Serum alkaline phosphatase reflects post-Fontan hemodynamics in children

Application of Principal Component Analysis to Heterogenous Fontan Registry Data Identifies Independent Contributing Factors to Decline

Single ventricle heart disease is a severe and life-threatening illness, and improvements in clinical outcomes of those with Fontan circulation have not yet yielded acceptable survival over the past two decades. Patients are at risk of developing a diverse variety of Fontan-associated comorbidities that ultimately requires heart transplant. Our observational cohort study goal was to determine if principal component analysis (PCA) applied to data collected from a substantial Fontan cohort can predict functional decline (N=140). Heterogeneous data broadly consisting of measures of cardiac and vascular function, exercise (VO2max), lymphatic biomarkers, and blood biomarkers were collected over 11 years at a single site; in that time, 16 events occurred that are considered here in a composite outcome measure. After standardization and PCA, principal components (PCs) representing >5% of total variance were thematically labeled based on their constituents and tested for association with the composite outcome. Our main findings suggest that the 6th PC (PC6), representing 7.1% percent of the total variance in the set, is greatly influenced by blood serum biomarkers and superior vena cava flow, is a superior measure of proportional hazard compared to EF, and displayed the greatest accuracy for classifying Fontan patients as determined by AUC. In bivariate hazard analysis, we found that models combining systolic function (EF or PC5) and lymphatic dysfunction (PC6) were most predictive, with the former having the greatest AIC, and the latter having the highest c-statistic. Our findings support our hypothesis that a multifactorial model must be considered to improve prognosis in the Fontan population.

Growth in Children with a Fontan Circulation

OBJECTIVE

To evaluate growth in a population of patients with Fontan circulation.

STUDY DESIGN

We performed a cross-sectional evaluation of patients followed in our multidisciplinary Fontan clinic from January 2011 through August 2015. We reviewed the historical data, anthropometry, clinical, and laboratory studies and performed bivariate and multivariate analysis of factors associated with height z score.

RESULTS

Patients (n = 210) were included in the study at median age 11.07 years (8.3, 14.73 years) (43% female); 138 (65%) had a dominant right systemic ventricle and 92 (44%) hypoplastic left heart syndrome. Median age at completion of Fontan circulation was 31 months (7.6, 135.8 months). Median height z score was -0.58 (-1.75, 0.26). Twenty-five (12%) had current or past history of protein-losing enteropathy (PLE). Median height z score for those with current or past history of PLE was -2.1 (-2.46, 1.24). Multivariate analysis revealed positive associations between height z score and body mass index z score, time since Fontan, mid-parental height, dominant systemic ventricle type, and serum alkaline phosphatase. Height correlated negatively with known genetic syndrome, PLE, use of stimulant or oral steroid medication.

CONCLUSIONS

Children with Fontan circulation have mild deficits in height, with greater deficits in those with PLE. Height z score improves with time postsurgery. Improving weight, leading to improved body mass index, may be a modifiable factor that improves growth in those who are underweight. Biochemical markers may be helpful screening tests for high-risk groups in whom to intensify interventions.

Prevalence of Subclinical Enteric Alpha-1-Antitrypsin Loss in Children with Univentricular Circulation Following Total Cavopulmonary Connection

Protein-Losing Enteropathy post Fontan palliation is associated with significant morbidity and mortality. To date, very little research has been carried out to improve early identification of enteric protein loss in these patients. We hypothesise that subclinical enteric protein loss may occur in patients post Fontan surgery. A cross-sectional study was performed on 43 patients post Fontan surgery. We collected specimens of stool and blood from patients with no symptoms of protein-losing enteropathy post Fontan. Stool samples were assessed for alpha one antitrypsin. The stool samples of two patients were discarded, leaving 41 stool samples. Blood samples were also collected to review albumin, C-reactive protein, liver and renal function. Twenty-eight (65%) of those enrolled were male. The median (IQR) age between Fontan and collection of study specimens was 3.5 (2-7) years. Two (5%) patients had elevated levels of alpha-1-antitrypsin. There was no correlation between blood biochemistry and elevated stool alpha-1-antitrypsin. Subclinical protein loss is rare in asymptomatic children after Fontan procedure with only 5% of patients having elevated stool alpha-1-antitrypsin but no other symptoms. These findings may relate to our small cohort size and the time to testing post cardiac surgery. Future longitudinal follow-up studies should assess the ability of alpha-1-antitrypsin to provide earlier detection of protein-losing enteropathy in asymptomatic patients post Fontan. Given the serious prognosis of protein-losing enteropathy in this patient group, further work is warranted.

Alkaline Phosphatase in Infant Cardiopulmonary Bypass: Kinetics and Relationship to Organ Injury and Major Cardiovascular Events

OBJECTIVES

To determine the kinetics of alkaline phosphatase (AP) activity and concentration after infant cardiopulmonary bypass, including isoform-specific changes, and to measure the association between postoperative AP activity and major postoperative cardiovascular events, organ injury/dysfunction, and postoperative support requirements STUDY DESIGN: Prospective cohort study of 120 infants ≤120 days of age undergoing cardiopulmonary bypass. AP total and isoform-specific activity was assessed at 6 time points (preoperation, rewarming, 6, 24, 48, and 72 hours postoperation). Low AP activity was defined as ≤80 U/L. AP concentrations and biomarkers of organ injury/dysfunction were collected through 24 hours postoperation. Major cardiovascular events were defined as cardiac arrest, mechanical circulatory support, or death.

RESULTS

AP activity loss occurred primarily during the operation (median decrease 89 U/L; P < .0001) secondary to decreased bone and liver 2 isoforms. Activity declined through 24 hours in 27% of patients. AP activity strongly correlated with serum concentration (r = 0.87-0.91; P < .0001). Persistent low AP activity at 72 hours was associated independently with occurrence of a major cardiac event (OR 5.6; P < .05). Early AP activity was associated independently with subsequent vasoactive-inotropic score (P < .001), peak lactate (P < .0001), peak creatinine (P < .0005), N-terminal pro-brain natriuretic peptide (P < .05), and intestinal fatty acid binding protein (P < .005).

CONCLUSIONS

AP activity decreases during infant cardiopulmonary bypass and may continue to decrease for 24 hours. Activity loss is secondary to decreased bone and liver 2 isoform concentrations. Early low AP activity is associated independently with subsequent postoperative support and organ injury/dysfunction, and persistence of AP activity ≤80 U/L at 72 hours is associated independently with increased odds of major cardiovascular events.

Alkaline Phosphatase: A Biomarker of Cardiac Function in Pediatric Patients

Myocardial dysfunction and heart failure are common in pediatric patients with congenital and acquired heart disease. Alkaline phosphatase (AP) has been suggested as a biomarker for myocardial dysfunction after Fontan operation. We hypothesized that pediatric patients with myocardial dysfunction requiring orthotopic heart transplant (OHT) have diminished AP compared to normal. A retrospective review was performed in all patients who underwent OHT at Arkansas Children's Hospital between January 2007 and October 2012. Anatomic diagnoses, therapeutic interventions, and ventricular ejection fraction (EF) were recorded. Z scores for AP levels in the study group were determined by comparing the observed AP levels to age- and gender-matched normative values. T tests were performed to compare the mean AP Z score prior to and after OHT. p values <0.05 were considered statistically significant. During the study period, 124 OHTs were performed. Complete study data were available and analyzed from 71/124 patients (mean age at OHT 3.9 years; 51% female). The mean AP Z score was significantly lower in the study group prior to OHT compared to normal (p < 0.0001). The initiation of ACE inhibitor therapy prior to OHT was associated with a significant increase in AP and the ventricular EF (p < 0.001 for both). Treatment with milrinone was associated with an increase in EF. AP is significantly lower in pediatric patients with myocardial dysfunction prior to OHT compared to normal. AP increases significantly after the initiation of therapies to improve myocardial function. Diminished AP is an indicator of myocardial dysfunction in pediatric patients.

Abnormalities in serum biomarkers correlate with lower cardiac index in the Fontan population

BACKGROUND

Fontan survivors have depressed cardiac index that worsens over time. Serum biomarker measurement is minimally invasive, rapid, widely available, and may be useful for serial monitoring. The purpose of this study was to identify biomarkers that correlate with lower cardiac index in Fontan patients. Methods and results This study was a multi-centre case series assessing the correlations between biomarkers and cardiac magnetic resonance-derived cardiac index in Fontan patients ⩾6 years of age with biochemical and haematopoietic biomarkers obtained ±12 months from cardiac magnetic resonance. Medical history and biomarker values were obtained by chart review. Spearman's Rank correlation assessed associations between biomarker z-scores and cardiac index. Biomarkers with significant correlations had receiver operating characteristic curves and area under the curve estimated. In total, 97 cardiac magnetic resonances in 87 patients met inclusion criteria: median age at cardiac magnetic resonance was 15 (6-33) years. Significant correlations were found between cardiac index and total alkaline phosphatase (-0.26, p=0.04), estimated creatinine clearance (0.26, p=0.02), and mean corpuscular volume (-0.32, p<0.01). Area under the curve for the three individual biomarkers was 0.63-0.69. Area under the curve for the three-biomarker panel was 0.75. Comparison of cardiac index above and below the receiver operating characteristic curve-identified cut-off points revealed significant differences for each biomarker (p<0.01) and for the composite panel [median cardiac index for higher-risk group=2.17 L/minute/m2 versus lower-risk group=2.96 L/minute/m2, (p<0.01)].

CONCLUSIONS

Higher total alkaline phosphatase and mean corpuscular volume as well as lower estimated creatinine clearance identify Fontan patients with lower cardiac index. Using biomarkers to monitor haemodynamics and organ-specific effects warrants prospective investigation.

Bone-Specific Alkaline Phosphatase in Patients Who Have Undergone the Fontan Operation

Bone-specific alkaline phosphatase (BALP) is produced by osteoblasts. A recent series noted a positive association between cardiac index (CI) and BALP in patients with Fontan circulation. CI is low at baseline in these patients, and small decreases in CI may result in diverting of blood away from bone. We prospectively enrolled 15 patients (males ≤ 14 yo, females ≤ 12 yo) who had previously undergone Fontan operation and were undergoing cardiac catheterization. Serum BALP was measured at catheterization, and analysis performed to evaluate association between age-/gender-specific BALP z-score and CI as well as other patient variables. The median age at catheterization was 5.6 years (3.1-13.1), and time from Fontan was 1.5 years (0.1-12.1). The median superior vena cava saturation (SVC) was 65 % (52-74), median average between SVC and inferior vena cava (IVC) saturations was 62.5 % (51-70), and median CI was 3.8 L/min/m(2) (2.0-8.4). The median BALP was 65 IU/L and BALP z-score was -2.1 (-3.2 to 0.9). BALP z-score was not associated with CI (ρ = -0.1, p = 0.7), but a positive correlation was noted with the average of SVC and IVC saturation (ρ = 0.5, p = 0.052) and with SVC saturation (ρ = 0.4, p = 0.07), both nearly reaching statistical significance. In our cohort of children with Fontan circulation undergoing catheterization, BALP z-score was not associated with CI, but an association with estimates of mixed venous saturation was noted that nearly reached statistical significance. We hypothesize that BALP is a marker of oxygen delivery in those with Fontan circulation and may represent a valuable biomarker in this population.

Low serum 25-hydroxyvitamin D levels and secondary hyperparathyroidism in Fontan patients

BACKGROUND

Limited data exist on the vitamin D status in Fontan patients. We determined the prevalence and potential risk factors of vitamin D deficiency in this patient subset. Methods and results Data were collected from 27 Fontan patients (55.6% male, mean age 8.1±5.3 years). Protein-losing enteropathy was diagnosed in six patients (22.2%). Vitamin D deficiency was defined as a serum 25-hydroxyvitamin D level of <20 ng/ml. The neutrophil-to-lymphocyte ratio, a marker of systemic inflammation, was calculated. Associations between laboratory measurements and patient characteristics were explored. Mean serum 25-hydroxyvitamin D level was 14.1±10.4 ng/ml. Vitamin D deficiency was found in 19/27 patients (70.3%). Only skin type was associated with vitamin D deficiency (p=0.04). Hyperparathyroidism was present in 5/21 (23.8%) patients, and was more prevalent in patients with protein-losing enteropathy (p<0.001). Parathyroid hormone levels correlated with parameters of systemic inflammation (neutrophil-to-lymphocyte ratio: r=0.484, p=0.026; relative lymphocyte count: r=-0.635, p=0.002). Vitamin D supplementation significantly increased serum 25-hydroxyvitamin D levels (p<0.0001), and was accompanied by a reduction in parathyroid hormone concentrations (p=0.032).

CONCLUSIONS

A high prevalence of vitamin D deficiency was found among Fontan patients, independent of age, time after Fontan procedure, ventricular morphology, and presence of protein-losing enteropathy. A potentially important link between parathyroid hormone levels and systemic inflammation is suggested.

Feeding, growth, nutrition, and optimal interstage surveillance for infants with hypoplastic left heart syndrome

Improvement in operative survival of patients with hypoplastic left heart syndrome has led to increasing emphasis on prevention of interstage mortality. Many centres have improved interstage results through programmes of home monitoring following discharge after the Norwood (Stage 1) operation. Experience with heightened interstage surveillance has identified failure to thrive during infancy as a modifiable risk factor for this population, one that has been linked to concerning outcomes at subsequent palliative surgeries. Ensuring normal growth as an infant has thus become a priority of management of patients with functionally univentricular hearts. Herein, we review the existing evidence for best practices in interstage surveillance and optimal nutrition in infants with functionally univentricular hearts. In addition, we highlight data presented at HeartWeek 2011, from Cardiology 2011, the 15th Annual Update on Pediatric and Congenital Cardiovascular Disease, and the 11th Annual International Symposium on Congenital Heart Disease.

Three-dimensional cortical bone microstructure in a rat model of hypoxia-induced growth retardation

Little is known about hypoxia-induced modification of the canal network in the cortical bone despite its involvement in intracortical vascularity and bone blood supply. In this study, we examined the effect of chronic hypoxia on the canal network in postnatal bone. Tibiae were harvested from 4- and 8-week-old rats (hyp-4 and -8, n = 8 each), whose growth was retarded owing to postnatal exposure to hypoxia (12-14% O₂), and from 3- and 4-week-old normoxic rats (cnt-4 and -5, n = 8 each), which were similar in tibial length and cortical cross-sectional area to hyp-4 and -8, respectively. The diaphyseal canals were detected by monochromatic synchrotron radiation CT with a 3.1-μm voxel resolution. The anatomical properties of the canal network were compared between age- or size-matched hypoxic and normoxic groups. The canals were larger in diameter, were more densely distributed and connected, and opened into the marrow cavity with a higher density in hyp-4 than in cnt-4. The canal density and connectivity were also higher in hyp-4 than in cnt-3. The canal diameter, density, and connectivity were smaller in hyp-8 than in cnt-4; however, the densities of endocortical and periosteal canal openings did not differ between hyp-8 and cnt-4. We concluded that chronic hypoxia enhanced the formation of cortical canal networks at the postnatal developmental stage, probably facilitating intra- and transcortical vascularization and bone perfusion accordingly.

Anthropometric measures after Fontan procedure: implications for suboptimal functional outcome

BACKGROUND

Abnormal height and adiposity are observed after the Fontan operation. These abnormalities may be associated with worse functional outcome.

METHODS

We analyzed data from the National Heart, Lung, and Blood Institute Pediatric Heart Network cross-sectional study of Fontan patients. Groups were defined by height (z-score<-1.5 or≥-1.5) and body mass index (body mass index [BMI] z-score<-1.5 or -1.5 to 1.5 or≥1.5). Associations of anthropometric measures with measurements from clinical testing (exercise, echocardiography, magnetic resonance imaging) were determined adjusting for demographics, anatomy, and pre-Fontan status. Relationships between anthropometric measures and functional health status (FHS) were assessed using the Child Health Questionnaire.

RESULTS

Mean age of the cohort (n=544) was 11.9±3.4 years. Lower height-z patients (n=124, 23%) were more likely to have pre-Fontan atrioventricular valve regurgitation (P=.029), as well as orthopedic and developmental problems (both P<.001). Lower height-z patients also had lower physical and psychosocial FHS summary scores (both P<.01). Higher BMI-z patients (n=45, 8%) and lower BMI-z patients (n=53, 10%) did not have worse FHS compared to midrange BMI-z patients (n=446, 82%). However, higher BMI-z patients had higher ventricular mass-to-volume ratio (P=.03) and lower % predicted maximum work (P=.004) compared to midrange and lower BMI-z patients.

CONCLUSIONS

Abnormal anthropometry is common in Fontan patients. Shorter stature is associated with poorer FHS and non-cardiac problems. Increased adiposity is associated with more ventricular hypertrophy and poorer exercise performance, which may have significant long-term implications in this at-risk population.

Insights After 40 Years of the Fontan Operation

Fontan’s visionary operation and its modifications over the ensuing decades have re-established nonturbulent flow and substantially reduced cyanosis for patients with severe hypoplasia of one ventricle. However, a long list of largely unexpected sequelae has emerged over the last 40 years. Although it is not difficult to understand how care providers could become discouraged, a number of myths have arisen, which we will attempt to dispel with real-world counterexamples as well as with lessons learned from other disciplines: evolutionary, developmental, and computational biology. We argue that distinctive biochemical abnormalities pointing to dysfunction in multiple organs, including the largest organ system in the body, the endothelium, occur long before grossly observable changes in cardiac imaging can be recognized. With a rational redesign of both our surveillance scheme and our wellness strategies, we hope that Fontan survivors and their families, as well as physicians, nurses, and therapists, will see why Fontan’s principle remains just as vibrant today as it was in 1971.