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Introduction:Recognizing that increased cardiac afterload drives pathologic remodeling and predisposes to heart failure, we developed a 3D engineered cardiac microtissue platform (CMT) with tunable and reversible afterload.Methods:Human CMTs self-assemble onto a tissue engineering platform after microfabicated wells containing cantilevers are seeded with induced pluripotent stem cell cardiomyocytes (96%) and cardiac fibroblasts (4%) (NCardia, Inc.). Fabricating cantilevers with a mixture of polydimethylsiloxane and carbonyl iron microspheres permits them to be dynamically stiffened in the presence of a magnetic field. After initial maturation over 48 - 72 hours, CMTs are then exposed to low or high afterload conditions via magnetic actuation (<0.6 vs. >0.6 N/m) for up to 48 hours. A subset of matured CMTs are exposed to sunitinib (0 ?M - 10 ?M) for 8 hours and subsequently analyzed.Results:During maturation, there were positive correlations between afterload and static force (r = 0.83, p < 10-8), dynamic force (r = 0.85, p < 10-6), work (r = 0.74, p < 10-4), contraction velocity (r = 0.72, p < 10-7), and relaxation velocity (r = 0.56, p < 10-6). After maturation, instantaneous increases in stiffness yielded increased static force (55 vs. 61 ?N, p < 0.05), dynamic force (26 vs. 30 ?N, p < 0.05), and work (44 vs. 52 ?N*?m, p < 0.05). However, sustained exposure after maturation to high afterload for 24 hours yielded increased static force (37 vs. 52 ?N, p < 0.05), with decreased work (92 vs. 51 ?N*?m, p < 0.05), contraction velocity (-87 vs. -51 ?m/s, p < 10-3) and relaxation velocity (50 vs. 31 ?m/s, p < 10-3). At 48 hours, higher in vitro afterload was associated with increased CMT thickness (98 vs. 128 ?m, p < 0.05). With sunitinib, contractility decreased (up to 2.2-fold) and caspase activation increased (up to 5.4-fold) in a dose- and stiffness-dependent fashion.Conclusions:Though increased in vitroafterload can condition CMTs during their maturation, subsequent prolonged exposure to increased afterload induces decrements in contractility, increases in tissue mass, and enhanced susceptibility to sunitinib toxicity. This versatile model provides new opportunities to study load-dependent myocardial adaptations for translational research applications.

Background:Single ventricle physiology can lead to heart failure necessitating diuretics, yet diuretic use and its prognostic value has not been fully explored in the adult Fontan patient. We aim to examine diuretic use in this population and its association with adverse outcomes.Methods:Single center retrospective review of Fontan patients ? 18 years from 2005-2017. Diuretic use at most recent outpatient clinic visit was recorded. Outcomes of interest were heart transplantation and death. Comparison of Fontan patients by diuretic use was performed using Chi-square and Wilcoxon rank-sum tests. Kaplan-Meier survival analysis stratified by diuretic use was performed to examine time to transplant or death. Cox Proportional Hazards models examined risk of outcome based on diuretic use.Results:Of 167 Fontan patients (age 30 [range 21 - 60] years, 49% female), 69 (41%) were taking diuretics at their last outpatient visit. Patients on diuretics were older, symptomatic, underwent Fontan surgery at an older age, and had more comorbidities (Table 1). During a median follow-up of 4.3 years (0.1 - 14.8), 16 patients underwent transplant or died (9.6%). Kaplan-Meier survival analysis showed significantly lower transplant-free survival for Fontan patients taking diuretics (Figure 1). Diuretic use was associated with a 17-fold increased risk of transplant or death (HR 17.4, 95% CI 2.3 - 131.9; p=0.006).Conclusion:Diuretic use is seen in older, symptomatic adult Fontan patients with comorbidities and is associated with worse transplant-free survival. Use of diuretics signals the onset of clinical heart failure and is prognostic of poor outcomes.