Mechanisms of chronic regional postischemic dysfunction in humans. New insights from the study of noninfarcted collateral-dependent myocardium

PET Imaging for Cardiomyopathy Challenges Simplistic Notions of Ischemia and Viability

PET of the myocardium in patients with low ejection fraction has classically focused on identifying ischemic and viable myocardium. In this review, we use a case-based format to challenge these simplistic notions while integrating the results from recent clinical trials. The basic message is that, for most patients, severely reduced left ventricular function is due predominantly to nonischemic cardiomyopathy, not scar or ischemia. Consequently, we emphasize several practical pitfalls when using cardiac PET imaging in this population to improve its clinical value.

Metabolomics of repetitive myocardial stunning in chronic multivessel coronary artery stenosis: Effect of non-selective and selective β1-receptor blockers

Chronic coronary artery stenosis can lead to regional myocardial dysfunction in the absence of myocardial infarction by repetitive stunning, hibernation or both. The molecular mechanisms underlying repetitive stunning-associated myocardial dysfunction are not clear. We used non-targeted metabolomics to elucidate responses to chronically stunned myocardium in a canine model with and without β-adrenergic blockade treatment. After development of left ventricular systolic dysfunction induced by ameroid constrictors on the coronary arteries, animals were randomized to 3 months of placebo, metoprolol or carvedilol. We compared these two β-blockers with their different β-adrenergic selectivities on myocardial function, perfusion and metabolic pathways involved in tissue undergoing chronic stunning. Control animals underwent sham surgery. Dysfunction in stunned myocardium was associated with reduced fatty acid oxidation and enhanced ketogenic amino acid metabolism, together with alterations in mitochondrial membrane phospholipid composition. These changes were consistent with impaired mitochondrial function and were linked to reduced nitric oxide and peroxisome proliferator-activated receptor signalling, resulting in a decline in adenosine monophosphate-activated protein kinase. Mitochondrial changes were ameliorated by carvedilol more than metoprolol, and improvement was linked to nitric oxide and possibly hydrogen sulphide signalling. In summary, repetitive myocardial stunning commonly seen in chronic multivessel coronary artery disease is associated with adverse metabolic remodelling linked to mitochondrial dysfunction and specific signalling pathways. These changes are reversed by β-blockers, with the non-selective inhibitor having a more favourable impact. This is the first investigation to demonstrate that β-blockade-associated improvement of ventricular function in chronic myocardial stunning is associated with restoration of mitochondrial function. KEY POINTS: The mechanisms responsible for the metabolic changes associated with repetitive myocardial stunning seen in chronic multivessel coronary artery disease have not been fully investigated. In a canine model of repetitive myocardial stunning, we showed that carvedilol, a non-selective β-receptor blocker, ameliorated adverse metabolic remodelling compared to metoprolol, a selective β1-receptor blocker, by improving nitric oxide synthase and adenosine monophosphate protein kinase function, enhancing calcium/calmodulin-dependent protein kinase, probably increasing hydrogen sulphide, and suppressing cyclic-adenosine monophosphate signalling. Mitochondrial fatty acid oxidation alterations were ameliorated by carvedilol to a larger extent than metoprolol; this improvement was linked to nitric oxide and possibly hydrogen sulphide signalling. Both β-blockers improved the cardiac energy imbalance by reducing metabolites in ketogenic amino acid and nucleotide metabolism. These results elucidated why metabolic remodelling with carvedilol is preferable to metoprolol when treating chronic ischaemic left ventricular systolic dysfunction caused by repetitive myocardial stunning.

Myocardial ischemia/reperfusion: Translational pathophysiology of ischemic heart disease

Ischemic heart disease is the greatest health burden and most frequent cause of death worldwide. Myocardial ischemia/reperfusion is the pathophysiological substrate of ischemic heart disease. Improvements in prevention and treatment of ischemic heart disease have reduced mortality in developed countries over the last decades, but further progress is now stagnant, and morbidity and mortality from ischemic heart disease in developing countries are increasing. Significant problems remain to be resolved and require a better pathophysiological understanding. The present review attempts to briefly summarize the state of the art in myocardial ischemia/reperfusion research, with a view on both its coronary vascular and myocardial aspects, and to define the cutting edges where further mechanistic knowledge is needed to facilitate translation to clinical practice.

The Evolving Paradigm of Revascularization in Ischemic Cardiomyopathy: from Recovery of Systolic Function to Protection Against Future Ischemic Events

PURPOSE OF REVIEW

We aim to reevaluate how the assessment of myocardial viability can guide optimal treatment strategies for patients with ischemic cardiomyopathy (ICM) based on a more contemporary understanding of the mechanism of benefit of revascularization.

RECENT FINDINGS

The assessment of viability in left ventricular (LV) segments with diminished contraction has been proposed as key to predict the benefit of revascularization and, therefore, as a requisite for the selection of patients to undergo this form of treatment. However, data from prospective trials have diverged from earlier retrospective studies. Traditional binary viability assessment may oversimplify ICM's complexity and the nuances of revascularization benefits. A conceptual shift from the traditional paradigm centered on the assessment of viability as a dichotomous variable to a more comprehensive approach encompassing a thorough understanding of ICM's complex pathophysiology and the salutary effect of revascularization in the prevention of myocardial infarction and ventricular arrhythmias is required.

Myocardial Viability Testing in the Management of Ischemic Heart Failure

Although major advances have occurred lately in medical therapy, ischemic heart failure remains an important cause of death and disability. Viable myocardium represents a cause of reversible ischemic left ventricular dysfunction. Coronary revascularization may improve left ventricular function and prognosis in patients with viable myocardium. Although patients with impaired left ventricular function and multi-vessel coronary artery disease benefit the most from revascularization, they are at high risk of complications related to revascularization procedure. An important element in selecting the patients for myocardial revascularization is the presence of the viable myocardium. Multiple imaging modalities can assess myocardial viability and predict functional improvement after revascularization, with dobutamine stress echocardiography, nuclear imaging tests and magnetic resonance imaging being the most frequently used. However, the role of myocardial viability testing in the management of patients with ischemic heart failure is still controversial due to the failure of randomized controlled trials of revascularization to reveal clear benefits of viability testing. This review summarizes the current knowledge regarding the concept of viable myocardium, depicts the role and tools for viability testing, discusses the research involving this topic and the controversies related to the utility of myocardial viability testing and provides a patient-centered approach for clinical practice.

A model combining rest-only ECG-gated SPECT myocardial perfusion imaging and cardiovascular risk factors can effectively predict obstructive coronary artery disease

Objective

The rest-only single photon emission computerized tomography (SPECT) myocardial perfusion imaging (MPI) had low sensitivity in diagnosing obstructive coronary artery disease (CAD). Improving the efficacy of resting MPI in diagnosing CAD has important clinical significance for patients with contraindications to stress. The purpose of this study was to develop and validate a model predicting obstructive CAD in suspected CAD patients, based on rest-only MPI and cardiovascular risk factors.

Methods

A consecutive retrospective cohort of 260 suspected CAD patients who underwent rest-only gated SPECT MPI and coronary angiography was constructed. All enrolled patients had stress MPI contraindications. Clinical data such as age and gender were collected. Automated quantitative analysis software QPS and QGS were used to evaluate myocardial perfusion and function parameters. The least absolute shrinkage and selection operator (LASSO) and multivariable logistic regression were used to select the variables and build the prediction model.

Results

Among the enrolled 260 patients with suspected CAD, there were 95 (36.5%, 95/260) patients with obstructive CAD. The prediction model was presented in the form of a nomogram and developed based on selected predictors, including age, sex, SRS ≥ 4, SMS ≥ 2, STS ≥ 2, hypertension, diabetes, and hyperlipidemia. The AUC of the prediction model was 0.795 (95% CI: 0.741–0.843), which was better than the traditional models. The AUC calculated by enhanced bootstrapping validation (500 bootstrap resamples) was 0.785. Subsequently, the calibration curve (intercept = − 0.106; slope = 0.843) showed a good calibration of the model. The decision curve analysis (DCA) shows that the constructed clinical prediction model had good clinical applications.

Conclusions

In patients with suspected CAD and contraindications to stress MPI, a prediction model based on rest-only ECG-gated SPECT MPI and cardiovascular risk factors have been developed and validated to predict obstructive CAD effectively.

Coronary blood flow in heart failure: cause, consequence and bystander

Heart failure is a clinical syndrome where cardiac output is not sufficient to sustain adequate perfusion and normal bodily functions, initially during exercise and in more severe forms also at rest. The two most frequent forms are heart failure of ischemic origin and of non-ischemic origin. In heart failure of ischemic origin, reduced coronary blood flow is causal to cardiac contractile dysfunction, and this is true for stunned and hibernating myocardium, coronary microembolization, myocardial infarction and post-infarct remodeling, possibly also for the takotsubo syndrome. The most frequent form of non-ischemic heart failure is dilated cardiomyopathy, caused by genetic mutations, myocarditis, toxic agents or sustained tachyarrhythmias, where alterations in coronary blood flow result from and contribute to cardiac contractile dysfunction. Hypertrophic cardiomyopathy is caused by genetic mutations but can also result from increased pressure and volume overload (hypertension, valve disease). Heart failure with preserved ejection fraction is characterized by pronounced coronary microvascular dysfunction, the causal contribution of which is however not clear. The present review characterizes the alterations of coronary blood flow which are causes or consequences of heart failure in its different manifestations. Apart from any potentially accompanying coronary atherosclerosis, all heart failure entities share common features of impaired coronary blood flow, but to a different extent: enhanced extravascular compression, impaired nitric oxide-mediated, endothelium-dependent vasodilation and enhanced vasoconstriction to mediators of neurohumoral activation. Impaired coronary blood flow contributes to the progression of heart failure and is thus a valid target for established and novel treatment regimens.

A pathophysiological compass to personalize antianginal drug treatment

Myocardial ischaemia results from coronary macrovascular or microvascular dysfunction compromising the supply of oxygen and nutrients to the myocardium. The underlying pathophysiological processes are manifold and encompass atherosclerosis of epicardial coronary arteries, vasospasm of large or small vessels and microvascular dysfunction - the clinical relevance of which is increasingly being appreciated. Myocardial ischaemia can have a broad spectrum of clinical manifestations, together denoted as chronic coronary syndromes. The most common antianginal medications relieve symptoms by eliciting coronary vasodilatation and modulating the determinants of myocardial oxygen consumption, that is, heart rate, myocardial wall stress and ventricular contractility. In addition, cardiac substrate metabolism can be altered to alleviate ischaemia by modulating the efficiency of myocardial oxygen use. Although a universal agreement exists on the prognostic importance of lifestyle interventions and event prevention with aspirin and statin therapy, the optimal antianginal treatment for patients with chronic coronary syndromes is less well defined. The 2019 guidelines of the ESC recommend a personalized approach, in which antianginal medications are tailored towards an individual patient's comorbidities and haemodynamic profile. Although no antianginal medication improves survival, their efficacy for reducing symptoms profoundly depends on the underlying mechanism of the angina. In this Review, we provide clinicians with a rationale for when to use which compound or combination of drugs on the basis of the pathophysiology of the angina and the mode of action of antianginal medications.

Myocardial Viability Assessment Before Surgical Revascularization in Ischemic Cardiomyopathy: JACC Review Topic of the Week

Ischemic cardiomyopathy results from the combination of scar with fibrosis replacement and areas of dysfunctional but viable myocardium that may improve contractile function with revascularization. Observational studies reported that only patients with substantial amounts of myocardial viability had better outcomes following surgical revascularization. Accordingly, dedicated noninvasive techniques have evolved to quantify viable myocardium with the objective of selecting patients for this form of therapeutic intervention. However, prospective trials have not confirmed the interaction between myocardial viability and the treatment effect of revascularization. Furthermore, recent observations indicate that recovery of left ventricular function is not the principal mechanism by which surgical revascularization improves prognosis. In this paper, the authors describe a more contemporary application of viability testing that is founded on the alternative concept that the main goal of surgical revascularization is to prevent further damage by protecting the residual viable myocardium from subsequent acute coronary events.

Improving Terminology to Describe Coronary Artery Procedures: JACC Review Topic of the Week

Coronary artery disease (CAD) is treated with medical therapy with or without percutaneous coronary intervention (PCI) or coronary artery bypass grafting (CABG). The latter 2 options are commonly referred to as "myocardial revascularization" procedures. We reason that this term is inappropriate because it is suggestive of a single treatment effect of PCI and CABG (ie, the reestablishment of blood flow to ischemic myocardium) and obscures key mechanisms, such as the improvement in coronary flow capability in the absence of ongoing ischemia, the reperfusion in the presence of ischemia, and the prevention of myocardial infarction from CAD progression. We review the current evidence on the topic and suggest the use of a purely descriptive terminology ("invasive treatment by PCI or CABG") which has the potential to improve clinical decision making and guide future trial design.

Prognostic implications of left ventricular myocardial work index in patients with ST-segment elevation myocardial infarction and reduced left ventricular ejection fraction

AIMS

This study aimed to determine whether lower values of left ventricular (LV) global work index (GWI) at baseline were associated with a reduction in LV functional recovery and poorer long-term prognosis in patients with reduced LV ejection fraction (LVEF ≤40%) following ST-segment elevation myocardial infarction (STEMI).

METHODS AND RESULTS

A total of 197 individuals (62 ± 12 years, 75% male) with STEMI treated with primary percutaneous coronary intervention and reduced LVEF were evaluated. All patients were followed up for the occurrence of all-cause mortality and the presence of LVEF normalization at 6 months (LVEF ≥50%). The median LVEF was 36% (interquartile range 32-38) and the mean value of LV GWI was 1041 ± 404 mmHg% at baseline. At 6-month follow-up, 41% of patients had normalized LVEF. On multivariable logistic regression, higher values of LV GWI were independently associated with LVEF normalization at 6 months of follow-up (odds ratio 1.32 per 250 mmHg%, P = 0.038). Over a median follow-up of 112 months, 40 patients (20%) died. LV GWI <750 mmHg% was independently associated with all-cause mortality (HR 3.85, P < 0.001) and was incremental to LV global longitudinal strain (P = 0.039) and LVEF (P < 0.001).

CONCLUSION

In individuals with an LVEF ≤40% following STEMI, higher values of LV GWI were associated with a greater probability of LVEF normalization at 6-month follow-up. In addition, lower values of LV GWI were independently associated with increased all-cause mortality at long-term follow-up, providing incremental prognostic value over LVEF and minor incremental prognostic value over LV global longitudinal strain.

Incremental value of regional wall motion abnormalities for detecting obstructive coronary artery disease by rest-only electrocardiogram-gated single-photon emission computerized tomography myocardial perfusion imaging in suspected coronary artery disease patients

OBJECTIVE

The purpose of this study was to determine whether regional wall motion (WM) abnormalities by rest-only 99mtechnetium-sestamibi (99mTc-MIBI) electrocardiogram (ECG)-gated single-photon emission computerized tomography (SPECT) myocardial perfusion imaging (MPI) had incremental diagnostic value for detecting obstructive coronary artery disease (CAD) in suspected CAD patients.

METHODS

This study retrospectively studied 255 consecutive suspected CAD patients who underwent rest-only ECG-gated SPECT MPI and were performed coronary angiography within 3 months. Obstructive CAD was defined as ≥70% narrowing of the inner diameter of the left anterior descending coronary artery, left circumflex coronary artery and right coronary artery or their main branches and ≥50% narrowing of the left main coronary artery. QPS and QGS were used to assess rest perfusion and WM. Summed rest score ≥4 and summed motion score ≥2 exhibited in two consecutive segments in one territory was considered abnormal.

RESULTS

The sensitivity of the combination of perfusion and regional WM abnormalities was significantly higher than perfusion alone for detecting obstructive CAD (46.8% vs. 30.9%; P < 0.001), with similar specificity (91.9% vs. 95.0; P = 0.063). The global chi-square value of combination of perfusion and WM increased from 31.40 to 50.71 (P < 0.001) compared to perfusion. The sensitivity of combination of perfusion and WM for detecting obstructive CAD in patients with multivessel disease was higher than single-vessel disease (56.1% vs. 25.0%; P < 0.001), with similar specificity.

CONCLUSION

Regional WM abnormalities at rest, as shown by rest-only 99mTc-MIBI ECG-gated SPECT MPI, have additional diagnostic value over perfusion alone for detecting obstructive CAD in suspected CAD patients.

Myocardial stunning and hibernation revisited

Unlike acute myocardial infarction with reperfusion, in which infarct size is the end point reflecting irreversible injury, myocardial stunning and hibernation result from reversible myocardial ischaemia-reperfusion injury, and contractile dysfunction is the obvious end point. Stunned myocardium is characterized by a disproportionately long-lasting, yet fully reversible, contractile dysfunction that follows brief bouts of myocardial ischaemia. Reperfusion precipitates a burst of reactive oxygen species formation and alterations in excitation-contraction coupling, which interact and cause the contractile dysfunction. Hibernating myocardium is characterized by reduced regional contractile function and blood flow, which both recover after reperfusion or revascularization. Short-term myocardial hibernation is an adaptation of contractile function to the reduced blood flow such that energy and substrate metabolism recover during the ongoing ischaemia. Chronic myocardial hibernation is characterized by severe morphological alterations and altered expression of metabolic and pro-survival proteins. Myocardial stunning is observed clinically and must be recognized but is rarely haemodynamically compromising and does not require treatment. Myocardial hibernation is clinically identified with the use of imaging techniques, and the myocardium recovers after revascularization. Several trials in the past two decades have challenged the superiority of revascularization over medical therapy for symptomatic relief and prognosis in patients with chronic coronary syndromes. A better understanding of the pathophysiology of myocardial stunning and hibernation is important for a more precise indication of revascularization and its consequences. Therefore, this Review summarizes the current knowledge of the pathophysiology of these characteristic reperfusion phenomena and highlights their clinical implications.

Myocardial revascularization in chronic coronary syndromes: does viability matter?

Coronary artery disease (CAD) is the leading cause of death worldwide and improving the prognosis and survival of patients with ischemic heart disease remains a priority of cardiovascular specialists. This article will review the principles of myocardial viability, present the noninvasive imaging tests available to clinicians, as well as critically appraise the latest literature on myocardial viability, coronary revascularization and outcome with a final outlook at studies in the pipelines and future evidence in myocardial viability that will be soon available.

Can the degree of coronary collateralization be used in clinical routine as a valid angiographic parameter of viability?

The success rate of percutaneous coronary artery intervention (PCI) of chronic total occlusion (CTO) lesions have increased in the recent years. However, improvement of function is only possible when significant myocardial viability is present. One of the most important factors of maintaining myocardial viability is the opening and development of collaterals. Our hypothesis was that with a higher degree of collaterals more viable myocardium is present. In 38 patients we compared the degree of collaterals, evaluated with a conventional coronary angiogram (CCA) and graded by the Rentrop classification to transmural extent of the scar obtained in a viability study with magnetic resonance (MRI). We found a statistically significant association of the degree of collaterals determined with Rentrop method and transmural extent of the scar as measured by CMR (p = 0.001; Tau = -0.144). Additionally, associations showed an increase in the ratio between viable vs. non-viable myocardium with the degree of collaterals. Our study suggests that it may be beneficial to routinely grade the collaterals at angiography in patients with CTO as an assessment of myocardial viability.

Coronary collaterals and myocardial viability in patients with chronic total occlusions

AIMS

This study aimed to evaluate associations between coronary collaterals and myocardial viability as assessed by quantitative cardiac magnetic resonance (CMR) imaging in patients with a chronic coronary total occlusion (CTO).

METHODS AND RESULTS

A total of 218 patients with a CTO who underwent CMR between 2013 and 2018 were included. A concomitant collateral connection (CC) score 2 and Rentrop grade 3 defined well-developed collaterals in 146 (67%) patients, whereas lower CC scores or Rentrop grades characterised poorly developed collaterals. Dysfunctional myocardium (<3 mm segmental wall thickening [SWT]) and ≤50% late gadolinium enhancement (LGE) defined viability. Extensive scar (LGE >50%) was observed in only 5% of CTO segments. In the CTO territory, SWT was greater (3.72±1.51 vs 3.05±1.60 mm, p<0.01) and the extent of scar was less (7.0 [0.1-16.7] vs 13.1% [2.8-22.2], p=0.048) in patients having well-developed versus poorly developed collaterals. Viability was more prevalent in CTO segments among patients with poorly developed versus well-developed collaterals (44% vs 30% of segments, p<0.01), predominantly due to a higher prevalence of dysfunctional myocardium (51% vs 34% of segments, p<0.01) in the poorly developed collateral group.

CONCLUSIONS

The infarcted area in myocardium subtended by a CTO is generally limited. Well-developed collaterals are associated with less myocardial scar and enhanced preserved function. However, viability was regularly present in patients with poorly developed collaterals.

Pediatric Cardiac PET/CT Imaging

With the routine availability of PET/CT imaging for oncologic purposes, there has been renewed interest in and acceptance of cardiac and neurologic applications of PET/CT. As our understanding of the pathophysiology underlying various pediatric heart diseases has improved, there has been a parallel advance in imaging modalities. Cardiac MR imaging and cardiac PET continue to improve in the pediatric domain. Molecular imaging holds promise to provide a more robust assessment of the cardiac pathophysiology in a 1-stop setting with less radiation exposure to the patient, an important consideration for the pediatric patient population.

Actual Problems of Diagnostics of Viable Myocardium

The article presents modern analysis of the studies and reflects the key problems concerning the feasibility of performing cardiac MRI for assessment of myocardial viability in patients with history of myocardial infarction (with postinfarction cardiosclerosis), as well as the effectiveness of the method for predicting restoration of the function of hibernating myocardium after myocardial revascularization.

Viability testing to guide myocardial revascularisation in patients with heart failure

Myocardial revascularisation has the potential to restore ventricular function and improve survival in patients with heart failure due to underlying coronary artery disease. Viability testing is routinely used to identify which patients are likely to benefit, given that revascularisation may entail substantial procedural risk. However, while the concept of viability testing and revascularisation of patients with ‘hibernating myocardium’ is strongly supported by observational series, randomised studies have failed to demonstrate clear benefit. This divergence in the evidence base is reflected in current European and US guidelines, in which viability testing has a class II recommendation. In this article, we review the current evidence for routine viability testing prior to revascularisation of patients with heart failure, outline its use in clinical practice and discuss ongoing trials in the field.

Identifying and Managing Hibernating Myocardium: What's New and What Remains Unknown?

PURPOSE OF REVIEW

Hibernation is an important and reversible cause of myocardial dysfunction in ischaemic heart failure.

RECENT FINDINGS

Hibernation is an adaptive process that promotes myocyte survival over maintaining contractile function. It is innate to mammalian physiology, sharing features with physiological hibernation in other species. Advanced imaging methods have reasonable accuracy in identifying hibernating myocardium. Novel superior hybrid methods may provide diagnostic potential. New evidence supports the role of surgical revascularisation in ischaemic heart failure, but the role of viability tests in planning such procedures remains unclear. Research to date has exclusively involved patients with ambulatory heart failure: Investigating the role of hibernation in ADHF is a key avenue for the future. Whilst our understanding of hibernation pathophysiology has improved dramatically, the clinical utility of identifying and targeting hibernation remains unclear.

Macrophage migration inhibitory factor (MIF) is associated with degree of collateralization in patients with totally occluded coronary arteries

BACKGROUND

Collaterals in patients with coronary artery disease (CAD) limit myocardial infarction and improve survival. Macrophage migration inhibitory factor (MIF) might play a role in collateral development. We aimed this study to evaluate the association of Macrophage migration Inhibitory Factor (MIF) with the extent of collateralization in patients with coronary occlusion.

METHODS AND RESULTS

We consecutively enrolled: a) 40 patients undergoing PCI of a chronic coronary total occlusion (CTO); b) 26 patients with ST-elevation myocardial infarction (STEMI) undergoing primary PCI (pPCI) of the infarct-related artery (IRA); c) 12 control patients undergoing angiography without significant coronary artery disease (CTRL). CTO patients were grouped in high (HCG) or low collateralization group (LCG). STEMI patients were grouped in COLL+ or COLL- group depending on the presence of collaterals to the IRA. Blood sampling was performed from the arterial sheath (SYSTEMIC), and distal to the occlusion (LOCAL). SYSTEMIC and LOCAL levels were significantly different between the 3 groups. A progressive increase in MIF ratio (defined as: % (LOCAL-SYSTEMIC)/SYSTEMIC) was observed (CTRL: -0.5[-23;28] vs. CTO: 4[-19;32] vs. STEMI: 55[37;87], p < 0.01). In CTO, MIF ratio was significantly higher in HCG vs. LCG (68 [45;120] vs. 46 [29;66], p = 0.02). In STEMI, MIF ratio was not different between COLL+ and COLL- patients; however, in COLL+, LOCAL was significantly higher as compared with SYSTEMIC (83 ng/ml [63;100] vs. 67 ng/ml [40;79], p = 0.04).

CONCLUSIONS

Local MIF is significantly associated with the extent of collateralization in both acute and chronic total coronary occlusions.

Guidelines for experimental models of myocardial ischemia and infarction

Myocardial infarction is a prevalent major cardiovascular event that arises from myocardial ischemia with or without reperfusion, and basic and translational research is needed to better understand its underlying mechanisms and consequences for cardiac structure and function. Ischemia underlies a broad range of clinical scenarios ranging from angina to hibernation to permanent occlusion, and while reperfusion is mandatory for salvage from ischemic injury, reperfusion also inflicts injury on its own. In this consensus statement, we present recommendations for animal models of myocardial ischemia and infarction. With increasing awareness of the need for rigor and reproducibility in designing and performing scientific research to ensure validation of results, the goal of this review is to provide best practice information regarding myocardial ischemia-reperfusion and infarction models.

Listen to this article’s corresponding podcast at ajpheart.podbean.com/e/guidelines-for-experimental-models-of-myocardial-ischemia-and-infarction/.

Mitochondrial Transplantation in Myocardial Ischemia and Reperfusion Injury

Ischemic heart disease remains the leading cause of death worldwide. Mitochondria are the power plant of the cardiomyocyte, generating more than 95% of the cardiac ATP. Complex cellular responses to myocardial ischemia converge on mitochondrial malfunction which persists and increases after reperfusion, determining the extent of cellular viability and post-ischemic functional recovery. In a quest to ameliorate various points in pathways from mitochondrial damage to myocardial necrosis, exhaustive pharmacologic and genetic tools have targeted various mediators of ischemia and reperfusion injury and procedural techniques without applicable success. The new concept of replacing damaged mitochondria with healthy mitochondria at the onset of reperfusion by auto-transplantation is emerging not only as potential therapy of myocardial rescue, but as gateway to a deeper understanding of mitochondrial metabolism and function. In this chapter, we explore the mechanisms of mitochondrial dysfunction during ischemia and reperfusion, current developments in the methodology of mitochondrial transplantation, mechanisms of cardioprotection and their clinical implications.

Evaluation of left ventricular longitudinal deformation in patients with and without ST segment depression during supraventricular tachycardia

BACKGROUND

The cumulative effect of repeated demand ischemia on left ventricular (LV) systolic function has been previously demonstrated. We evaluated the longitudinal deformation of LV myocardial fibers at systole and diastole using two-dimensional speckle-tracking echocardiography (2DSTE) in patients with and without ST-segment depression during supraventricular tachycardia.

METHODS

We recruited 104 consecutive patients, who were admitted to our hospital for the ablation of atrioventricular nodal reentrant tachycardia or atrioventricular reentrant tachycardia. The patients were thereafter evaluated by transthoracic echocardiography and 2DSTE, and longitudinal systolic strain and strain rate as well as early and late diastolic strain rates were measured.

RESULTS

We found no statistically significant differences in longitudinal systolic strain and strain rate as well as in early and late diastolic strain rates between the two study groups.

CONCLUSIONS

The longitudinal deformation properties of LV muscle fibers were not different between patients with and without ST-segment depression during supraventricular tachycardia. © 2016 Wiley Periodicals, Inc. J Clin Ultrasound 45:343-349, 2017.

Taxonomy of segmental myocardial systolic dysfunction

The terms used to describe different states of myocardial health and disease are poorly defined. Imprecision and inconsistency in nomenclature can lead to difficulty in interpreting and applying trial outcomes to clinical practice. In particular, the terms 'viable' and 'hibernating' are commonly applied interchangeably and incorrectly to myocardium that exhibits chronic contractile dysfunction in patients with ischaemic heart disease. The range of inherent differences amongst imaging modalities used to define myocardial health and disease add further challenges to consistent definitions. The results of several large trials have led to renewed discussion about the classification of dysfunctional myocardial segments. This article aims to describe the diverse myocardial pathologies that may affect the myocardium in ischaemic heart disease and cardiomyopathy, and how they may be assessed with non-invasive imaging techniques in order to provide a taxonomy of myocardial dysfunction.

Identification of cardiac progenitors that survive in the ischemic human heart after ventricular myocyte death

Atypically-shaped cardiomyocytes (ACMs) are beating heart cells identified in the cultures of cardiomyocyte-removed fractions obtained from adult mouse hearts. Since ACMs spontaneously develop into beating cells in the absence of hormones or chemicals, these cells are likely to be a type of cardiac progenitors rather than stem cells. “Native ACMs” are found as small interstitial cells among ventricular myocytes that co-express cellular prion protein (PrP) and cardiac troponin T (cTnT) in mouse and human heart tissues. However, the endogenous behavior of human ACMs is unclear. In the present study, we demonstrate that PrP⁺ cTnT⁺ cells are present in the human heart tissue with myocardial infarction (MI). These cells were mainly found in the border of necrotic cardiomyocytes caused by infarcts and also in the hibernating myocardium subjected to the chronic ischemia. The ratio of PrP⁺ cTnT⁺ cells to the total cells observed in the normal heart tissue section of mouse and human was estimated to range from 0.3–0.8%. Notably, living human PrP⁺ cTnT⁺ cells were identified in the cultures obtained at pathological autopsy despite exposure to lethal ischemic conditions for hours after death. These findings suggest that ACMs could survive in the ischemic human heart and develop into a sub-population of cardiac myocytes.

The Relation Between Chronic Obstructive Pulmonary Disease and Coronary Collateral Vessels

Coronary collateral vessels can provide a perfusion reserve in case of increased myocardial oxygen demand. Development of coronary collateral vessels (CCV) is triggered by the pressure gradient between the coronary bed of arteries caused by an obstruction and myocardial ischemia. Myocardial hypoxia can facilitate development of CCVs. There is a chronic hypoxemia in patients with chronic obstructive pulmonary disease (COPD). The aim of this study was to evaluate the effect of COPD on CCVs. The study included 98 patients with COPD who underwent coronary angiography. Those patients in whom coronary angiography is normal or severity of coronary artery stenosis in thought not to be sufficient for the development of CCVs (<80%) were excluded from the study. A total of 98 patients (mean age, 62 ±9 years) met the criteria for the COPD group. For case-control matching, 98 consecutive without COPD patients (mean age 62 ±10) who had one or more diseased vessels with 80% or greater stenosis were included in the control group. The CCVs were graded according to the Rentrop scoring system, and the collateral score was calculated by summing the Rentrop numbers of every patient. The mean number of diseased vessels in patients with COPD and without COPD were 1.61 ±0.69 and 1.77 ±0.89 (p=0.155), respectively. The mean collateral score was 2.15 ±2.03 in the COPD group and 1.32 ±1.54 in the control group. After confounding variables were controlled for, the collateral score in patients with COPD group was significantly different from that in patients without COPD group (p=0.002). These findings suggest that CCV development is better in patients with COPD than in those patients without COPD. Thus, COPD may be an important factor affecting CCV development, which may be related to the presence of chronic hypoxemia in patients with COPD.

Rationale, design, and methods for Canadian alliance for healthy hearts and minds cohort study (CAHHM) - a Pan Canadian cohort study

Background

The Canadian Alliance for Healthy Hearts and Minds (CAHHM) is a pan-Canadian, prospective, multi-ethnic cohort study being conducted in Canada. The overarching objective of the CAHHM is to understand the association of socio-environmental and contextual factors (such as societal structure, activity, nutrition, social and tobacco environments, and access to health services) with cardiovascular risk factors, subclinical vascular disease, and cardiovascular and other chronic disease outcomes.

Methods/Design

Participants between 35 and 69 years of age are being recruited from existing cohorts and a new First Nations Cohort to undergo a detailed assessment of health behaviours (including diet and physical activity), cognitive function, assessment of their local home and workplace environments, and their health services access and utilization. Physical measures including weight, height, waist/hip circumference, body fat percentage, and blood pressure are collected. In addition, eligible participants undergo magnetic resonance imaging (MRI) of the brain, heart, carotid artery and abdomen to detect early subclinical vascular disease and ectopic fat deposition.

Discussion

CAHHM is a prospective cohort study designed to investigate the impact of community level factors, individual health behaviours, and access to health services, on cognitive function, subclinical vascular disease, fat distribution, and the development of chronic diseases among adults living in Canada.

Electronic supplementary material

The online version of this article (doi:10.1186/s12889-016-3310-8) contains supplementary material, which is available to authorized users.

Pathophysiology of coronary collaterals

While the existence of structural adaptation of coronary anastomoses is undisputed, the potential of coronary collaterals to be capable of functional adaptation has been questioned. For many years, collateral vessels were thought to be rigid tubes allowing only limited blood flow governed by the pressure gradient across them. This concept was consistent with the notion that although collaterals could provide adequate blood flow to maintain resting levels, they would be unable to increase blood flow sufficiently in situations of increased myocardial oxygen demand.

However, more recent studies have demonstrated the capability of the collateral circulation to deliver sufficient blood flow even during exertion or pharmacologic stress. Moreover, it has been shown that increases in collateral flow could be attributed directly to collateral vasomotion.

This review summarizes the pathophysiology of the coronary collateral circulation, ie the functional adapation of coronary collaterals to acute alterations in the coronary circulation.

Chronic ischemic viable myocardium in man: Aspects of dedifferentiation

Histologic analysis of biopsies derived from patients with chronic dysfunctional but viable (hibernating) myocardium showed characteristic cell alterations. These changes consisted of a partial to complete loss of sarcomeres, accumulation of glycogen, and disorganization and loss of sarcoplasmic reticulum. Most of the adaptive changes that these affected cells undergo are suggestive of dedifferentiation. In the present study the expression and organizational pattern of contractile and cytoskeletal proteins such as titin, cardiotin, and α-smooth muscle actin were assessed in hibernating and normal myocardium because the expression and organization of these constituents have been related to certain stages of cardiomyocyte differentiation. In normal cells titin shows a cross-striated staining pattern, whereas cardiotin displays a fibrillar array, parallel to the sarcomeres. α-Smooth muscle actin is not expressed in adult cardiomyocytes. The expression of titin in a punctated pattern and the marked decrease to virtual absence of cardiotin in hibernating cardiomyocytes speak in favor of an embryonic phenotype of these cells. The re-expression of α-smooth muscle actin in hibernating cells strongly supports this hypothesis. The observations on three different structural proteins of heart muscle suggest that hibernating myocardium acquired aspects of muscle cell dedifferentiation.

Revascularization of chronic hibernating myocardium stimulates myocyte proliferation and partially reverses chronic adaptations to ischemia

BACKGROUND

The time course and extent of recovery after revascularization of viable dysfunctional myocardium are variable. Although fibrosis is a major determinant, myocyte structural and molecular remodeling may also play important roles.

OBJECTIVES

This study sought to determine whether persistent myocyte loss and/or irreversibility of protein changes that develop in hibernating myocardium have an impact on functional recovery in the absence of infarction.

METHODS

Swine implanted with a chronic left anterior descending artery (LAD) stenosis to produce hibernating myocardium underwent percutaneous revascularization, with serial functional recovery evaluated for 1 month (n = 12). Myocardial tissue was evaluated to assess myocyte size, nuclear density, and proliferation indexes in comparison with those of normal animals and nonrevascularized controls. Proteomic analysis by 2-dimensional differential in-gel electrophoresis was used to determine the reversibility of molecular adaptations of hibernating myocytes.

RESULTS

At 3 months, physiological features of hibernating myocardium were confirmed, with depressed LAD wall thickening and no significant infarction. Revascularization normalized LAD flow reserve, with no immediate change in LAD wall thickening. Regional LAD wall thickening slowly improved but remained depressed 1 month post-percutaneous coronary intervention. Surprisingly, revascularization was associated with histological evidence of myocytes re-entering the growth phase of the cell cycle and increases in the number of c-Kit(+) cells. Myocyte nuclear density returned to normal, whereas regional myocyte hypertrophy regressed. Proteomic analysis demonstrated heterogeneous effects of revascularization. Up-regulated stress and cytoskeletal proteins normalized, whereas reduced contractile and metabolic proteins persisted.

CONCLUSIONS

Delayed recovery of hibernating myocardium in the absence of scar may reflect persistent reductions in the amounts of contractile and metabolic proteins. Although revascularization appeared to stimulate myocyte proliferation, the persistence of small immature myocytes may have contributed to delayed functional recovery.

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.

Potential influence of invisible coronary collateral circulation on fractional flow reserve of donor artery in the presence of severe stenosis of receiving artery

We reported a case of 78-year-old male who had a severe stenosis in the right coronary artery (RCA) and an intermediate stenosis in the left anterior descending artery (LAD) without visible collateral flow to the RCA on angiogram. Fractional flow reserve (FFR) in the LAD lesion, which revealed significant value as 0.70, increased to 0.78 after revascularization of the RCA lesion. The FFR in an intermediate stenosis should be performed after PCI for severe stenosis in the other coronary arteries. Otherwise, the severity of the stenosis could be overestimated due to the presence of invisible collateral circulation.

Cardiac ⁹⁹mTc sestamibi SPECT and ¹⁸F FDG PET as viability markers in Takotsubo cardiomyopathy

In patients with heart failure (HF) due to coronary disease, a combined evaluation of perfusion and glucose metabolism by cardiac single photon emission computed tomography (SPECT)/positron emission tomography (PET) can be used to distinguish viable from non-viable myocardium, and current guidelines recommend cardiac SPECT and fluorodeoxyglucose (FDG) PET for viability assessment. Takotsubo cardiomyopathy (TTC) is a disease characterized by acute but reversible HF leaving no scarring. To explore how robust the semi-quantitative viability criteria used in cardiac SPECT and FDG PET stands their ground in a population with TTC. From 1 September 2009 to 1 October 2012, 24 patients suspected of TTC were enrolled in a multimodality cardiac imaging research project. Echocardiography, (99m)Tc SPECT, and (18)F FDG PET were performed during the acute admission and at follow-up 4 months later. Nineteen patients had a final diagnosis of TTC consistent with Mayo Clinic Diagnostic Criteria. Three of these patients were excluded from further analysis, since wall motion abnormalities were not persistent at the time of nuclear imaging. The remaining sixteen patients exhibited a distinct pattern with HF, "apical ballooning" and a perfusion-metabolism defect in the midventricular/apical region. When viability criteria were applied, they identified significant scarring/limited hibernation in the akinetic part of the left ventricle. However, full recovery was found in all TTC patients on follow-up. Using the current guideline-endorsed viability criteria for semiquantitative cardiac SPECT and FDG PET, these modalities failed to demonstrate the presence of viability in the acute state of TTC.

Electrocardiogram for predicting cardiac functional recovery

To investigate if the 12-lead resting electrocardiogram (ECG) is a predictor of left ventricular (LV) functional recovery after revascularization of chronic total coronary artery occlusions (CTO). Revascularization was performed in 58 CTO patients who had impaired regional wall motion. The 12-lead resting ECG was used to evaluate Q-wave, QT dispersion, and other parameters. Pre- and postoperative LV regional wall motions were evaluated by real-time three-dimensional echocardiography (RT-3DE). In patients with non-Q-wave, the wall motion score index (WMSI) was dropped from 1.56 ± 0.31 to 1.12 ± 0.21 (P < 0.05), while there was no significant changes (1.73 ± 0.12 and 1.59 ± 0.23, P > 0.05) for WMSI in patients with Q-wave. Preoperative non-Q-wave at baseline was predicted recovery with 88 % sensitivity and 68 % specificity. Positive predictive value for recovery was 67 % in patients with non-Q-wave. The presence of Q-wave can predict non-recovery of the regional wall motion with 68 % sensitivity and 88 % specificity. For CTO patients treated by revascularization, recovery can be predicted reliably through the analysis of pathological Q-wave on the 12-lead resting ECG.

Regional mapping of myocardial hibernation phenotype in idiopathic end-stage dilated cardiomyopathy

Myocardial hibernation (MH) is a well-known feature of human ischaemic cardiomyopathy (ICM), whereas its presence in human idiopathic dilated cardiomyopathy (DCM) is still controversial. We investigated the histological and molecular features of MH in left ventricle (LV) regions of failing DCM or ICM hearts. We examined failing hearts from DCM (n = 11; 41.9 ± 5.45 years; left ventricle-ejection fraction (LV-EF), 18 ± 3.16%) and ICM patients (n = 12; 58.08 ± 1.7 years; LVEF, 21.5 ± 6.08%) undergoing cardiac transplantation, and normal donor hearts (N, n = 8). LV inter-ventricular septum (IVS) and antero-lateral free wall (FW) were transmurally (i.e. sub-epicardial, mesocardial and sub-endocardial layers) analysed. LV glycogen content was shown to be increased in both DCM and ICM as compared with N hearts (P < 0.001), with a U-shaped transmural distribution (lower values in mesocardium). Capillary density was homogenously reduced in both DCM and ICM as compared with N (P < 0.05 versus N), with a lower decrease independent of the extent of fibrosis in sub-endocardial and sub-epicardial layers of DCM as compared with ICM. HIF1-α and nestin, recognized ischaemic molecular hallmarks, were similarly expressed in DCM-LV and ICM-LV myocardium. The proteomic profile was overlapping by ˜50% in DCM and ICM groups. Morphological and molecular features of MH were detected in end-stage ICM as well as in end-stage DCM LV, despite epicardial coronary artery patency and lower fibrosis in DCM hearts. Unravelling the presence of MH in the absence of coronary stenosis may be helpful to design a novel approach in the clinical management of DCM.

Hibernating myocardium in heart failure

Ischemic left ventricular systolic dysfunction may result from myocardial necrosis or from hypocontractile areas of viable myocardium. In some cases, recovery of contractility may occur on revascularization--this reversibly dysfunctional tissue is commonly referred to as hibernating myocardium. Observational data suggest that revascularization of patients with ischemic left ventricular systolic dysfunction and known viable myocardium provides a survival benefit over medical therapy. Identification of viable, dysfunctional myocardium may be especially worthwhile in deciding which patients with ischemic left ventricular systolic dysfunction will benefit from revascularization procedures. Randomized, prospective trials evaluating this are currently ongoing. This review will provide an overview of the complex pathophysiology of viable, dysfunctional myocardium, and will discuss outcomes after revascularization. Of the techniques used to determine the presence of hibernating myocardium, functional methods such as stress echocardiography and cardiac magnetic resonance appear more specific, but less sensitive, than the nuclear modalities, which assess perfusion and metabolic activity. Currently, the availability of all methods is variable.