Background: Measurement of trough levels for calcineurin inhibitors by venipuncture sampling is a mainstay of patient management in solid organ transplant recipients but challenging in pediatric patients. Volumetric Absorptive Microsampling (VAMS) is a patient-friendly, minimally invasive sampling technique to accurately collect blood. An assay for measurement of tacrolimus in blood using VAMS, coupled with parallel reaction monitoring (PRM) mass spectrometry, was validated in pediatric heart transplant patients. Methods: Tacrolimus was measured by a newly developed high-resolution PRM assay and compared with low-resolution tandem mass spectrometry (MRM). Dried blood samples were collected from pediatric heart transplant patients (n = 35) using VAMS devices and a satisfaction survey was completed by patients/guardians. Tacrolimus concentrations were compared across whole liquid blood, dried blood spots, and capillary blood, and shipping stability determined. Results: The PRM assay was linear over a range 1-50 ng/mL, similar to MRM but had greater specificity due to reduced background noise. No significant differences in tacrolimus concentrations were observed between VAMS and venous blood. Tacrolimus dried on VAM tips was stable for 14 days and concentrations were unaffected by postal shipping. The variability in two simultaneously collected at-home patient samples was minimal - average concentration difference was 0.12 ± 0.94 ng/mL (p = 0.6) between paired samples. Conclusion: A high resolution PRM mass spectrometry assay was developed for home-based dried blood collections for therapeutic monitoring of tacrolimus. The advantage of PRM was enhanced specificity and the VAMS devices provided a simple and convenient approach to blood sampling at home in pediatric heart transplant patients.
Coronary angiography remains the standard for diagnosis of cardiac transplant vasculopathy (CAV), but it is invasive. Non-invasively derived left ventricle (LV) global myocardial work (GMW) indices have not been evaluated. We aimed to assess for correlations between LV GMW and the presence of CAV in a pediatric population. 24 heart transplant patients and 24 normal controls were prospectively enrolled. Patients were age-matched into groups with: orthotopic heart transplant and CAV (OHT-CAV; 6 patients, 33% male, mean age 13.5 years [SD 4.2]), orthotopic heart transplant without CAV (OHT; 18 patients, 67% male, mean age 11.1 years [SD 4.8]), and normal healthy controls (42% male, mean age 12.8 years [SD 5.0]). Transplant patients underwent cardiac catheterization with coronary angiography within 3 months of echocardiogram. Post-processing of echocardiograms with speckle-tracking echocardiography and derivation of GMW indices was performed. OHT-CAV patients had decreased global work efficiency (GWE) compared to OHT (mean difference = 7.01 [1.76, 12.25], adjusted p < 0.01). LV global longitudinal strain (GLS) and LV ejection fraction were not different between groups. Both global work index and GWE were decreased in OHT-CAV and OHT when compared to normal controls (OHT-CAV 1311.23 mmHg% vs OHT 1426.22 mmHg% vs controls 1802.81 mmHg%, adjusted p < 0.01; OHT-CAV 83.87% vs. OHT 90.87% vs. controls 95.41%, adjusted p < 0.01). GWE correlated negatively with the presence of CAV (r = - 0.44 [- 0.72, - 0.05]). This pilot study demonstrates decreased GWE correlates with pediatric CAV. This supports the need for further investigation of this promising diagnostic tool.
Heart Transplantation , Adolescent , Child , Coronary Angiography , Echocardiography , Female , Heart , Heart Transplantation/adverse effects , Humans , Male , Pilot Projects
