Kenneth R. Knecht

Rapid reduction in donor-specific anti-human leukocyte antigen antibodies and reversal of antibody-mediated rejection with bortezomib in pediatric heart transplant patients.

Background. High titer donor-specific antibodies (DSA) and positive crossmatch in cardiac transplant recipients is associated with increased mortality from antibody-mediated rejection (AMR). Although treatment to reduce anti-human leukocyte antigen antibodies using plasmapheresis, intravenous immunoglobulin, and rituximab has been reported to be beneficial, in practice these are often ineffective. Moreover, these interventions do not affect the mature antibody producing plasma cell. Bortezomib, a proteasome inhibitor active against plasma cells, has been shown to reduce DSA in renal transplant patients with AMR. We report here the first use of bortezomib for cardiac transplant recipients in four pediatric heart recipients with biopsy-proven AMR, hemodynamic compromise, positive crossmatch, and high titer class I DSA. Methods. Patients received four intravenous dose of bortezomib (1.3 mg/m2) over 2 weeks with plasmapheresis and rituximab. DSA specificity and strength (mean fluorescence intensity) was determined with Luminex. All had received previous treatment with plasmapheresis, intravenous immunoglobulin, and rituximab that was ineffective. Results. AMR resolved in all patients treated with bortezomib with improvement in systolic function, conversion of biopsy to C4d negative in three patients and IgG negative in one patient, and a prompt, precipitous reduction in DSAs. In three patients who received plasmapheresis before bortezomib, plasmapheresis failed to reduce DSA. In one case, DSA increased after bortezomib but decreased after retreatment. Conclusions. Bortezomib reduces DSA and may be an important adjunct to treatment of AMR in cardiac transplant recipients. Bortezomib may also be useful in desensitization protocols and in prevention of AMR in sensitized patients with positive crossmatch and elevated DSA.

Predictors of myocardial recovery in pediatric tachycardia-induced cardiomyopathy

BACKGROUND Tachycardia-induced cardiomyopathy (TIC) carries significant risk of morbidity and mortality, although full recovery is possible. Little is known about the myocardial recovery pattern. OBJECTIVE The purpose of this study was to determine the time course and predictors of myocardial recovery in pediatric TIC. METHODS An international multicenter study of pediatric TIC was conducted. Children ≤18 years with incessant tachyarrhythmia, cardiac dysfunction (left ventricular ejection fraction [LVEF] <50%), and left ventricular (LV) dilation (left ventricular end-diastolic dimension [LVEDD] z-score ≥2) were included. Children with congenital heart disease or suspected primary cardiomyopathy were excluded. Primary end-points were time to LV systolic functional recovery (LVEF ≥55%) and normal LV size (LVEDD z-score <2). RESULTS Eighty-one children from 17 centers met inclusion criteria: median age 4.0 years (range 0.0-17.5 years) and baseline LVEF 28% (interquartile range 19-39). The most common arrhythmias were ectopic atrial tachycardia (59%), permanent junctional reciprocating tachycardia (23%), and ventricular tachycardia (7%). Thirteen required extracorporeal membrane oxygenation (n = 11) or ventricular assist device (n = 2) support. Median time to recovery was 51 days for LVEF and 71 days for LVEDD. Two (4%) underwent heart transplantation, and 1 died (1%). Multivariate predictors of LV systolic functional recovery were age (hazard ratio [HR] 0.61, P = .040), standardized tachycardia rate (HR 1.16, P = .015), mechanical circulatory support (HR 2.61, P = .044), and LVEF (HR 1.33 per 10% increase, p=0.005). For normalization of LV size, only baseline LVEDD (HR 0.86, P = .008) was predictive. CONCLUSION Pediatric TIC resolves in a predictable fashion. Factors associated with faster recovery include younger age, higher presenting heart rate, use of mechanical circulatory support, and higher LVEF, whereas only smaller baseline LV size predicts reverse remodeling. This knowledge may be useful for clinical evaluation and follow-up of affected children.

Time-dependent action of carbon monoxide on the newborn cerebrovascular circulation

Carbon monoxide (CO) causes cerebral arteriolar dilation in newborn pigs by the activation of large-conductance Ca(2+)-activated K(+) channels. In adult rat cerebral and skeletal muscle arterioles, CO has been reported to produce constriction caused by the inhibition of nitric oxide (NO) synthase (NOS). We hypothesized that, in contrast to dilation to acute CO, more prolonged exposure of newborn cerebral arterioles to elevated CO produces constriction by reducing NO. In piglets with closed cranial windows, pial arteriolar responses to isoproterenol (10(-6) M), sodium nitroprusside (SNP; 10(-7) and 3 x 10(-7) M), and L-arginine ethyl ester (L-Arg; 10(-5) and 10(-4) M) were determined before and after 2 h of treatment with CO. CO (10(-7) M) caused transient dilation and had no further effects. CO (2 x 10(-7) and 10(-6) M) initially caused vasodilation, but over the 2-h exposure, pial arterioles constricted and removal of the CO caused dilation. Exposure to elevated CO (2 h) did not alter dilation to SNP or isoproterenol. Conversely, the NOS substrate L-Arg caused dilation before CO that was progressively lost over 90 min of elevated CO. If NO was held constant, CO caused dilation that was sustained for 2 h. We conclude that in neonates, cerebral arteriole responses to CO are biphasic: dilation to acute elevation with subsequent constriction from NOS inhibition after more prolonged exposure. As a result, short episodic production of CO allows function as a dilator gasotransmitter, whereas prolonged elevation can reduce NO to elevate cerebrovascular tone. The interaction between heme oxygenase/CO and NOS/NO could form a negative feedback system in the control of cerebral vascular tone.

NTproBNP as a marker of rejection in pediatric heart transplant recipients

Knecht KR, Alexander ML, Swearingen CJ, Frazier EA. NTproBNP as a marker of rejection in pediatric heart transplant recipients.

Quantification, identification, and relevance of anti-human leukocyte antigen antibodies formed in association with the berlin heart ventricular assist device in children.

Background Ventricular assist devices (VADs) are increasingly being used in pediatric patients to provide long-term cardiac support. One potential complication of VAD therapy is the development of antibodies directed against human leukocyte antigens (HLA). This phenomenon has not been well described with the Berlin Heart EXCOR VAD, the most commonly used VAD in pediatric patients. Methods The records of all pediatric patients undergoing VAD support using the Berlin Heart device at our institution between April 2005 and August 2011 were reviewed retrospectively. Demographic and clinical data regarding the VAD course were collected. Assessment of anti-HLA antibodies was performed using Luminex, and antibodies were quantified using mean fluorescence intensity (MFI). Assessment for anti-HLA antibodies was performed before VAD implantation and in serial fashion after VAD implantation. Clinically significant anti-HLA antibodies (sensitization) were defined by an MFI of more than 1000. Results Thirty-six patients were supported with the Berlin Heart VAD; 13 met inclusion criteria. The majority (85%) carried the diagnosis of dilated cardiomyopathy. Evidence of sensitization pre-VAD was found in 69%; new-onset sensitization (the development of new antibodies on VAD) occurred in 69%. All patients survived to transplantation. In two patients, the retrospective crossmatch was positive, but only in one patient was the crossmatch positive for antibodies formed while on VAD. Conclusions Using Luminex and MFI quantification, anti-HLA antibodies are common before VAD implantation in pediatric patients. While on VAD support, new anti-HLA antibodies formed in a majority, but the immediate impact of these antibodies appears to be limited.

Statin therapy is not associated with improved outcomes after heart transplantation in children and adolescents

BACKGROUND Although used routinely, the pleiotropic benefits of statins remain understudied in children after heart transplantation. We hypothesized that statin therapy would reduce the incidence of rejection, cardiac allograft vasculopathy (CAV) and post-transplant lymphoproliferative disease (PTLD). METHODS This study was a retrospective review of 964 pediatric (ages 5 to 18 years) heart transplant recipients in the multicenter Pediatric Heart Transplant Study registry from 2001 to 2012. Patients were excluded if they were undergoing re-transplantation, survived <1 year post-transplant, or had missing data regarding statin use. The effects of statins beyond the first year were estimated by Kaplan-Meier and Cox regression multivariable analysis for freedom from PTLD, rejection requiring treatment, any severity of CAV, and survival. RESULTS Statin use was variable among participating centers with only 30% to 35% of patients ≥10 years of age started on a statin at <1 year post-transplant. After the first year post-transplant, statin-treated children (average age at transplant 13.24 ± 3.29 years) had significantly earlier rejection (HR 1.42, 95% CI 1.11 to 1.82, p = 0.006) compared with untreated children (transplanted at 12 ± 3.64 years) after adjusting for conventional risk factors for rejection. Freedom from PTLD, CAV and overall survival up to 5 years post-transplant were not affected by statin use, although the number of events was small. CONCLUSIONS Statin therapy did not confer a survival benefit and was not associated with delayed onset of PTLD or CAV. Early (<1 year post-transplant) statin therapy was associated with increased later frequency of rejection. These findings suggest that a prospective trial evaluating statin therapy in pediatric heart transplant recipients is warranted.

Distinct effects of intravascular and extravascular angiotensin II on cerebrovascular circulation of newborn pigs

Angiotensin II (AngII) is important in regulation of vascular resistance and control of blood flow among organs and tissues. The effect of AngII on the cerebral microvasculature may be mediated or altered by endothelial-derived signals. The aim of this study was to test the hypothesis that blood AngII dilates neonatal pial arterioles via an endothelial-dependent mechanism but brain AngII can constrict pial arterioles by activating smooth muscle AT1 receptors. Studies used anesthetized newborn pigs with surgically implanted closed cranial windows. AngII was given either by infusion into the carotid artery ipsilateral to the cranial window or topically. Intracarotid infusion of AngII dilated pial arterioles. The dilation was blocked by systemic administration of the AT1-receptor antagonist, losartan, but unaffected by topical losartan. Topical AngII also caused dilation, but this dilation was converted to constriction by topical losartan. In piglets pretreated with the angiotensin-converting enzyme (ACE) inhibitor, enalapril, topical AngII constricted, rather than dilated, pial arterioles. In enalapril-treated piglets, light/dye endothelial injury blocked dilation to intracarotid AngII but did not affect constriction to topical AngII. Either indomethacin or l-nitroarginine methyl ester blocked the dilation to intraluminal AngII, but neither affected constriction to topical AngII. Chromium mesoporphyrin, that inhibits heme oxygenase, did not affect responses to either topical or intravascular AngII. These data are consistent with the hypotheses that: (a) circulating AngII dilates pial arterioles via endothelial AT1 receptor-derived relaxing factors, notably prostanoids and nitric oxide; (b) direct AT1 receptor activation on the brain side of the blood–brain barrier by AngII causes AT1 receptor-mediated constriction that can mask underlying AT1 receptor-independent dilation when ACE is inhibited. Clinical manipulation of the renin–angiotensin system will have disparate actions on cerebral circulation depending on the functional integrity of the intima and ACE.

Maintenance steroid use at 30 days post-transplant and outcomes of pediatric heart transplantation: A propensity matched analysis of the Pediatric Heart Transplant Study database

BACKGROUND Maintenance steroid (MS) use in pediatric heart transplantation is variable. The purpose of this study was to evaluate the impact of MS use on graft outcomes. METHODS All patients <18 years old in the Pediatric Heart Transplant Study database at the time of first heart transplant between 1993 and 2011 who survived ≥30 days post-transplant and were from centers with a protocolized approach to MS use were included (N = 2,178). Patients were grouped by MS use at 30 days post-transplant as MS+ or MS- (no MS use). Propensity score analysis was used to generate matched groups of MS+ and MS- patients based on pre-transplant and peri-transplant factors. Kaplan-Meier survival analysis was used to compare freedom from graft loss, graft loss secondary to rejection, rejection, rejection with severe hemodynamic compromise (RSHC), malignancy, and infection between groups. RESULTS Of patients, 1,393 (64%) were MS+ and 785 (36%) were MS-. There were 315 MS- patients who had propensity matched MS+ controls. Kaplan-Meier estimates showed no difference in graft loss (p = 0.9) or graft loss secondary to rejection (p = 0.09). At 1 year post-transplant, there was no difference in freedom from rejection (p = 0.15) or malignancy (p = 0.07), but there was lower freedom from RSHC and infection in the MS- group (p = 0.05 and p = 0.02, respectively). CONCLUSIONS MS use at 30 days post-transplant was not associated with enhanced graft survival after pediatric heart transplant. MS- patients had a higher incidence of RSHC and infection. These risks should be taken into consideration when determining MS use for pediatric recipients of heart transplants.

Antibody-mediated rejection is associated with impaired graft function in pediatric heart transplant recipients.

Antibody-mediated rejection is associated with impaired graft function in pediatric heart transplant recipients Kenneth R. Knecht, MD, Ashley Glover, Amy M. Dossey, MD, Mallik Rettiganti, PhD, Jeffrey Gossett, MSc, and Elizabeth A. Frazier, MD From the Cardiology Section; and the Biostatistics Section, Department of Pediatrics, University of Arkansas for Medical Sciences, Arkansas Children’s Hospital, Little Rock, Arkansas

Korotkoff Sounds in Neonates, Infants, and Toddlers

Korotkoff sounds (KSs) are the clinical norm for noninvasively estimating systemic arterial blood pressure (BP) in children and adults. Their existence and reliability in children <3 years old was unknown. This study addressed the presence and accuracy of KSs in children <3 years. Measurements of the first KS (K1), K4, and K5 (the commonly used sounds) were compared with invasive measurements of systolic and diastolic BP in > or =3 inflations/subject. Subjects were prospectively divided by age <1 (n = 20), 1 to 12 (n = 29), and 13 to 36 months (n = 17). KSs were audible with low frequency in subjects <1 month old and they were excluded from further analysis. In 143 inflations, K1 was audible in 125, K4 in 104, and K5 in 114; the frequency of audible KSs increased with subject age. Reliability of KSs as a surrogate for measured systolic and diastolic BP was assessed using paired t tests. K1 was not significantly different for the entire group or any subgroup. K4 was significantly different in all age groups. K5 was significantly different in only subjects <6 months. In conclusion, K1, K4, and K5 are routinely audible and K1 and K5 provide a reliable estimate of systolic and diastolic BP in children age 1 to 36 months.