo operations, a Ross-Konno provides another valuable option for a durable repair. Though smaller preoperative LVOT structures predict the need for reoperation, careful preoperative planning may minimize the need for LVOT reintervention and improve long-term survival.

Mechanical circulatory support in children: past, present and future

Rapid advances in the field of mechanical circulatory support (MCS) have dramatically changed the management of pediatric patients with heart failure. There is now emphasis on timely implantation of ventricular assist devices (VADs) to preserve or recover end-organ function, and increased focus on post-implant management to improve the stroke rate. Transplant waitlist mortality has significantly decreased in the era of VAD use. Devices approved for adults are being used off-label in children with excellent outcomes, allowing chronic therapy and discharge home to become part of pediatric VAD therapy.

First report of successfully palliating a hypoplastic left heart syndrome patient with anomalous left coronary artery from the pulmonary artery beyond Fontan

We report a case of hypoplastic left heart syndrome with an anomalous left coronary artery from the pulmonary artery (ALCAPA) identified intraoperatively during the Stage-II palliation. Due to recurring ventricular fibrillation on sternotomy, a hybrid Stage-I palliation was performed. During comprehensive Stage-II, the ALCAPA was reimplanted in the neoaorta and measures, including a nontraditional Damus connection/arch reconstruction and classic bilateral Glenn procedures, were taken to avoid compression of the coronary artery. After a successful Fontan procedure, he continues to do well at 5 years old, becoming the first patient reported in the literature to survive all the three stages of single-ventricle palliation.

Norwood Procedure With Left Ventricle Exclusion in Complex Single Ventricle Patients: A Novel Technique

Background:

Hypoplastic left heart disease and its variants complicated by severe semilunar and atrioventricular valve insufficiency are associated with a high mortality risk in utero and postnatally. Through the description of three cases, this report outlines the evolution of a successful strategy of morphological left ventricle isolation (ie, “left-sided Starnes”) in caring for this rare cohort of patients with hypoplastic left heart syndrome (HLHS).

Methods:

This study includes three patients: two patients prenatally diagnosed and one transferred from an outside hospital. All patients presented with complex univentricular heart disease with a nonfunctional left ventricle and severe left-sided atrioventricular and/or semilunar valve insufficiency.

Results:

Two patients were delivered with an operating room on standby due to the possibility of emergent surgery being necessary; however, all patients were able to be medically stabilized after birth. Patient 1 underwent successful left ventricle exclusion with a fenestrated polytetrafluoroethylene (PTFE) patch, despite severe mitral valve regurgitation. Patient 2 reinforced the efficacy of PTFE patch occlusion in addition to having aortic valve closure with a small washing jet. Patient 3’s clinical course was successfully predicted based on the previous patients and outlined for the family prenatally. All patients are currently growing well at home, awaiting Fontan with marked improvement in cardiac function.

Conclusion:

This rare cohort of patients with HLHS having severe left-sided atrioventricular and/or semilunar valve insufficiency appear to survive to birth and can be medically stabilized prior to semiurgent intervention. The Norwood procedure with left ventricle exclusion appears to be a successful strategy for these unique patients.

Adult Congenital Heart Disease: Current Early Expectations After Cardiac Transplantation

BACKGROUND

Early mortality has plagued the otherwise good outcomes of heart transplantation in patients with adult congenital heart disease (ACHD), but perioperative care is improving. This study sought to identify risk factors for 1-year mortality currently and examine the results of patients without those risk factors compared with patients who did not have ACHD (nACHD).

METHODS

The United Network of Organ Sharing database was searched for all adult (>17 years of age) heart transplant recipients from 2000 to 2018. They were divided into an early era and a late era. A multivariate analysis identified risk factors for 1-year mortality in the late era. Patients without these risk factors were compared with the nACHD group by Kaplan-Meier analysis.

RESULTS

A total of 495 patients with ACHD were identified from 2000 to 2008, and 666 were identified from 2009 to 2018. The recent era had better 1-year survival (P <.001) and overall survival (P = .003) than did the era from 2000 to 2008. Patients with ACHD were different from the nACHD population in age (37 years vs 57 years), body mass index greater than 25 kg/m² (45% vs 66%), incidence of renal dysfunction (23% vs 28%) and liver dysfunction (29% vs 23%), sensitization (38% vs 29%), and ischemic times (3.5 hours vs 3.1 hours). Multivariate analysis identified body mass index greater than 25 kg/m² (hazard ratio [HR], 1.79), renal dysfunction (HR, 1.85), liver dysfunction (HR, 1.69), and longer ischemic time (HR, 1.46) as risk factors for early mortality. Patients with only 1 of the first 3 categorical risk factors had 1-year survival comparable to that reported in patients with nACHD.

CONCLUSIONS

Patients with ACHD had better early and long-term outcomes in the recent era. When only 1 of 3 pretransplant risk factors for early mortality was present, patients had survival equal to that of nACHD patients and perhaps better long-term survival.

Abstract 131: Cardiomyocyte Renewal and Cardiac Outcomes Following Injury in Young Swine

Objective: Infants with severe congenital heart defects (CHD) typically require lifesaving cardiac surgery. Performing this surgery during a time when the myocardium can proliferate and repair could improve successful outcomes. The mouse heart can regenerate in the first week post-partum, but the mitotic activity of cardiomyocytes (CM) is extended to 1-2-months post-partum in the pig. Thus, the regulation of CM cell cycling ability and renewal in the hearts of young large mammals after injury was examined.

Methods & Results: Pigs at postnatal day 30 (n=6) were subjected to cardiac ischemia (1-hour) by temporary occlusion of the left anterior descending (LAD) artery followed by reperfusion (IR), or to sham operation (n=6, no LAD occlusion). LAD occlusion, below the second diagonal branch, provided an effective injury as indicated by increased circulating cardiac troponin-I 2-hours after injury. In addition, ejection fraction (EF) decreased by 46% (57% to 31%) at 2 hours post-ischemia, which was then maintained to the 4-week study end point. Pigs were sacrificed 4 weeks after surgery and histology demonstrated evidence of scar formation in the area of injury. However, no change in number of proliferating CM or cell death (via pHH3 or TUNEL immunohistochemistry respectively) was detected in IR pigs vs sham, or between regions of the left ventricle.

Conclusions: Here we report a successful ischemic injury method, at an age previously not reported in swine. Pigs did not continue to decline towards heart failure following an IR injury at 1 month of life, with preservation of EF up to 4-weeks post-injury. This is also without a change in CM cell cycling activity at 2 months of age. This study highlights that even in the presence of a scar, young, large mammals can adapt to cardiac injury to maintain cardiac function. The pathways regulating scar formation and CM cell cycling are being further investigated by RNA-seq studies. If similar mechanisms operate in humans, it may be beneficial to perform CHD surgeries at a younger age when the heart is able to better tolerate injury, to ultimately improve long term outcomes.

Abstract 423: Cardiomyocyte Maturation and Multinucleation in Postnatal Swine

Objectives: Cardiomyocyte (CM) cell cycle arrest and decline of mononucleated diploid CMs have been implicated in loss of regenerative potential in postnatal mouse hearts. Sarcomeric and extracellular matrix (ECM) maturation also occur concurrently in mice, influencing CM proliferative arrest. Recent studies show a 3-day neonatal period of cardiac regeneration in pigs similar to mice, but the dynamics of postnatal pig CM growth are unknown. Our objective is to explore cardiac cell cycling, growth and maturation in postnatal pigs to understand the events guiding loss of cardiac regenerative capacity in large mammals.

Methods & Results: Left-ventricular tissue from farm pigs (White Yorkshire-Landrace) at Postnatal day (P)0, P7, P15, P30, 2 months (2mo) and 6mo were utilized. CM dissociations revealed predominant CM mononucleation at birth in swine, with persistence of ~50% (1186/2537 cells, n=5) mononucleated CMs at P15, and ~10% (227/1785 cells, n=4) at 2mo. By 6mo, pig CMs are entirely multinucleated, exhibiting 4-16 nuclei per cell. Assessing hypertrophic growth in dissociated pig CMs revealed longitudinal CM growth relative to increased nucleation at all ages. However, onset of diametric hypertrophy only occurs beyond 2mo. When nuclear pHH3 and mRNA expression of cell cycle genes was assessed, pig hearts show robust cell-cycling up to 2mo. Also, fetal TNNI1 and MYH6 are active up to 2mo in pig hearts. Ongoing studies on collagen remodeling indicate ECM remodeling in swine occurs beyond P7. Future studies are designed to identify nuclear ploidy in postnatal pig CMs and measure cytokinesis.

Conclusions: Cardiac maturational events are staggered over a 2-6 month postnatal window in pigs, with older pig hearts exhibiting extensive CM multinucleation and differences in longitudinal versus diametric CM growth. These fundamental variations in CM growth characteristics are important to consider when designing preclinical trials for cardiac regenerative strategies in pigs. Also, despite a similar period of regenerative capacity as mice, pig hearts do not undergo loss of CM cell cycling and mononucleation until 2mo after birth. Utilizing pigs may thus offer unique opportunities to study aspects of heart regeneration unavailable in other animal models.

Time for evidence-based, standardized donor size matching for pediatric heart transplantation

BACKGROUND

Accurately predicting cardiac size by other body parameters has long been problematic to determine whether a donor heart will serve a given waitlist candidate, yet hundreds of heart donors are turned down annually for size mismatch.

OBJECTIVES

We sought to describe how donor body weight parameters are currently utilized in cardiac transplantation and its influence on waitlist outcomes.

METHODS

From the United Network for Organ Sharing database, pediatric (age <18 years) heart transplant candidates were divided into lower quartile, interquartile, and upper quartile categories based on final maximum acceptable donor-candidate weight ratio (DCW), expressed as percentage. Baseline characteristics and waitlist outcomes, including monthly offers/candidate and survival were compared.

RESULTS

Overall median DCW was 200% (range, 159%-241%). Patients with congenital heart disease had higher DCW than those with cardiomyopathy (223% vs 203%; P < .001). Number of monthly offers/candidate (5.0, 5.6, and 7.2, respectively; P < .001) increased with quartile of DCW. Posttransplant survival was similar amongst the groups (log-rank P > .05). Subgroup analysis of critically ill children showed a waitlist survival advantage in those listed with a DCW ≥200% (P < .001).

CONCLUSIONS

Despite substantial practice variation in acceptable donor weight in pediatric heart transplantation, patients listed with variable DCW had similar posttransplant survival. However, in critically ill patients, higher DCW was associated with greater waitlist survival. Better understanding of the importance of donor weight could reduce practice variability and improve organ use and waitlist outcomes for pediatric cardiac transplant candidates.

Cardiac Surgery in Patients With Trisomy 13 and 18: An Analysis of The Society of Thoracic Surgeons Congenital Heart Surgery Database

Background Congenital heart disease is common in patients with Trisomy 13 (T13) and Trisomy 18 (T18), but offering cardiac surgery to these patients has been controversial. We describe the landscape of surgical management across the United States, perioperative risk factors, and surgical outcomes in patients with T13 and T18. Methods and Results Patients in the Society of Thoracic Surgeons Congenital Heart Surgery Database with T13 and T18 who underwent cardiac surgery (2010-2017) were included. There were 343 operations (T13: n=73 and T18: n=270) performed on 304 patients. Among 125 hospitals, 87 (70%) performed at least 1 operation and 26 centers (30%) performed ≥5 T13/T18 operations. Operations spanned the full spectrum of complexity with 29% (98/343) being in the highest categories of estimated risk. The operative mortality rate was 15%, with a 56% complication rate. Preoperative mechanical ventilation was associated with an odds ratio of mortality >8 for both patients with T13 and T18 (both P<0.012) while presence of a gastrostomy tube (odds ratio, 0.3; P=0.03) or prior cardiac surgery (odds ratio, 0.2; P=0.02) was associated with better survival in patients with T18 but not patients with T13. Conclusions Data from this nationally representative sample indicate that most centers offer surgical intervention for both patients with T13 and T18, even in highly complex patients. However, the overall mortality rate was high in this select patient cohort. The association of preoperative mechanical ventilation with mortality suggests that this subset of patients with T13 and T18 should perhaps not be considered surgical candidates. This information is valuable to clinicians and families for counseling and deciding what interventions to offer.

Heart-Lung Transplant via an Eighth-Time Sternotomy

We report a combined heart–lung transplantation following seven prior sternotomies in a patient born with a transitional atrioventricular septal defect. Previous surgeries to repair and replace the mitral valve led to pulmonary vein stenosis and pulmonary vascular disease. Eighth-time sternotomy and significant vascular adhesions led to a prolonged operation and to placing the heart–lung block anterior to the phrenic nerves. Despite this, the patient was ready for discharge after two weeks and continues to do well over nine months later. As more patients survive multiple cardiac palliations with some developing pulmonary vascular disease, heart–lung transplantation may become relevant again.

Mechanical Support for Patients With Congenitally Corrected Transposition of the Great Arteries and End-Stage Ventricular Dysfunction

Despite great advances in caring for patients with congenitally corrected transposition of the great arteries (ccTGA), a high proportion of these patients go on to develop heart failure and death in early adulthood. Adults with congenital heart disease (ACHD) only comprise a small number of patients receiving ventricular assist devices (VAD), but ccTGA accounted for 36% of ACHD patients in the INTERMACS database. Review of the literature describing ccTGA patients receiving VAD therapy shows promising results. With newer devices and the assistance of advanced imaging, mechanical circulatory support is becoming a desirable option for this population of patients and has the potential to provide significant long-term support, relieving them of heart failure symptoms and delaying and perhaps in the future avoiding, the need for cardiac transplantation.

Three-dimensional printing and virtual surgery for congenital heart procedural planning

Complex unrepaired congenital heart disease requires extensive planning to determine the optimal procedural approach. Conventional noninvasive diagnostic imaging initially provides only two-dimensional (2D) representations of the complex, three-dimensional cardiovascular anatomy. With the expansion of 3D visualization techniques in imaging, a paradigm shift has occurred in complex congenital heart disease surgical planning using digital and 3D printed heart models. There has been early success in demonstrating the benefit of these models in interdisciplinary communication and education. The future goal of this work is to demonstrate a clinical outcome benefit using digital and 3D printed models to plan both surgical and catheterization-based interventional procedures. Ultimately, the hope is that advanced procedural planning with virtual surgery and 3D printing will enhance decision-making in complex congenital heart disease cases resulting in improved perioperative performance by reducing operative times, complications, and reoperations.

3D-printed models optimize preoperative planning for pediatric cardiac tumor debulking

BACKGROUND

This study reports the first known application of 3-dimensional (3D) printing of cardiac tumors to preoperatively plan debulking in infants. 3D-printed cardiac tumor models were used to identify the spacial relationship between the tumors and coronary arteries as well as understand the depth and infiltration of the tumors.

METHODS

Physical 3D cardiac tumor models of two children were obtained using medical imaging, image 3D rendering and modeling, and 3D printing. The hearts were 3D-printed in an opaque material while the tumors were made transparent to allow optimal visualization of the cardiovascular anatomy within the tumor. The surgical team used these models to plan exposure of the tumor, as well as, the extent of debulking.

RESULTS

Patient 1 had a cardiac tumor arising from the anterior surface of the right ventricle causing significant right ventricular outflow tract obstruction and involving the right and left coronary artery courses. Patient 2 had a cardiac tumor arising from the left ventricle and extending beyond the left atrium compressing the airway preventing extubation, and surrounding the left coronary artery system. In both patients, 3D-printed models were used to maximize debulking and avoid injury to the coronaries.

CONCLUSIONS

3D-printed cardiac tumor and anatomic models were effectively used to preoperatively plan two pediatric tumor debulkings. Both patients had tumors that were integrally involved with the coronary arteries. The 3D models helped devise a safe surgical strategy for maximal tumor debulking while protecting the coronary circulation.

Three-dimensional printing in surgical planning: A case of aortopulmonary window with interrupted aortic arch

Better anatomical understanding and conceptualization of complex congenital heart defects using three-dimensional (3D) printing may improve surgical planning, especially in rare defects. In this report, we utilized 3D printing to delineate the exact cardiac anatomy of a neonate with an aortopulmonary window associated with interrupted aortic arch to devise a novel approach to the repair.

Dose-dependent pharmacokinetics and metabolism of valproic acid in newborn lambs and adult sheep

Dose-dependent pharmacokinetics and metabolism of valproic acid (VPA) were studied in newborn and adult sheep to assess age-related differences in plasma protein binding and metabolic elimination. Newborn lambs received either a 10- (n = 8), 50- (n = 5), 100- (n = 4), or 250-mg/kg (n = 4) VPA i.v. bolus. Individual adult sheep (n = 5) received all four doses in a random order with an appropriate washout period between experiments. Unbound or metabolic clearance of VPA was significantly higher in adult sheep at the two lower doses when compared with lambs, and similar to the lambs at the two higher doses. Plasma protein binding was nonlinear at all doses. Estimates of binding capacity (B(max1)) at the saturable site were higher in adults (91.8 microg/ml) when compared with lambs (44.9 microg/ml), whereas the opposite trend was observed for binding affinity [K(d1) = 9.6 microg/ml (adult) versus 3.2 microg/ml (lambs)]. Characterization of developmental differences in overall VPA metabolic elimination involved fitting of unbound VPA plasma concentration data to a two-compartment model with Michaelis-Menten elimination. This resulted in similar in vivo estimates of apparent V(max) [445.0 microg/min/kg (adult) versus 429.9 microg/min/kg (lambs)]. However, apparent K(m) estimates appeared to be higher in lambs [30.0 microg/ml (adult) versus 69.6 microg/ml (lambs)]. Similar findings were obtained from in vivo estimates of V(max) and K(m) for VPA glucuronidation obtained from VPA-glucuronide metabolite urinary excretion data. Thus, it appears that age-related differences in metabolic clearance may be related to differences in the apparent in vivo K(m) as opposed to V(max) of VPA glucuronidation.

Altered fetal pituitary-adrenal function in the ovine fetus treated with RU486 and meloxicam, an inhibitor of prostaglandin synthase-II

Term and preterm labor are associated with increased fetal hypothalamic-pituitary-adrenal (HPA) activation and synthesis of prostaglandins (PGs) generated through the increased expression of prostaglandin H synthase-II (PGHS-II) in the placenta. Inhibition of PGHS-II has been advocated as a means of producing uterine tocolysis, but the effects of such treatment on fetal endocrine functions have not been thoroughly examined. Because PGE(2) is known to activate the fetal HPA axis, we hypothesized that administration of meloxicam, a PGHS-II inhibitor, to sheep in induced labor would suppress fetal HPA function. Chronically catheterized pregnant ewes were treated with RU486, a progesterone receptor antagonist, to produce active labor, and then treated with either high-maintenance-dose meloxicam, graded-maintenance-dose meloxicam, or a saline infusion. Maternal uterine contraction frequency increased 24 h after the RU486 injection and the animals were in active labor by 48 +/- 4 h. RU486 injection led to increased concentrations of PGE(2), ACTH, and cortisol in the fetal circulation, and increased concentrations of 13,14 dihydro 15-ketoprostaglandin F(2 alpha) (PGFM) in the maternal circulation. Uterine activity was inhibited within 12 h of beginning meloxicam infusion at both infusion regimes. During meloxicam infusion there were significant decreases in fetal plasma PGE(2), ACTH, and cortisol concentrations, and PGFM concentrations in maternal plasma. In control animals, frequency of uterine contractions, maternal plasma PGFM, fetal plasma PGE(2), ACTH, and cortisol concentrations increased after RU486 administration, and continued to rise during saline infusion until delivery occurred. We conclude that RU486-provoked labor in sheep is associated with activation of fetal HPA function, and that this is attenuated during meloxicam treatment to a level considered compatible with pregnancy maintenance.

Paroxetine levels in postpartum depressed women, breast milk, and infant serum

BACKGROUND

The purpose of this study was to determine the concentrations of paroxetine in maternal serum, breast milk, and infant serum samples and to estimate infant exposure through breastfeeding.

METHOD

A total of 25 sample sets was obtained: I sample set each from 23 mother-infant dyads and 2 sample sets from 1 mother-infant dyad. All mothers met DSM-IV criteria for major depressive disorder. The maternal fixed dosage of paroxetine was 10, 20, or 40 mg/day for a minimum of 30 days before the samples were drawn. Samples were collected 6 hours after dose intake, and the concentration of paroxetine in each sample was determined using gas chromatography/mass spectrometry. The analytic method employed in this study is the most sensitive to date, with the ability to detect drug concentrations as low as 0.1 ng/mL.

RESULTS

Detectable levels of paroxetine were present in all maternal serum samples and in 24 of the 25 breast milk samples. In all of the infant serum samples, the paroxetine concentrations were below the lower limit of quantification. No unusual adverse effects were reported in any of the infants.

CONCLUSION

The results of this study demonstrate that paroxetine, like the other selective serotonin reuptake inhibitors studied to date, is excreted into the breast milk of nursing mothers. The mean infant dose of paroxetine was 1. 1% of the maternal dose. Although no short-term adverse effects were reported in any of the infants in this study, future studies are needed to address a more systematic method for observing and recording any adverse effects. In addition, future studies should incorporate follow-up studies in order to evaluate possible long-term effects of paroxetine exposure.

Transdermal fentanyl compared with parenteral buprenorphine in post-surgical pain in swine: a case study

The use of pigs as research animals in survival surgery has increased greatly in the last 15 years. Personnel conducting pig research have been hampered by a lack of proven long-acting analgesics for treatment of surgical pain of longer duration, and by a lack of reliable non-subjective parameters for the assessment of pain relief. The efficacy of the mixed opioid agonist-antagonist buprenorphine hydrochloride 0.10 mg/kg pr (n = 2) in the treatment of post-thoracotomy pain was compared with that of a transdermal therapeutic system (TTS) delivering 25 microg/h (n = 3) or 50 microg/h (n = 2) of the mu opioid agonist fentanyl hydrochloride. Food consumption, pain score, activity level and rate of movement were assessed under four conditions: normal pre-operative control (24h), pre-operative with analgesic alone (24h) and post-operative days 1, 2, 3 (72h). Serum concentration-time curves for fentanyl in clinical cases revealed that female Yorkshire cross pigs weighing 26.2+ 2.1 kg achieved serum values in the recognized human therapeutic range when treated with TTS fentanyl at 50 microg/h and experienced adequate pain control. Pigs treated with 25 microg/h TTS fentanyl had serum levels below the human analgesic range, experienced less adequate analgesia, and required supplemental analgesia in some cases. Based on existing pharmacokinetic data for fentanyl in pigs, the rate of uptake of TTS fentanyl when attached on inter-scapular skin was lower than predicted. Clinical pain scores and time intervals between each major postural change were not affected by analgesics in the absence of pain, but increased in all groups after surgery regardless of treatment. Food consumption was unaffected by analgesic treatment alone but decreased in all groups after surgery regardless of treatment. Analgesic effects on postoperative activity level were variable. TTS fentanyl at appropriate doses is a cost effective means of delivering basal analgesia following major surgery in pigs.

Pharmacokinetics and renal excretion of diphenhydramine and its metabolites, diphenylmethoxyacetic acid and diphenhydramine-N-oxide, in developing lambs

The developmental disposition of diphenhydramine (DPHM) and its metabolites, diphenylmethoxyacetic acid (DPMA) and DPHM-N-oxide (DPHMNO), was investigated in postnatal lambs. Lambs received a DPHM intravenous (iv) bolus 15 days (Group A; n = 5) or 2 months (Group B; n = 6) after birth. Total body clearance of DPHM in postnatal lambs (Group A = 138.7 +/- 80.5 mL/min/kg; Group B = 165.7 +/- 51.3 mL/min/kg) was similar to the nonplacental clearance values (i.e., the component of fetal total body clearance that is not due to elimination via the placenta) estimated for fetal lamb (116.3 +/- 49. 6 mL/min/kg), and significantly greater than estimates in adult sheep (38.5 +/- 12.3 mL/min/kg). In addition, Group A DPHM renal clearance (CL(r), >1.80 +/- 1.24 mL/min/kg) was similar to that of the fetus (2.06 +/- 0.24 mL/min/kg), and significantly greater than that for Group B (0.26 +/- 0.17 mL/min/kg) and the adult (0.012 +/- 0.005 mL/min/kg). In contrast, similar to the fetal situation, postnatal DPMA CL(r) (Group A = 0.02 +/- 0.02 mL/min/kg; Group B = 0.05 +/- 0.01 mL/min/kg) was significantly less than adult values (0. 53 +/- 0.19 mL/min/kg). Because DPMA is not sequentially metabolized in sheep, the lower CL(r) in postnatal lambs results in longer apparent elimination half-lives of this metabolite (Group A = 90.4 +/- 32.2 h; Group B = 13.13 +/- 11.0 h) compared with that in the adult (2.9 +/- 1.6 h). No age-related difference in DPHMNO CL(R) was observed. Alterations in the CL(r) of DPHM and DPMA are likely related to differences in the rate of development of mechanisms (i.e. , tubular secretion and reabsorption and glomerular filtration rate) involved in the urinary drug excretion of organic acids and bases.

Ontogeny of valproic acid disposition and metabolism: a developmental study in postnatal lambs and adult sheep

The ontogeny of valproic acid (VPA) disposition and metabolism was investigated in developing lambs and adult sheep (Dorset or Suffolk breed). Specifically, we wished to investigate the role of glucuronidation and beta-oxidation on VPA elimination during development. Catheters were implanted in a carotid artery, a jugular vein, and the urinary bladder in 10-day-old (10 d; n = 8), 1-month-old (1 M; n = 4), and 2-month-old lambs (2 M; n = 5). In adult sheep (n = 5), catheters were implanted in a femoral artery and vein. After the administration of a 10 mg/kg VPA i.v. bolus, serial blood samples and cumulative urine samples were collected for 36 h in the adult ewes and for 72 h in the lambs. Due to saturable protein binding, age-related differences in VPA clearance were more obvious when examining the total body clearance of unbound drug (Cl(u)tb). Mean Cl(u)tb increased significantly with age up to 2 months (10 d = 2.65 +/- 1.16 ml/min/kg; 1 M = 5.11 +/- 2.49 ml/min/kg; 2 M = 12.84 +/- 3.88 ml/min/kg) before decreasing to adult levels (7.73 +/- 2.64 ml/min/kg). Similarly, the urinary recovery of the major metabolite, VPA-glucuronide, was significantly less in 10 d lambs (29.2 +/- 16.0% of the dose) when compared with the adult and 2 M groups (both approximately 74% of the dose). No differences with age were observed in the portion of the dose excreted as the beta-oxidation metabolite, 2-n-propyl-3-oxopentanoic acid. The results suggest that alterations in Cl(u)tb with age may be attributable to postnatal development of enzymes involved in VPA glucuronidation.

Disposition of valproic acid in maternal, fetal, and newborn sheep. II: metabolism and renal elimination

Metabolism and renal excretion of valproic acid (VPA) were examined in maternal, fetal, and newborn sheep to identify the underlying reasons for the previously observed reduced VPA clearance in newborn lambs. Plasma and urine from VPA infusion studies in maternal, fetal, and newborn sheep were analyzed for VPA and its metabolites [VPA-glucuronide; beta-oxidation products: (E)-2-ene, (E)-3-ene, and 3-keto VPA; hydroxylated metabolites: 3-hydroxy, 4-hydroxy, and 5-hydroxy VPA (5-OH VPA); and 4-ene VPA, 4-keto VPA, 2-propylglutaric acid, and 2-propylsuccinic acid] using gas chromatography-mass spectrometry. All measured metabolites were detectable in maternal and fetal plasma, with 3-keto and 5-OH VPA being at higher concentrations in the fetus. Plasma concentrations of (E)-2-ene, (E)-3-ene, 3-keto, and 5-OH VPA were higher in the newborn compared with the mother, whereas those of the other metabolites were similar. A smaller percentage of the dose was excreted as VPA-glucuronide in newborn lamb urine (28.3 +/- 12.0%) compared with the mother (77.0 +/- 7.8%). Similarly, a lower fraction of the dose was excreted unchanged in newborn urine (11.0 +/- 5.8%) relative to the urine of the mother (19.3 +/- 5.8%); however, significantly larger percentages were excreted as (E)-2-ene (0.11 +/- 0.04 versus 0.02 +/- 0.01%), 3-keto (11.6 +/- 3.5 versus 1. 6 +/- 0.8%), 4-hydroxy (6.1 +/- 3.2 versus 2.3 +/- 1.3%), and 5-OH VPA (2.2 +/- 0.6 versus. 0.8 +/- 0.6%). The major reason for the reduced VPA elimination in newborn lambs appears to be impaired renal excretion and glucuronidation capacity. As a result, a larger fraction of the dose is channeled to beta-oxidation and hydroxylation pathways. The beta-oxidation activities are high at birth; this may explain the high plasma concentrations of (E)-2-ene and 3-keto VPA observed in newborn lambs and human newborns exposed to VPA.

Disposition of valproic acid in maternal, fetal, and newborn sheep. I: placental transfer, plasma protein binding, and clearance

Separate 24-h maternal and fetal infusions of valproic acid (VPA) were administered to five pregnant sheep at 125 to 138 days gestation (term approximately 145 days) to determine maternal-fetal disposition. The pharmacokinetics of VPA were also investigated in five newborn 1-day-old lambs after a 6-h drug infusion. Plasma, urine, and amniotic and fetal tracheal fluid samples were analyzed for VPA using gas chromatography-mass spectrometry. During maternal drug infusion, the average steady-state fetal/maternal unbound VPA plasma concentration ratio was 0.81 +/- 0.09. Unbound maternal-to-fetal VPA placental clearance (69.0 +/- 20.2 ml/min/kg) was similar to that in the other direction (61.9 +/- 24.2 ml/min/kg); this indicates passive placental diffusion and intermediate placental permeability of VPA in sheep. Newborn unbound VPA clearance (0.66 +/- 0.28 ml/min/kg) was much lower than in the mother (5.4 +/- 2.7 ml/min/kg) or the fetus (62.1 +/- 22.4 ml/min/kg), and exhibited pronounced Michaelis-Menten characteristics. The elimination half-life of the drug was much longer in the newborn (18.6 +/- 2.6 h) relative to the mother (5.6 +/- 1.4 h) and the fetus (4.6 +/- 1.9 h). Thus, VPA elimination in newborn lambs is much slower as compared with adult sheep, a situation similar to that in humans. Plasma protein binding of VPA was saturable, with similar VPA binding capacities and affinities in maternal and fetal plasma. VPA was extensively displaced from binding sites in the newborn lamb during the first 1 to 2 days of life, possibly because of increased plasma free fatty acid concentrations at birth. Thereafter, newborn plasma appeared to have a similar VPA binding capacity but lower affinity compared with the mother and the fetus.

Diphenhydramine disposition in the sheep maternal-placental-fetal unit: gestational age, plasma drug protein binding, and umbilical blood flow effects on clearance

The objective of this study was to examine the interrelationships between maternal and fetal plasma drug protein binding, umbilical blood flow (Q(um)), gestational age (GA), and maternal-fetal diphenhydramine (DPHM) clearances in chronically instrumented pregnant sheep. Maternal and fetal DPHM placental (CL(mf) and CL(fm), respectively) and nonplacental (CL(mo) and CL(fo), respectively) clearances and steady-state plasma protein binding were determined in 18 pregnant sheep at 124 to 140 days' gestation (term, approximately 145 days). The data demonstrated a highly significant fall of approximately 66% in CL(fm) and a decreasing trend in CL(fo) ( approximately 47%) over the GA range studied. However, no such relationships existed between GA and CL(mf) or CL(mo). Concomitant with this was a decrease in fetal DPHM plasma unbound fraction with GA, with no such change being evident in the mother. Both CL(mo) and CL(fo) were related to the respective DPHM plasma unbound fraction. A strong relationship also existed between fetal plasma unbound fraction and CL(fm). Thus, the decrease in fetal unbound fraction of DPHM during gestation could contribute to the fall in CL(fm), and possibly CL(fo). However, over the GA range studied, fetal DPHM free fraction decreased by approximately 47%, whereas CL(fm) fell by approximately 66%. Because fetal unbound fraction and CL(fm) are linearly related, the GA-associated fall in unbound fraction appears to be insufficient to account for the entire decline in CL(fm). In separate studies in pregnant sheep, we observed a approximately 40% fall in weight-normalized Q(um) between 125 and 137 days' gestation. Because CL(fm) for DPHM is similar to that of flow-limited compounds (e.g., ethanol, antipyrine), this decrease in Q(um) may also contribute to the GA-related fall in CL(fm).

Diphenhydramine disposition in the sheep maternal-placental-fetal unit: determinants of plasma drug concentrations in the mother and the fetus

The objective of this study was to identify the important factors that determine plasma concentrations of diphenhydramine (DPHM) in the mother and the fetus after maternal as well as fetal steady-state drug administration. Inter-relationships were evaluated between maternal and fetal placental and nonplacental clearances, plasma protein binding, and steady-state plasma concentrations of DPHM among data obtained from 18 pregnant sheep during late gestation. The major determinant of plasma DPHM concentrations in the mother after maternal as well as fetal administration appears to be maternal plasma protein binding and maternal nonplacental clearance. In contrast, the major determinant of fetal plasma DPHM concentrations after maternal drug administration was the extent of fetal first-pass hepatic drug uptake from the umbilical vein. However, after fetal drug administration, the fetal plasma concentrations were related to the extent of fetal plasma protein binding and fetal placental and nonplacental clearances. The index of fetal-to-maternal placental drug transfer after fetal drug administration (steady-state maternal-to-fetal plasma concentration ratio) was related to steady-state fetal plasma unbound fraction and fetal placental and nonplacental clearance. However, this index was not related to the magnitude of the factors operating on the maternal side of the placenta such as maternal plasma protein binding and maternal nonplacental clearance. This might indicate a lack of complete equilibration of the unbound drug concentrations on the two sides of the placenta at the exchange site.

Morphine pharmacokinetics and pain assessment in premature newborns

OBJECTIVES

To determine morphine pharmacokinetics in premature neonates varying in postconceptional age (PCA) and evaluate behavioral pain response in relationship to serum morphine concentrations.

METHODS

Premature neonates (n = 48), stratified by weeks of PCA (group 1 = 24-27 weeks, group 2 = 28-31 weeks, group 3 = 32-35 weeks, and group 4 = 36-39 weeks) received morphine infusions. Blood samples were drawn at 48, 60, and 72 hours and at discontinuation of morphine, followed by 3 samples obtained during the next 24 hours. Newborns were videotaped during heel lances and restful states, with morphine at steady-state concentrations and without morphine. Pain was assessed by using the Neonatal Facial Coding System (NFCS). Statistical analysis included regression between NFCS score changes from baseline to painful procedure with and without morphine.

RESULTS

Morphine clearance for groups 1, 2, 3, and 4 was calculated as 2.27 +/- 1.07, 3.21 +/- 1.57, 4.51 +/- 1.97, and 7.80 +/- 2.67 mL/kg/min, respectively, and correlated with PCA (r = 0.63, P <.001). Pain measured by facial expression was diminished; however, it did not correlate with morphine concentrations.

CONCLUSION

Morphine clearance in premature neonates is less than reported, increasing with PCA. Facial activity discloses morphine analgesia; however, it is unrelated to morphine concentrations.

Doxorubicin encapsulated in sterically stabilized liposomes exhibits renal and biliary clearance properties that are independent of valspodar (PSC 833) under conditions that significantly inhibit nonencapsulated drug excretion

Coadministration of anticancer drugs and multidrug resistance modulators directed against P-glycoprotein over-expressed in tumors also results in nonspecific blockade of this drug efflux pump in excretory tissues such as the liver and kidneys. These interactions often result in impaired renal and biliary clearance for anticancer agents such as doxorubicin (DOX). In the present investigation, we characterized the excretory processes associated with liposomal DOX administration to elucidate how liposome encapsulation may bypass adverse pharmacokinetic interactions between DOX and (3'-keto-Bmt1)-(Val2)-cyclosporin (Valspodar). Renal and biliary clearance properties of liposome-encapsulated DOX were compared with those for nonencapsulated DOX in the presence and absence of Valspodar using an instrumented rat model with implanted jugular vein and bile duct catheters for continuous sampling. Two types of liposomal DOX formulations were used, a drug-permeable egg phosphatidyl choline/cholesterol system and a sterically stabilized polyethylene glycol/1,2 distearoyl-sn-glycero-3-phosphocholine/cholesterol system to establish the relative roles of liposome-encapsulated and released drug on the pharmacokinetic and excretion alterations induced by Valspodar. DOX and its primary metabolites were quantitated using high-performance liquid chromatography. When Valspodar was coadministered with nonencapsulated DOX, 3.5- and 37.5-fold reductions in renal clearance (CLr) and biliary clearance (CLb), respectively, were observed, which resulted in increased plasma DOX concentrations and total exposure. However, Valspodar-induced alterations in CLr and CLb were less profound with egg phosphatidyl choline/cholesterol DOX (1.7- and 2.0-fold reductions, respectively) and negligible with the long-circulating polyethylene glycol-containing liposomal formulation. These results indicate that liposomes may circumvent Valspodar-induced DOX pharmacokinetic changes by reducing the rate of drug excretion in liver and kidney tissue to a level that is within the renal and biliary excretion capacity in the presence of P-glycoprotein blockade.

Comparative formation, distribution, and elimination kinetics of diphenylmethoxyacetic acid (a diphenhydramine metabolite) in maternal and fetal sheep

Deamination to diphenylmethoxyacetic acid (DPMA) is the major route of diphenhydramine (DPHM) clearance in many species. In this study, we assessed the contribution of this pathway to nonplacental DPHM elimination and disposition of DPMA in maternal and fetal sheep. Paired maternal-fetal experiments were conducted in five chronically catheterized pregnant sheep (124-140 days gestation) with an appropriate washout period in between. Both maternal and fetal dosing experiments involved administration of an i.v bolus of deuterium-labeled DPMA ([2H10]-DPMA) combined with a 6-h infusion of DPHM (or a bolus of unlabeled DPMA with an infusion of deuterium-labeled DPHM). Maternal and fetal arterial plasma and urine samples were collected and analyzed for DPMA, [2H10]-DPMA, DPHM, and deuterium-labeled DPHM concentrations using gas chromatography-mass spectrometry. The preformed DPMA (or [2H10]-DPMA) had a substantially lower clearance (maternal: 0.55 +/- 0.18 versus 40.9 +/- 14.0 ml/min/kg; fetal: 0.37 +/- 0.11 versus 285. 6 +/- 122.2 ml/min/kg) and steady-state volume of distribution (Vdss, maternal: 0.10 +/- 0.02 versus 2.1 +/- 1.1 l/kg; fetal: 0.40 +/- 0. 06 versus 13.1 +/- 3.1 l/kg) as compared with the parent drug. The contribution of DPMA formation to maternal and fetal DPHM nonplacental clearance in vivo was 1.78 +/- 2.12% and 0.87 +/- 0.56%, respectively, indicating that DPMA formation is not a major route of DPHM clearance in fetal or maternal sheep. The recoveries of DPMA (or [2H10]-DPMA) in maternal urine were 88.0 +/- 6.5 and 92.1 +/- 7. 4% of the administered dose during maternal and fetal dosing experiments, respectively. Thus, this metabolite does not appear to be secondarily metabolized in fetal or maternal sheep. These findings are in contrast to other species (dog, rhesus monkey, human) where DPMA and its conjugates constitute approximately 40 to 60% of the total DPHM metabolites.