Jacob N. Schroder

Targeted β-Adrenergic Receptor Kinase (βARK1) Inhibition by Gene Transfer in Failing Human Hearts

Background—Failing human myocardium is characterized by an attenuated contractile response to &bgr;-adrenergic receptor (&bgr;AR) stimulation due to changes in this signaling cascade, including increased expression and activity of the &bgr;-adrenergic receptor kinase (&bgr;ARK1). This leads to desensitization and downregulation of &bgr;ARs. Previously, expression of a peptide inhibitor of &bgr;ARK1 (&bgr;ARKct) has proven beneficial in several animal models of heart failure (HF). Methods and Results—To test the hypothesis that inhibition of &bgr;ARK1 could improve &bgr;-adrenergic signaling and contractile function in failing human myocytes, the &bgr;ARKct was expressed via adenovirus-mediated (Ad&bgr;ARKct) gene transfer in ventricular myocytes isolated from hearts explanted from 10 patients with end-stage HF undergoing cardiac transplantation. Ad&bgr;ARKct also contained the marker gene, green fluorescent protein, and successful gene transfer was confirmed via fluorescence and immunoblotting. Compared with uninfected failing myocytes (control), the velocities of both contraction and relaxation in the Ad&bgr;ARKct-treated cells were increased in response to the &bgr;-agonist isoproterenol (contraction: 57.5±6.6% versus 37.0±4.2% shortening per second, P <0.05; relaxation: 43.8±5.5% versus 27.5±3.9% lengthening per second, P <0.05). Fractional shortening was similarly enhanced (12.2±1.2% versus 8.0±0.9%, P <0.05). Finally, adenylyl cyclase activity in response to isoproterenol was also increased in Ad&bgr;ARKct-treated myocytes. Conclusions—These results demonstrate that as in animal models of HF, expression of the &bgr;ARKct can improve contractile function and &bgr;-adrenergic responsiveness in failing human myocytes. Thus, &bgr;ARK1 inhibition may represent a therapeutic strategy for human HF.

Midterm Results for Endovascular Repair of Complicated Acute and Chronic Type B Aortic Dissection

BACKGROUND Thoracic endovascular aortic repair (TEVAR) for the management of type B aortic dissections has become more commonplace despite some controversy. Results of endovascular management of complicated acute (<2 weeks from symptom onset) and chronic (>2 weeks) type B aortic dissection with a view towards determining safety, efficacy, and requirement for secondary procedures are reviewed. METHODS Between June 2005 and November 2008, 55 patients (41 men) with a mean age of 59 +/- 12 years (range, 31 to 77 years) underwent TEVAR for the management of complicated acute (n = 22) or chronic (n = 33) type B dissection. Indications in acute dissection included impending or frank rupture in 11 and malperfusion syndromes in 11; the indication in chronic dissections was aneurysmal degeneration in 33. RESULTS Primary technical success was 100%. In-hospital and 30-day rates of death, stroke, and permanent paraplegia/paresis were 2% (n = 1), 0%, and 2% (n = 1), respectively. Median follow-up was 7.1 months (range, 1 to 38 months). Overall actuarial midterm survival was 63% at 38 months, with an aorta-specific actuarial survival of 94%. Two patients (4%) required late conversion to open repair. Postoperative type I or III endoleak occurred in 3 (6%) and type II endoleak in 7 (15%). Two patients underwent subsequent endovascular occlusion. The composite reintervention rate in follow-up was 23.4% (n = 13). CONCLUSIONS Endovascular repair for complicated acute and chronic type B dissection is safe and effective at early midterm follow-up. TEVAR for type B dissection requires more secondary interventions and imaging surveillance than conventional open reconstruction. Longer-term follow-up is needed to determine the durability of this approach.

Impact of Mitral Valve Regurgitation Evaluated by Intraoperative Transesophageal Echocardiography on Long-Term Outcomes After Coronary Artery Bypass Grafting

Background—It is unclear if mild or moderate mitral valve regurgitation (MR) should be repaired at the time of coronary artery bypass grafting (CABG). We sought to determine the long-term effect of uncorrected MR, measured by intraoperative transesophageal echocardiography (TEE), in CABG patients. Methods and Results—Between May 1999 and September 2003, data were gathered for 3264 consecutive patients who underwent isolated CABG and had MR graded by intraoperative TEE. MR was graded on the following 5 levels: none, trace, mild, moderate, and severe. Patients who had severe MR or who underwent mitral valve surgery were eliminated from the analysis. The remaining patients were combined into the following 3 groups: none or trace, mild, and moderate MR. Preoperative and follow-up data were 99% complete. The median length of follow-up was 3.0 years. Multivariable analysis controlling for important preoperative risk factors was performed to determine predictors of death and death/hospitalization for heart failure. Increasing MR was a risk factor for death [hazard ratio (HR), 1.44; P<0.001] and death/heart failure hospitalization (HR, 1.34; P<0.01). When patients with moderate MR were eliminated from the analysis, mild MR was a risk factor for death (HR, 1.34; P=0.011) and death/hospitalization for heart failure (HR, 1.34; P<0.001). Conclusions—Even mild MR, identified by intraoperative TEE, predicts worse outcomes after CABG. Revascularization alone did not eliminate the negative long-term effects of mild MR. CABG patients with uncorrected mild or moderate MR are at increased risk for death and heart-failure hospitalization; consideration for surgical repair or more aggressive medical management and follow-up is warranted.

Restoration of β-Adrenergic Receptor Signaling and Contractile Function in Heart Failure by Disruption of the βARK1/Phosphoinositide 3-Kinase Complex

Background—Desensitization and downregulation of myocardial &bgr;-adrenergic receptors (&bgr;ARs) are initiated by the increase in &bgr;AR kinase 1 (&bgr;ARK1) levels. By interacting with &bgr;ARK1 through the phosphoinositide kinase (PIK) domain, phosphoinositide 3-kinase (PI3K) is targeted to agonist-stimulated &bgr;ARs, where it regulates endocytosis. We tested the hypothesis that inhibition of receptor-targeted PI3K activity would alter receptor trafficking and ameliorate &bgr;AR signaling, ultimately improving contractility of failing cardiomyocytes. Methods and Results—To competitively displace PI3K from &bgr;ARK1, we generated mice with cardiac-specific overexpression of the PIK domain. Seven-day isoproterenol administration in wild-type mice induced desensitization of &bgr;ARs and their redistribution from the plasma membrane to early and late endosomes. In contrast, transgenic PIK overexpression prevented the redistribution of &bgr;ARs away from the plasma membrane and preserved their responsiveness to agonist. We further tested whether PIK overexpression could normalize already established &bgr;AR abnormalities and ameliorate contractile dysfunction in a large animal model of heart failure induced by rapid ventricular pacing in pigs. Failing porcine hearts showed increased &bgr;ARK1-associated PI3K activity and marked desensitization and redistribution of &bgr;ARs to endosomal compartments. Importantly, adenoviral gene transfer of the PIK domain in failing pig myocytes resulted in reduced receptor-localized PI3K activity and restored to nearly normal agonist-stimulated cardiomyocyte contractility. Conclusions—These data indicate that the heart failure state is associated with a maladaptive redistribution of &bgr;ARs away from the plasma membrane that can be counteracted through a strategy that targets the &bgr;ARK1/PI3K complex.

Dynamic Regulation of Phosphoinositide 3-Kinase-γ Activity and β-Adrenergic Receptor Trafficking in End-Stage Human Heart Failure

Background— Downregulation of &bgr;-adrenergic receptors (&bgr;ARs) under conditions of heart failure requires receptor targeting of phosphoinositide 3-kinase (PI3K)–&ggr; and redistribution of &bgr;ARs into endosomal compartments. Because support with a left ventricular assist device (LVAD) results in significant improvement of cardiac function in humans, we investigated the effects of mechanical unloading on regulation of PI3K&ggr; activity and intracellular distribution of &bgr;ARs. Additionally, we tested whether displacement of PI3K&ggr; from activated &bgr;ARs would restore agonist responsiveness in failing human cardiomyocytes. Methods and Results— To test the role of PI3K on &bgr;AR endocytosis in failing human hearts, we assayed for PI3K activity in human left ventricular samples before and after mechanical unloading (LVAD). Before LVAD, failing human hearts displayed a marked increase in &bgr;AR kinase 1 (&bgr;ARK1)–associated PI3K activity that was attributed exclusively to enhanced activity of the PI3K&ggr; isoform. Increased &bgr;ARK1-coupled PI3K activity in the failing hearts was associated with downregulation of &bgr;ARs from the plasma membrane and enhanced sequestration into early and late endosomes compared with unmatched nonfailing controls. Importantly, LVAD support reversed PI3K&ggr; activation, normalized the levels of agonist-responsive &bgr;ARs at the plasma membrane, and depleted the &bgr;ARs from the endosomal compartments without changing the total number of receptors (sum of plasma membrane and early and late endosome receptors). To test whether the competitive displacement of PI3K from the &bgr;AR complex restored receptor responsiveness, we overexpressed the phosphoinositide kinase domain of PI3K (which disrupts &bgr;ARK1/PI3K interaction) in primary cultures of failing human cardiomyocytes. Adenoviral-mediated phosphoinositide kinase overexpression significantly increased basal contractility and rapidly reconstituted responsiveness to &bgr;-agonist. Conclusions— These results suggest a novel paradigm in which human &bgr;ARs undergo a process of intracellular sequestration that is dynamically reversed after LVAD support. Importantly, mechanical unloading leads to complete reversal in PI3K&ggr; and &bgr;ARK1-associated PI3K activation. Furthermore, displacement of active PI3K from &bgr;ARK1 restores &bgr;AR responsiveness in failing myocytes.

Risk-Adjusted Short- and Long-Term Outcomes for On-Pump Versus Off-Pump Coronary Artery Bypass Surgery

Background—Surgeons have adopted off-pump coronary artery bypass grafting (OPCAB) in an effort to reduce the morbidity of surgical revascularization. However, long-term outcome of OPCAB compared with conventional coronary artery bypass grafting (CABG) remains poorly defined. Methods and Results—Using logistic regression analysis and proportional hazards modeling, short-term and long-term outcomes (perioperative mortality and complications, risk-adjusted survival, and survival/freedom from revascularization) were investigated for patients who underwent OPCAB (641 patients) and CABG-cardiopulmonary bypass (5026 patients) from 1998 to 2003 at our institution. For these variables, follow-up was 98% complete. OPCAB patients were less likely to receive transfusion (odds ratio for OPCAB, 0.80; P=0.037), and there were trends toward improvement in other short-term outcomes compared with CABG-cardiopulmonary bypass. Long-term outcomes analysis demonstrated no difference in survival, but OPCAB patients were more likely to require repeat revascularization (OPCAB hazard ratio, 1.29; P=0.020). Conclusions—OPCAB patients were less likely to receive transfusion during their hospitalization for surgery but had higher risk for revascularization in follow-up. These results highlight the need for a large randomized, controlled trial to compare these 2 techniques.

Two-Phase Hospital-Associated Outbreak of Mycobacterium abscessus: Investigation and Mitigation

Background Nontuberculous mycobacteria (NTM) commonly colonize municipal water supplies and cause healthcare-associated outbreaks. We investigated a biphasic outbreak of Mycobacterium abscessus at a tertiary care hospital. Methods Case patients had recent hospital exposure and laboratory-confirmed colonization or infection with M. abscessus from January 2013 through December 2015. We conducted a multidisciplinary epidemiologic, field, and laboratory investigation. Results The incidence rate of M. abscessus increased from 0.7 cases per 10000 patient-days during the baseline period (January 2013-July 2013) to 3.0 cases per 10000 patient-days during phase 1 of the outbreak (August 2013-May 2014) (incidence rate ratio, 4.6 [95% confidence interval, 2.3-8.8]; P < .001). Thirty-six of 71 (51%) phase 1 cases were lung transplant patients with positive respiratory cultures. We eliminated tap water exposure to the aerodigestive tract among high-risk patients, and the incidence rate decreased to baseline. Twelve of 24 (50%) phase 2 (December 2014-June 2015) cases occurred in cardiac surgery patients with invasive infections. Phase 2 resolved after we implemented an intensified disinfection protocol and used sterile water for heater-cooler units of cardiopulmonary bypass machines. Molecular fingerprinting of clinical isolates identified 2 clonal strains of M. abscessus; 1 clone was isolated from water sources at a new hospital addition. We made several water engineering interventions to improve water flow and increase disinfectant levels. Conclusions We investigated and mitigated a 2-phase clonal outbreak of M. abscessus linked to hospital tap water. Healthcare facilities with endemic NTM should consider similar tap water avoidance and engineering strategies to decrease risk of NTM infection.

The Risk of Acute Kidney Injury With Co-Occurrence of Anemia and Hypotension During Cardiopulmonary Bypass Relative to Anemia Alone

BACKGROUND Postoperative acute kidney injury (AKI) is a common serious consequence of cardiac surgery. One recent study found higher AKI rates when anemia and hypotension occurred during cardiopulmonary bypass (CPB) relative to anemia alone. To revalidate this post hoc observation we analyzed detailed data from a large cardiac surgery cohort. METHODS Patient, procedural, and outcome data were collected for nonemergent aortocoronary bypass and valve surgeries between July 2001 and September 2012. The occurrence of AKI (as defined by the Acute Kidney Injury Network criteria) was analyzed relative to known renal risk factors, and CPB hematocrit and blood pressure determinations in univariate and multivariable linear regression analyses. RESULTS In our 3,963-patient cohort, we did not observe different AKI rates with the co-occurrence of anemia and hypotension relative to anemia alone (41.6% versus 44.3%; p = 0.39). Secondary analyses using linear definitions for AKI, CPB anemia, and hypotensive burden, and assessing for coincident timing also did not demonstrate significant association of anemia and hypotension with AKI risk relative to anemia alone. CONCLUSIONS In a large cohort of cardiac surgery patients, we did not confirm any association of cardiac surgery-related AKI risk with the co-occurrence of hypotension and anemia during CPB relative to anemia alone. More detailed analyses also failed to support an anemia-hypotension interaction. Additional studies are required to better understand the relationship among anemia, hypotension during CPB, and postoperative AKI, but existing evidence is insufficient to support changes in clinical practice.

X-Linked Inhibitor of Apoptosis Protein-Mediated Attenuation of Apoptosis, Using a Novel Cardiac-Enhanced Adeno-Associated Viral Vector

Successful amelioration of cardiac dysfunction and heart failure through gene therapy approaches will require a transgene effective at attenuating myocardial injury, and subsequent remodeling, using an efficient and safe delivery vehicle. Our laboratory has established a well-curated, high-quality repository of human myocardial tissues that we use as a discovery engine to identify putative therapeutic transgene targets, as well as to better understand the molecular basis of human heart failure. By using this rare resource we were able to examine age- and sex-matched left ventricular samples from (1) end-stage failing human hearts and (2) nonfailing human hearts and were able to identify the X-linked inhibitor of apoptosis protein (XIAP) as a novel target for treating cardiac dysfunction. We demonstrate that XIAP is diminished in failing human hearts, indicating that this potent inhibitor of apoptosis may be central in protecting the human heart from cellular injury culminating in heart failure. Efforts to ameliorate heart failure through delivery of XIAP compelled the design of a novel adeno-associated viral (AAV) vector, termed SASTG, that achieves highly efficient transduction in mouse heart and in cultured neonatal rat cardiomyocytes. Increased XIAP expression achieved with the SASTG vector inhibits caspase-3/7 activity in neonatal cardiomyocytes after induction of apoptosis through three common cardiac stresses: protein kinase C-γ inhibition, hypoxia, or β-adrenergic receptor agonist. These studies demonstrate the potential benefit of XIAP to correct heart failure after highly efficient delivery to the heart with the rationally designed SASTG AAV vector.

Trends and outcomes of patients with adult congenital heart disease and pulmonary hypertension listed for orthotopic heart transplantation in the United States.

BACKGROUND Heart transplantation is increasing in patients with adult congenital heart disease (ACHD). In this population, the association of pulmonary hypertension (PH) with post-transplant outcomes is not well-defined. METHODS Using data from the United Network for Organ Sharing database (1987 to 2014), we identified ACHD patients listed for heart transplantation, and examined survival between those with and without PH (pre-transplant PH defined as transpulmonary pressure gradient >12 mm Hg). RESULTS Among 983 ACHD patients, 216 (22%) had PH. At time of listing, PH patients had a transpulmonary pressure gradient of 17.0 mm Hg vs 6.0 mm Hg (p < 0.01) in the no-PH group. Although left ventricular assist device (LVAD) use was infrequent, 3.1% of PH patients were treated with an LVAD versus 6.8% of the no-PH patients. Days from listing to transplant, days from listing to death on the waitlist and length of post-transplant hospitalization were not significantly different between the PH and no-PH groups. However, PH was associated with higher waitlist mortality (HR 1.73, CI 1.25 to 2.41). Pre-transplant PH was not associated with post-transplant mortality at 30 days (HR 0.51, CI 0.23 to 1.13), 1 year (HR 0.68, 95% CI 0.40 to 1.18) or 5 years (HR 0.84, 95% CI 0.55 to 1.29). CONCLUSIONS PH is common among ACHD patients listed for transplant and is associated with increased waitlist mortality. Conversely, PH was not associated with worse survival after transplant. Bridge-to-transplant LVAD therapy was uncommon in this ACHD population.