Michael A. Mathier

Nitrite Potently Inhibits Hypoxic and Inflammatory Pulmonary Arterial Hypertension and Smooth Muscle Proliferation via Xanthine Oxidoreductase–Dependent Nitric Oxide Generation

Background— Pulmonary arterial hypertension is a progressive proliferative vasculopathy of the small pulmonary arteries that is characterized by a primary failure of the endothelial nitric oxide and prostacyclin vasodilator pathways, coupled with dysregulated cellular proliferation. We have recently discovered that the endogenous anion salt nitrite is converted to nitric oxide in the setting of physiological and pathological hypoxia. Considering the fact that nitric oxide exhibits vasoprotective properties, we examined the effects of nitrite on experimental pulmonary arterial hypertension. Methods and Results— We exposed mice and rats with hypoxia or monocrotaline-induced pulmonary arterial hypertension to low doses of nebulized nitrite (1.5 mg/min) 1 or 3 times a week. This dose minimally increased plasma and lung nitrite levels yet completely prevented or reversed pulmonary arterial hypertension and pathological right ventricular hypertrophy and failure. In vitro and in vivo studies revealed that nitrite in the lung was metabolized directly to nitric oxide in a process significantly enhanced under hypoxia and found to be dependent on the enzymatic action of xanthine oxidoreductase. Additionally, physiological levels of nitrite inhibited hypoxia-induced proliferation of cultured pulmonary artery smooth muscle cells via the nitric oxide–dependent induction of the cyclin-dependent kinase inhibitor p21Waf1/Cip1. The therapeutic effect of nitrite on hypoxia-induced pulmonary hypertension was significantly reduced in the p21-knockout mouse; however, nitrite still reduced pressures and right ventricular pathological remodeling, indicating the existence of p21-independent effects as well. Conclusion— These studies reveal a potent effect of inhaled nitrite that limits pathological pulmonary arterial hypertrophy and cellular proliferation in the setting of experimental pulmonary arterial hypertension.

Effect of the Asp298 Variant of Endothelial Nitric Oxide Synthase on Survival for Patients With Congestive Heart Failure

Background—Significant variation exists within the endothelial nitric oxide synthase (NOS3) gene that may influence cardiovascular risk. The Asp298 variant of NOS3 has a shorter half-life in endothelial cells. Given the importance of nitric oxide in the heart failure syndrome, we evaluated the effect of this variant on event-free survival in a population with systolic dysfunction. Methods and Results—Four hundred sixty-nine patients (72% male, 49% ischemic; mean age, 56±12 years) with systolic dysfunction (left ventricular ejection fraction ≤0.45) were enrolled in a study of Genetic Risk Assessment of Cardiac Events (GRACE). The polymorphism in exon 7 of NOS3, a G-T transition at position 894 that results in a Glu to Asp amino acid substitution for codon 298, was genotyped and subjects were followed prospectively to the end point of death or heart transplantation. Event-free survival was compared on the basis of the presence (group 1, n=266) or absence (group 2, n=203) of the Asp298 variant. Event-free survival was significantly poorer in patients with the Asp298 variant (percent event-free survival group 1 at 1/2/3 years=78/65/54; group 2=82/72/64, P =0.03). In subset analysis, the adverse impact of the Asp298 variant was primarily in patients with nonischemic cardiomyopathy (group 1=82/73/63; group 2=87/79/71, P =0.03) and was not apparent among patients with ischemic heart disease (group 1=75/59/47; group 2=74/62/54, P =0.71). Conclusions—For patients with heart failure caused by systolic function, the Asp298 variant of NOS3 is associated with poorer event-free survival, particularly in patients with nonischemic cardiomyopathy.

RV-pulmonary arterial coupling predicts outcome in patients referred for pulmonary hypertension

Objective Prognosis in pulmonary hypertension (PH) is largely determined by RV function. However, uncertainty remains about what metrics of RV function might be most clinically relevant. The purpose of this study was to assess the clinical relevance of metrics of RV functional adaptation to increased afterload. Methods Patients referred for PH underwent right heart catheterisation and RV volumetric assessment within 48 h. A RV maximum pressure (Pmax) was calculated from the RV pressure curve. The adequacy of RV systolic functional adaptation to increased afterload was estimated either by a stroke volume (SV)/end-systolic volume (ESV) ratio, a Pmax/mean pulmonary artery pressure (mPAP) ratio, or by EF (RVEF). Diastolic function of the RV was estimated by a diastolic elastance coefficient β. Survival analysis was via Cox proportional HR, and Kaplan–Meier with the primary outcome of time to death or lung transplant. Results Patients (n=50; age 58±13 yrs) covered a range of mPAP (13–79 mm Hg) with an average RVEF of 39±17% and ESV of 143±89 mL. Average estimates of the ratio of end-systolic ventricular to arterial elastance were 0.79±0.67 (SV/ESV) and 2.3±0.65 (Pmax/mPAP-1). Transplantation-free survival was predicted by right atrial pressure, mPAP, pulmonary vascular resistance, β, SV, ESV, SV/ESV and RVEF, but after controlling for right atrial pressure, mPAP, and SV, SV/ESV was the only independent predictor. Conclusions The adequacy of RV functional adaptation to afterload predicts survival in patients referred for PH. Whether this can simply be evaluated using RV volumetric imaging will require additional confirmation.

Noninvasive Estimation of Pulmonary Vascular Resistance in Pulmonary Hypertension

Background: Determination of pulmonary vascular resistance (PVR) in patients with suspected or known pulmonary hypertension (PH) requires right heart catheterization. Our purpose was to use Doppler echocardiography to estimate PVR in patients with PH. Methods: Patient population consisted of 52 patients (53 ± 12 years; 35 females) who underwent Doppler echocardiography and right heart catheterization within 24 hours of each other. The ratio of peak tricuspid regurgitation velocity (TRV) and right ventricular outflow time‐velocity integral (VTIRVOT) was measured via transthoracic echocardiography and correlated to invasively determined PVR. A linear regression equation was generated to determine PVR by echocardiography based upon the TRV/VTIRVOT ratio. PVR by echocardiography was compared to invasive PVR using Bland‐Altman analysis. Results: Significant correlation was demonstrated between TRV/VTIRVOT and PVR by catheterization (r = 0.73; P < 0.001). However, Bland‐Altman analysis showed that agreement between PVR determined by echocardiography and invasive PVR was poor (bias = 0; standard deviation = 4.3 Wood units). In a subset of patients with invasive PVR < 8 Wood units (26 patients), correlation between TRV/VTIRVOT and invasive PVR was strong (r = 0.94; P < 0.001). In these patients, agreement between PVR by echocardiography and invasive PVR was satisfactory (bias = 0; standard deviation = 0.5 Wood units). There was no correlation between TRV/VTIRVOT and invasive PVR in patients with PVR > 8 Wood units (n = 26; r = 0.17). Conclusion: While TRV/VTIRVOT correlates significantly with PVR, using it to estimate PVR in a PH patient population cannot be recommended.

ARIES-3: ambrisentan therapy in a diverse population of patients with pulmonary hypertension.

INTRODUCTION Ambrisentan is an oral, once daily, endothelin receptor antagonist approved for treatment of pulmonary arterial hypertension (PAH). Previous studies of ambrisentan were limited to patients with Group 1 PAH and often excluded patients receiving other pulmonary hypertension (PH) therapies. AIMS ARIES-3 was an open-label study evaluating efficacy and safety of ambrisentan in patients with various PH etiologies and background PH medications. Patients received 5 mg ambrisentan once daily for 24 weeks. The primary endpoint was change from baseline in 6-minute walk distance (6MWD) at week 24. RESULTS A total of 224 patients with PH due to idiopathic and familial PAH (31%), connective tissue disease (18%), chronic hypoxemia (22%), chronic thromboembolic disease (13%), or other etiologies (16%) were enrolled and 53% of patients received stable background PAH therapies. After 24 weeks of therapy, an increase in 6MWD (+21 m; 95% CI: 12-29) and a decrease in B-type natriuretic peptide (-26%; 95% CI: -34 to -16%) was observed in the overall population compared to baseline; however, increases in 6MWD were not observed in several non-Group 1 PH subpopulations. Peripheral edema, headache, and dyspnea were the most common adverse events. CONCLUSION This study reconfirms the results of previous placebo-controlled studies, which demonstrate that ambrisentan is well tolerated and provides benefit in patients with PAH. Definitive conclusions regarding the safety and efficacy of ambrisentan in specific non-Group 1 PH etiologies cannot be determined and larger, controlled studies will be necessary to determine the efficacy and safety of ambrisentan in these populations.

Pulsatile left ventricular assist device support as a bridge to decision in patients with end-stage heart failure complicated by pulmonary hypertension

BACKGROUND Severe pulmonary hypertension (PH) in heart failure (HF) is a risk factor for adverse outcomes after heart transplantation (HTx). Left ventricular assist devices (LVADs) improve pulmonary hemodynamics, but our understanding of the degree of improvement and the effect on outcomes is still evolving. METHODS We reviewed invasive pulmonary hemodynamics from 58 consecutive patients receiving LVAD support as a bridge to HTx from 1996 to 2003. The primary outcome was change in baseline transpulmonary gradient (TPG) during LVAD support and after HTx/recovery. The secondary outcome was post-HTx survival. RESULTS All patients (age, 49 +/- 14 years, 79% male, 40% ischemic) received a pulsatile LVAD (median support, 97 days; interquartile range [IQR], 31-222). Hemodynamic measurements were obtained at baseline (median, 1 day; IQR, 1-3), during early (median, 1 day; IQR, 0-4) and late (median, 75 days; IQR, 24-186) LVAD support, and after HTx/recovery (median, 28 days; IQR, 17-40). Improvement in TPG occurred throughout LVAD support and was sustained after HTx/recovery. Levels of TPG reductions in patients with a baseline TPG in the highest quartile (14.1-26.0 mm Hg) were 8.6 +/- 3.5 vs 6.5 +/- 3.1 mm Hg in the lowest quartile (2.0-7.7 mm Hg) during LVAD support (p = 0.102), with 90% vs 100% 30-day post-HTx survival (P = 0.113). CONCLUSION Pulmonary hemodynamics and post-HTx survival were similar after pulsatile LVAD support in patients with and without pre-implant PH. LVAD support may be a useful strategy to reverse PH in carefully selected patients, thus improving candidacy for HTx.

Long-Term Outcome of Lung and Heart-Lung Transplantation for Idiopathic Pulmonary Arterial Hypertension

BACKGROUND The survival after lung and heart-lung transplantation for idiopathic pulmonary arterial hypertension has been reportedly the lowest among the major diagnostic categories of lung transplant recipients. METHODS Retrospective analysis was performed for lung and heart-lung transplant recipients for idiopathic pulmonary arterial hypertension from 1982 to 2006. The patients were divided into 2 groups, based on the era; group 1: 1982 to 1993, and group 2: 1994 to 2006. Since 1994, we have introduced our current protocols including prostaglandin E1 and nitroglycerin for donor lung preservation, and lung protection with cold and terminal warm blood pneumoplegia as well as immunosuppression with alemtuzumab induction. These modifications were introduced in different years over a wide span of time (1994 to 2003). RESULTS Group 1 had 59 patients (35 +/- 1 years old, ranging 15 to 53, 20 male and 39 female) with 7 single lung, 11 double lung, and 41 heart-lung, whereas group 2 had 30 (43 +/- 2 years old, ranging 17 to 65, 9 male and 21 female) with 2 single, 20 double, and 8 heart-lung transplantations. The recipient age was significantly (p = 0.004) higher in group 2, and group 2 had significantly older (35 +/- 3 vs 26 +/- 1, p = 0.002) and more female donors (73% vs 41%, p = 0.007) compared with group 1. The actuarial survival was significantly (p = 0.004) better in group 2 with 86% at 1 year, 75% at 5 years, and 66% at 10 years compared with group 1 with 58% at 1 year, 39% at 5 years, and 27% at 10 years. CONCLUSIONS With our current pulmonary protection and immunosuppression, the long-term outcome of lung and heart-lung transplantation for idiopathic pulmonary arterial hypertension is excellent.

Biventricular Assist Device Utilization for Patients with Morbid Congestive Heart Failure A Justifiable Strategy

Background—The rationale for the use of a biventricular assist device (BiVAD) for morbid congestive heart failure (MCHF) has been questioned because of historically unacceptable rates of postimplant and post-transplant mortality as well as perceived barriers to their outpatient management. Methods and Results—All patients who received a Thoratec BiVAD from January 1990 to December 2003 at the University of Pittsburgh were studied retrospectively. There were a total of 73 patients (32% ischemic, 21% idiopathic, and 47% other) who had a BiVAD implanted. Before implantation, 100% were on ≥1 inotropic agent, and 77% had an intra-aortic balloon pump. Overall survival was 69%; 42 patients (84%) received cardiac transplantation, 5 patients (10%) were weaned, and 3 (6%) remained supported on BiVAD. If the 14 patients with postcardiotomy failure and acute myocardial infarction with shock are excluded, the overall survival improves to 75%. Five-year actuarial survival after heart transplantation was 58%. Of the 29 patients implanted before 2000, the 4-month actuarial freedom from driveline infections, bloodstream infections, and neurological events was 10%, 54%, and 48%, respectively, whereas the rates of these events for the 44 patients implanted after 2000 improved to 70%, 79%, and 80%, respectively. Since 2000, 21 (48%) patients were discharged from the hospital, of whom 38% went to an outpatient residence, 33% to a skilled nursing facility, and 29% to home. Once discharged, ≥1 readmission occurred in 45% and ≥2 readmissions in 48%. Conclusions—BiVAD support for MCHF has an acceptable overall mortality and survival to transplantation. Morbidity has been significantly reduced in the past 4 years, and management as an outpatient is achievable.

The Role of Cardiac Troponin T Quantity and Function in Cardiac Development and Dilated Cardiomyopathy

Background Hypertrophic (HCM) and dilated (DCM) cardiomyopathies result from sarcomeric protein mutations, including cardiac troponin T (cTnT, TNNT2). We determined whether TNNT2 mutations cause cardiomyopathies by altering cTnT function or quantity; whether the severity of DCM is related to the ratio of mutant to wildtype cTnT; whether Ca2+ desensitization occurs in DCM; and whether absence of cTnT impairs early embryonic cardiogenesis. Methods and Findings We ablated Tnnt2 to produce heterozygous Tnnt2 +/− mice, and crossbreeding produced homozygous null Tnnt2 −/− embryos. We also generated transgenic mice overexpressing wildtype (TGWT) or DCM mutant (TGK210Δ) Tnnt2. Crossbreeding produced mice lacking one allele of Tnnt2, but carrying wildtype (Tnnt2 +/−/TGWT) or mutant (Tnnt2 +/−/TGK210Δ) transgenes. Tnnt2 +/− mice relative to wildtype had significantly reduced transcript (0.82±0.06[SD] vs. 1.00±0.12 arbitrary units; p = 0.025), but not protein (1.01±0.20 vs. 1.00±0.13 arbitrary units; p = 0.44). Tnnt2 +/− mice had normal hearts (histology, mass, left ventricular end diastolic diameter [LVEDD], fractional shortening [FS]). Moreover, whereas Tnnt2 +/−/TGK210Δ mice had severe DCM, TGK210Δ mice had only mild DCM (FS 18±4 vs. 29±7%; p<0.01). The difference in severity of DCM may be attributable to a greater ratio of mutant to wildtype Tnnt2 transcript in Tnnt2 +/−/TGK210Δ relative to TGK210Δ mice (2.42±0.08, p = 0.03). Tnnt2 +/−/TGK210Δ muscle showed Ca2+ desensitization (pCa50 = 5.34±0.08 vs. 5.58±0.03 at sarcomere length 1.9 µm, p<0.01), but no difference in maximum force generation. Day 9.5 Tnnt2 −/− embryos had normally looped hearts, but thin ventricular walls, large pericardial effusions, noncontractile hearts, and severely disorganized sarcomeres. Conclusions Absence of one Tnnt2 allele leads to a mild deficit in transcript but not protein, leading to a normal cardiac phenotype. DCM results from abnormal function of a mutant protein, which is associated with myocyte Ca2+ desensitization. The severity of DCM depends on the ratio of mutant to wildtype Tnnt2 transcript. cTnT is essential for sarcomere formation, but normal embryonic heart looping occurs without contractile activity.

Chronic intermittent hypoxia increases left ventricular contractility in C57BL/6J mice

Intermittent hypoxia (IH) commonly occurs in patients with obstructive sleep apnea and can cause a wide range of pathology, including reduced left ventricular (LV) ejection fraction in rats as determined by echocardiography, in rodent models. We utilized echocardiography and pressure-volume (PV) loop analyses to determine whether LV contractility was decreased in inbred C57BL/6J mice exposed to IH and whether blockade of beta-adrenergic receptors modified the response to hypoxia. Adult male 9- to 10-wk-old mice were exposed to 4 wk of IH (nadir inspired O(2) 5-6% at 60 cycles/h for 12 h during the light period) or intermittent air (IA) as control. A second group of animals were exposed to the same regimen of IH or IA, but in the presence of nonspecific beta-blockade with propranolol. Cardiac function was assessed by echocardiography and PV loop analyses, and mRNA and protein expression in ventricular homogenates was determined. Contrary to our expectations, we found with PV loop analyses that LV ejection fraction (63.4 +/- 3.5 vs. 50.5 +/- 2.6%, P = 0.015) and other measures of LV contractility were increased in IH-exposed animals compared with IA controls. There were no changes in contractile proteins, atrial natriuretic peptide levels, LV posterior wall thickness, or heart weight with IH exposure. However, cAMP levels were elevated after IH, and propranolol administration attenuated the increase in LV contractility induced by IH exposure. We conclude that, contrary to our hypothesis, 4 wk of IH exposure in C57BL/6J mice causes an increase in LV contractility that occurs independent of ventricular hypertrophy and is, in part, mediated by activation of cardiac beta-adrenergic pathways.