Diagnostik und Therapie der chronischen Myokardischämie

In patients with chronic coronary artery disease different therapeutic strategies, such as optimal medical therapy, revascularization by percutaneous coronary intervention or coronary artery bypass grafting have been shown to improve the prognosis and symptoms and yield proven superiority over other treatment strategies in different patient populations. Thus, individual assessment of cardiac function and structure is of paramount importance to choose the optimal therapeutic strategy and subsequently improve patient prognosis. In this setting cardiac magnetic resonance imaging (CMR) has been shown to provide important diagnostic information. Myocardial ischemia can be detected by either perfusion stress CMR demonstrating perfusion deficits indicative of hemodynamically relevant coronary artery stenosis or dobutamin stress CMR for objectifying wall motion abnormalities during stress. Both techniques are superior to single photon emission computerized tomography and stress echocardiography in specific patient populations. Myocardial viability can be assessed by means of end-diastolic wall thickness or delayed enhancement imaging which allows quantification of the transmural extent of scarring. Furthermore, low-dose dobutamin stress CMR can detect a contractile reserve. Delayed enhancement imaging leads to accurate results due to its high resolution, can be performed at rest requiring no stress within a short time period and is easy to analyze. Thus this technique can be recommended as the favored technique to assess myocardial viability. In the following article the CMR techniques for ischemia and viability testing will be presented and their role in diagnosis and therapy of chronic myocardial ischemia will be discussed.     

Myocardial perfusion imaging by cardiac magnetic resonance.

Cardiovascular magnetic resonance (CMR) has been shown to provide high quality data on cardiac and valvular function, perfusion, viability, blood flow, and potentially, on cardiac metabolism as well. Several of these CMR applications (eg, function and viability assessment) matured during the past years and are now established components of a cardiac workup. Perfusion-CMR is close to this status and is already a major contributor to cardiac examinations in a growing number of expert centers. Large multicenter perfusion-CMR trials comparing the diagnostic performance of CMR with other techniques were recently reported yielding areas under the receiver-operator-characteristics curve as a high as 0.85 for coronary artery disease detection (MR-IMPACT). Anticipating a growing role for perfusion-CMR in cardiology in the near future, this article discusses the principles of perfusion-CMR and its integration into the workup of patient with coronary artery disease (CAD). In addition to a functional study, this integration is mainly composed of a perfusion-CMR part, followed by a viability assessment by late enhancement CMR techniques. The principal characteristics of these CMR techniques are compared with those of single photon emission computed tomography (SPECT) and positron emission tomography (PET). After introduction into principles and techniques of perfusion-CMR, some open questions in perfusion-CMR and challenges for the future are addressed. Finally, newer CMR applications are shortly mentioned utilizing hyperpolarized carbon-13 compounds in experimental models for quantification of myocardial perfusion and for real-time assessment of metabolic pathways in postischemic myocardium.     

Advances in the Understanding of the Pathophysiology and Management of Aortic Stenosis: Role of Novel Imaging Techniques

The management of asymptomatic patients with aortic stenosis (AS) is controversial and the mechanisms leading to symptom generation and adverse outcome are not fully understood. Novel imaging techniques offer a noninvasive tool for in vivo assessment of AS and its pathophysiological consequences on the myocardium. Exercise echocardiography provides insight into the mechanisms responsible for exercise limitation and symptom generation. Speckle tracking allows the detection of reduced myocardial strain, which is associated with adverse events in asymptomatic patients. Computed tomography scanning can accurately quantify valve calcification and is associated with disease severity. Positron emission tomography/computed tomography imaging has the potential to monitor disease activity (inflammation and microcalcification) for the first time. Cardiac magnetic resonance (CMR) imaging uniquely allows tissue characterization with identification of fibrosis, a key characteristic of failing myocardium. T1 mapping allows estimation of diffuse interstitial fibrosis and late gadolinium enhancement demonstrates focal fibrosis/scarring. Myocardial steatosis, assessed using CMR spectroscopy, is increased in severe AS and might contribute to myocardial dysfunction. Positron emission tomography and CMR imaging can quantify myocardial blood flow and assess microvascular dysfunction, which might contribute to symptom development and myocardial remodelling. These novel imaging techniques are now being assessed in prospective prognostic studies that will clarify their utility in risk stratification in AS, and lead to improved management and outcomes for these patients.     

MRI of left ventricular function.

Cardiac magnetic resonance imaging (CMR) is widely recognized as the most accurate noninvasive imaging modality for the assessment of left ventricular (LV) function. By use of state-of-the-art magnetic resonance imaging (MRI) scanners, electrocardiography (ECG)-gated cine images depicting LV function with high contrast and excellent spatial and temporal resolution are readily acquired in breath-holds of 5 to 10 heartbeats. For patients in whom breath-holding and ECG gating are difficult, real-time cine imaging without ECG gating and breath-holding can be performed. LV function can be qualitatively assessed from cine images, or alternatively, parameters such as LV volumes, ejection fraction, and mass may be quantified via computer-based analysis software. In addition, techniques such as myocardial tagging and newer variants can be used to qualitatively or quantitatively assess regional intramyocardial strain, twist, and torsion. Many of the CMR methods have undergone clinical evaluation in the settings of high-dose dobutamine stress testing and determination of myocardial viability. These methods are also very accurate for prognosis in coronary heart disease patients and may be quite useful for the detection of contractile dyssynchrony. When used together with other CMR techniques such as first-pass perfusion imaging or late gadolinium enhancement, CMR of LV function provides a wealth of information in a single imaging study.     

Measuring myocardial salvage

The efficacy of cardioprotective strategies can be quantified by myocardial salvage as an indicator of therapeutic benefit. Salvage is calculated as the difference between the area at risk (AAR) and the final infarct size (FIS). AAR has been quantified by angiographic assessment followed by quantification of FIS by biochemical ischaemic markers or imaging modalities such as cardiovascular magnetic resonance (CMR). Angiographical methods may overestimate AAR and since methodological differences may exist between different modalities, the use of different modalities for estimating AAR and FIS may not be recommended. (99m)Technetium (Tc)-Sestamibi single-photon emission tomography (SPECT) allows quantification of AAR and FIS by tracer injection prior to revascularization and after 1 month, respectively. SPECT provides the most validated measure of myocardial salvage and has been utilized in multiple randomized clinical trials. However, SPECT is logistically challenging, expensive, and includes radiation exposure. More recently, a large number of studies have suggested that CMR can determine salvage in a single examination by combining measures of myocardial oedema in the AAR exposed to ischaemia reperfusion with FIS quantification by late gadolinium enhancement. The T1- and T2-weighted CMR approaches for quantification of AAR utilize non-contrast, early and late gadolinium enhancement techniques. The technical progress, high spatial resolution and the potential for retrospective quantification of the AAR makes CMR the most appropriate technique for assessment of myocardial salvage. However, the optimum CMR technique for assessment of myocardial AAR remains to be defined. Consequently, we recommend a comprehensive CMR protocol to ensure reliable assessment of myocardial salvage.     

Detection of induced myocardial ischemia during stress cardiovascular magnetic resonance

In the past decade, cardiovascular magnetic resonance (CMR) has evolved considerably. Its clinical applications enable the diagnosis and prognostic assessment of patients with ischemic heart disease. CMR is safe, with absence of any ionizing radiation, and offers the greatest information from a single test, allowing the assessment of myocardial morphology, myocardial function and viability. Stress-CMR can be used for detection and quantification of ischemia. This article analyses the technical approach, the limits and reviews the available literature about diagnostic performance of stress CMR testing and its results in the prognostication of cardiac patients. With further improvements in CMR techniques and the establishment of a standardized study protocol, stress-CMR will play a pivotal role in managing patients with ischemic heart disease.     

Cardiovascular magnetic resonance and the evaluation of heart failure

Cardiovascular magnetic resonance (CMR) has established itself as probably the single best way of phenotyping the failing heart. It is the accepted gold standard for measuring cardiac function, volumes, and mass, but within the same scan session additional techniques are available for greater definition. Tissue characterization with the contrast agent gadolinium is well validated and allows the precise visualization and quantification of myocardial infarction. This can be used for viability assessment and to determine heart failure etiology. Dobutamine stress CMR and CMR perfusion hold advantages over conventional techniques. The new frontiers of CMR in heart failure hold the promise of unique insights quantifying myocardial iron, nonischemic fibrosis, microvascular perfusion, plaque characterization, and CMR-targeted intervention. The development and validation of these techniques represent major research challenges for the future. From a clinical perspective, an equal challenge is in increasing the availability of the modality for patients and physicians.     

Emerging MRI Methods in Translational Cardiovascular Research

Cardiac magnetic resonance imaging (CMR) has become a reference standard modality for imaging of left ventricular (LV) structure and function and, using late gadolinium enhancement, for imaging myocardial infarction. Emerging CMR techniques enable a more comprehensive examination of the heart, making CMR an excellent tool for use in translational cardiovascular research. Specifically, emerging CMR methods have been developed to measure the extent of myocardial edema, changes in ventricular mechanics, changes in tissue composition as a result of fibrosis, and changes in myocardial perfusion as a function of both disease and infarct healing. New CMR techniques also enable the tracking of labeled cells, molecular imaging of biomarkers of disease, and changes in calcium flux in cardiomyocytes. In addition, MRI can quantify blood flow velocity and wall shear stress in large blood vessels. Almost all of these techniques can be applied in both pre-clinical and clinical settings, enabling both the techniques themselves and the knowledge gained using such techniques in pre-clinical research to be translated from the lab bench to the patient bedside.     

Diagnostik der koronaren Herzerkrankung mit Computer- und Magnetresonanztomographie

Coronary angiography by computed tomography (CTCA) is most suitable for symptomatic patients with an intermediate likelihood to exclude a coronary stenosis as the cause of the symptoms. It would also be appropriate in a patient in whom an equivoval stress test result has led to uncertainty about the patient’s further management. CTCA may occasionally be acceptable in a high risk symptomatic patient who refuses the necessary invasive coronary angiography if the results of CTCA are likely to alter patient management. The main indication for cardiac magnetic resonance imaging (CMR) is for pharmacologic stress testing. If such a test is indicated, dobutamine stress CMR is an alternative to stress echocardiography and adenosine perfusion CMR is the alternative to nuclear myocardial perfusion imaging but without radiation. Late gadolinium enhancement CMR is the current gold standard for the assessment of myocardial scars and hence is well suited to predict recovery of function in dysfunctional myocardial regions following revascularisation (viability testing).     

Cardiac MRI For Myocardial Ischemia

Proper assessment of the physiologic impact of coronary artery stenosis on the LV myocardium can affect patient prognosis and treatment decisions. Cardiac magnetic resonance imaging (CMR) assesses myocardial perfusion by imaging the myocardium during a first-pass transit of an intravenous gadolinium bolus, with spatial and temporal resolution substantially higher than nuclear myocardial perfusion imaging. Coupled with late gadolinium enhancement (LGE) imaging for infarction during the same imaging session, CMR with vasodilating stress perfusion imaging can qualitatively and quantitatively assess the myocardial extent of hypoperfusion from coronary stenosis independent of infarcted myocardium. This approach has been validated experimentally, and multiple clinical trials have established its diagnostic robustness when compared to stress single-photon emission computed tomography. In specialized centers, dobutamine stress CMR has been shown to have incremental diagnostic value above stress echocardiography due to its high imaging quality and ability to image the heart with no restriction of imaging window. This paper reviews the technical aspects, diagnostic utility, prognostic values, challenges to clinical adaptation, and future developments of stress CMR imaging.     

Myocardial Edema Imaging by Cardiovascular Magnetic Resonance: Current Status and Future Potential

Cardiovascular magnetic resonance (CMR) imaging is widely established, free of radioactive material or ionizing radiation, and the accepted noninvasive gold standard for numerous noninvasive cardiac markers. Using a technique called T2-weighted imaging, CMR can be used to assess myocardial edema as a reliable marker for acute, potentially reversible myocardial injury. Contrast agents are not required as the myocardial free water content affects the magnetic properties of the tissue, thus providing inherent image contrast. In this review, we illustrate the utility of T2-weighted techniques in the assessment of myocardial edema in a range of clinical scenarios. The detection of myocardial edema is clinically relevant in many acute settings and may be further helpful to better understand the pathophysiology of many non-acute clinical diseases. Currently, T2-weighted CMR represents the only imaging modality that can accurately depict and quantify the presence of myocardial edema in a noninvasive fashion. Thus, T2-weighted imaging should be included in a comprehensive CMR imaging protocol, especially if an acute injury is suspected.     

Left Ventricular Hypertrophy: The Relationship between the Electrocardiogram and Cardiovascular Magnetic Resonance Imaging

Conventional assessment of left ventricular hypertrophy (LVH) using the electrocardiogram (ECG), for example, by the Sokolow–Lyon, Romhilt–Estes or Cornell criteria, have relied on assessing changes in the amplitude and/or duration of the QRS complex of the ECG to quantify LV mass. ECG measures of LV mass have typically been validated by imaging with echocardiography or cardiovascular magnetic resonance imaging (CMR). However, LVH can be the result of diverse etiologies, and LVH is also characterized by pathological changes in myocardial tissue characteristics on the genetic, molecular, cellular, and tissue level beyond a pure increase in the number of otherwise normal cardiomyocytes. For example, slowed conduction velocity through the myocardium, which can be due to diffuse myocardial fibrosis, has been shown to be an important determinant of conventional ECG LVH criteria regardless of LV mass. Myocardial tissue characterization by CMR has emerged to not only quantify LV mass, but also detect and quantify the extent and severity of focal or diffuse myocardial fibrosis, edema, inflammation, myocarditis, fatty replacement, myocardial disarray, and myocardial deposition of amyloid proteins (amyloidosis), glycolipids (Fabry disease), or iron (siderosis). This can be undertaken using CMR techniques including late gadolinium enhancement (LGE), T1 mapping, T2 mapping, T2* mapping, extracellular volume fraction (ECV) mapping, fat/water‐weighted imaging, and diffusion tensor CMR. This review presents an overview of current and emerging concepts regarding the diagnostic possibilities of both ECG and CMR for LVH in an attempt to narrow gaps in our knowledge regarding the ECG diagnosis of LVH.     

CMR of ventricular function

Cardiovascular magnetic resonance (CMR) is the reference standard for the assessment of ventricular dimensions, function, and mass in terms of accuracy and reproducibility. It has been thoroughly validated both ex vivo and against other imaging techniques. Measurements are highly accurate and no geometrical assumptions need to be made about the ventricle. A routine ventricular dataset of images can be acquired in less than 5 minutes and analyzed in about the same time. The field is rapidly advancing with increasing automation and simplification in both image acquisition and analysis. Using parallel and real time imaging techniques, good quality data can be obtained even in patients who are unable to hold their breath. While providing useful information in all patients with suspected heart failure, CMR should particularly be considered in those with poor echo windows, where it can also be combined with myocardial stress. Tagging techniques can provide highly detailed information about myocardial torsion and strain for individual myocardial segments. In a research environment, the very high degree of interscan reproducibility can dramatically reduce the number of patients needed to perform clinical trials.     

Diagnosis and management of ischemic cardiomyopathy: Role of cardiovascular magnetic resonance imaging

Coronary artery disease (CAD) represents an important cause of mortality. Cardiovascular magnetic resonance (CMR) imaging evolved as an imaging modality that allows the assessment of myocardial function, perfusion, contractile reserve and extent of fibrosis in a single comprehensive exam. This review highlights the role of CMR in the differential diagnosis of acute chest pain by detecting the location of obstructive CAD or necrosis and identifying other conditions like stress cardiomyopathy or myocarditis that can present with acute chest pain. Besides, it underlines the prognostic implication of perfusion abnormalities in the setting of acute chest pain. Furthermore, the review addresses the role of CMR to detect significant CAD in patients with stable CAD. It elucidates the accuracy and clinical utility of CMR with respect to other imaging modalities like single-photon emission computed tomography and positron emission tomography. Besides, the prognostic value of CMR stress testing is discussed. Additionally, it summarizes the available CMR techniques to assess myocardial viability and describes algorithm to identify those patient who might profit from revascularization those who should be treated medically. Finally, future promising imaging techniques that will provide further insights into the fundamental disease processes in ischemic cardiomyopathy are discussed.     

Identification of Left Ventricular Myocardial Ischemia and Cardiac Prognosis with Cardiovascular Magnetic Resonance: Updates from 2008 to 2010

Noninvasive imaging modalities are often used to manage patients with cardiovascular disease. Cardiovascular magnetic resonance (CMR) is increasingly used for diagnosing and evaluating myocardial ischemia and viability; moreover, stress CMR study results can be used to determine cardiac prognosis. In this article, we review recently published material regarding the performance of stress testing with CMR including a brief update regarding techniques, stress agents, diagnostic accuracy, prognosis, economic implications, and ongoing trials and future developments.     

Assessment of myocardial viability: comparison of echocardiography versus cardiac magnetic resonance imaging in the current era

Detecting viable myocardium, whether hibernating or stunned, is of clinical significance in patients with coronary artery disease and left ventricular dysfunction. Echocardiographic assessments of myocardial thickening and endocardial excursion during dobutamine infusion provide a highly specific marker for myocardial viability, but with relatively less sensitivity. The additional modalities of myocardial contrast echocardiography and tissue Doppler have recently been proposed to provide further, quantitative measures of myocardial viability assessment. Cardiac magnetic resonance (CMR) has become popular for the assessment of myocardial viability as it can assess cardiac function, volumes, myocardial scar, and perfusion with high-spatial resolution. Both 'delayed enhancement' CMR and dobutamine stress CMR have important roles in the assessment of patients with ischaemic cardiomyopathy. This article reviews the recent advances in both echocardiography and CMR for the clinical assessment of myocardial viability. It attempts to provide a pragmatic approach toward the patient-specific assessment of this important clinical problem.     

Whole-heart dynamic three-dimensional magnetic resonance perfusion imaging for the detection of coronary artery disease defined by fractional flow reserve: determination of volumetric myocardial ischaemic burden and coronary lesion location

Aims Dynamic three-dimensional-cardiac magnetic resonance (3D-CMR) perfusion proved highly diagnostic for the detection of angiographically defined coronary artery disease (CAD) and has been used to assess the efficacy of coronary stenting procedures. The present study aimed to relate significant coronary lesions as assessed by fractional flow reserve (FFR) to the volume of myocardial hypoenhancement on 3D-CMR adenosine stress perfusion imaging and to define the inter-study reproducibility of stress inducible 3D-CMR hypoperfusion. Methods and results A total of 120 patients with known or suspected CAD were examined in two CMR centres using 1.5 T systems. The protocol included cine imaging, 3D-CMR perfusion during adenosine infusion, and at rest followed by delayed enhancement (DE) imaging. Fractional flow reserve was recorded in epicardial coronary arteries and side branches with ≥2 mm luminal diameter and >40% severity stenosis (pathologic FFR < 0.75). Twenty-five patients underwent an identical repeat CMR examination for the determination of inter-study reproducibility of 3D-CMR perfusion deficits induced by adenosine. Three-dimensional CMR perfusion scans were visually classified as pathologic if one or more segments showed an inducible perfusion deficit in the absence of DE. Myocardial ischaemic burden (MIB) was measured by segmentation of the area of inducible hypoenhancement and normalized to left ventricular myocardial volume (MIB, %). Three-dimensional CMR perfusion resulted in a sensitivity, specificity, and diagnostic accuracy of 90, 82, and 87%, respectively. Substantial concordance was found for inter-study reproducibility [Lin's correlation coefficient: 0.98 (95% confidence interval: 0.96-0.99)]. Conclusion Three-dimensional CMR stress perfusion provided high diagnostic accuracy for the detection of functionally significant CAD. Myocardial ischaemic burden measurements were highly reproducible and allowed the assessment of CAD severity.     

Prognostic value of normal adenosine-stress cardiac magnetic resonance imaging

We investigated the prognostic value of normal adenosine stress cardiac magnetic resonance (CMR) in suspected coronary artery disease (CAD). Prospectively enrolled in the study were 218 patients with suspected CAD, no stress hypoperfusion, and no delayed enhancement in CMR, and consecutively deferred coronary angiography. The primary end point was a 12-month rate of major adverse cardiac events (MACE; cardiovascular mortality, myocardial infarction, revascularization, hospitalization due to cardiovascular event). CMR indication was symptomatic angina (Canadian Cardiovascular Society II in 42% and III in 7%) or evaluation of myocardial ischemia in patients with arrhythmia, syncope, and/or equivocal stress tests and cardiovascular risk factors (51%). As the main result, the 12-month MACE rate was 2/218 (1 stent implantation, 1 bypass surgery) and CMR negative predictive value 99.1%. There was no cardiac death or myocardial infarction. In conclusion, normal adenosine stress CMR predicts a very low MACE rate and an excellent 1-year prognosis in patients with suspected CAD. Our results provide clinical reassurance that patients at risk for CAD-associated MACE were not missed by CMR. Hence, CMR may serve as a reliable noninvasive gatekeeper to reduce the number of redundant coronary angiographies.     

心脏核磁共振成像技术在肥厚型心肌病中的应用现状及最新进展

Hypertrophic cardiomyopathy(HCM)is the most common genetic cardiomyopathy and the leading cause of sudden death in young people and a major cause of heart failure symptoms at any age.Due to its genetic etiology,there is substantial heterogeneity in the phenotypic expression and clinical course of patients with HCM.Traditionally,two-dimensional echocardiography has been the easiest and reliable technique for establishing a diagnosis of HCM.However,cardiovascular magnetic resonance(CMR)has emerged as a novel,3-dimensional tomographic imaging technique,which provides high spatial and temporal resolution images of the heart (not limited by thoracic or pulmonary parenchyma),in any plane and without ionizing radiation.As a result,CMR is particularly well suited to provide detailed characterization of the HCM phenotype,including a precise assessment of the location and distribution of LV wall thickening(as well as other myocardial structures such as the right ventricle and papillary muscles).In this regard,CMR has been demonstrated to provide a diagnosis of HCM in cases where the echocardiogam was non-diagnostic.Furthermore,CMR provides an accurate assessment of total LV mass which is a more robust marker of hypertrophy,with potential implications for risk stratification.In addition,with the intravenous administration of gadolinium,first-pass perfusion sequences can identify myocardial perfusion abnormalities,while late gadolinium enhancement sequences can identify areas of myocardial fibrosis/scarring.Although the clinical implications of late gadolinium enhancement in HCM are still uncertain this information may,in the near-future,have important implications with regard to identifying HCM patients at high risk of sudden death and progressive heart failure,including evolution into the end-stage phase of HCM.Therefore,at present,CMR provides important information impacting on diagnosis and clinical management strategies in patients with HCM and will likely have an expanding role in the evaluation of patients with this complex disease.     

Cardio-MRT. The multimodal functional analysis of the future

Since initial reports in the early 1990s cardiac magnetic resonance imaging (CMR) has matured and is likely to become an established method for routine cardiac diagnostics. The development of faster gradient-echo sequences and stronger magnetic fields has led to improved temporal and spatial resolution. Myocardial viability can be examined by morphological and functional analysis. Contrast enhanced MRI (ceMRI), perfusion measurements and regional wall motion analysis are the major diagnostic tools. The ability to image in arbitrary double oblique planes provides comprehensive visualization of the heart. The introduction of the MR navigator technique allowed for free-breathing motion corrected 3D coronary MR angiography with improved spatial resolution. Using this approach proximal and mid parts of the coronary arteries have been visualized. Subsequently, sensitivity and specificity for the detection of significant coronary stenoses has been evaluated in a multicenter trial demonstrating good sensitivity and specificity for the detection of significant left main and three vessel disease. However, specificity for the detection of single vessel disease was relatively low. Improved motion compensation techniques and novel imaging sequences (SSFP) are currently under investigation to further refine this technique. Despite these promising results coronary MR-angiography is not likely to replace conventional coronary angiography especially with regard to in-plane spatial resolution, coronary collateralization and in-stent restenosis. In contrast, coronary MR-angiography can provide useful morphological informations including functional analysis of the coronary vascular bed. The combination of a conventional cathlab with CMR may provide CMR-guided myocardial interventions. With further improvements in the catheter technology, CMR interventions using real-time imaging guidance will allow to take advantage of the excellent soft tissue contrast of CMR and the simultaneous visualization of the pulmonary, aortic and coronary vessels. CMR is advantageous for screening and follow-up examinations, and it offers comprehensive assessment of cardiac morphology and function in one single examination.