An Adjuvant Stem Cell Patch with Coronary Artery Bypass Graft Surgery Improves Diastolic Recovery in Porcine Hibernating Myocardium.

Diastolic dysfunction persists despite coronary artery bypass graft surgery (CABG) in patients with hibernating myocardium (HIB). We studied whether the adjunctive use of a mesenchymal stem cells (MSCs) patch during CABG improves diastolic function by reducing inflammation and fibrosis. HIB was induced in juvenile swine by placing a constrictor on the left anterior descending (LAD) artery, causing myocardial ischemia without infarction. At 12 weeks, CABG was performed using the left-internal-mammary-artery (LIMA)-to-LAD graft with or without placement of an epicardial vicryl patch embedded with MSCs, followed by four weeks of recovery. The animals underwent cardiac magnetic resonance imaging (MRI) prior to sacrifice, and tissue from septal and LAD regions were collected to assess for fibrosis and analyze mitochondrial and nuclear isolates. During low-dose dobutamine infusion, diastolic function was significantly reduced in HIB compared to the control, with significant improvement after CABG + MSC treatment. In HIB, we observed increased inflammation and fibrosis without transmural scarring, along with decreased peroxisome proliferator-activated receptor-gamma coactivator (PGC1α), which could be a possible mechanism underlying diastolic dysfunction. Improvement in PGC1α and diastolic function was noted with revascularization and MSCs, along with decreased inflammatory signaling and fibrosis. These findings suggest that adjuvant cell-based therapy during CABG may recover diastolic function by reducing oxidant stress-inflammatory signaling and myofibroblast presence in the myocardial tissue.

Myocardial Infarction in the ISCHEMIA Trial: Impact of Different Definitions on Incidence, Prognosis, and Treatment Comparisons.

BACKGROUND: In the ISCHEMIA trial (International Study of Comparative Health Effectiveness with Medical and Invasive Approaches), an initial invasive strategy did not significantly reduce rates of cardiovascular events or all-cause mortality in comparison with a conservative strategy in patients with stable ischemic heart disease and moderate/severe myocardial ischemia. The most frequent component of composite cardiovascular end points was myocardial infarction (MI). METHODS: ISCHEMIA prespecified that the primary and major secondary composite end points of the trial be analyzed using 2 MI definitions. For procedural MI, the primary MI definition used creatine kinase-MB as the preferred biomarker, whereas the secondary definition used cardiac troponin. Procedural thresholds were >5 times the upper reference level for percutaneous coronary intervention and >10 times for coronary artery bypass grafting. Procedural MI definitions included (1) a category of elevated biomarker only events with much higher biomarker thresholds, (2) new ST-segment depression of ≥1 mm for the primary and ≥0.5 mm for the secondary definition, and (3) new coronary dissections >National Heart, Lung, and Blood Institute grade 3. We compared MI type, frequency, and prognosis by treatment assignment using both MI definitions. RESULTS: Procedural MIs accounted for 20.1% of all MI events with the primary definition and 40.6% of all MI events with the secondary definition. Four-year MI rates in patients undergoing revascularization were more frequent with the invasive versus conservative strategy using the primary (2.7% versus 1.1%; adjusted hazard ratio [HR], 2.98 [95% CI, 1.87-4.73]) and secondary (8.2% versus 2.0%; adjusted HR, 5.04 [95% CI, 3.64-6.97]) MI definitions. Type 1 MIs were less frequent with the invasive versus conservative strategy using the primary (3.40% versus 6.89%; adjusted HR, 0.53 [95% CI, 0.41-0.69]; P<0.0001) and secondary (3.48% versus 6.89%; adjusted HR, 0.53 [95% CI, 0.41-0.69]; P<0.0001) definitions. The risk of subsequent cardiovascular death was higher after a type 1 MI than after no MI using the primary (adjusted HR, 3.38 [95% CI, 2.03-5.61]; P<0.001) or secondary MI definition (adjusted HR, 3.52 [2.11-5.88]; P<0.001). CONCLUSIONS: In ISCHEMIA, type 1 MI events using the primary and secondary definitions during 5-year follow-up were more frequent with an initial conservative strategy and associated with subsequent cardiovascular death. Procedural MI rates were greater in the invasive strategy and with the use of the secondary MI definition. Registration: URL: https://www.clinicaltrials.gov; Unique identifier: NCT01471522.

Outcomes after Angiography with Sodium Bicarbonate and Acetylcysteine.

BACKGROUND: Intravenous sodium bicarbonate and oral acetylcysteine are widely used to prevent acute kidney injury and associated adverse outcomes after angiography without definitive evidence of their efficacy. METHODS: Using a 2-by-2 factorial design, we randomly assigned 5177 patients at high risk for renal complications who were scheduled for angiography to receive intravenous 1.26% sodium bicarbonate or intravenous 0.9% sodium chloride and 5 days of oral acetylcysteine or oral placebo; of these patients, 4993 were included in the modified intention-to-treat analysis. The primary end point was a composite of death, the need for dialysis, or a persistent increase of at least 50% from baseline in the serum creatinine level at 90 days. Contrast-associated acute kidney injury was a secondary end point. RESULTS: The sponsor stopped the trial after a prespecified interim analysis. There was no interaction between sodium bicarbonate and acetylcysteine with respect to the primary end point (P=0.33). The primary end point occurred in 110 of 2511 patients (4.4%) in the sodium bicarbonate group as compared with 116 of 2482 (4.7%) in the sodium chloride group (odds ratio, 0.93; 95% confidence interval [CI], 0.72 to 1.22; P=0.62) and in 114 of 2495 patients (4.6%) in the acetylcysteine group as compared with 112 of 2498 (4.5%) in the placebo group (odds ratio, 1.02; 95% CI, 0.78 to 1.33; P=0.88). There were no significant between-group differences in the rates of contrast-associated acute kidney injury. CONCLUSIONS: Among patients at high risk for renal complications who were undergoing angiography, there was no benefit of intravenous sodium bicarbonate over intravenous sodium chloride or of oral acetylcysteine over placebo for the prevention of death, need for dialysis, or persistent decline in kidney function at 90 days or for the prevention of contrast-associated acute kidney injury. (Funded by the U.S. Department of Veterans Affairs Office of Research and Development and the National Health and Medical Research Council of Australia; PRESERVE ClinicalTrials.gov number, NCT01467466 .).

Utility of nuclear stress imaging in predicting long-term outcomes one-year post CABG Surgery.

BACKGROUND: Early MPI after CABG is currently considered rarely appropriate in asymptomatic patients. This study aimed to identify prognostic value of nuclear stress-imaging post-CABG. METHODS: This was a single center prospective study looking at long-term outcomes post-CABG. Per protocol participants underwent SPECT-MPI stress testing and coronary angiogram on the same day, 1-year following CABG. Defect size was semi-quantified. The primary outcomes were the composite of death and congestive heart failure. RESULTS: Eighty-four participants underwent nuclear stress-imaging and angiography, with a median follow-up of 11.1 years. Three separate stress findings predicted the primary outcome: inability to reach stage 3 of a Bruce protocol (OR 7.3, CI 2.4-22.1, P < 0.001), LVEF < 45% (OR 4.0, CI 1.1-15.3, P = 0.041) and a moderate-large stress defect size (HR 2.31, CI 1.1-1.5, P = 0.04). These findings appear to be additive and strongest among patients who underwent exercise stress testing (HR 10.6, CI 3.6-30.6, P < 0.001). Graft disease was identified in 39 (46%) patients and compared to those individuals with no graft disease, did not predict long-term adverse outcomes (P = 0.29). CONCLUSION: In clinically stable patients early after revascularization with CABG, SPECT-MPI can identify patients at higher risk of heart failure and death.

NT-Pro BNP Predicts Myocardial Injury Post-vascular Surgery and is Reduced with CoQ10: A Randomized Double-Blind Trial.

BACKGROUND: NT-Pro BNP levels provide incremental value in perioperative risk assessment prior to major noncardiac surgery. Whether they can be pharmacologically modified in patients prior to an elective vascular operation is uncertain. METHODS: A double-blind, randomized controlled trial was implemented at a single institution. Patients were screened during their preoperative vascular clinic appointment and randomly assigned to CoQ10 (400 mg per day) versus Placebo for 3 days prior to surgery. Biomarkers, including NT-Pro BNP, troponin I and C-reactive protein were obtained prior to and following surgery for up to 48 hours. The primary endpoint was postoperative NT-Pro BNP levels, and secondary endpoint measures included myocardial injury, defined by an elevated cardiac troponin level and length of stay. RESULTS: One hundred and twenty-three patients were randomized to receive either CoQ10 (N = 62) versus Placebo (N = 61) for 3 days before vascular surgery. Preoperative cardiac risks included ischemic heart disease (N = 52), CHF (N = 12), stroke (N = 23), and diabetes mellitus (N = 48) and the planned vascular procedures were infrainguinal (N = 78), carotid (N = 36), and intraabdominal (N = 9). There were no intergroup differences in these clinical variables. NT-Pro BNP levels (median; IQs) in the CoQ10 and Placebo groups were 179 (75-347) and 217 (109-585) pg/ml, respectively, (P = 0.08) preoperatively, and 397 (211-686) and 591 (288-1,433) pg/ml respectively, (P = 0.01) at 24 hours following surgery. Patients with an elevated NT-Pro BNP had a higher incidence of myocardial injury, (58% vs. 20%; P < 0.01) and a longer hospital stay (4.4 ± 3.8 vs. 2.8 ± 3.2 days; P < 0.02) compared with individuals without an elevated NT-Pro BNP level. CONCLUSIONS: NT-Pro BNP levels predict adverse events post-vascular surgery and are lowered in those patients assigned to preoperative administration of CoQ10. TRIAL REGISTRATION: clinicaltrials.gov Identifier: NCT03956017. Among patients undergoing elective vascular surgery, 123 patients were randomized to either CoQ10 (400 mg/day) versus placebo for three days preoperatively. NT-Pro BNP levels (median; IQs) in the CoQ10 and Placebo groups were 179 (75-347) and 217 (109-585) pg/ml, respectively, (P = 0.08) preoperatively, and 397 (211-686) and 591 (288-1,433) pg/ml, respectively, (P = 0.01) post-surgery. Patients with an elevated NT-Pro BNP had a higher incidence of myocardial injury (58% vs. 20%; P < 0.01) and a longer hospital stay (4.4 ± 3.8 vs. 2.8 ± 3.2 days; P < 0.02) compared with individuals without an NT-Pro BNP elevation. In conclusion, BNP predicts adverse outcomes and can be reduced with preoperative CoQ10.

Hospital Readmission Rates Following AMI: Potential Interventions to Improve Efficiency.

OBJECTIVES: Quality of care utilization measures for patients admitted to the hospital with an acute myocardial infarction (AMI) include length of stay (LOS) and 30-day readmission rates. Our aim was to test whether efforts resulting in reduced LOS in patients diagnosed as having AMI would result in a higher risk of readmission within 30 days of hospital discharge and whether specific interventions could be targeted to reduce readmissions. METHODS: Using data supplied by the Veterans Affairs Inpatient Evaluation Center, we analyzed both the readmissions within 30 days of an AMI and LOS and determined the timing of readmissions and associated diagnoses. RESULTS: During 2013-2015, 35 (13.3%) of 263 patients with AMI were readmitted within 30 days of discharge compared with 19 (13.4%) of 142 patients during 2016 (not significant). During the same time, LOS was <3 days in most patients. From 2013 to 2015, the initial hospital time was 6 ± 6 days, whereas time out of the hospital before readmission was 11 ± 8 days; these times did not differ from 2016. Initial therapeutic decisions were based on coronary anatomy in >90% of patients with a decision to proceed with revascularization in most patients. Diagnoses during readmission to the hospital were also similar during early and later time periods and most frequently were a result of either coronary artery bypass grafting-related complications from the initial hospitalization or elective coronary artery bypass grafting. Acute coronary syndrome-related diagnoses and recurrent noncardiac causes of chest pain also were common diagnoses during both time periods and did not involve extensive workup during the readmission. CONCLUSIONS: Readmissions for patients with AMI were stable during a 4-year period, at a time that efforts to reduce LOS were emphasized. Because a significant proportion of readmissions involved noncardiac sources of chest pain, improved communication between the emergency department and in-patient cardiology services at the time of triage may be a feasible way to improve efficiency of utilization.

Pioglitazone increases PGC1-α signaling within chronically ischemic myocardium.

The peroxisome proliferator-activated receptor (PPAR)-γ drug pioglitazone (PIO) has been shown to protect tissue against oxidant stress. In a swine model of chronic myocardial ischemia, we tested whether PIO increases PGC1-α signaling and the expression of mitochondrial antioxidant peptides. Eighteen pigs underwent a thoracotomy with placement of a fixed constrictor around the LAD artery. At 8 weeks, diet was supplemented with either PIO (3 mg/kg) or placebo for 4 weeks. Regional myocardial function and blood flow were determined at the time of the terminal study. PGC1-α expression was quantified from nuclear membranes by gels and respiration, oxidant stress markers and proteomics by iTRAQ were determined from isolated mitochondria. In the chronically ischemic LAD region, wall thickening from the PIO and control groups was 42 ± 6 and 45 ± 5 %, respectively (NS) with no intergroup differences in basal blood flow (0.72 ± 0.04 versus 0.74 ± 0.04 ml/min g, respectively; NS). In the PIO group, the expression of nuclear bound PGC1-α was higher (11.3 ± 2.6 versus 4.4 ± 1.4 AU; P < 0.05) and the content of mitochondrial antioxidant peptides including superoxide dismutase 2, aldose reductase, glutathione S-transferase and thioredoxin reductase were greater than controls. Although isolated mitochondria from the PIO group showed lower state 3 respiration (102 ± 13 versus 161 ± 22 nmol/min mg; P < 0.05), no differences in oxidant stress were noted by protein carbonyl (1.7 ± 0.7 versus 1.1 ± 0.1 nmol/mg). Chronic pioglitazone does not reduce regional myocardial blood flow or function in a swine model of chronic myocardial ischemia, but may have an important role in increasing expression of antioxidant proteins through PGC1-α signaling.

Mitochondrial fusion proteins in revascularized hibernating hearts.

BACKGROUND: Hibernating myocardium is characterized by viable yet dysfunctional myocardium secondary to chronic ischemia, with studies demonstrating incomplete early recovery after coronary artery bypass graft (CABG). We tested whether mitochondrial fusion proteins, an indicator of mitochondrial biogenesis, are increased in hibernating myocardium post-CABG. METHODS: A constrictor was placed on the left anterior descending (LAD) artery of nine pigs. Four of these pigs additionally underwent CABG 12 wk later with a left internal mammary artery graft to the LAD distal to the constrictor. Five pigs had a constrictor placed but did not undergo CABG (Hib). Five pigs did not have a constrictor placed (control). Computerized tomography angiography was used to confirm stenosis at the site of constrictor placement and patency of left internal mammary artery grafts. Regional blood flows were determined at baseline and during 40 µg/kg/min dobutamine infusion. Mitochondrial proteins were quantified by Western blot. RESULTS: Blood flow in the LAD region after CABG was lower than remote regions during dobutamine infusion (2.54 ± 0.24 versus 3.46 ± 0.33 mL/min/g; P < 0.05). Electron transport chain proteins were ∼70% lower in Hib compared with those in control and failed to normalize after CABG. Post-CABG, PGC1α nuclear-bound content was increased compared with Hib (9.02 ± 0.48 versus 5.54 ± 0.98 arbitrary units, respectively; P < 0.05), and expression of mitofusins-1 and 2 and optic atrophy-1 more than doubled. CONCLUSIONS: PGC1α and mitochondrial fusion proteins are increased 4 wk post-CABG in hibernating hearts, indicating mitochondrial fusion has begun to occur and signaling early mitochondrial recovery. Future studies should address changes in maximal myocardial oxygen consumption relative to mitochondrial protein expression.

Expression of uncoupling protein-2 remains increased within hibernating myocardium despite successful coronary artery bypass grafting at 4 wk post-revascularization.

BACKGROUND: We have previously shown that mitochondrial uncoupling protein-2 (UCP-2) is increased in a swine model of hibernating myocardium (HM). Although UCP-2 reduces oxidant stress, it can promote inefficiency of the electron transport chain. In this study, we tested whether UCP-2 remains increased in revascularized HM (RHM) after coronary artery bypass grafting (CABG). METHODS: Seven swine underwent thoracotomy with placement of a constrictor on the left anterior descending artery (LAD). Twelve weeks later, a left internal mammary artery graft was placed on the distal LAD. Four weeks post-CABG, computed tomography angiography documented patent grafts and function. At the terminal study, blood flow to the LAD and remote territories were assessed during high dose dobutamine and mitochondria isolated from both regions for analysis. Comparisons were made to a group of swine with HM who underwent constrictor placement without bypass grafting (n = 4). RESULTS: During dobutamine infusion, RHM demonstrated lower blood flows (2.44 ± 0.23 versus 3.43 ± 0.30 mL/min/g; P < 0.05) and reduced wall thickening (33 ± 9% versus 52 ± 13%; P < 0.05) compared with remote regions. RHM had lower respiratory control indices (3.7 ± 0.3 versus 4.3 ± 0.4; P < 0.05) with persistently increased UCP-2 content. CONCLUSIONS: Despite patent grafts, RHM demonstrates a submaximal response to dobutamine infusion and increased mitochondrial UCP-2 expression. These data support the notion that recovery of the mitochondria in RHM is delayed early post-CABG and may contribute to impaired oxygen consumption and contractile reserve during catecholamine challenges.

Recovery of hibernating myocardium: what is the role of surgical revascularization?

Myocardial responses to chronic ischemia represent a continuum of adaptations resulting, over time, in a stress-resistant phenotype. One such adaptation, hibernating myocardium (HM), has increased antioxidant capacity that protects against ischemia-induced oxidative stress. Studies have suggested that revascularization alone may not fully restore cardiac function, highlighting the need for targeted therapies to serve as adjuncts to the innate healing process following revascularization. In our review, we discuss current understanding of HM and the recovery process following surgical revascularization, focusing on animal models of HM to understand implications for human patients.

Reduced expression of mitochondrial electron transport chain proteins from hibernating hearts relative to ischemic preconditioned hearts in the second window of protection.

Although protection against necrosis has been observed in both hibernating (HIB) and ischemic preconditioned hearts in the second window of protection (SWOP), a comparison of the mitochondrial proteome between the two entities has not been previously performed. Anesthetized swine underwent instrumentation with a fixed constrictor around the LAD artery and were followed for 12 weeks (HIB; N=7). A second group of anesthetized swine underwent ischemic preconditioning by inflating a balloon within the LAD artery 10 times for 2 min, each separated by 2 min reperfusion and were sacrificed 24h later (SWOP; N=7). Myocardial blood flow and high-energy nucleotides were obtained in the LAD region and normalized to remote regions. Post-sacrifice, protein content as measured with iTRAQ was compared in isolated mitochondria from the LAD area of a Sham heart. Basal regional blood flow in the LAD region when normalized to the remote region was 0.86±0.04 in HIB and 1.02±0.02 in SWOP tissue (P<0.05). Despite reduced regional blood flows in HIB hearts, ATP content in the LAD region, when normalized to the remote region was similar in HIB versus SWOP (1.06±0.06 and 1.02±0.05 respectively; NS) as was the transmural phosphocreatine (PCr) to ATP ratio (2.1±0.2 and 2.2±0.2 respectively; NS). Using iTRAQ, 64 common proteins were identified in HIB and SWOP hearts. Compared with SWOP, the relative abundance of mitochondrial proteins involved with electron transport chain (ETC) were reduced in HIB including NADH dehydrogenase, Cytochrome c reductase and oxidase, ATP synthase, and nicotinamide nucleotide transhydrogenase. Within chronically HIB heart tissue with reduced blood flow, the relative abundance of mitochondrial ETC proteins is decreased when compared with SWOP tissue. These data support the concept that HIB heart tissue subjected to chronically reduced blood flow is associated with a down-regulation in the expression of key mitochondrial proteins involved in electron transport.

Prognostic value of 12-lead electrocardiogram and peak troponin I level after vascular surgery.

OBJECTIVE: The aim of this investigation was to determine if the presence of ischemic electrocardiographic (ECG) changes in patients undergoing vascular surgery provides incremental prognostic information about the long-term risk of death compared with a single peak troponin level within 48 hours after surgery. METHODS: This was a retrospective analysis of 337 patients undergoing moderate-risk to high-risk vascular surgery at our institution whose ECG and biomarker data were complete. Peak cardiac troponin (cTn) I values that exceeded the upper reference limit (URL) were categorized as low-positive (+), at or exceeding the URL but less than three times the URL, or high-positive (+), at or exceeding three times the URL. ECGs were classified as ischemic or nonischemic. The primary outcome was death at 1 year after the vascular operation. Independent predictors of long-term mortality were determined by Cox proportional hazards regression analysis. RESULTS: The most common vascular problem was an expanding abdominal aortic aneurysm (n=185 [55%]). With regard to cTnI, 53 patients (16%) were classified as high (+) and 82 (24%) as low (+). The ECG in 21 patients (6%) showed evidence of myocardial ischemia. An increase in 1-year mortality of 3% for normal, 11% for low (+), and 17% for high (+) (P<.01) was seen with incremental cTn values. Independent predictors of long-term mortality were age (odds ratio [OR], 1.05, 95% confidence interval [CI], 1.02-1.07; P<.01), stratified troponin (OR, 1.62; 95% CI, 1.25-2.10; P<.01), tissue loss (OR, 3.30; 95% CI, 1.72-6.33; P<.01), stratified Revised Cardiac Risk Index (OR, 1.32; 95% CI, 0.97-1.81; P<.07), and statin use (OR, 0.62; 95% CI, 0.40-0.98; P=.04). The presence of ischemia on ECG was not a predictor of long-term mortality. CONCLUSIONS: In the presence of an elevated cTn I, the ECG is not an independent predictor of long-term mortality after vascular surgery. These results support a strategy of routine surveillance of cTns after vascular surgery for the detection of cardiac events and postoperative risk stratification.

Troponin elevations following vascular surgery in patients without preoperative myocardial ischemia.

OBJECTIVES: A normal preoperative myocardial perfusion-imaging (MPI) test in advance of vascular surgery predicts a low risk of postoperative clinical events at 30 days. Among patients undergoing vascular surgery with a normal preoperative MPI, cardiac troponin I (cTnI) elevations are common and predictive of a poor long-term outcome. METHODS: The study cohort comprised 182 patients. Between January 2005 and December 2009, we studied these patients, who had no evidence of myocardial ischemia on preoperative MPI and were undergoing vascular surgery. Blood was obtained in all of the patients in the first 2 days following vascular surgery, and cTnI levels were measured. The values that exceeded the upper reference limit (URL) were categorized as either low (+) (greater than or equal to the URL but less than three times the URL) or high (+) (greater than or equal to three times the URL). Long-term survival was determined from the time of the vascular operation. RESULTS: The mean age of the population was 69 ± 8 years, and the mean revised cardiac risk index was 1.80 ± 0.77. The most common indication for vascular intervention was an expanding abdominal aortic aneurysm (n = 96, 52.5%). Within 48 hours of surgery, 58 patients (32%) had a typical rise and fall in TnI, with at least one value exceeding the URL. Of these patients, 17 (9%) were classified as high (+) and 41 (22.5%) as low (+). At 1 year post-vascular surgery, mortality was 8% for the overall cohort. A high (+) Tn elevation was an identifier of decreased 1-year survival (29%) relative to normal (3%) and low (+) (14%; P < 0.001). Stratified cTn was an independent predictor of the long-term risk of death. CONCLUSIONS: Among patients undergoing vascular procedures without evidence of myocardial ischemia on MPI, an elevation in TnI is common and predictive of long-term mortality risk.

Surgical Porcine Model of Chronic Myocardial Ischemia Treated by Exosome-laden Collagen Patch and Off-pump Coronary Artery Bypass Graft.

Chronic myocardial ischemia resulting from progressive coronary artery stenosis leads to hibernating myocardium (HIB), defined as myocardium that adapts to reduced oxygen availability by reducing metabolic activity, thereby preventing irreversible cardiomyocyte injury and infarction. This is distinct from myocardial infarction, as HIB has the potential for recovery with revascularization. Patients with significant coronary artery disease (CAD) experience chronic ischemia, which puts them at risk for heart failure and sudden death. The standard surgical intervention for severe CAD is coronary artery bypass graft surgery (CABG), but it has been shown to be an imperfect therapy, yet no adjunctive therapies exist to recover myocytes adapted to chronic ischemia. To address this gap, a surgical model of HIB using porcine that is amenable to CABG and mimics the clinical scenario was used. The model involves two surgeries. The first operation involves implanting a 1.5 mm rigid constrictor on the left anterior descending (LAD) artery. As the animal grows, the constrictor gradually causes significant stenosis resulting in reduced regional systolic function. Once the stenosis reaches 80%, the myocardial flow and function are impaired, creating HIB. An off-pump CABG is then performed with the left internal mammary artery (LIMA) to revascularize the ischemic region. The animal recovers for one month to allow for optimal myocardial improvement prior to sacrifice. This allows for physiologic and tissue studies of different treatment groups. This animal model demonstrates that cardiac function remains impaired despite CABG, suggesting the need for novel adjunctive interventions. In this study, a collagen patch embedded with mesenchymal stem cell (MSC)-derived exosomes was developed, which can be surgically applied to the epicardial surface distal to LIMA anastomosis. The material conforms to the epicardium, is absorbable, and provides the scaffold for the sustained release of signaling factors. This regenerative therapy can stimulate myocardial recovery that does not respond to revascularization alone. This model translates to the clinical arena by providing means of physiological and mechanistic explorations regarding recovery in HIB.

Stem cell-derived exosome patch with coronary artery bypass graft restores cardiac function in chronically ischemic porcine myocardium.

OBJECTIVE: This study aimed to investigate whether or not the application of a stem cell-derived exosome-laden collagen patch (EXP) during coronary artery bypass grafting (CABG) can recover cardiac function by modulating mitochondrial bioenergetics and myocardial inflammation in hibernating myocardium (HIB), which is defined as myocardium with reduced blood flow and function that retains viability and variable contractile reserve. METHODS: In vitro methods involved exposing H9C2 cardiomyocytes to hypoxia followed by normoxic coculture with porcine mesenchymal stem cells. Mitochondrial respiration was measured using Seahorse assay. GW4869, an exosomal release antagonist, was used to determine the effect of mesenchymal stem cells-derived exosomal signaling on cardiomyocyte recovery. Total exosomal RNA was isolated and differential micro RNA expression determined by sequencing. In vivo studies comprised 48 Yorkshire-Landrace juvenile swine (6 normal controls, 17 HIB, 19 CABG, and 6 CABG + EXP), which were compared for physiologic and metabolic changes. HIB was created by placing a constrictor on the proximal left anterior descending artery, causing significant stenosis but preserved viability by 12 weeks. CABG was performed with or without mesenchymal stem cells-derived EXP application and animals recovered for 4 weeks. Before terminal procedure, cardiac magnetic resonance imaging at rest, and with low-dose dobutamine, assessed diastolic relaxation, systolic function, graft patency, and myocardial viability. Tissue studies of inflammation, fibrosis, and mitochondrial morphology were performed posttermination. RESULTS: In vitro data demonstrated improved cardiomyocyte mitochondrial respiration upon coculture with MSCs that was blunted when adding the exosomal antagonist GW4869. RNA sequencing identified 8 differentially expressed micro RNAs in normoxia vs hypoxia-induced exosomes that may modulate the expression of key mitochondrial (peroxisome proliferator-activator receptor gamma coactivator 1-alpha and adenosine triphosphate synthase) and inflammatory mediators (nuclear factor kappa-light-chain enhancer of activated B cells, interferon gamma, and interleukin 1ß). In vivo animal magnetic resonance imaging studies demonstrated regional systolic function and diastolic relaxation to be improved with CABG + EXP compared with HIB (P = .02 and P = .02, respectively). Histologic analysis showed increased interstitial fibrosis and inflammation in HIB compared with CABG + EXP. Electron microscopy demonstrated increased mitochondrial area, perimeter, and aspect ratio in CABG + EXP compared with HIB or CABG alone (P < .0001). CONCLUSIONS: Exosomes recovered cardiomyocyte mitochondrial respiration and reduced myocardial inflammation through paracrine signaling, resulting in improved cardiac function.

Persistent diastolic dysfunction in chronically ischemic hearts following coronary artery bypass graft.

OBJECTIVE: A porcine model was used to study diastolic dysfunction in hibernating myocardium (HM) and recovery with coronary artery bypass surgery (CABG). METHODS: HM was induced in Yorkshire-Landrace juvenile swine (n = 30) by placing a c-constrictor on left anterior descending artery causing chronic myocardial ischemia without infarction. At 12 weeks, animals developed the HM phenotype and were either killed humanely (HIB group; n = 11) or revascularized with CABG and allowed 4 weeks of recovery (HIB+CABG group; n = 19). Control pigs were matched for weight, age, and sex to the HIB group. Before the animals were killed humanely, cardiac magnetic resonance imaging (MRI) was done at rest and during a low-dose dobutamine infusion. Tissue was obtained for histologic and proinflammatory biomarker analyses. RESULTS: Diastolic peak filling rate was lower in HIB compared with control (5.4 ± 0.7 vs 6.7 ± 1.4 respectively, P = .002), with near recovery with CABG (6.3 ± 0.8, P = .06). Cardiac MRI confirmed preserved global systolic function in all groups. Histology confirmed there was no transmural infarction but showed interstitial fibrosis in the endomysium in both the HIB and HIB+CABG groups compared with normal myocardium. Alpha-smooth muscle actin stain identified increased myofibroblasts in HM that were less apparent post-CABG. Cytokine and proteomic studies in HM showed decreased peroxisome proliferator-activator receptor gamma coactivator 1-alpha (PGC1-α) expression but increased expression of granulocyte-macrophage colony-stimulating factor and nuclear factor kappa-light-chain enhancer of activated B cells (NFκB). Following CABG, PGC1-α and NFκB expression returned to control whereas granulocyte-macrophage colony-stimulating factor, tumor necrosis factor-α, and interferon gamma remained increased. CONCLUSIONS: In porcine model of HM, increased NFκB expression, enhanced myofibroblasts, and collagen deposition along with decreased PGC1-α expression were observed, all of which tended toward normal with CABG. Estimates of impaired relaxation with MRI within HM during increased workload persisted despite CABG, suggesting a need for adjuvant therapies during revascularization.

Altered expression of mitochondrial electron transport chain proteins and improved myocardial energetic state during late ischemic preconditioning.

Altered expression of mitochondrial electron transport proteins has been shown in early preconditioned myocardial tissue. We wished to determine whether these alterations persist in the Second Window of Protection (SWOP) and if so, whether a favorable energetic state is facilitated during subsequent ischemia. Fourteen pigs underwent a SWOP protocol with ten 2-minute balloon inflations in the LAD artery, each separated by 2 minutes reperfusion. Twenty-four hours later, mitochondria were isolated from SWOP and SHAM pig hearts and analyzed for uncoupling protein (UCP)-2 content by western blot analysis, proteomic changes by iTRAQ(®) and respiration by an oxygen electrode. In parallel in vivo studies, high-energy nucleotides were obtained by transmural biopsy from anesthetized SWOP and SHAM pigs at baseline and during sustained low-flow ischemia. Compared with SHAM mitochondria, ex vivo SWOP heart tissue demonstrated increased expression of UCP-2, Complex IV (cytochrome c oxidase) and Complex V (ATPase) proteins. In comparison with SHAM pigs during in vivo conditions, transmural energetics in SWOP hearts, as estimated by the free energy of ATP hydrolysis (ΔG(0)), were similar at baseline but had decreased by the end of low-flow ischemia (-57.0 ± 2.1 versus -51.1 ± 1.4 kJ/mol; P < 0.05). In conclusion, within isolated mitochondria from preconditioned SWOP hearts, UCP-2 is increased and in concert with enhanced Complex IV and V proteins, imparts a favorable energetic state during low-flow ischemia. These data support the notion that mitochondrial adaptations that may reduce oxidant damage do not reduce the overall efficiency of energetics during sustained oxygen deprivation.

Utility of nuclear stress imaging for detecting coronary artery bypass graft disease.

BACKGROUND: The value of single photon emission computed tomography stress myocardial perfusion imaging (SPECT-MPI) for detecting graft disease after coronary artery bypass surgery (CABG) has not been studied prospectively in an unselected cohort. METHODS: Radial Artery Versus Saphenous Vein Graft Study is a Veterans Affairs Cooperative Study to determine graft patency rates after CABG surgery. Seventy-nine participants agreed to SPECT-MPI within 24 hours of their coronary angiogram, one-year after CABG. The choice of the stress protocol was made at the discretion of the nuclear radiologist and was either a symptom-limited exercise test (n = 68) or an adenosine infusion (n = 11). The SPECT-MPI results were interpreted independent of the angiographic results and estimates of sensitivity, specificity and accuracy were based on the prediction of a graft stenosis of ≥70% on coronary angiogram. RESULTS: A significant stenosis was present in 38 (48%) of 79 patients and 56 (22%) of 251 grafts. In those stress tests with an optimal exercise heart rate response (>80% maximum predicted heart rate) (n = 26) sensitivity, specificity and accuracy of SPECT-MPI for predicting the graft stenosis was 77%, 69% and 73% respectively. With adenosine (n = 11) it was 75%, 57% and 64%, respectively. Among participants with a suboptimal exercise heart rate response, the sensitivity of SPECT-MPI for predicting a graft stenosis was <50%. The accuracy of SPECT-MPI for detecting graft disease did not vary significantly with ischemic territory. CONCLUSIONS: Under optimal stress conditions, SPECT-MPI has a good sensitivity and accuracy for detecting graft disease in an unselected patient population 1 year post-CABG.

The Troponin Complex: Discriminating the Signal from the Noise.

Patients presenting to the emergency department with consideration of an acute coronary syndrome (ACS) are risk-stratified with sensitive troponin assays. Among many patients who present with symptoms other than chest pain, they are admitted for observation if the troponin assay is above the upper reference limit of that specific assay. With the advent of high-sensitivity troponin assays, it is estimated that the prevalence of admissions for secondary myocardial infarctions, termed type 2 myocardial infarctions and myocardial injury, will increase by 100%. This is a heterogeneous population, and although adverse outcomes such as readmission and death are high, outcome-based therapies with guideline-directed treatments have not been advanced in this subset. As such, the clinician is often confused about the optimal treatment at hospital discharge. More studies should address the value of specific known therapies in this cohort that have been shown to improve outcomes in patients with an acute coronary syndrome or type 1 myocardial infarction.

Novel Therapeutic Approaches Enhance PGC1-alpha to Reduce Oxidant Stress-Inflammatory Signaling and Improve Functional Recovery in Hibernating Myocardium.

Ischemic heart disease affects millions of people around the world. Current treatment options, including coronary artery bypass grafting, do not result in full functional recovery, highlighting the need for novel adjunctive therapeutic approaches. Hibernation describes the myocardial response to prolonged ischemia and involves a set of complex cytoprotective metabolic and functional adaptations. PGC1-alpha, a key regulator of mitochondrial energy metabolism and inhibitor of oxidant-stress-inflammatory signaling, is known to be downregulated in hibernating myocardium. PGC1-alpha is a critical component of cellular stress responses and links cellular metabolism with inflammation in the ischemic heart. While beneficial in the acute setting, a chronic state of hibernation can be associated with self-perpetuating oxidant stress-inflammatory signaling which leads to tissue injury. It is likely that incomplete functional recovery following revascularization of chronically ischemic myocardium is due to persistence of metabolic changes as well as prooxidant and proinflammatory signaling. Enhancement of PGC1-alpha signaling has been proposed as a possible way to improve functional recovery in patients with ischemic heart disease. Adjunctive mesenchymal stem cell therapy has been shown to induce PGC1-alpha signaling in hibernating myocardium and could help improve clinical outcomes for patients undergoing bypass surgery.