Orthotopic Heart Transplant Recipient with Enteric-coated Mycophenolate Sodium (Myfortic) Induced Colitis

Patient: Male, 66-year-old

Final Diagnosis: Drug-induced colitis

Symptoms: Abdominal discomfort • anorexia • diarrhea • weight loss

Medication: Enteric-coated mycophenolate sodium (Myfortic)

Clinical Procedure: Colonoscopy • colon biopsy

Specialty: Cardiology • Infectious Disease

Increased Cardiac Arrhythmogenesis Associated With Gap Junction Remodeling With Upregulation of RNA-Binding Protein FXR1

BACKGROUND

Gap junction remodeling is well established as a consistent feature of human heart disease involving spontaneous ventricular arrhythmia. The mechanisms responsible for gap junction remodeling that include alterations in the distribution of, and protein expression within, gap junctions are still debated. Studies reveal that multiple transcriptional and posttranscriptional regulatory pathways are triggered in response to cardiac disease, such as those involving RNA-binding proteins. The expression levels of FXR1 (fragile X mental retardation autosomal homolog 1), an RNA-binding protein, are critical to maintain proper cardiac muscle function; however, the connection between FXR1 and disease is not clear.

METHODS

To identify the mechanisms regulating gap junction remodeling in cardiac disease, we sought to identify the functional properties of FXR1 expression, direct targets of FXR1 in human left ventricle dilated cardiomyopathy (DCM) biopsy samples and mouse models of DCM through BioID proximity assay and RNA immunoprecipitation, how FXR1 regulates its targets through RNA stability and luciferase assays, and functional consequences of altering the levels of this important RNA-binding protein through the analysis of cardiac-specific FXR1 knockout mice and mice injected with 3xMyc-FXR1 adeno-associated virus.

RESULTS

FXR1 expression is significantly increased in tissue samples from human and mouse models of DCM via Western blot analysis. FXR1 associates with intercalated discs, and integral gap junction proteins Cx43 (connexin 43), Cx45 (connexin 45), and ZO-1 (zonula occludens-1) were identified as novel mRNA targets of FXR1 by using a BioID proximity assay and RNA immunoprecipitation. Our findings show that FXR1 is a multifunctional protein involved in translational regulation and stabilization of its mRNA targets in heart muscle. In addition, introduction of 3xMyc-FXR1 via adeno-associated virus into mice leads to the redistribution of gap junctions and promotes ventricular tachycardia, showing the functional significance of FXR1 upregulation observed in DCM.

CONCLUSIONS

In DCM, increased FXR1 expression appears to play an important role in disease progression by regulating gap junction remodeling. Together this study provides a novel function of FXR1, namely, that it directly regulates major gap junction components, contributing to proper cell-cell communication in the heart.

Abstract 344: Cardiac Grafts Engineered From Human Induced Pluripotent Stem Cell Ventricular Pure or Heterogeneous Cardiomyocytes Display Synchronous and Spontaneous Contraction and Reduce Ventricular Tachycardia in Rats with Chronic Heart Failure

Background: Twenty six million people worldwide are diagnosed with chronic heart failure (CHF). With only 5000 heart transplants performed annually, the prognosis for the remaining individuals is poor and new therapeutic options are needed. Previously we have described a cardiac engineered graft comprised of human induced pluripotent stem cell (iPSC) derived cardiomyocytes co-cultured with fibroblasts in a bio-absorbable mesh. Few studies to date have examined comparatively the therapeutic benefits of different cardiac populations. In the present study we engineered grafts generated with either hiPSC derived heterogeneous cardiac myocytes (hetCMs) or ventricular pure myocyte (VMs) populations to compare functional outcomes in a rat model of CHF.

Methods: Cardiac grafts were generated with hetCMs or VMs (Axiogenesis) by co-culture into a 3D bioabsorbable mesh with human dermal fibroblasts. The hetCMs contain 60% ventricular, 40% atrial and nodal-like cardiomyocytes. The VMs contain 90% ventricular and 10% atrial cardiomyocytes. Grafts were evaluated in culture out to 6 days. Adult male Sprague-Dawley rats underwent permanent left coronary artery ligation and were randomized to Sham, CHF or graft treatment. Hemodynamic pressure measurements were performed at 6 weeks post-ligation with Millar solid state micromanometer pressure catheters. Ventricular tachycardia (VT) induction studies were performed at study endpoint (3 weeks after implant) to evaluate VT susceptibility using methods developed in the laboratory.

Results: Both HetCM and VM generated cardiac grafts displayed synchronous and spontaneous contractions after 48hrs in culture and maintained an average contraction rate of 67±6 (hetCM) and 71±9 (VM) beats per minute (n=10 per group). Implantation of HetCM and VM grafts lowered (p<0.05) EDP 45% and 14% (n=10) and resulted in decreased susceptibility of VT induction 54% and 65%, respectively (n=4).

Conclusion: Cardiac grafts engineered with hetCMs or VMs and implanted in a rat CHF model can lower LV EDP in-vivo while decreasing susceptibility of induced VT. This approach raises the possibility that iPSC derived engineered grafts may be used as a treatment for VT in patients with CHF.

Changes in Sonographically Measured Inferior Vena Caval Diameter in Response to Fluid Loading in Term Pregnancy

OBJECTIVES

The purpose of this study was to determine whether the inferior vena caval (IVC) diameter is influenced by intravascular volume changes in pregnancy.

METHODS

A prospective observational study was done on 2 groups of normal term gravidas. In 24 patients, we measured the IVC diameter, blood pressure, and heart rate (HR) before and after a 1-L fluid infusion in preparation for regional anesthesia, after initiation of an epidural block, and within 24 hours postpartum. In a second group of 15 women, we measured the IVC diameter sequentially during a 1-L crystalloid infusion.

RESULTS

In the first group, the mean baseline IVC diameter ± SD at end-inspiration was 1.45 ± 0.32 cm, which was 19% smaller than at end-expiration (1.73 ± 0.31 cm; P= .003). This respiratory cycle variation remained significant at each measurement epoch. The mean caval diameter at end-inspiration increased by 23% after the fluid bolus (P = .012). Hydration was not, however, accompanied by any significant change in the HR, mean arterial pressure, or collapsibility index of the inferior vena cava. With epidural anesthesia, the mean arterial pressure decreased from 88 ± 9 to 80 ± 7 mm Hg (P= .018), but the HR and collapsibility index remained unchanged. Postpartum values were not significantly different from their baseline measurements, except for the mean arterial pressure, which was lower by about 6 mm Hg (P = .042). In the second group, the IVC diameter at end-inspiration increased by 31% after the 1-L infusion, and there was a positive correlation between the volume infused and the IVC diameter (r= 0.67; P< .0001).

CONCLUSIONS

Measurable variations in the IVC diameter occur in response to volume changes in normal term pregnancy and postpartum.

Shocks from pacemaker cardioverter defibrillators increase with amiodarone in patients at high risk for sudden cardiac death

The efficacy of amiodarone used in combination with a pacemaker cardioverter defibrillator (PCD) to decrease episodes of ventricular tachycardia and subsequent PCD shocks is not clear. We examined a retrospective registry of 82 patients with PCD implantation to define the efficacy of amiodarone treatment. We compared patients treated with amiodarone (for 24 consecutive months without interruption) versus no amiodarone. In patients treated with amiodarone there was a 3-fold increase (p = 0.02) in PCD shocks; in patients not on beta-blockers, amiodarone resulted in a 6-fold increase (p < 0.05) in PCD shocks. Patients with a left ventricular ejection fraction >30% on amiodarone and patients <72 years old had increases (p < 0.05) in PCD shocks. In conclusion, patients treated with amiodarone had more PCD shocks than those not treated. These findings are unexpected and merit a prospective study.