Myocardial viability: what we knew and what is new. Cardiol Res Pract. 2012;2012:607486. [PMID: 22988540 PMCID: PMC3440854 DOI: 10.1155/2012/607486]

Selecting the appropriate patients for coronary artery bypass grafting in ischemic cardiomyopathy-importance of myocardial viability

Patients who undergo coronary artery bypass graft (CABG) surgery in ischemic cardiomyopathy have a survival advantage over medical therapy at 10 years. The survival advantage of CABG over medical therapy is due to its ability to reduce future myocardial infarction, and by conferring electrical stability. The presence of myocardial viability does not provide a differential survival advantage for CABG over medical therapy. Presence of angina and inducible ischemia are also less predictive of outcome. Moreover, CABG is associated with significant early mortality. Hence, careful patient selection is more important for reducing the early mortality and improving the long-term outcome than relying on results of myocardial viability. Younger patients with good exercise tolerance benefit the most, while patients who are frail and patients with renal dysfunction and dysfunctional right ventricle seem to have very high operative mortality. Elderly patients, because of poor life expectancy, do not benefit from CABG, but the age cutoff is not clear. Patients also need to have revascularizable targets, but this decision is often based on experience of the surgical team and heart team discussion. These recommendations are irrespective of the myocardial viability tests. Optimal medical treatment remains the cornerstone for management of ischemic cardiomyopathy.

Validity of resting strain/strain rate in prediction of myocardial viability

To evaluate the validity of the resting strain/strain rate measurements in predicting myocardial viability taking delayed enhancement cardiac magnetic resonance imaging as the gold standard. A cohort of 60 patients at three months followed up after acute myocardial infarction were recruited for this study. Resting echocardiography with offline analysis of deformation indices and gadolinium contrast enhanced cardiac magnetic resonance imaging were applied for all patients. For the final assessment, 268 segments with significant resting wall motion abnormalities were presented. Resting longitudinal strain was significantly (p < 0.05) higher in viable, compared with non-viable segments in all the studied individual myocardial segments (apical inferior, mid antro-lateral, mid-inferolateral, mid inferoseptum, and all other segments). Likewise, resting longitudinal strain rate was significantly (p < 0.05) higher in viable, compared with non-viable segments in almost all studied individual myocardial segments apart from apical inferior, mid inferolateral and basal antro-septum (p = 0.245, p = 0.098, p = 0.097 respectively). Resting Strain and Resting Strain rate could be used as accurate predictors of myocardia viability following acute myocardial infarction.

Myocardial viability imaging using a novel non-breath-hold cardiac MRI protocol: a comparative assessment with 18F-FDG PET

Background

Delayed contrast enhancement on cardiac magnetic resonance imaging is a well-established MRI technique for the evaluation of myocardial tissue viability. A comprehensive cardiac MRI protocol for myocardial viability comprises of multiple breath hold sequences to provide information regarding chamber volumes, myocardial mass, and function in addition to viability. However, its routine use is limited mainly by lengthy acquisition time and patient’s inability to hold breath in multiple breath hold sequences. The important question to which the referring cardiologists/cardiac surgeons are seeking answer is that “What are the viable vascular territories that will benefit from revascularization?” In this study, we have analyzed the utility of non-breath-hold rapid delayed contrast-enhanced cardiac MR imaging protocol for myocardial viability assessment with 18-flourodeoxyglucose positron emission tomography (18F-FDG PET) as the reference standard.

Results

Forty patients of ischemic heart disease who met the inclusion criteria were included. All patients underwent both 18F-FDG PET and delayed contrast-enhanced cardiac magnetic resonance imaging as per the non-breath-hold protocol. In this free-breathing protocol, the breath hold cine sequences were omitted and, after localizers, post-contrast scans were obtained with a time gap of 15 min post-contrast administration. A total number of 680 myocardial segments and corresponding 120 vascular territories were assessed. MRI and 18F-FDG PET images were analyzed using a 17-segment model as proposed by AHA. Sensitivity, specificity, positive predictive value, and negative predictive value of non-breath-hold rapid delayed contrast-enhanced cardiac MR imaging protocol for assessing myocardial viability (on segment analysis) was 95.5%, 65.59%, 88.0%, and 84.72%, respectively, and of vascular territory analysis were 96.77%, 92.59%, 97.83%, and 89.29%, respectively, in relation to 18F-FDG PET used as the reference standard. Spearman’s rank correlation coefficient is 0.62.

Conclusion

This modified non-breath-hold delayed contrast-enhanced cardiac MR imaging protocol is a reliable tool to answer the clinically relevant question of myocardial viability with a significant reduction in acquisition time and overcomes the limiting need of breath hold.

Accuracy of myocardial viability imaging by cardiac MRI and PET depending on left ventricular function

AIM

To compare myocardial viability assessment accuracy of cardiac magnetic resonance imaging (CMR) compared to [¹⁸F]-fluorodeoxyglucose (FDG)- positron emission tomography (PET) depending on left ventricular (LV) function.

METHODS

One-hundred-five patients with known obstructive coronary artery disease (CAD) and anticipated coronary revascularization were included in the study and examined by CMR on a 1.5T scanner. The CMR protocol consisted of cine-sequences for function analysis and late gadolinium enhancement (LGE) imaging for viability assessment in 8 mm long and contiguous short axis slices. All patients underwent PET using [¹⁸F]-FDG. Myocardial scars were rated in both CMR and PET on a segmental basis by a 4-point-scale: Score 1 = no LGE, normal FDG-uptake; score 2 = LGE enhancement < 50% of wall thickness, reduced FDG-uptake ( ≥ 50% of maximum); score 3 = LGE ≥ 50%, reduced FDG-uptake (< 50% of maximum); score 4 = transmural LGE, no FDG-uptake. Segments with score 1 and 2 were categorized “viable”, scores 3 and 4 were categorized as “non-viable”. Patients were divided into three groups based on LV function as determined by CMR: Ejection fraction (EF), < 30%: n = 45; EF: 30%-50%: n = 44; EF > 50%: n = 16). On a segmental basis, the accuracy of CMR in detecting myocardial scar was compared to PET in the total collective and in the three different patient groups.

RESULTS

CMR and PET data of all 105 patients were sufficient for evaluation and 5508 segments were compared in total. In all patients, CMR detected significantly more scars (score 2-4) than PET: 45% vs 40% of all segments (P < 0.0001). In the different LV function groups, CMR found more scar segments than PET in subjects with EF< 30% (55% vs 46%; P < 0.0001) and EF 30%-50% (44% vs 40%; P < 0.005). However, CMR revealed less scars than PET in patients with EF > 50% (15% vs 23%; P < 0.0001). In terms of functional improvement estimation, i.e., expected improvement after revascularization, CMR identified “viable” segments (score 1 and 2) in 72% of segments across all groups, PET in 80% (P < 0.0001). Also in all LV function subgroups, CMR judged less segments viable than PET: EF < 30%, 66% vs 75%; EF = 30%-50%, 72% vs 80%; EF > 50%, 91% vs 94%.

CONCLUSION

CMR and PET reveal different diagnostic accuracy in myocardial viability assessment depending on LV function state. CMR, in general, is less optimistic in functional recovery prediction.

Cardiac Magnetic Resonance and Myocardial Viability: Why Is It so Important?

For a better assessment of ischemic heart diseases, myocardial viability should be quantified. Current studies underline the importance and the evolution of several techniques and methods used in the evaluation of myocardial viability. Taking into account these considerations, the aim of this manuscript was to present the recent points of view regarding myocardial viability and its clinical significance in patients with ischemic cardiomyopathies and left ventricular dysfunction. On the other hand, the manuscript points out the role of magnetic resonance imaging (MRI), one of the most useful noninvasive imaging techniques, in the assessment of myocardial viability. By comparing the advantages and disadvantages of cardiac MRI, its usefulness can be better appreciated by the clinician. In the following years, it is considered that MRI will be an indispensable imaging tool in the assessment of ischemic heart disease, guiding interventions for revascularization and long-term risk stratification in patients with stable angina or myocardial infarction.

Prolonged QT and myocardium recovery after primary PCI: a cMRI study

BACKGROUND

The presence of viable stunned myocardium recovering after primary angioplasty is not easy to identify in the early phase of acute myocardial infarction (AMI) by noninvasive bed-side methods. We therefore aimed to assess whether a simple electrocardiogram parameter may be of help in identifying the presence of stunned viable myocardium recovering after reperfusion with primary angioplasty.

MATERIALS AND METHODS

A total of 14 consecutive patients with ST-elevation AMI (STEMI) were enrolled in the study and underwent QT duration assessment after admission: the difference between QT corrected (QTc) in the ischaemic areas and QTc values in nonischaemic areas was therefore calculated and compared with the presence and the extension of viable stunned myocardium, assessed by comparing akinetic/dyskinetic areas at admission echocardiography with akinetic/dyskinetic areas and extension of scar at 6-month cardiac magnetic resonance imaging (cMRI).

RESULTS

In subjects with viable recovering myocardium, 75% had a QTc max > 440 ms (vs. 17%, P = 0·03); higher differential QTc values and smaller scar areas were found (33 ms vs. -17 ms, 14% vs. 27%, P = 0·03, 0·06 respectively). Differential QTc values > 0 were able to identify the presence of viable myocardium with an odds ratio of 35 (P < 0·05, sensitivity 88%, specificity 83%, positive predictive power 88%, negative predictive power of 83%). Differential QTc values were related to the extension of viable recovering myocardium (P < 0·001).

CONCLUSION

Viable myocardium recovering after primary angioplasty in STEMI may be predicted by the presence of increased QTc values in ischaemic areas in comparison with nonischaemic areas.

Diagnostic accuracy of resting left ventricular akinesia/hypokinesia in predicting abnormal coronary angiography

Background

Although several reports demonstrate the efficacy of stress echocardiography in diagnosing coronary artery disease, comparable studies on the competence of the same imaging technique at rest are limited. This study aimed to evaluate whether ventricular akinesia/hypokinesia and left ventricular ejection fraction (LVEF) < 55 % at rest are useful in predicting abnormal coronary angiography.

Methods

This study prospectively enrolled 100 diagnostic coronary catheterization candidates. Any routine echocardiography that the candidates had undergone before diagnostic coronary catheterization was reviewed. Patients were subclassified according to the presence and location of ventricular akinesia/hypokinesia, LVEF, and the results of diagnostic coronary catheterization. LVEF < 55 % was considered below the normal physiological limit. Abnormal coronary angiography was defined as narrowing of half or more of the caliber of at least one major coronary artery.

Results

Abnormal coronary angiography was significantly associated with akinesia/hypokinesia (OR = 4.85, P = 0.002) and LVEF < 55 % (OR = 5.75, P = 0.001). Screening of akinesia/hypokinesia and LVEF < 55 % as diagnostic tools for abnormal coronary angiography achieved comparable sensitivities (87.2 % vs. 88.9 %), specificities (41.5 vs. 41.8), and diagnostic accuracies (41.5 vs. 41.8). Left ventricular anterior wall akinesia/hypokinesia achieved a higher diagnostic odds ratio (9.7), sensitivity (95 %), and negative predictive value (96.4 %) compared with other types of akinesia/hypokinesia.

Conclusion

The overall diagnostic accuracy of akinesia/hypokinesia and LVEF < 55 % to predict abnormal coronary angiography was poor, probably owing to significant influences of macro- as well as micro-vascular ischemia on left ventricular function.

Non-invasive imaging in detecting myocardial viability: Myocardial function versus perfusion

Coronary artery disease (CAD) is the most prevalent and single most common cause of morbidity and mortality [1] with the resulting left ventricular (LV) dysfunction an important complication. The distinction between viable and non-viable myocardium in patients with LV dysfunction is a clinically important issue among possible candidates for myocardial revascularization. Several available non-invasive techniques are used to detect and assess ischemia and myocardial viability. These techniques include echocardiography, radionuclide images, cardiac magnetic resonance imaging and recently myocardial computed tomography perfusion imaging. This review aims to distinguish between the available non-invasive imaging techniques in detecting signs of functional and perfusion viability and identify those which have the most clinical relevance in detecting myocardial viability in patients with CAD and chronic ischemic LV dysfunction. The most current available studies showed that both myocardial perfusion and function based on non-invasive imaging have high sensitivity with however wide range of specificity for detecting myocardial viability. Both perfusion and function imaging modalities provide complementary information about myocardial viability and no optimum single imaging technique exists that can provide very accurate diagnostic and prognostic viability assessment. The weight of the body of evidence suggested that non-invasive imaging can help in guiding therapeutic decision making in patients with LV dysfunction.

Advanced tracers in PET imaging of cardiovascular disease

Cardiovascular disease is the leading cause of death worldwide. Molecular imaging with targeted tracers by positron emission tomography (PET) allows for the noninvasive detection and characterization of biological changes at the molecular level, leading to earlier disease detection, objective monitoring of therapies, and better prognostication of cardiovascular diseases progression. Here we review, the current role of PET in cardiovascular disease, with emphasize on tracers developed for PET imaging of cardiovascular diseases.