Cindy M. Martin

Gastrointestinal bleeding rates in recipients of nonpulsatile and pulsatile left ventricular assist devices

OBJECTIVE Pulsatile and nonpulsatile left ventricular assist devices are effective in managing congestive heart failure. Despite early evidence for clinical efficacy, the long-term impact of nonpulsatile flow on end-organ function remains to be determined. Our goal was to compare rates of gastrointestinal bleeding in nonpulsatile and pulsatile device recipients. METHODS In a retrospective review of 101 left ventricular assist device recipients (55 nonpulsatile, 46 pulsatile) from October 31, 2003, to June 1, 2007, at a single center, gastrointestinal bleeding was defined as guaiac-positive stool with hemoglobin drop requiring transfusion of at least 2 units of packed red blood cells. To assess bleeding risk outside the initial postoperative course, any patients with a device in place for 15 days or less was excluded. RESULTS Twelve nonpulsatile and 3 pulsatile left ventricular assist device recipients had gastrointestinal bleeding 16 days or longer after device implantation. The event rates were 63 events/100 patient-years for nonpulsatile devices and 6.8 events/100 patient-years for pulsatile devices (P = .0004). This difference persisted for bleeding occurring 31 days or longer after device implantation, with 46.5 events/100 patient-years for nonpulsatile devices versus 4.7 events/100 patient-years for pulsatile devices (P = .0028). Mortalities were similar between groups (15% nonpulsatile vs 17% pulsatile, P = .6965). CONCLUSION Patients with nonpulsatile left ventricular assist devices appear to have a higher rate of gastrointestinal bleeding events than do pulsatile left ventricular assist device recipients. Further prospective evaluation is needed to determine potential etiologies and strategies for reducing gastrointestinal bleeding in this population.

Nkx2-5 transactivates the Ets-related protein 71 gene and specifies an endothelial/endocardial fate in the developing embryo.

Recent studies support the existence of a common progenitor for the cardiac and endothelial cell lineages, but the underlying transcriptional networks responsible for specification of these cell fates remain unclear. Here we demonstrated that Ets-related protein 71 (Etsrp71), a newly discovered ETS family transcription factor, was a novel downstream target of the homeodomain protein, Nkx2–5. Using genetic mouse models and molecular biological techniques, we demonstrated that Nkx2–5 binds to an evolutionarily conserved Nkx2–5 response element in the Etsrp71 promoter and induces the Etsrp71 gene expression in vitro and in vivo. Etsrp71 was transiently expressed in the endocardium/endothelium of the developing embryo (E7.75-E9.5) and was extinguished during the latter stages of development. Using a gene disruption strategy, we found that Etsrp71 mutant embryos lacked endocardial/endothelial lineages and were nonviable. Moreover, using transgenic technologies and transcriptional and chromatin immunoprecipitation (ChIP) assays, we further established that Tie2 is a direct downstream target of Etsrp71. Collectively, our results uncover a novel functional role for Nkx2–5 and define a transcriptional network that specifies an endocardial/endothelial fate in the developing heart and embryo.

Hypoxia-Inducible Factor-2α Transactivates Abcg2 and Promotes Cytoprotection in Cardiac Side Population Cells

Stem and progenitor cell populations occupy a specialized niche and are consequently exposed to hypoxic as well as oxidative stresses. We have previously established that the multidrug resistance protein Abcg2 is the molecular determinant of the side population (SP) progenitor cell population. We observed that the cardiac SP cells increase in number more than 3-fold within 3 days of injury. Transcriptome analysis of the SP cells isolated from the injured adult murine heart reveals increased expression of cytoprotective transcripts. Overexpression of Abcg2 results in an increased ability to consume hydrogen peroxide and is associated with increased levels of &agr;-glutathione reductase protein expression. Importantly, overexpression of Abcg2 also conferred a cell survival benefit following exposure to hydrogen peroxide. To further examine the molecular regulation of the Abcg2 gene, we demonstrated that hypoxia-inducible factor (HIF)-2&agr; binds an evolutionary conserved HIF-2&agr; response element in the murine Abcg2 promoter. Transcriptional assays reveal a dose-dependent activation of Abcg2 expression by HIF-2&agr;. These results support the hypothesis that Abcg2 is a direct downstream target of HIF-2&agr; which functions with other factors to initiate a cytoprotective program for this progenitor SP cell population that resides in the adult heart.

Chronic Heart Failure in Congenital Heart Disease: A Scientific Statement from the American Heart Association

### Introduction The past 60 years have brought remarkable advancements in the diagnosis and treatment of congenital heart disease (CHD). Early diagnosis and improvements in cardiac surgery and interventional cardiology have resulted in unprecedented survival of patients with CHD, even those with the most complex lesions. Despite remarkable success in treatments, many interventions are palliative rather than curative, and patients often develop cardiac complications, including heart failure (HF). HF management in the setting of CHD is challenged by the wide range of ages at which HF occurs, the heterogeneity of the underlying anatomy and surgical repairs, the wide spectrum of HF causes, the lack of validated biomarkers for disease progression, the lack of reliable risk predictors or surrogate end points, and the paucity of evidence demonstrating treatment efficacy. The purposes of this statement are to review the literature pertaining to chronic HF in CHD and to elucidate important gaps in our knowledge, emphasizing the need for specific studies of HF mechanisms and improving outcomes for those with HF. In this document, the definition of CHD severity is the definition common in CHD documents, including the American College of Cardiology (ACC)/American Heart Association (AHA) guidelines1 for the management of adults with CHD (Table 11–3). The definition of HF corresponds to that found in the multiple guidelines on diagnosis and management of HF. Although nuances and specific details may be controversial,4 the broad definition from the Heart Failure Society of America guidelines states the following: “In physiologic terms, HF is a syndrome characterized by either or both pulmonary and systemic venous congestion and/or inadequate peripheral oxygen delivery, at rest or during stress, caused by cardiac dysfunction.”5 The definition of chronic HF in this document concurs with that of the European Society of Cardiology guidelines, which emphasize chronic HF …

Hypoxia reprograms calcium signaling and regulates myoglobin expression

Myoglobin is an oxygen storage molecule that is selectively expressed in cardiac and slow-twitch skeletal muscles that have a high oxygen demand. Numerous studies have implicated hypoxia in the regulation of myoglobin expression as an adaptive response to hypoxic stress. However, the details of this relationship remain undefined. In the present study, adult mice exposed to 10% oxygen for periods up to 3 wk exhibited increased myoglobin expression only in the working heart, whereas myoglobin was either diminished or unchanged in skeletal muscle groups. In vitro and in vivo studies revealed that hypoxia in the presence or absence of exercise-induced stimuli reprograms calcium signaling and modulates myoglobin gene expression. Hypoxia alone significantly altered calcium influx in response to cell depolarization or depletion of endoplasmic reticulum calcium stores, which inhibited the expression of myoglobin. In contrast, our whole animal and transcriptional studies indicate that hypoxia in combination with exercise enhanced the release of calcium from the sarcoplasmic reticulum via the ryanodine receptors triggered by caffeine, which increased the translocation of nuclear factor of activated T-cells into the nucleus to transcriptionally activate myoglobin expression. The present study unveils a previously unrecognized mechanism where the hypoxia-mediated regulation of calcium transients from different intracellular pools modulates myoglobin gene expression. In addition, we observed that changes in myoglobin expression, in response to hypoxia, are not dependent on hypoxia-inducible factor-1 or changes in skeletal muscle fiber type. These studies enhance our understanding of hypoxia-mediated gene regulation and will have broad applications for the treatment of myopathic diseases.

Transplantation and Mechanical Circulatory Support in Congenital Heart Disease: A Scientific Statement From the American Heart Association.

Dramatic evolution in the medical and surgical care of children with congenital heart disease (CHD) has led to a growing number of adults with late-onset complications, including heart failure (HF).1 In parallel with an overall increase in hospital admissions for adults with CHD (ACHD) and HF,2 CHD complexity has increased substantially in survivors over the past 2 decades.3 Heart transplant (HTx) specialists face the challenge of determining eligibility for advanced HF treatments among an increasingly complex population of CHD patients in whom guidelines for HTx and mechanical circulatory support (MCS) are scant. The purpose of this review is to provide a state-of-the-art update on HTx and MCS in CHD. HTx remains the surgical procedure of choice for eligible patients with severe advanced HF,4,5 with little change in the number of transplants performed yearly over the past decade. The body of information related to transplantation for CHD is derived almost entirely from registry and single-center–based outcome data; no randomized clinical trial or meta-analysis data are available. CHD presents additional challenges to successful HTx compared with HTx in patients with acquired HF. Many CHD patients require complex vascular reconstruction at the time of transplantation. The presence of antibodies to human leukocyte antigen (HLA) and ABO blood group sensitization are also impediments to timely transplantation. The ability of patients with single-ventricle physiology to survive during the waiting period is also limited by the additional burden of “outgrowing” their pulmonary blood flow and the resultant cyanosis. It is not surprising that CHD remains a risk factor during the waiting period and after transplantation. Therefore, although the management of the CHD patient with end-stage HF must include the option of HTx, its indication and timing are very different from that for acquired HF. Patients with ACHD represent an increasing …

Minnesota Resuscitation Consortium's Advanced Perfusion and Reperfusion Cardiac Life Support Strategy for Out‐of‐Hospital Refractory Ventricular Fibrillation

Background In 2015, the Minnesota Resuscitation Consortium (MRC) implemented an advanced perfusion and reperfusion life support strategy designed to improve outcome for patients with out‐of‐hospital refractory ventricular fibrillation/ventricular tachycardia (VF/VT). We report the outcomes of the initial 3‐month period of operations. Methods and Results Three emergency medical services systems serving the Minneapolis–St. Paul metro area participated in the protocol. Inclusion criteria included age 18 to 75 years, body habitus accommodating automated Lund University Cardiac Arrest System (LUCAS) cardiopulmonary resuscitation (CPR), and estimated transfer time from the scene to the cardiac catheterization laboratory of ≤30 minutes. Exclusion criteria included known terminal illness, Do Not Resuscitate/Do Not Intubate status, traumatic arrest, and significant bleeding. Refractory VF/VT arrest was defined as failure to achieve sustained return of spontaneous circulation after treatment with 3 direct current shocks and administration of 300 mg of intravenous/intraosseous amiodarone. Patients were transported to the University of Minnesota, where emergent advanced perfusion strategies (extracorporeal membrane oxygenation; ECMO), followed by coronary angiography and primary coronary intervention (PCI), were performed, when appropriate. Over the first 3 months of the protocol, 27 patients were transported with ongoing mechanical CPR. Of these, 18 patients met the inclusion and exclusion criteria. ECMO was placed in 83%. Seventy‐eight percent of patients had significant coronary artery disease with a high degree of complexity and 67% received PCI. Seventy‐eight percent of patients survived to hospital admission and 55% (10 of 18) survived to hospital discharge, with 50% (9 of 18) achieving good neurological function (cerebral performance categories 1 and 2). No significant ECMO‐related complications were encountered. Conclusions The MRC refractory VF/VT protocol is feasible and led to a high functionally favorable survival rate with few complications.

Sox7 Is Regulated by ETV2 During Cardiovascular Development

Vasculogenesis/angiogenesis is one of the earliest processes that occurs during embryogenesis. ETV2 and SOX7 were previously shown to play a role in endothelial development; however, their mechanistic interaction has not been defined. In the present study, concomitant expression of Etv2 and Sox7 in endothelial progenitor cells was verified. ETV2 was shown to be a direct upstream regulator of Sox7 that binds to ETV2 binding elements in the Sox7 upstream regulatory region and activates transcription. We observed that SOX7 over-expression can mimic ETV2 and increase endothelial progenitor cells in embryonic bodies (EBs), while knockdown of Sox7 is able to block ETV2-induced increase in endothelial progenitor cell formation. Angiogenic sprouting was increased by ETV2 over-expression in EBs, and it was significantly decreased in the presence of Sox7 shRNA. Collectively, these studies support the conclusion that ETV2 directly regulates Sox7, and that ETV2 governs endothelial development by regulating transcriptional networks which include Sox7.

Abcg2-Labeled Cells Contribute to Different Cell Populations in the Embryonic and Adult Heart.

ATP-binding cassette transporter subfamily G member 2 (Abcg2)-expressing cardiac-side population cells have been identified in the developing and adult heart, although the role they play in mammalian heart growth and regeneration remains unclear. In this study, we use genetic lineage tracing to follow the cell fate of Abcg2-expressing cells in the embryonic and adult heart. During cardiac embryogenesis, the Abcg2 lineage gives rise to multiple cardiovascular cell types, including cardiomyocytes, endothelial cells, and vascular smooth muscle cells. This capacity for Abcg2-expressing cells to contribute to cardiomyocytes decreases rapidly during the postnatal period. We further tested the role of the Abcg2 lineage following myocardial injury. One month following ischemia reperfusion injury, Abcg2-expressing cells contributed significantly to the endothelial cell lineage, however, there was no contribution to regenerated cardiomyocytes. Furthermore, consistent with previous results showing that Abcg2 plays an important cytoprotective role during oxidative stress, we show an increase in Abcg2 labeling of the vasculature, a decrease in the scar area, and a moderate improvement in cardiac function following myocardial injury. We have uncovered a difference in the capacity of Abcg2-expressing cells to generate the cardiovascular lineages during embryogenesis, postnatal growth, and cardiac regeneration.

Nkx2-5 Mediates Differential Cardiac Differentiation Through Interaction with Hoxa10

The regulation of cardiac differentiation is complex and incompletely understood. Recent studies have documented that Nkx2-5-positive cells are not limited to the cardiac lineage, but can give rise to endothelial and smooth muscle lineages. Other work has elucidated that, in addition to promoting cardiac development, Nkx2-5 plays a larger role in mesodermal patterning although the transcriptional networks that govern this developmental patterning are undefined. By profiling early Nkx2-5-positive progenitor cells, we discovered that the progenitor pools of the bisected cardiac crescent are differentiating asynchronously. This asymmetry requires Nkx2-5 as it is lost in the Nkx2-5 mutant. Surprisingly, the posterior Hox genes Hoxa9 and Hoxa10 were expressed on the right side of the cardiac crescent, independently of Nkx2-5. We describe a novel, transient, and asymmetric cardiac-specific expression pattern of the posterior Hox genes, Hoxa9 and Hoxa10, and utilize the embryonic stem cell/embryoid body (ES/EB) model system to illustrate that Hoxa10 impairs cardiac differentiation. We suggest a model whereby Hoxa10 cooperates with Nkx2-5 to regulate the timing of cardiac mesoderm differentiation.