Transgenic expression of matrix metalloproteinase-2 induces coronary artery ectasia

MMP-2 and its implications on cardiac function and structure: Interplay with inflammation in hypertension

Hypertension is one of the leading risk factors for the development of heart failure. Despite being a multifactorial disease, in recent years, preclinical and clinical studies suggest strong evidence of the pivotal role of inflammatory cells and cytokines in the remodeling process and cardiac dysfunction. During the heart remodeling, activation of extracellular matrix metalloproteinases (MMPs) occurs, with MMP-2 being one of the main proteases secreted by cardiomyocytes, fibroblasts, endothelial and inflammatory cells in cardiac tissue. In this review, we will address the process of cardiac remodeling and injury induced by the increase in MMP-2 and the main signaling pathways involving cytokines and inflammatory cells in the process of transcriptional, secretion and activation of MMP-2. In addition, an interaction and coordinated action between MMP-2 and inflammation are explored and significant in maintaining the cardiac cycle. These observations suggest that new therapeutic opportunities targeting MMP-2 could be used to reduce inflammatory biomarkers and reduce cardiac damage in hypertension.

Effect of type 2 diabetes on coronary artery ectasia: smaller lesion diameter and shorter lesion length but similar adverse cardiovascular events

Background

Coronary artery ectasia (CAE) is a rare finding in coronary angiography and associated with poor clinical outcomes. Unlike atherosclerosis, diabetes mellitus (DM) is not commonly associated with CAE. This study aims to investigate the effect of type 2 diabetes mellitus (DM2) on coronary artery ectasia, especially the differences in angiographic characteristics and clinical outcomes.

Methods

Patients with angiographically confirmed CAE from 2009 to 2015 were included. Quantitative coronary angiography (QCA) was performed to measure the diameter and length of the dilated lesion. The primary endpoint was the maximum diameter and maximum length of the dilated lesion at baseline coronary angiography. The secondary endpoint was 5-year major adverse cardiovascular events (MACE), which was a component of cardiovascular death and nonfatal myocardial infarction (MI). Propensity score weighting (PSW) and propensity score matching (PSM) were used to balance covariates. Kaplan–Meier method and Cox regression were performed to assess the clinical outcomes.

Results

A total of 1128 patients were included and 258 were combined with DM2. In the DM2 group, the maximum diameter of dilated lesion was significantly lower (5.26 mm vs. 5.47 mm, P  = 0.004) and the maximum length of the dilated lesion was significantly shorter (25.20 mm vs. 31.34 mm, P  = 0.002). This reduction in dilated lesion diameter (5.26 mm vs. 5.41 mm, P  = 0.050 in PSW; 5.26 mm vs. 5.46 mm, P  = 0.007 in PSM, respectively) and length (25.17 mm vs. 30.17 mm, P  = 0.010 in PSW; 25.20 mm vs. 30.81 mm, P  = 0.012 in PSM, respectively) was consistently observed in the propensity score analysis. A total of 27 cardiovascular deaths and 41 myocardial infarctions occurred at 5-year follow-up. Compared with non-DM group, there were similar risks of MACE (6.02% vs. 6.27%; HR 0.96, 95% CI 0.54–1.71, P  = 0.894), cardiovascular death (2.05% vs. 2.61%; HR 0.78, 95% CI 0.29–2.05, P  = 0.605) and MI (4.07% vs. 3.72%; HR 1.11, 95% CI 0.54–2.26, P  = 0.782) in patients with DM2. Consistent result was observed in multivariable regression.

Conclusions

Compared to non-DM patients, patients with CAE and type 2 diabetes were associated with a smaller diameter and shorter length of dilated vessels, suggesting the important effect of DM2 on the pathophysiological process of CAE. Similar risks of MACE were found during 5-year follow up among diabetic and non-DM patients.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12933-022-01444-5.

The Impact of C-Peptide and Diabetes Mellitus on Coronary Ectasia and Effect of Coronary Ectasia and C-Peptide on Long-Term Outcomes: A Retrospective Cohort Study

BACKGROUND

Coronary artery ectasia (CAE) is an entity frequently associated with atherosclerotic coronary artery disease (CAD) in clinical practice. Although it has common risk factors with atherosclerotic CAD in its development, the pathophysiology of CAE is not fully known and it is not seen in every CAD suggesting that different determinants may play a pivotal role in the development of CAD. This study aimed to reveal the impact of C-peptide and diabetes mellitus (DM) on CAE and the effect of C-peptide and coronary ectasia on long-term outcomes in patients who underwent coronary angiography.

METHODS

A total of 6611 patients who underwent coronary angiography were followed up retrospectively, and their major adverse cardiovascular event (MACE) status of an average of sixty months was recorded. According to their angiographic features, the patients were divided into two groups those with and without CAE. MACE development was accepted as the primary endpoint.

RESULTS

A total of 552 patients had CAE and MACE developed in 573 patients. Patients with CAE and higher C-peptide levels (Q4 + Q3) showed higher rates of MACE as compared to those without CAE and lower C-peptide levels (Q1 + Q2) (20.8% vs 7.6%; 70.1% vs 29.1%; p < 0.001, for both of them). In multivariate regression analysis, high C-peptide levels were determined as an independent risk factor for CAE (OR 2.417; 95% CI 2.212-2.641; p < 0.001). The Kaplan-Meier cumulative survival curves showed that the risks for MACE increased as the C-peptide levels increased. The Cox regression analysis for 5-years MACE related to the plasma C-peptide levels and presence of CAE, C-peptide, and CAE were found to be independent predictors of MACE (HR = 1.255, 95% CI: 1.164-1.336, p < 0.001 and HR = 1.012, 95% CI: 1.002-1.023, p=0.026, respectively).

CONCLUSION

Our study revealed that a high C-peptide level is an independent risk factor for CAE and that CAE and C-peptide are independent predictors for the development of MACE.

Plasma Big Endothelin-1 Level Predicted 5-Year Major Adverse Cardiovascular Events in Patients With Coronary Artery Ectasia

Background: Coronary artery ectasia (CAE) is found in about 1% of coronary angiography and is associated with poor clinical outcomes. The prognostic value of plasma big Endothelin-1 (ET-1) in CAE remains unknown. Methods: Patients with angiographically confirmed CAE from 2009 to 2015, who had big ET-1 data available were included. The primary outcome was 5-year major adverse cardiovascular events (MACE), defined as a component of cardiovascular death and non-fatal myocardial infarction (MI). Patients were divided into high or low big ET-1 groups using a cut-off value of 0.58 pmol/L, according to the receiver operating characteristic curve. Kaplan-Meier method, propensity score method, and Cox regression were used to assess the clinical outcomes in the 2 groups. Results: A total of 992 patients were included, with 260 in the high big ET-1 group and 732 in the low big ET-1 group. At 5-year follow-up, 57 MACEs were observed. Kaplan-Meier analysis and univariable Cox regression showed that patients with high big ET-1 levels were at increased risk of MACE (9.87 vs. 4.50%; HR 2.23, 95% CI 1.32-3.78, P = 0.003), cardiovascular death (4.01 vs. 1.69%; HR 2.37, 95% CI 1.02-5.48, P = 0.044), and non-fatal MI (6.09 vs. 2.84%; HR 2.17, 95% CI 1.11-4.24, P = 0.023). A higher risk of MACE in the high big ET-1 group was consistent in the propensity score matched cohort and propensity score weighted analysis. In multivariable analysis, a high plasma big ET-1 level was still an independent predictor of MACE (HR 1.82, 95% CI 1.02-3.25, P = 0.043). A combination of high plasma big ET-1 concentrate and diffuse dilation, when used to predict 5-year MACE risk, yielded a C-statistic of 0.67 (95% CI 0.59-0.74). Conclusion: Among patients with CAE, high plasma big ET-1 level was associated with increased risk of MACE, a finding that could improve risk stratification.

Metabolomic Characterization of Fatty Acids in Patients With Coronary Artery Ectasias

Background: We used a targeted metabolomics approach to identify fatty acid (FA) metabolites that distinguished patients with coronary artery ectasia (CAE) from healthy Controls and patients with coronary artery disease (CAD). Materials and methods: Two hundred fifty-two human subjects were enrolled in our study, such as patients with CAE, patients with CAD, and Controls. All the subjects were diagnosed by coronary angiography. Plasma metabolomic profiles of FAs were determined by an ultra-high-performance liquid chromatography coupled to triple quadrupole mass spectrometric (UPLC-QqQ-MS/MS). Results: Ninety-nine plasma metabolites were profiled in the discovery sets (n = 72), such as 35 metabolites of arachidonic acid (AA), eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA), 10 FAs, and 54 phospholipids. Among these metabolites, 36 metabolites of AA, EPA, and DHA showed the largest difference between CAE and Controls or CAD. 12-hydroxyeicosatetraenoic acid (12-HETE), 17(S)-hydroxydocosahexaenoic acid (17-HDoHE), EPA, AA, and 5-HETE were defined as a biomarker panel in peripheral blood to distinguish CAE from CAD and Controls in a discovery set (n = 72) and a validation set (n = 180). This biomarker panel had a better diagnostic performance than metabolite alone in differentiating CAE from Controls and CAD. The areas under the ROC curve of the biomarker panel were 0.991 and 0.836 for CAE versus Controls and 1.00 and 0.904 for CAE versus CAD in the discovery and validation sets, respectively. Conclusions: Our findings revealed that the metabolic profiles of FAs in the plasma from patients with CAE can be distinguished from those of Controls and CAD. Differences in FAs metabolites may help to interpret pathological mechanisms of CAE.

Association of the lymphocyte-to-monocyte ratio, mean diameter of coronary arteries, and uric acid level with coronary slow flow in isolated coronary artery ectasia

Background

The pathophysiology of isolated coronary artery ectasia (CAE) with the coronary slow flow (CSF) phenomenon is still unclear. The purpose of this study was to investigate the risk factors for isolated CAE complicated with CSF.

Methods

A total of 126 patients with isolated CAE were selected retrospectively. The patients were grouped into the no CSF (NCSF) group (n = 55) and the CSF group (n = 71) according to the corrected thrombolysis in myocardial infarction (TIMI) frame count (CTFC). Data on demographics, laboratory measurements, left ventricular ejection fraction (LVEF), left ventricular end-diastolic diameter (LVEDd), CTFC and diameters of three coronary arteries were collected.

Results

The proportions of males (84.5% vs. 61.8%, p = 0.004) and patients with a smoking history (63.4% vs. 43.6%, p = 0.021) were higher in the CSF group than in the NCSF group. The neutrophil-to-lymphocyte ratio (NLR) (2.08(1.68–3.21) vs. 1.89 ± 0.58, p = 0.001), mean diameter of coronary arteries (mean D) (5.50 ± 0.85 vs. 5.18 ± 0.91, p < 0.001), and uric acid (URIC) level (370.78 ± 109.79 vs. 329.15 ± 79.71, p = 0.019) were significantly higher in the CSF group, while the lymphocyte-to-monocyte ratio (LMR) (4.81 ± 1.66 vs. 5.96 ± 1.75, p < 0.001) and albumin (ALB) level (44.13 ± 4.10 vs. 45.69 ± 4.11, p = 0.036) were lower. Multivariable logistic analysis showed that the LMR (odds ratio: 0.614, 95% CI: 0.464–0.814, p = 0.001), mean D (odds ratio: 2.643, 95% CI: 1.54–4.51, p < 0.001) and URIC level (odds ratio: 1.006, 95% CI: 1.001–1.012, p = 0.018) were independent predictors of CSF in CAE.

Conclusions

The LMR was a negative independent predictor of CSF in isolated CAE, while URIC level and mean D were positive independent predictors.

Evaluation of longitudinal left ventricular function in patients with coronary artery ectasia and vitamin D deficiency by 2D speckle tracking echocardiography

OBJECTIVES

Coronary artery ectasia (CAE) is defined as the dilation of at least one segment of the coronary arteries that reaches at least 1.5 times the size of a normal neighboring segment. It has been shown that left ventricular (LV) diastolic function is impaired in patients with CAE. Also, it has been shown that LV function is impaired in vitamin D-deficient subjects compared with vitamin D-sufficient subjects and vitamin D deficiency is prevalent in CAE patients. We hypothesized that LV function is impaired in patients with CAE so we evaluated longitudinal LV myocardial function by 2D speckle tracking echocardiography (2DSTE) in patients with CAE and vitamin D deficiency without significant coronary artery stenosis and compared the results with those of subjects with vitamin D deficiency and near-normal coronary arteries.

METHODS

Our study population comprised 21 consecutive patients with CAE and without significant coronary artery stenosis (<50%) and 31 control subjects with near-normal coronary arteries. All subjects had vitamin D deficiency.

RESULTS

All 2DSTE-derived indices of longitudinal LV function, comprised of the absolute values of systolic strain (14.0±2.7% vs 15.4±2.3%, P=.039), systolic strain rate (1.2±0.2/s vs 1.3±0.2/s, P=.015), early diastolic strain rate (1.1±0.3/s vs 1.3±0.3 s^-1 , P=.030), and late diastolic strain rate (0.8±0.2/s vs 1±0.2/s^, P=.005), were reduced in the patients with CAE and vitamin D deficiency.

CONCLUSIONS

The systolic and diastolic functions of the LV in the patients with CAE and vitamin D deficiency were impaired as evaluated by 2DSTE.

Big endothelin-1 level is a useful marker for predicting the presence of isolated coronary artery ectasia

CONTEXT

Endothelin-1(ET-1) has been implicated in coronary artery disease (CAD) and may be associated with coronary artery ectasia (CAE).

OBJECTIVE

To clarify the relationship between big ET-1 and isolated CAE.

METHODS

We measured big ET-1 with ELISA in 216 patients (CAE, n = 72; CAD, n = 72; normal, n = 72) and evaluated the link with isolated CAE.

RESULTS

The level of plasma big ET-1 was significantly higher in patients with isolated CAE (p < 0.001). Big ET-1 was strongly and independently associated with CAE by multivariate analysis (OR 95%CI: 1.026 (1.018-1.034), p = 0.000).

CONCLUSIONS

Big ET-1 may be a useful predictor for the presence of isolated CAE.

Novel intracellular N-terminal truncated matrix metalloproteinase-2 isoform in skeletal muscle ischemia-reperfusion injury

Ischemia-reperfusion injury (IRI) occurs when blood returns to tissues following a period of ischemia. Reintroduction of blood flow results in the production of free radicals and reactive oxygen species that damage cells. Skeletal muscle IRI is commonly seen in orthopedic trauma patients. Experimental studies in other organ systems have elucidated the importance of extracellular and intracellular matrix metalloproteinase-2 (MMP-2) isoforms in regulating tissue damage in the setting of oxidant stress resulting from IRI. Although the extracellular full-length isoform of MMP-2 (FL-MMP-2) has been previously studied in the setting of skeletal muscle IRI, studies investigating the role of the N-terminal truncated isoform (NTT-MMP-2) in this setting are lacking. In this study, we first demonstrated significant increases in FL- and NTT-MMP-2 gene expression in C2C12 myoblast cells responding to re-oxygenation following hypoxia in vitro. We then evaluated the expression of FL- and NTT-MMP-2 in modulating skeletal muscle IRI using a previously validated murine model. NTT-MMP-2, but not FL-MMP-2 expression was significantly increased in skeletal muscle following IRI. Moreover, the expression of toll-like receptors (TLRs) -2 and -4, IL-6, OAS-1A, and CXCL1 was also significantly up-regulated following IRI. Treatment with the potent anti-oxidant pyrrolidine dithiocarbamate (PDTC) significantly suppressed NTT-MMP-2, but not FL-MMP-2 expression and improved muscle viability following IRI. This data suggests that NTT-MMP-2, but not FL-MMP-2, is the major isoform of MMP-2 involved in skeletal muscle IRI.

Extracellular Ubiquitin: Role in Myocyte Apoptosis and Myocardial Remodeling

Ubiquitin (UB) is a highly conserved low molecular weight (8.5 kDa) protein. It consists of 76 amino acid residues and is found in all eukaryotic cells. The covalent linkage of UB to a variety of cellular proteins (ubiquitination) is one of the most common posttranslational modifications in eukaryotic cells. This modification generally regulates protein turnover and protects the cells from damaged or misfolded proteins. The polyubiquitination of proteins serves as a signal for degradation via the 26S proteasome pathway. UB is present in trace amounts in body fluids. Elevated levels of UB are described in the serum or plasma of patients under a variety of conditions. Extracellular UB is proposed to have pleiotropic roles including regulation of immune response, anti-inflammatory, and neuroprotective activities. CXCR4 is identified as receptor for extracellular UB in hematopoietic cells. Heart failure represents a major cause of morbidity and mortality in western society. Cardiac remodeling is a determinant of the clinical course of heart failure. The components involved in myocardial remodeling include-myocytes, fibroblasts, interstitium, and coronary vasculature. Increased sympathetic nerve activity in the form of norepinephrine is a common feature during heart failure. Acting via β-adrenergic receptor (β-AR), norepinephrine is shown to induce myocyte apoptosis and myocardial fibrosis. β-AR stimulation increases extracellular levels of UB in myocytes, and UB inhibits β-AR-stimulated increases in myocyte apoptosis and myocardial fibrosis. This review summarizes intracellular and extracellular functions of UB with particular emphasis on the role of extracellular UB in cardiac myocyte apoptosis and myocardial remodeling.

Among Ectasia Patients with Coexisting Coronary Artery Disease, TIMI Frame Count Correlates with Ectasia Size and Markis Type IV Is the Commonest

Background. Coronary artery ectasia (CAE) occurs in 0.3 to 5.3% of patients undergoing coronary angiography. TIMI frame count (TFC) is an index of coronary flow that correlates with flow velocity. In ectasia patients, there is delayed coronary flow with increased TFC. Methods. We evaluated angiograms of 789 patients for presence of CAE, coronary artery disease (CAD), and Markis type of CAE. We measured ectasia size and length and their correlation with TFC in ectatic right coronary arteries (RCA) of patients with CAE and CAD. Results. 30 patients had CAE (3.8%). Of these 16.7% had isolated CAE, while 83.87% had CAE and CAD. Among CAE and CAD patients, the RCA was most involved (70.4%), and Markis type IV CAE was the commonest (64%). In isolated CAE, the RCA, LAD, and LCx were equally involved (33.3%). Patients with CAE and CAD had significantly higher TFC compared to controls, P = 0.035. There was a positive correlation of moderate strength, between ectasia size and TFC, r(17) = 0.598, P = 0.007. Ectasia length was not significantly correlated with TFC, rho (17) = 0.334, P = 0.163. Conclusion. Among patients undergoing angiography, CAE has a prevalence of 3.8% and Markis type IV is the commonest. Larger ectasias are associated with slower coronary flow.

Matrix metalloproteinases are involved in cardiovascular diseases

This MiniReview describes the essential biochemical and molecular aspects of matrix metalloproteinases (MMPs) and briefly discusses how they engage in different diseases, with particular emphasis on cardiovascular diseases. There is compelling scientific evidence that many MMPs, especially MMP-2, play important roles in the development of cardiovascular diseases; inhibition of these enzymes is beneficial to many cardiovascular conditions, sometimes precluding or postponing end-organ damage and fatal outcomes. Conducting comprehensive discussions and further studies on how MMPs participate in cardiovascular diseases is important, because inhibition of these enzymes may be an alternative or an adjuvant for current cardiovascular disease therapy.

N-terminal truncated intracellular matrix metalloproteinase-2 induces cardiomyocyte hypertrophy, inflammation and systolic heart failure

Matrix metalloproteinase-2 (MMP-2) is increasingly recognized as a major contributor to progressive cardiac injury within the setting of ischemia-reperfusion injury and ischemic ventricular remodeling. A common feature of these conditions is an increase in oxidative stress, a process that engages multiple pro-inflammatory and innate immunity cascades. We recently reported on the identification and characterization of an intracellular isoform of MMP-2 generated by oxidative stress-mediated activation of an alternative promoter located within the first intron of the MMP-2 gene. Transcription from this site generates an N-terminal truncated 65 kDa isoform of MMP-2 (NTT-MMP-2) that lacks the secretory sequence and the inhibitory prodomain region. The NTT-MMP-2 isoform is intracellular, enzymatically active and localizes in part to mitochondria. Expression of the NTT-MMP-2 isoform triggers Nuclear Factor of Activated T-cell (NFAT) and NF-κB signaling with the expression of a highly defined innate immunity transcriptome, including Interleukin-6, MCP-1, IRF-7 and pro-apoptotic transcripts. To determine the functional significance of the NTT-MMP-2 isoform in vivo we generated cardiac-specific NTT-MMP-2 transgenic mice. These mice developed progressive cardiomyocyte and ventricular hypertrophy associated with systolic heart failure. Further, there was evidence for cardiomyocyte apoptosis and myocardial infiltration with mononuclear cells. The NTT-MMP-2 transgenic hearts also demonstrated more severe injury following ex vivo ischemia-reperfusion injury. We conclude that a novel intracellular MMP-2 isoform induced by oxidant stress directly contributes, in the absence of superimposed injury, to cardiomyocyte hypertrophy. inflammation, systolic heart failure and enhanced susceptibility to ischemia-reperfusion injury.

Prevalence of coronary artery ectasia in older adults and the relationship with epicardial fat volume by cardiac computed tomography angiography

OBJECTIVE

Coronary artery ectasia (CAE) refers to abnormal dilation of coronary artery segments to 1.5 times of adjacent normal ones. Epicardial fat is associated with cardiovascular risk factors. The relationship between CAE and epicardial fat has not yet been investigated. This study aimed to assess the relationship between CAE and epicardial fat volume (EFV) in older people by dual-source computed tomography coronary angiography (CTCA).

METHODS

We prospectively enrolled 1400 older adults who were scheduled for dual-source CTCA. Under reconstruction protocols, patients with abnormal segments 1.5 times larger than the adjacent segments were accepted as CAE. EFV was measured by semi-automated software. Traditional risk factors in CAE patients, as well as the extent of EFV, were analyzed and compared to non-CAE group.

RESULTS

A total of 885 male and 515 female older patients were enrolled. CAE was identified by univariable analysis in 131 patients and significantly correlated to hypertension, smoking, hyperlipidemia, prior percutaneous coronary intervention and ascending aorta aneurysm. EFV was shown to be significantly higher in CAE patients than patients without ectasia. In multivariable analyses, EFV (P = 0.018), hypertension (P < 0.001) and hyperlipidemia (P < 0.001) were significantly correlated to CAE. There was a significant negative correlation between EFV and Markis classification.

CONCLUSIONS

CAE can be reliably recognized by dual-source CTCA. Epicardial fat might play a role in etiopathogenesis and progression of CAE, providing a new target for treating ectasia.

A novel intracellular isoform of matrix metalloproteinase-2 induced by oxidative stress activates innate immunity

BACKGROUND

Experimental and clinical evidence has pinpointed a critical role for matrix metalloproteinase-2 (MMP-2) in ischemic ventricular remodeling and systolic heart failure. Prior studies have demonstrated that transgenic expression of the full-length, 68 kDa, secreted form of MMP-2 induces severe systolic failure. These mice also had unexpected and severe mitochondrial structural abnormalities and dysfunction. We hypothesized that an additional intracellular isoform of MMP-2, which affects mitochondrial function is induced under conditions of systolic failure-associated oxidative stress.

METHODOLOGY AND PRINCIPAL FINDINGS

Western blots of cardiac mitochondria from the full length MMP-2 transgenics, ageing mice and a model of accelerated atherogenesis revealed a smaller 65 kDa MMP-2 isoform. Cultured cardiomyoblasts subjected to transient oxidative stress generated the 65 kDa MMP-2 isoform. The 65 kDa MMP-2 isoform was also induced by hypoxic culture of cardiomyoblasts. Genomic database analysis of the MMP-2 gene mapped transcriptional start sites and RNA transcripts induced by hypoxia or epigenetic modifiers within the first intron of the MMP-2 gene. Translation of these transcripts yields a 65 kDa N-terminal truncated isoform beginning at M(77), thereby deleting the signal sequence and inhibitory prodomain. Cellular trafficking studies demonstrated that the 65 kDa MMP-2 isoform is not secreted and is present in cytosolic and mitochondrial fractions, while the full length 68 kDa isoform was found only in the extracellular space. Expression of the 65 kDa MMP-2 isoform induced mitochondrial-nuclear stress signaling with activation of the pro-inflammatory NF-κB, NFAT and IRF transcriptional pathways. By microarray, the 65 kDa MMP-2 induces an innate immunity transcriptome, including viral stress response genes, innate immunity transcription factor IRF7, chemokines and pro-apoptosis genes.

CONCLUSION

A novel N-terminal truncated intracellular isoform of MMP-2 is induced by oxidative stress. This isoform initiates a primary innate immune response that may contribute to progressive cardiac dysfunction in the setting of ischemia and systolic failure.