Chronic ischemic left ventricular dysfunction: from pathophysiology to imaging and its integration into clinical practice

Assessment of ICD eligibility in non-ischaemic cardiomyopathy patients: a position statement by the Task Force of the Dutch Society of Cardiology

International guidelines recommend implantation of an implantable cardioverter-defibrillator (ICD) in non-ischaemic cardiomyopathy (NICM) patients with a left ventricular ejection fraction (LVEF) below 35% despite optimal medical therapy and a life expectancy of more than 1 year with good functional status. We propose refinement of these recommendations in patients with NICM, with careful consideration of additional risk parameters for both arrhythmic and non-arrhythmic death. These additional parameters include late gadolinium enhancement on cardiac magnetic resonance imaging and genetic testing for high-risk genetic variants to further assess arrhythmic risk, and age, comorbidities and sex for assessment of non-arrhythmic mortality risk. Moreover, several risk modifiers should be taken into account, such as concomitant arrhythmias that may affect LVEF (atrial fibrillation, premature ventricular beats) and resynchronisation therapy. Even though currently no valid cut-off values have been established, the proposed approach provides a more careful consideration of risks that may result in withholding ICD implantation in patients with low arrhythmic risk and substantial non-arrhythmic mortality risk.

[Cognitive impairments in various types of cardiac remodeling]

The review of the literature highlights current studies proving the relationship between cognitive impairment and various types of myocardial remodeling. The main pathophysiological mechanisms of development of concentric and eccentric myocardial hypertrophy and their influence on the formation of cognitive impairments are described. Direct causal relationships have not yet been found, but several linking factors in the development of cognitive impairment and myocardial remodeling are being investigated: arterial hypertension, increased arterial stiffness, endothelial dysfunction, microglial activation, hyperreactivity of the sympathetic nervous system, and obesity.

Cardiac Metabolic Deregulation Induced by the Tyrosine Kinase Receptor Inhibitor Sunitinib is rescued by Endothelin Receptor Antagonism

The growing field of cardio-oncology addresses the side effects of cancer treatment on the cardiovascular system. Here, we explored the cardiotoxicity of the antiangiogenic therapy, sunitinib, in the mouse heart from a diagnostic and therapeutic perspective. We showed that sunitinib induces an anaerobic switch of cellular metabolism within the myocardium which is associated with the development of myocardial fibrosis and reduced left ventricular ejection fraction as demonstrated by echocardiography. The capacity of positron emission tomography with [18F]fluorodeoxyglucose to detect the changes in cardiac metabolism caused by sunitinib was dependent on fasting status and duration of treatment. Pan proteomic analysis in the myocardium showed that sunitinib induced (i) an early metabolic switch with enhanced glycolysis and reduced oxidative phosphorylation, and (ii) a metabolic failure to use glucose as energy substrate, similar to the insulin resistance found in type 2 diabetes. Co-administration of the endothelin receptor antagonist, macitentan, to sunitinib-treated animals prevented both metabolic defects, restored glucose uptake and cardiac function, and prevented myocardial fibrosis. These results support the endothelin system in mediating the cardiotoxic effects of sunitinib and endothelin receptor antagonism as a potential therapeutic approach to prevent cardiotoxicity. Furthermore, metabolic and functional imaging can monitor the cardiotoxic effects and the benefits of endothelin antagonism in a theranostic approach.

Usefulness of late gadolinium enhancement MRI combined with stress imaging in predictive significant coronary stenosis in new-diagnosed left ventricular dysfunction

BACKGROUND

To evaluate the accuracy of late gadolinium enhancement (LGE) cardiac magnetic resonance (CMR) and imaging stress test in predicting significant coronary artery disease (CAD) in left ventricular (LV) dysfunction.

METHODS

We enrolled 187 consecutive out-patients (61±17years) with new evidence of depressed (<45%) ejection fraction and no history of previous heart diseases and absence of Q-waves. All patients underwent coronary angiography (CA) and to LGE-CMR examination to identify ischemic and non-ischemic LGE. All patients underwent stress imaging to determine the presence of myocardial ischemia.

RESULTS

Ischemic-LGE was found in 83 patients and non-ischemic-LGE in 104. Significant CAD on CA was found in 86/187 patients. Ischemic-LGE showed a specificity of 94%, a sensitivity of 89% and an accuracy of 92% in identifying significant CAD. Imaging stress test was negative in 98/105 patients without CAD, and positive in 42/82 with significant CAD, showing a specificity of 93%, a sensitivity of 51% and an accuracy of 75% in identifying CAD. Combining CMR and stress test imaging, 94 patients had ischemic-LGE pattern and/or positive stress test for ischemia; of these 81/94 had significant CAD on CA and 13 had no CAD. Among the 93 patients with both tests negative, significant CAD was found in 5/93 patients. The combination of LGE and stress respect to only LGE did not improve the diagnostic accuracy (90 vs 92% respectively).

CONCLUSION

LGE-CMR had high accuracy in predicting significant CAD in ischemic LV dysfunction or as a bystander in non ischemic dysfunction.

Tools for cardiovascular magnetic resonance imaging

In less than fifteen years, as a non-invasive imaging option, cardiovascular MR has grown from a being a mere curiosity to becoming a widely used clinical tool for evaluating cardiovascular disease. Cardiovascular magnetic resonance imaging (CMRI) is now routinely used to study myocardial structure, cardiac function, macro vascular blood flow, myocardial perfusion, and myocardial viability. For someone entering the field of cardiac MR, this rapid pace of development in the field of CMRI might make it difficult to identify a cohesive starting point. In this brief review, we have attempted to summarize the key cardiovascular imaging techniques that have found widespread clinical acceptance. In particular, we describe the essential cardiac and respiratory gating techniques that form the backbone of all cardiovascular imaging methods. It is followed by four sections that discuss: (I) the gradient echo techniques that are used to assess ventricular function; (II) black-blood turbo spin echo (SE) methods used for morphologic assessment of the heart; (III) phase-contrast based techniques for the assessment of blood flow; and (IV) CMR methods for the assessment of myocardial ischemia and viability. In each section, we briefly summarize technical considerations relevant to the clinical use of these techniques, followed by practical information for its clinical implementation. In each of those four areas, CMRI is considered either as the benchmark imaging modality against which the diagnostic performance of other imaging modalities are compared against, or provides a complementary capability to existing imaging techniques. We have deliberately avoided including cutting-edge CMR imaging techniques practiced at few academic centers, and restricted our discussion to methods that are widely used and are likely to be available in a clinical setting. Our hope is that this review would propel an interested reader toward more comprehensive reviews in the literature.

Histopathologic characteristics of atherosclerotic coronary disease and implications of the findings for the invasive and noninvasive detection of vulnerable plaques

OBJECTIVES

The goal of this study was to identify histomorphologic characteristics of atherosclerotic plaques and to determine the amenability of some of these components to be used as markers for invasive and noninvasive imaging.

BACKGROUND

Rupture of the atherosclerotic plaques is responsible for the majority of acute coronary events, and the culprit lesions demonstrate distinct histopathologic features. It has been tacitly believed that plaque rupture (PR) is associated with angiographically minimally occlusive lesions.

METHODS

We obtained 295 coronary atherosclerotic plaques, including stable (fibroatheroma [FA]; n = 105), vulnerable (thin-cap fibroatheroma [TCFA]; n = 88), and disrupted plaques (plaque rupture [PR]; n = 102) from the hearts of 181 men and 32 women who had died suddenly. The hierarchical importance of fibrous cap thickness, percent luminal stenosis, macrophage area, necrotic core area, and calcified plaque area was evaluated by using recursive partitioning analysis. Because clinical assessment of fibrous cap thickness is not possible by noninvasive imaging, it was excluded from the second set of partitioning analysis.

RESULTS

Thickness of the fibrous cap emerged as the best discriminator of plaque type; the cap thickness measured <55 μm in ruptured plaques, and all FA were associated with >84-μm cap thickness. Although the majority of TCFA were found in the 54- to 84-μm thickness group, those with <54-μm thickness were more likely to show <74% luminal stenosis (area under the curve: FA, 1.0; TCFA, 0.89; PR, 0.90). After exclusion of cap thickness, analysis of the plaque characteristics revealed macrophage infiltration and necrotic core to be the 2 best discriminators of plaque types (area under the curve: FA, 0.82; TCFA, 0.58; PR, 0.72). More than 75% cross-section area stenosis was seen in 70% of PR and 40% of TCFA; only 5% PR and 10% TCFA were <50% narrowed.

CONCLUSIONS

This postmortem study defines histomorphologic characteristics of vulnerable plaques, which may help develop imaging strategies for identification of such plaques in patients at a high risk of sustaining acute coronary events.

[Experience with cardiac magnetic resonance imaging in patient management at the Markusovszky Hospital, Vas County, Hungary]

INTRODUCTION

At the Markusovszky Hospital, Vas County, Hungary, cardiac magnetic resonance imaging has been routinely used since July, 2009. In the majority of cases this method has been applied for the assessment of myocardial viability in patients with chronic ischemic heart disease and, in a smaller number of cases, for the evaluation of patients with myocarditis, cardiomyopathy and syncope with uncertain etiology in young athletes.

AIMS

The aim of the study was to analyze the clinical value of cardiac magnetic resonance imaging in assessing the viability of affected myocardial regions due to chronic occlusion of major coronary arteries.

METHODS

Delayed-enhancement cardiac magnetic resonance examination was performed in 88 patients who had 103 myocardial regions affected with chronic occlusion of the coronary arteries. The number of affected myocardial regions which proved to be treatable with coronary artery intervention and the number of regions where revascularization strategy was based on cardiac magnetic resonance imaging findings were analyzed.

RESULTS

Based on findings from cardiac magnetic resonance imaging, revascularization strategy was set up in 88 myocardial regions corresponding to 83.5% of all affected myocardial regions included in this study.

CONCLUSIONS

Delayed-enhancement cardiac magnetic resonance imaging appears to be a powerful tool to choose the optimal reperfusion strategy in patients with chronic coronary occlusion. Although this diagnostic method is relatively expensive, its accuracy regarding the features of myocardial viability such as transmural extension of the lesion within the affected region is higher than that of other methods (e.g. myocardium scintigraphy or stress echocardiography).

Temporal changes of strain parameters in the progress of chronic ischemia: with comparison to transmural infarction

The aim of this study was to reveal the temporal and spatial changes of strain parameters during the progression of chronic coronary ischemia. Fourteen pigs received occluder implantation to create gradual ischemia (CI), while six pigs underwent a sham surgery (Control). Six pigs after myocardial infarction were also studied (MI). Strain analysis was performed using a speckle-tracking algorithm. Eleven of the 14 animals with occluder implantation had total occlusion of the left anterior descending artery with collaterals at 1 month (early occlusion group), whereas three pigs had occlusion at 3 months (late occlusion group). Both radial strain (RS) and circumferential strain (CS) of ischemic area deteriorated at 1 month in the early occlusion group and remained at the same level throughout the remaining 2 months of the experiment. In the late occlusion group, RS gradually declined, while CS took the same course as Control until the 2 month time point. Thereafter, both metrics reached the same level as the early occlusion group at the time of occlusion. Interestingly, RS in the remote area decreased moderately, whereas CS remained normal in CI pigs. The comparison between CI and MI revealed preserved CS at the ischemic area in CI pigs. Both RS and CS deteriorate by the time total coronary occlusion was established and remain at the same level thereafter. Altered RS in the remote area may be an indicator of remodeling in the non-ischemic area, whereas CS may be useful for distinguishing between transmural and non-transmural scar.

Improvement of myocardial performance (Tei) index closely reflects intrinsic improvement of cardiac function: assessment in revascularized hibernating myocardium

BACKGROUND

Myocardial performance index (MPI), or Tei index, is an indicator of systolic and diastolic myocardial function. MPI increases in case of cardiac dysfunction; however, whether reversal of left ventricular dysfunction is also reflected by concomitant improvement (i.e., decrease) of MPI is unknown.

METHODS

Fifty-two patients with chronic ischemic cardiomyopathy and viable myocardium by dobutamine stress echocardiography were studied by echocardiography before and more than 4 months after cardiac revascularization. Patients were in optimal medical therapy, which remained unchanged following revascularization.

RESULTS

At baseline, ejection fraction (EF: 32 ± 6%) and wall motion score index (WMSI: 2.37 ± 0.32) were impaired, and MPI averaged 0.71 ± 0.19. Revascularization markedly improved EF (44 ± 10%, P < 0.0001) and WMSI (1.77 ± 0.44, P < 0.0001). MPI also improved (0.59 ± 0.26, P < 0.0001), and its decrease was significantly correlated with the improvement in EF (r =-0.68, P < 0.0001) and to the extent of viable myocardium (r =-0.45, P = 0.0007). Responders to revascularization (≥5% increase in EF at follow-up, n = 40% and 77%) achieved a significant improvement in MPI at follow-up in contrast with nonresponders (-23 ± 25% vs. 0.02 ± 0.18%, P = 0.001). Improvement in MPI was largely driven by a significant reduction in isovolumic contraction time (P < 0.001) with consequent prolongation of the ejection phase.

CONCLUSION

In patients with chronic ischemic cardiomyopathy, MPI improves along with recovery of function, reflecting the intrinsic improvement of viable segments induced by revascularization.

Myocardial perfusion and contraction in acute ischemia and chronic ischemic heart disease

A large body of evidence has demonstrated that there is a close coupling between regional myocardial perfusion and contractile function. When ischemia is mild, this can result in the development of a new balance between supply and energy utilization that allows the heart to adapt for a period of hours over which myocardial viability can be maintained, a phenomenon known as "short-term hibernation". Upon reperfusion after reversible ischemia, regional myocardial function remains depressed. The "stunned myocardium" recovers spontaneously over a period of hours to days. The situation in myocardium subjected to chronic repetitive ischemia is more complex. Chronic dysfunction can initially reflect repetitive stunning with insufficient time for the heart to recover between episodes of spontaneous ischemia. As the frequency and/or severity of ischemia increases, the heart undergoes a series of adaptations which downregulate metabolism to maintain myocyte viability at the expense of contractile function. The resulting "hibernating myocardium" develops regional myocyte cellular hypertrophy as a compensatory response to ischemia-induced apoptosis along with a series of molecular adaptations that while regional, are similar to global changes found in advanced heart failure. As a result, flow-function relations become independently affected by tissue remodeling and interventions that stimulate myocyte regeneration. Similarly, chronic vascular remodeling may alter flow regulation in a fashion that increases myocardial vulnerability to ischemia. Here we review our current understanding of myocardial flow-function relations during acute ischemia in normal myocardium and highlight newly identified complexities in their interpretation in viable chronically dysfunctional myocardium with myocyte cellular and molecular remodeling. This article is part of a Special Issue entitled "Coronary Blood Flow".

Long-term extracorporeal membrane oxygenator support in resuscitation for intractable hibernating myocardium after coronary artery bypass grafting

We report our experience of long-term extracorporeal membrane oxygenator (ECMO) support to resuscitate a 62-year-old man who had critical three-vessel disease of coronary artery complicating intractable hibernating myocardium (HM) and sudden cardiogenic shock. Intra-aortic balloon pump and ECMO were deployed to restore the circulatory support while emergent revascularization surgery was performed.The patient was weaned from ECMO successfully after 15 days of support and discharged with recovered left ventricular function. ECMO is effective in resuscitation of patients with cardiogenic shock and HM. To our knowledge the present case necessitated the longest term of ECMO support to get rid of HM.

Value of scar imaging and inotropic reserve combination for the prediction of segmental and global left ventricular functional recovery after revascularisation

BACKGROUND

This study sought to prospectively and directly compare three cardiovascular magnetic resonance (CMR) viability parameters: inotropic reserve (IR) during low-dose dobutamine (LDD) administration, late gadolinium enhancement transmurality (LGE) and thickness of the non-contrast-enhanced myocardial rim surrounding the scar (RIM). These parameters were examined to evaluate their value as predictors of segmental left ventricular (LV) functional recovery in patients with LV systolic dysfunction undergoing surgical or percutaneous revascularisation. The second goal of the study was to determine the optimal LDD-CMR- and LGE-CMR-based predictor of significant (≥ 5%) LVEF improvement 6 months after revascularisation.

METHODS

In 46 patients with chronic coronary artery disease (CAD) (63 ± 10 years of age, LVEF 35 ± 8%), wall motion and the above mentioned CMR parameters were evaluated before revascularisation. Wall motion and LGE were repeatedly assessed 6 months after revascularisation. Logistic regression analysis models were created using 333 dysfunctional segments at rest.

RESULTS

An LGE threshold value of 50% (LGE50) and a RIM threshold value of 4 mm (RIM4) produced the best sensitivities and specificities for predicting segmental recovery. IR was superior to LGE50 for predicting segmental recovery. When the areas under the ROC curves is compared, the combined viability prediction model (LGE50 + IR) was significantly superior to IR alone in all analysed sets of segments, except the segments with an LGE from 26% to 75% (p = 0.08). The RIM4 model was not superior to the LGE50 model. A myocardial segment was considered viable if it had no LGE or had any LGE and produced IR during LDD stimulation. ROC analysis demonstrated that ≥ 50% of viable segments from all dysfunctional and revascularised segments in a patient predict significant improvement in LVEF with a 69% sensitivity and 70% specificity (AUC 0.7, p = 0.05). The cut-off of ≥ 3 viable segments was a less useful predictor of significant global LV recovery.

CONCLUSIONS

LDD-CMR is superior to LGE-CMR as a predictor of segmental recovery. The advantage is greatest in the segments with an LGE from 26% to 75%. The RIM cut-off value of 4 mm had no superiority over the LGE cut-off value of 50% in predicting the segmental recovery. Patients with ≥ 50% of viable segments from all dysfunctional and revascularised had a tendency to improve LVEF by ≥ 5% after revascularisation.

Use of an intracoronary Doppler guidewire for evaluation of coronary hemodynamics in the porcine model of acute hibernating myocardium during dobutamine stress tests

PURPOSE

To determine the coronary hemodynamic characteristics of acute hibernating myocardium (AHM), evaluate the changes in coronary hemodynamics during dobutamine infusion, and investigate the mechanisms by which dobutamine stress echocardiography (DSE) detects AHM.

METHODS

The porcine model of acute hibernating myocardium was created in 10 animals, all of which underwent DSE with doses of 0-40 μg/kg/min. Myocardial segments abnormality was used as a DSE criterion for evaluating AHM. An intracoronary Doppler guidewire was used to measure the coronary hemodynamics; electrocardiography and systemic hemodynamics were recorded simultaneously. The ischemic regions of myocardium were reperfused, and all variables were recorded. Finally, the animals were euthanized and pathologic changes in the heart tissue were documented.

RESULTS

There was no myocardium necrosis. There were 55 myocardial segments with abnormal DSE responses after stenosis, among which 41 segments were judged as AHM because of a biphasic response. Average peak velocity (APV) and coronary flow velocity reserve were improved during DSE. Coronary and systemic hemodynamics were increased during dobutamine infusion. There were significant differences for APV at all evaluated doses and for heart rate blood pressure product at higher doses. The difference between APV resting values and the values for peak dosage (ΔAPV) correlated with the amount of AHM during DSE. Coronary volume blood flow and coronary flow velocity reserve decreased after stenosis.

CONCLUSIONS

ΔAPV may reflect the number of hibernating segments. The relative imbalance between blood supply and oxygen consumption in regional myocardium may be one of the mechanisms by which DSE detects AHM.

Cardiac imaging after myocardial infarction

After myocardial infarction, optimal clinical management depends critically on cardiac imaging. Remodelling and heart failure, presence of inducible ischaemia, presence of dysfunctional viable myocardium, future risk of adverse events including risk of ventricular arrhythmias, need for anticoagulation, and other questions should be addressed by cardiac imaging. Strengths and weaknesses, recent developments, choice, and timing of the different non-invasive techniques are reviewed for this frequent clinical scenario.

Attenuation of endoplasmic reticulum stress-related myocardial apoptosis by SERCA2a gene delivery in ischemic heart disease

Previous studies suggested that endoplasmic reticulum (ER) stress-associated apoptosis plays an important role in the pathogenesis of ischemic heart disease. Gene transfer of sarco/endoplasmic reticulum Ca(2+) ATPase 2a (SERCA2a) attenuates myocardial apoptosis in a variety of heart failure models. This study is to investigate the effects of SERCA2a gene delivery on the myocardial apoptosis and ER stress pathway in a porcine ischemic heart disease model. Eighteen pigs were either subjected to ameroid implantation in the coronary artery or sham operation. Eight wks after gene delivery, the protein level and activity of SERCA2a were measured. Myocardial apoptosis was determined using terminal deoxynucleotidyl transferase-mediated DNA nick-end labeling assay. Regional myocardial perfusion and function were evaluated by (99m)Tc-sestamibi ((99m)Tc-MIBI) single photon emission computed tomography and echocardiography. The ER stress signaling was assessed by Western blot. SERCA2a protein level and activity were significantly decreased in the ischemic myocardium and restored to normal after SERCA2a gene transfer. Restoration of SERCA2a expression significantly improved the cardiac function, although no improvement of regional myocardial perfusion was detected. Restoration of SERCA2a significantly attenuated myocardial apoptosis and reversed the activation of unfolded protein response (UPR) pathway and the ER stress-associated apoptosis pathways. These findings demonstrate a robust role of SERCA2a in attenuation of ischemic myocardial apoptosis, correlating with reverse activation of the ER stress-associated apoptosis pathways, suggesting that the beneficial effects of SERCA2a gene transfer may involve the attenuation of ER stress-associated myocardial apoptosis.

Clinical relevance of hibernating myocardium in ischemic left ventricular dysfunction

Patients with chronic ischemic left ventricular dysfunction may have a substantial amount of viable, hibernating myocardium, which is a state of chronic contractile dysfunction with reduced blood flow at rest. Coronary revascularization in these patients may result in improvement of left ventricular function; in the absence of viability, left ventricular function will not improve postrevascularization. Various noninvasive imaging techniques are available for detection of viable myocardium, including magnetic resonance imaging, dobutamine stress echocardiography, and nuclear imaging with single photon emission computed tomography or positron emission tomography. Because these techniques probe different characteristics of viable myocardium, the sensitivities and specificities of the techniques are not precisely identical; in general, dobutamine stress echocardiography has the highest specificity, whereas the nuclear techniques have the highest sensitivity. The presence of myocardial viability also is related to prognosis: patients with viable myocardium who undergo revascularization have a good prognosis, whereas patients with viable myocardium who are treated medically have poor outcome. Accordingly, assessment of viability is important in the therapeutic decision-making process of patients with chronic ischemic left ventricular dysfunction.

Is detection of hibernating myocardium necessary in deciding revascularization in systolic heart failure?

Although the prognosis of systolic heart failure, also called heart failure with reduced ejection fraction, has improved with advances in therapy, the prognosis remains poor in patients who become refractory to such therapies. That cardiac transplantation improves the quality of life and survival of such patients has been established, but it is available to a very small number of patients. Thus, newer pharmacologic and nonpharmacologic therapies for patients with refractory systolic heart failure are being explored. Because chronic ischemic heart disease is the most common cause of systolic heart failure, potential exists for revascularization therapy. Although revascularization can be performed with low procedural mortality, improvement in left ventricular function, relief of symptoms, and long-term prognosis appear to be related to the presence and extent of viable ischemic hibernating myocardium. In conclusion, the detection of hibernating myocardium is highly desirable before revascularization treatment is undertaken.