Clinical impact of multimodality assessment of myocardial viability

Coronary artery disease (CAD) is a prevalent cause of left ventricular dysfunction. Nevertheless, effective elective revascularization, particularly surgical revascularization, can enhance long-term outcomes and, in selected cases, global left ventricular contractility. The assessment of myocardial viability and scars is still relevant in guiding treatment decisions and selecting patients who are likely to benefit most from blood flow restoration. Although the most recent randomized studies challenge the notion of "hibernating myocardium" and the clinical usefulness of assessing myocardial viability, the advancement of imaging techniques still renders this assessment valuable in specific situations. According to the guidelines of the European Society of Cardiology, non-invasive stress imaging may be employed to define myocardial ischemia and viability in patients with CAD and heart failure before revascularization. Currently, several non-invasive imaging techniques are available to evaluate the presence and extent of viable myocardium. The selection of the most suitable technique should be based on the patient, clinical context, and resource availability. This narrative review evaluates the characteristics of available imaging modalities for assessing myocardial viability to determine the most appropriate therapeutic strategy.

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.

Myocardial viability assessment and utility in contemporary management of ischemic cardiomyopathy

Background

In clinical practice, we encounter ischemic cardiomyopathy (ICM) with underlying viable, dysfunctional myocardium on a regular basis. Evidence from the Surgical Treatment for Ischemic Heart failure (STICH) and its Extension Study is supportive of improved outcomes with coronary revascularization, irrespective of myocardial viable status. However, Dobutamine stress echocardiography (DSE) and single‐photon emission computed tomography (SPECT), used in STICH to assess myocardial viability may fail to distinguish hibernating myocardium from scar due to suboptimal image resolution and poor tissue characterization.

Hypothesis

Cardiac magnetic resonance (CMR) and positron emission tomography (PET) can precisely quantify myocardial scar and identify metabolically active, viable myocardium respectively. Unlike DSE and SPECT, CMR and PET allow examining myocardial status as a contiguous spectrum from viable to partially viable myocardium with varying degrees of subendocardial scar and nonviable myocardium with predominantly transmural scar, the therapeutic and prognostic determinants of ICM.

Methods

Under the guidance of CMR and PET imaging, myocardium can be distinguished viable from partially viable with subendocardial scar and predominantly transmural scar. In ICM, optimal medical therapy and coronary revascularization of viable/partially viable myocardium but not transmural scar may improve outcomes in patients with acceptable procedural risk.

Results

Coronary revascularization of partially viable and viable myocardial territory may improve clinical outcomes by preventing future ischemic, infarct events and further worsening of left ventricular remodeling and function.

Conclusions

When deciding if coronary revascularization is appropriate in a patient with ICM, it is essential to take a patient‐tailored, comprehensive approach incorporating myocardial viability, ischemia, and scar data with others such as procedural risk, and patient's comorbidities.

1.

Viability of myocardium is assessed by different imaging modalities, probing different characteristics of the living myocyte – uptake of radioactive isotope, TC‐99m or Tl‐201 (SPECT MPI), contractile reserve (Dobutamine stress imaging, echo or CMR), metabolic properties (FDG uptake on PET), absence of scar (CMR).

2.

Dysfunctional, viable myocardium as compared to nonviable myocardium carries a better prognosis with appropriate therapy.

3.

Dysfunctional myocardium may not be simplified into a binary state of viable or not. It can be a continuum process, with a myocardial segment in a hybrid state with an intermix of viable myocytes in early to late phases of hibernation and fibrosis.

4.

Nonviable myocardium on Dobutamine Stress Echocardiography or SPECT Nuclear imaging may be partially viable (with varying degrees of fibrosis) or viable with no scar, on CMR.

5.

Coronary revascularization of partially viable or viable myocardium should be considered if the procedural risk is acceptable, as it improves long‐term outcomes by preventing further myocardial ischemia/infarction and possibly improving left ventricular function and remodeling.

Association of carotid intima-media thickness with exercise tolerance test in type 2 diabetic patients

Aims

Atherosclerosis and ischemic heart disease are more common in diabetic patients. Atherosclerosis process can disturb the normal functioning of the vascular endothelium and increase vessel wall thickness. The aim of this study was the comparison of Carotid intima-media thickness (CIMT) with Exercise tolerance test as an alternative way to evaluate cardiac ischemia in diabetic patients.

Methods

In a cross-sectional study, 30 diabetic patients with positive exercise test and 30 diabetic patients with negative exercise test were enrolled. CIMT of the carotid artery in both groups of patients was measured.

Result

CIMT in the patients with positive and negative exercise test were 1.04 ± 0.21 mm and 0.61 ± 0.11 mm, respectively (P < 0.001). CIMT in positive exercise test group was positively associated with age and negatively associated with gender, FBS, HDL and LDL cholesterol and in negative exercise group was negatively associated with gender, age, FBS, HDL and LDL cholesterol.

Conclusion

Considering observed significant positive association between CIMT with result of exercise tolerance test (ETT) in type 2 diabetic patients, it may possible to use CIMT as an inexpensive and non-invasive method for evaluation of ischemic heart disease in diabetic patients.

Myocardial Viability: From Proof of Concept to Clinical Practice

Ischaemic left ventricular (LV) dysfunction can arise from myocardial stunning, hibernation, or necrosis. Imaging modalities have become front-line methods in the assessment of viable myocardial tissue, with the aim to stratify patients into optimal treatment pathways. Initial studies, although favorable, lacked sufficient power and sample size to provide conclusive outcomes of viability assessment. Recent trials, including the STICH and HEART studies, have failed to confer prognostic benefits of revascularisation therapy over standard medical management in ischaemic cardiomyopathy. In lieu of these recent findings, assessment of myocardial viability therefore should not be the sole factor for therapy choice. Optimization of medical therapy is paramount, and physicians should feel comfortable in deferring coronary revascularisation in patients with coronary artery disease with reduced LV systolic function. Newer trials are currently underway and will hopefully provide a more complete understanding of the pathos and management of ischaemic cardiomyopathy.

Synthesis and Preclinical Evaluation of Radioiodinated Hypericin Dicarboxylic Acid as a Necrosis Avid Agent in Rat Models of Induced Hepatic, Muscular, and Myocardial Necroses

Myocardial infarction (MI) leads to substantial morbidity and mortality around the world. Accurate assessment of myocardial viability is essential to assist therapies and improve patient outcomes. (131)I-hypericin dicarboxylic acid ((131)I-HDA) was synthesized and evaluated as a potential diagnostic agent for earlier assessment of myocardium viability compared to its preceding counterpart (131)I-hypericin ((131)I-Hyp) with strong hydrophobic property, long plasma half-life, and high uptake in mononuclear phagocyte system (MPS). Herein, HDA was synthesized and characterized, and self-aggregation constant Kα was analyzed by spectrophotometry. Plasma half-life was determined in healthy rats by γ-counting. (131)I-HDA and (131)I-Hyp were prepared with iodogen as oxidant. In vitro necrosis avidity of (131)I-HDA and (131)I-Hyp was evaluated in necrotic cells induced by hyperthermia. Biodistribution was determined in rat models of induced necrosis using γ-counting, autoradiography, and histopathology. Earlier imaging of necrotic myocardium to assess myocardial viability was performed in rat models of reperfused myocardium infarction using single photon emission computed tomography/computed tomography (SPECT/CT). As a result, the self-aggregation constant Kα of HDA was lower than that of Hyp (105602 vs 194644, p < 0.01). (131)I-HDA displayed a shorter blood half-life compared with (131)I-Hyp (9.21 vs 31.20 h, p < 0.01). The necrotic-viable ratio in cells was higher with (131)I-HDA relative to that with (131)I-Hyp (5.48 vs 4.63, p < 0.05). (131)I-HDA showed a higher necrotic-viable myocardium ratio (7.32 vs 3.20, p < 0.01), necrotic myocardium-blood ratio (3.34 vs 1.74, p < 0.05), and necrotic myocardium-lung ratio (3.09 vs 0.61, p < 0.01) compared with (131)I-Hyp. (131)I-HDA achieved imaging of necrotic myocardium at 6 h postinjection (p.i.) with SPECT/CT, earlier than what (131)I-Hyp did. Therefore, (131)I-HDA may serve as a promising necrosis-avid diagnostic agent for earlier imaging of necrotic myocardium compared with (131)I-Hyp. This may support further development of radiopharmaceuticals ((123)I and (99m)Tc) based on HDA for SPECT/CT of necrotic myocardium.