Predicting benefit from revascularization in patients with ischemic heart failure: imaging of myocardial ischemia and viability

Role of Late Gadolinium Enhancement in the Assessment of Myocardial Viability

Background: Prior to any revascularization procedure for coronary artery disease, it is essential to identify viable myocardium which will likely benefit from it. In such a situation, delayed enhanced cardiac MRI is beneficial.

Methods: Our study consisted of 50 patients with at least a one-month prior history of myocardial infarction (MI), abnormal findings on electrocardiography (ECG), and 2D-echocardiography (2D-ECHO), who were subjected to cardiac MRI performed on a 3T MRI machine. The MRI scans were evaluated for anatomical and especially functional characteristics of the heart, such as wall motion. On late gadolinium enhancement (LGE), the diseased segments were classified into two categories: < 50% LGE (viable) and > 50% LGE (non-viable).

Results: Of the 378 diseased segments detected on LGE, 137 (36.2%) segments showed < 50% LGE and 241 (63.8%) segments showed > 50% LGE. The segments showing < 50% LGE showed normokinesia or hypokinesia, with none of the segments showing akinesia or dyskinesia, whereas the segments showing > 50% LGE showed akinesia or dyskinesia predominantly. This was found to be statistically highly significant (p-value < 0.001). 

Conclusion: Delayed enhanced-cardiac magnetic resonance (DE-CMR) imaging in patients with ischemic heart disease (IHD) helps evaluate the severity of the infarcted myocardium by classifying the diseased myocardium into viable and non-viable, as viable myocardium is more likely to regain functional recovery than non-viable myocardium. It also predicts the functional recovery of the myocardium after revascularization therapy.

Multimodality imaging in chronic heart failure

The prevalence of heart failure (HF) is approximately 1-2% of the adult population in developed countries, rising to  ≥ 10% among people over 70. The common symptoms of HF include shortness of breath, ankle swelling and fatigue, determined by a reduced cardiac output. Multimodality imaging is crucial to define HF etiology, determine prognosis and guiding tailored treatments. Echocardiography is the most widely used imaging modality and maintains a pivotal role in the initial diagnostic work-up and in the follow-up of HF patients. Cardiac magnetic resonance (CMR) may support the morpho-functional assessment provided by echocardiography when the acoustic window is limited or a gold standard evaluation is required. Furthermore, CMR is frequently used due to the unmatched capability to characterize myocardial structure. Coronary computed tomography angiography has become the non-invasive imaging of choice to diagnose or rule-out coronary artery disease, acquiring remarkable importance in the management of HF patients. Moreover, emerging capabilities of CT-based tissue characterization may be useful, especially when CMR is contraindicated. Finally, chest CT may contribute to precisely define the framework of HF patients, revealing new insight about cardiopulmonary pathophysiological interactions with potential high prognostic value.

[Remote results of myocardial endovascular revascularization in patients with low ejection fraction]

Despite the present-day level of the development of cardiac surgery, a low left ventricular ejection fraction (LLVEF) is an important independent predictor of high complication rates and increased in-hospital mortality related to open surgical interventions. The method of myocardial endovascular revascularization is associated with the lowest rates of both intraoperative and early postoperative complications. However, percutaneous coronary intervention (PCI) does not always make it possible to perform anatomically complete myocardial revascularization. Comparisons of the remote results of anatomically complete and incomplete revascularization of the myocardium in the world literature seem to be extremely scarce and ambiguous, with a low ejection fraction in the majority of cases being an exclusion criterion. In order to elucidate these problems we carried out a prospective, single-centre study, including a total of 151 patients suffering from ischaemic heart disease with a left ventricular ejection fraction of less than 35%, who were subjected to myocardial endovascular revascularization. The patients were divided into 2 groups: those with complete (n=87) and incomplete (n=64) revascularization, followed by comparing the alterations in the echocardiographic parameters, assessing the incidence of repeat myocardial revascularization due to a relapse of the clinical course of angina pectoris, and the survival rate in the remote period. The obtained findings were suggestive of efficacy of both complete and incomplete endovascular revascularization of the myocardium in patients with a low left ventricular ejection fraction (LLVEF), with no statistically significant differences between the patients of both groups in the examined parameters revealed.

Myocardial Viability Testing to Guide Coronary Revascularization

Left ventricular dysfunction remains one of the best prognostic determinants of survival in patients with coronary artery disease. Revascularization has been shown to improve survival compared with medical therapy alone. Viability testing can help direct patients who will benefit the most from revascularization. Single-photon emission computed tomography, dobutamine stress echo, cardiac MRI, and PET imaging with F18-fluorodeoxyglucose are the most common modalities for assessing myocardial viability. Viability testing can help differentiate which patients benefit most from chronic total occlusion interventions.

Revascularization in Severe Left Ventricular Dysfunction: Does Myocardial Viability Even Matter?

Left ventricular dysfunction is a powerful prognostic predictor in patients with coronary artery disease and increasing number of patients with CAD and ischemic left ventricular (LV) dysfunction is a major clinical problem. Congestive heart failure is a frequent complication which is associated with significant health care costs and two-third of cases have ischemic cardiomyopathy. In such patients, coronary revascularization can lead to symptomatic and prognostic improvement and reversal of LV remodeling which led to the concept of viable myocardium to select patients in whom recovery of LV function and improvement of prognosis will outweigh the risk of surgical revascularization. The aim of this review article is to understand the different modalities for assessing myocardial viability and clinical impact of revascularization in relation to the evidence of viability in patients with LV dysfunction.

Current state of the art cardiovascular MR imaging techniques for assessment of ischemic heart disease

Cardiac magnetic resonance (CMR) imaging is increasingly being used to evaluate patients with known or suspected ischemic heart disease, because of its ability to acquire images in any orientation and the wide variety of sequences available to characterize normal and abnormal structure and function. Substantial improvements have been made in the hardware and software used to perform CMR, resulting in better and more consistent image quality. There has been a greater emphasis recently in developing and validating quantitative CMR techniques. This article reviews advances in CMR techniques for assessing cardiac function, myocardial perfusion, late gadolinium enhancement, and tissue characterization with T1 and T2 mapping sequences.

Prognostic value of myocardial ischemia and necrosis in depressed left ventricular function: a multicenter stress cardiac magnetic resonance registry

INTRODUCTION AND OBJECTIVES

The incremental prognostic value of inducible myocardial ischemia over necrosis derived by stress cardiac magnetic resonance in depressed left ventricular function is unknown. We determined the prognostic value of necrosis and ischemia in patients with depressed left ventricular function referred for dipyridamole stress perfusion magnetic resonance.

METHODS

In a multicenter registry using stress magnetic resonance, the presence (≥ 2 segments) of late enhancement and perfusion defects and their association with major events (cardiac death and nonfatal infarction) was determined.

RESULTS

In 391 patients, perfusion defect or late enhancement were present in 224 (57%) and 237 (61%). During follow-up (median, 96 weeks), 47 major events (12%) occurred: 25 cardiac deaths and 22 myocardial infarctions. Patients with major events displayed a larger extent of perfusion defects (6 segments vs 3 segments; P <.001) but not late enhancement (5 segments vs 3 segments; P =.1). Major event rate was significantly higher in the presence of perfusion defects (17% vs 5%; P =.0005) but not of late enhancement (14% vs 9%; P =.1). Patients were categorized into 4 groups: absence of perfusion defect and absence of late enhancement (n = 124), presence of late enhancement and absence of perfusion defect (n = 43), presence of perfusion defect and presence of late enhancement (n = 195), absence of late enhancement and presence of perfusion defect (n = 29). Event rate was 5%, 7%, 16%, and 24%, respectively (P for trend = .003). In a multivariate regression model, only perfusion defect (hazard ratio = 2.86; 95% confidence interval, 1.37-5.95]; P = .002) but not late enhancement (hazard ratio = 1.70; 95% confidence interval, 0.90-3.22; P =.105) predicted events.

CONCLUSIONS

In depressed left ventricular function, the presence of inducible ischemia is the strongest predictor of major events.

MR imaging of myocardial infarction

Magnetic resonance (MR) imaging plays an important role in evaluation of various aspects of myocardial infarction (MI). MR imaging is useful in establishing the diagnosis of acute MI, particularly in patients who present with symptoms of MI but outside the diagnostic time frame of altered cardiac enzyme levels or with clinical features of acute MI but without an angiographic culprit lesion. MR imaging is valuable in establishing a diagnosis of chronic MI and distinguishing this condition from nonischemic cardiomyopathies, mainly through use of delayed-enhancement patterns. MR imaging also provides clinicians with several prognostic indicators that enable risk stratification, such as scar burden, microvascular obstruction, hemorrhage, and peri-infarct ischemia. The extent and transmurality of scar burden have been shown to have independent and incremental prognostic power over a range of left ventricular function. The extent of scarring at MR imaging is an important predictor of successful outcome after revascularization procedures, and extensive scarring in the lateral wall indicates poor outcome after cardiac resynchronization therapy. Scar size at MR imaging is also a useful surrogate end point in clinical trials. Finally, MR imaging can be used to detect complications of MI, such as aneurysms, pericarditis, ventricular septal defect, thrombus, and mitral regurgitation. Supplemental material available at http://radiographics.rsna.org/lookup/suppl/doi:10.1148/rg.335125722/-/DC1.

In vitro mitral valve simulator mimics systolic valvular function of chronic ischemic mitral regurgitation ovine model

BACKGROUND

This study was undertaken to evaluate an in vitro mitral valve (MV) simulator's ability to mimic the systolic leaflet coaptation, regurgitation, and leaflet mechanics of a healthy ovine model and an ovine model with chronic ischemic mitral regurgitation (IMR).

METHODS

Mitral valve size and geometry of both healthy ovine animals and those with chronic IMR were used to recreate systolic MV function in vitro. A2-P2 coaptation length, coaptation depth, tenting area, anterior leaflet strain, and MR were compared between the animal groups and valves simulated in the bench-top model.

RESULTS

For the control conditions, no differences were observed between the healthy animals and simulator in coaptation length (p = 0.681), coaptation depth (p = 0.559), tenting area (p = 0.199), and anterior leaflet strain in the radial (p = 0.230) and circumferential (p = 0.364) directions. For the chronic IMR conditions, no differences were observed between the models in coaptation length (p = 0.596), coaptation depth (p = 0.621), tenting area (p = 0.879), and anterior leaflet strain in the radial (p = 0.151) and circumferential (p = 0.586) directions. MR was similar between IMR models, with an asymmetrical jet originating from the tethered A3-P3 leaflets.

CONCLUSIONS

This study is the first to demonstrate the effectiveness of an in vitro simulator to emulate the systolic valvular function and mechanics of a healthy ovine model and one with chronic IMR. The in vitro IMR model provides the capability to recreate intermediary and exacerbated levels of annular and subvalvular distortion for which IMR repairs can be simulated. This system provides a realistic and controllable test platform for the development and evaluation of current and future IMR repairs.

Mitral valve surgery in low ejection fraction, severe ischemic mitral regurgitation patients: should we repair them all?

PURPOSE OF REVIEW

The optimal surgical treatment of chronic ischemic mitral regurgitation still is the subject of much debate in the surgical and cardiological communities. Although combined restrictive mitral annuloplasty and revascularization has demonstrated good results with regard to improvement of clinical status, low rates of recurrent mitral regurgitation and sustained left ventricular reverse remodeling, a survival benefit still has not been demonstrated. In addition, not all patients improve. Remaining issues in this field relate to identification of patients who will benefit from treatment, and to further improve and individualize treatment modalities.

RECENT FINDINGS

More data support the use of restrictive mitral annuloplasty and revascularization. New surgical techniques to improve mitral competence (posterior leaflet augmentation) and to promote left ventricular reverse remodeling in severely dilated hearts (addressing the subvalvular apparatus) are promising. Disease-specific annuloplasty rings have not (yet) proven additional value. New imaging modalities are available to assess the many components that constitute the complex pathophysiology of remodeling.

SUMMARY

The remaining challenge for cardiologists and surgeons is how to integrate data from different imaging techniques that assess mitral valve geometry and left ventricular size, geometry, function and potential functional recovery in order to individualize and optimize the surgical approach to patients with chronic ischemic mitral regurgitation.

Influence of baseline left ventricular function on the clinical outcome of surgical ventricular reconstruction in patients with ischaemic cardiomyopathy

AIMS

The Surgical Treatment for Ischemic Heart Failure (STICH) trial demonstrated no overall benefit when surgical ventricular reconstruction (SVR) was added to coronary artery bypass grafting (CABG) in patients with ischaemic cardiomyopathy. The present analysis was to determine whether, based on baseline left ventricular (LV) function parameters, any subgroups could be identified that benefited from SVR.

METHODS AND RESULTS

Among the 1000 patients enrolled, Core Lab measures of baseline LV function with adequate quality were obtained in 710 patients using echocardiography, in 352 using cardiovascular magnetic resonance, and in 344 using radionuclide imaging. The relationship between LV end-systolic volume index (ESVI), end-diastolic volume index, ejection fraction (EF), regional wall motion abnormalities, and outcome were first assessed only by echocardiographic measures, and then by 13 algorithms using a different hierarchy of imaging modalities and their quality. The median ESVI and EF were 78.0 (range: 22.8-283.8) mL/m2 and 28.0%, respectively. Hazard ratios comparing the randomized arms by subgroups of LVESVI and LVEF measured by echocardiography found that patients with smaller ventricles (LVESVI <60 mL/m2) and better LVEF (≥33%) may have benefitted by SVR, while those with larger ventricles (LVESVI >90 mL/m(2)) and lower LVEF (≤25%) did worse with SVR. Algorithms using all three imaging modalities found a weaker relationship between LV global function and the effects of SVR. The extent of regional wall motion abnormality did not influence the effects of SVR.

CONCLUSIONS

Subgroup analyses of the STICH trial suggest that patients with less dilated LV and better LVEF may benefit from SVR, while those with larger LV and poorer LVEF may do worse. Clinical Trial Registration #: NCT00023595.