European Journal of Cardiovascular Medicine

The cardiac magnetic resonance (CMR) imaging has become the new gold standard in non-invasive evaluation of myocardial viability, which has fundamentally changed the approach towards clinical assessment of patients with ischemic cardiomyopathy and left ventricular dysfunction. This is because correct definition of viable and non-viable myocardium is vital in the clinical decision-making process, especially in patients undergoing a myocardial revascularization procedure. CMR has unmatched spatial resolution, superior tissue characterization, and a full examination of cardiac anatomy, cardiac function, cardiac perfusion, and cardiac viability in a single study[1][2].

Late gadolinium enhancement (or delayed enhancement) magnetic resonance imaging (LGE) is the cornerstone methodology of myocardial viability assessment by CMR. This process takes advantage of the difference in the distribution of gadolinium based contrast medium between viable and non-viable myocardium, giving a splendid delineation of myocardial scar tissue. After administering gadolinium contrast intravenously, the images are usually imaged (10-20 minutes) with a breath-hold acquisition using an inversion recovery gradient-recalled echo sequence. The inversion time is optimized to cancel the signal of normal myocardium and creates a dramatic effect with viable myocardium appears as dark (nulled) and scarred tissue as bright (hyperenhanced).[3][4][5].

The pathophysiology of LGE imaging is based on the underlying cellular differences of membrane integrity and extracellular volume of viable and non-viable myocardium. Gadolinium contrast is localized in the infarction areas of the myocyte membrane destruction and cell death in the acute myocardial infarction. In chronic infarction, the increased extracellular space of the fibrotic scar tissue enables the increased gadolinium distribution and retention, forming the typical hyperenhancement pattern. This process allows the identification of acute and chronic myocardial damage with great sensitivity and specificity[6][7].

In general, the quantitative measurement of myocardial viability with CMR is usually founded on the transmural degree of infarction (TEI), which is the proportion of wall thickness occupied by scar tissue. The generally agreed standard in determining viability is 50% transmural involvement with any part below 50% TEI deemed viable and capable of exhibiting functional improvement following revascularization. This binary system of classification has been widely tested vs. histopathological studies and functional recovery outcomes and has proved to be highly predictive of post-revascularization contractile recovery.

Phase-sensitive inversion recovery (PSIR) reconstruction is one of the important technical improvements made in LGE imaging, which overcomes shortcomings linked to traditional magnitude reconstruction. The large dynamic range that PSIR maintains positive and negative magnetization polarities in the course of tissue recovery after the first inversion pulse has been delivered effectively doubles the dynamic range available and demonstrates consistent contrast of viable and non-viable tissue despite small differences in the inversion time choice. The method improves diagnostic confidence and minimizes the acquisition repetitions necessary to optimize the nulling parameters[11] [12].

In addition to the detection of a simple scar, the role of CMR viability assessment will also include the measurement of microvascular obstruction (MVO) that is defined by insufficient myocardial reperfusion despite an effective recanalization of the epicardial vessels. MVO presents as chronic hypointense foci in hyperenhanced infarct areas on LGE images, which is an area of grossly impaired microvascular integrity. MVO is significantly associated with poor left ventricular remodelling, risk of arrhythmic occurrences and decreased probability of functional recovery[13][14].

Other methods of viability assessment using CMR are low-dose stress imaging with dobutamine, which is used to assess the contractile reserve of dysfunctional myocardial segments. Christophe Dobutamine stress CMR has procedures that are similar to stress echocardiography, whereby graded doses of dobutamine are administered whilst abnormalities of regional wall motion are monitored. Biphasic response, which is improvement and then worsening of a higher dosage, is evidence of viable but hibernating myocardium. Although dobutamine stress CMR offers good functional data, LGE is the method of choice because it has a better spatial resolution compared to dobutamine stress CMR and it can identify subendocardial infarction[15][16].

The clinical uses of CMR viability assessment are not limited to the simplicity of revascularization decision-making. Accurate determination of scar burden is useful in risk stratification of sudden cardiac death, in the decisions on future implantable cardioverter-defibrillator placement, and in the prognostic information that is not dependent on the left ventricular ejection fraction. It has been found especially useful in the distinction between ischemic and non-ischemic cardiomyopathy and in patients with silent myocardial infarction, and in the treatment follow-up of many cardiovascular diseases[17][18].

The technical considerations of optimal CMR viability assessment are proper contrast dosing (usually 0.1-0.2 mmol/kg), sufficient relaxation period between contrast injection and imagining, and proper choice of inversion time in order to get maximum nulling of normal myocardium. More elaborate quantification-based approaches have superseded plain visual methods, to automated thresholding methods, although standardization is still an unresolved issue in the area.[19,20]

Study Design: This was a prospective observational study conducted over a period of 18 months at the SAIMS Cardiology and Radiology Departments. The primary aim of the study was to explore the association between metabolic syndrome and coronary artery disease (CAD) by evaluating myocardial viability and left ventricular (LV) function using advanced imaging techniques, including MRI, echocardiography, and coronary angiography. The study aimed to provide a comprehensive understanding of the role of metabolic syndrome in the pathogenesis of CAD, along with assessing the viability of myocardial tissue and the clinical outcomes associated with different levels of myocardial damage.

Study Population

A total of 50 patients were enrolled in the study. Inclusion criteria included:

1. Adults aged 18 years or older with a clinical diagnosis of CAD confirmed by coronary angiography.
2. Patients who were referred for imaging studies due to suspected or diagnosed CAD.
3. Patients with or without a history of metabolic syndrome.
   Exclusion criteria included:
4. Patients with a prior history of coronary artery bypass surgery (CABG) or percutaneous coronary intervention (PCI).
5. Patients with non-cardiac conditions that could interfere with metabolic parameters, such as active cancer or severe renal failure.
6. Patients with incomplete clinical records or unwillingness to participate in the study.

Patient Selection and Consent: Patients were selected from the outpatient and inpatient departments of SAIMS Cardiology and Radiology. Following the initial consultation and diagnostic work-up, patients were approached for participation in the study. Written informed consent was obtained from all participants before data collection, ensuring that they understood the nature of the study and its potential risks.

Data Collection

1. Demographic and Clinical Data:

A comprehensive clinical history was obtained from each patient, which included demographic details (age, gender, ethnicity) and clinical characteristics such as risk factors (hypertension, diabetes, smoking, family history of CAD) and previous medical history (myocardial infarction, previous surgeries).

1. Assessment of Metabolic Syndrome:

Metabolic syndrome was diagnosed based on the following criteria from the International Diabetes Federation (IDF):

• Abdominal obesity (waist circumference ≥94 cm for males and ≥80 cm for females)
• Elevated blood pressure (systolic BP ≥130 mmHg or diastolic BP ≥85 mmHg or on antihypertensive medication)
• Elevated fasting blood glucose (≥100 mg/dL or on antidiabetic medication)
• Elevated triglycerides (≥150 mg/dL or on treatment for elevated triglycerides)
• Low HDL cholesterol (<40 mg/dL in males and <50 mg/dL in females)

Patients who met at least three of the above criteria were classified as having metabolic syndrome.

1. Imaging Studies:
• Magnetic Resonance Imaging (MRI):

All patients underwent cardiac MRI to assess myocardial viability. The MRI scan focused on evaluating the left ventricular wall for viable myocardium, non-viable myocardium, and scar tissue. The percentage of viable myocardium in each patient was calculated based on imaging results.

• Echocardiography:
  Standard echocardiographic evaluations were performed to assess left ventricular ejection fraction (LVEF) and overall left ventricular function. The LVEF was recorded as a percentage.
• Coronary Angiography:

Coronary angiography was performed for all patients to identify the presence, location, and severity of vascular blockages. This procedure was used as a reference for diagnosing CAD and understanding the extent of coronary artery involvement.

Clinical Data Analysis
The following parameters were analyzed:

1. Myocardial Viability:
   The percentage of viable myocardium, non-viable myocardium, and scar tissue in each patient was determined from the MRI results. This data was used to assess myocardial health and guide treatment recommendations.
2. Left Ventricular Function (LVEF):

LVEF was measured via echocardiography and correlated with myocardial viability as assessed by MRI. The relationship between LVEF and myocardial health was evaluated to determine whether improved heart function was associated with a higher percentage of viable myocardium.

1. Vascular Blockages:
   Data from coronary angiography was used to evaluate the degree of vascular blockage and its relationship with myocardial viability and LV function. Patients were classified based on the severity of their coronary artery blockages.

Treatment Plan

Based on the MRI findings and LVEF, a tailored treatment plan was developed for each patient. Those with significant viable myocardium were recommended for myocardial revascularization procedures, such as percutaneous coronary intervention (PCI) or coronary artery bypass grafting (CABG). Patients with less viable myocardium were advised to continue with medical management, and a stress perfusion test was suggested for further evaluation of ischemia.

Table 1: Patient Demographics and Clinical Characteristics

Table 1 outlines the key demographic and clinical characteristics of the 50 patients included in the study. The average age of the patients is 58.5 years, with a predominance of male participants (70%). The table highlights common risk factors such as hypertension, diabetes, and smoking, with 60% of the participants having a history of myocardial infarction (MI) and coronary artery disease (CAD).

Table 2: MRI Findings of Myocardial Viability

This table provides an overview of the MRI findings related to myocardial viability in each patient. It presents the percentage of viable, non-viable, and scar tissue in the left ventricular (LV) walls, showing variability in myocardial health across patients. The table demonstrates that some patients, particularly those with anterior or inferior wall involvement, have a significant portion of their myocardium non-viable or scarred.

Table 3: Comparison of MRI Findings with Conventional Methods (Echocardiography and Coronary Angiography)

Table 3 compares MRI results with other conventional diagnostic methods such as echocardiography and coronary angiography. The table reveals that MRI generally shows a higher percentage of myocardial viability compared to echocardiography, while coronary angiography identifies more vascular blockages. Despite these differences, MRI provides valuable insights into myocardial tissue integrity, complementing the functional assessments from echocardiography and angiography.

Table 4: Relationship Between Myocardial Viability and Left Ventricular Function (LVEF)

This table explores the relationship between left ventricular function, as measured by LVEF, and myocardial viability. As LVEF improves, the proportion of viable myocardium increases, while non-viable tissue decreases. This table highlights that patients with better LV function tend to have higher percentages of viable myocardium and lower scar tissue, suggesting a direct correlation between heart function and myocardial health.

Table 5: Treatment Plan Based on MRI Results

Patients with >50% viable myocardium are recommended for myocardial revascularization (e.g., PCI or CABG). Patients with ≤50% viable myocardium are advised to follow medical management, and a stress perfusion test is recommended to evaluate further ischemia and treatment options.

The findings of the current research give valuable information regarding the correlation between myocardial viability, left ventricular functioning, and coronary artery disease (CAD) among the group of patients. The demographic and clinical profile of the patients show that there is a population with a high-risk factor burden of CAD, such as hypertension (40%), diabetes (30%), and smoking (25%). In combination with a history of myocardial infarction (60%), CAD (50%), these risk factors provide evidence that a considerable number of patients in the study already had important cardiovascular pathology at baseline. The mean age of 58.5, and the dominance of males (70percent) are typical characteristics in CAD, which is linked to older age and males being prone to the disease. These results are consistent with a landmark study by Lakka et al. that revealed that cardiovascular mortality rates were significantly higher among middle-aged men with metabolic syndrome. Also, Allman et al. performed a meta-analysis of 3,088 patients in general and established a similar pattern of demographics as always linked to poorer cardiovascular outcomes. [21,22].

The MRI results provide highly significant information on myocardial viability and the degree of myocardial infarction of the left ventricle. The differences in the percentage of normal and damaged myocardium in patients suggest that there is heterogeneity in myocardial damage, as some patients, especially those with an anterior or inferior wall, have large proportions of non-viable or scar tissue. Such results are important in determining the extent of the myocardial injury and whether recovery or amelioration is possible through therapeutic measures. All these indicate that patients with a large viable myocardium (that is, over 50 percent) can be offered myocardial revascularization techniques, including percutaneous coronary intervention (PCI) or coronary artery bypass grafting (CABG) to restore blood supply to the ischemic area(s). Kim et al. set this 50 percent level through a vast amount of validation research where segments with an infarction that were less than 50 percent transmural showed considerable functional gain after revascularization. Mahrholdt et al. also confirmed this threshold showing that by the time the contractile dysfunction can be identified systematically, the transmural extent of infarction has already been 50 percent of the entire area[23,24].

Comparing the findings of the MRI to traditional ones such as the echocardiography and the coronary angiography, the findings can be explained by certain interesting trends. The pattern was that myocardial viability was higher in percentage as it was detected by MRI, which is understandable given the fact that MRI provides a more detailed characterization of the tissue compared to echocardiography. Gutberlet et al. also support this observation by reporting that delayed enhancement MRI has the highest sensitivity (99%), specificity (94%), of viability assessment versus echocardiography and nuclear imaging methods. A thorough comparison of echocardiography and CMR by Tomlinson et al. found that CMR has a better spatial resolution and is able to detect subendocardial infarction that could have been overlooked by echocardiography. Coronary angiography, however, gave a better picture of vascular blockages so that 70% of patients were found to have significant blockage of the coronary artery. This points to the complementary role of MRI to conventional imaging modalities. Although that echocardiography and angiography are necessary to assess the functional and anatomical evaluations, MRI provides special information on myocardial tissue integrity, which is crucial in making treatment choices. In a comparative study, Kazakauskaite et al. showed that CMR revealed non-viable myocardium in 28.1% of segments, which is significantly lower than in SPECT (11.8) and PET (6.5), indicating that CMR is more cautious in viability determination compared to the techniques (Kazakauskaite et al.).[25,26,27].

The correlation between myocardial viability and the left ventricular ejection fraction (LVEF) can be seen in the results. With improvement of LVEF percentage of viable myocardium is increased and scar tissue is reduced. This observation highlights the need to preserve or enhance LV performance as one of the determinants of myocardial service quality. The patients who had a good LV were found to have a greater percentage of viable myocardium and this implied a better prognosis and possible recovery through proper interventions. On the other hand, patients with worse LV functioning had a greater percentage of non-viable myocardium, which could be a sign of an advanced heart failure and reduced chances of recovery. Cao et al. tested this association in 118 patients with heart failure and reduced ejection fraction and reported that patients with high myocardial viability (10% viable myocardium) were significantly better in terms of left ventricular function parameters and long-term survival rates than their counterparts of low viability. Kundina et al. showed that there was a great correlation between myocardial viability scores and LVEF in post-revascularization patients, and that viability measurement was greatly enhanced in both preserved and reduced ejection fraction groups.[28,29]

Lastly, the MRI results-based treatment plan offers a customized treatment plan of a patient. In patients with a more than 50% viable myocardium, myocardial revascularization is indicated because such patients are likely to have the benefit of restoring the blood flow into the involved areas. In patients with less viable myocardium (50%), the medical management is preferred, and other examinations including stress perfusion imaging can be prescribed to further consider the ischemic zones. Such a personalized mode of therapy, founded on myocardial viability, highlights the significance of accurate diagnostic imaging in the clinical judgment to make sure that all interventions are focused and suitable in each case of a specific patient state. Recent research findings however by Perera et al. in the REVIVED-BCIS2 trial however disputed the classic model and demonstrated viability testing proved useless in detecting ischemic cardiomyopathy patients who would respond to PCI and so the clinical utility of routine viability testing has come into question. However, Alzahrani et al. discovered that patients with viable myocardium reportedly reported much better results with enhanced LVEF after treatment and lower hospital readmission rates[30,31].

The findings of this paper indicate the usefulness of the advanced imaging methods, including MRI in the determination of myocardial viability and treatment decisions in CAD patients. The results underscore the need to identify patients with major viable myocardium as a revascularization option, and those with less viable myocardium can be treated with medical treatment and close observation. Also, the paper indicates the importance of conventional diagnostic techniques such as echocardiography and coronary angiography in supplementing MRI results to give the full picture of myocardial quality and the involvement of coronary arteries. Future studies need to be aimed at generalizing these results to larger groups of people and assessing the long-term results of MRI-guided treatment plans CAD. Kidambi et al. hypothesized that extracellular volume mapping could offer more prognostic data than conventional transmural extent analysis, which could enhance the viability prediction accuracy of extracellular volume mapping applications [32].

This study emphasizes the value of CMR in assessing myocardial viability and guiding treatment choices for patients with coronary artery disease (CAD). When compared to conventional techniques such as echocardiography, CMR provides a superior and more detailed evaluation of myocardial integrity, which supports more precise decisions regarding myocardial revascularization. The findings advocate for the integration of CMR into everyday clinical practice to improve both prognostic assessment and treatment strategies for CAD patients

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