Cine MR imaging after myocardial infarction--assessment and follow-up of regional and global left ventricular function

Multimodality imaging of myocardial viability: an expert consensus document from the European Association of Cardiovascular Imaging (EACVI)

In clinical decision making, myocardial viability is defined as myocardium in acute or chronic coronary artery disease and other conditions with contractile dysfunction but maintained metabolic and electrical function, having the potential to improve dysfunction upon revascularization or other therapy. Several pathophysiological conditions may coexist to explain this phenomenon. Cardiac imaging may allow identification of myocardial viability through different principles, with the purpose of prediction of therapeutic response and selection for treatment. This expert consensus document reviews current insight into the underlying pathophysiology and available methods for assessing viability. In particular the document reviews contemporary viability imaging techniques, including stress echocardiography, single photon emission computed tomography, positron emission tomography, cardiovascular magnetic resonance, and computed tomography and provides clinical recommendations for how to standardize these methods in terms of acquisition and interpretation. Finally, it presents clinical scenarios where viability assessment is clinically useful.

Postinfarct Left Ventricular Remodelling: A Prevailing Cause of Heart Failure

Heart failure is a chronic disease with high morbidity and mortality, which represents a growing challenge in medicine. A major risk factor for heart failure with reduced ejection fraction is a history of myocardial infarction. The expansion of a large infarct scar and subsequent regional ventricular dilatation can cause postinfarct remodelling, leading to significant enlargement of the left ventricular chamber. It has a negative prognostic value, because it precedes the clinical manifestations of heart failure. The characteristics of the infarcted myocardium predicting postinfarct remodelling can be studied with cardiac magnetic resonance and experimental imaging modalities such as diffusion tensor imaging can identify the changes in the architecture of myocardial fibers. This review discusses all the aspects related to postinfarct left ventricular remodelling: definition, pathogenesis, diagnosis, consequences, and available therapies, together with experimental interventions that show promising results against postinfarct remodelling and heart failure.

Quantitative assessment of cardiac output and left ventricular function by noninvasive phase-contrast and cine MRI: validation study with invasive pressure-volume loop analysis in a swine model

PURPOSE

To validate noninvasive cardiac output measurements of phase-contrast magnetic resonance imaging (PC-MRI) and cine MRI using an invasive pressure-volume (PV) loop technique on a swine model.

MATERIALS AND METHODS

We compared three methods for evaluating cardiac function at rest and under pharmaceutical low-dose inotropic infusion conditions: 1) phase-contrast MRI, 2) cine MRI, and 3) PV loop relationship. These measurements were made in 14 domestic pigs under rest conditions. Identical MRI acquisitions and PV loop analysis were performed on six pigs from the same group that received an infusion of dobutamine 2.5 μg/kg/min. Cardiac outputs from all measurements were analyzed and compared using linear regression and Bland-Altman analysis.

RESULTS

Noninvasive PC-MRI and cine MRI did not show any significant differences compared to an invasive PV loop technique for measurement of cardiac output under both rest (PC-MRI, cine MRI, and PV loop, 3.17 ± 0.45, 3.18 ± 0.61, 3.45 ± 0.41 L/min, respectively) and pharmaceutical low-dose inotropic infusion conditions (PC-MRI, cine MRI, and PV loop, 4.78 ± 0.53, 4.7 ± 0.6, 4.96 ± 0.48 L/min, respectively). Statistical analysis showed good agreement of cardiac output measurements at rest (R(2) = 0.83) and under low-dose inotropic infusion conditions (R(2) = 0.74) using PC-MRI and PV loop techniques. Cardiac output measurement using cine MRI and PV loop techniques also showed good agreement at rest (R(2) = 0.85) and under low-dose inotropic infusion conditions (R(2) = 0.76). Furthermore, cardiac outputs determined with the three modalities showed good agreement over a wide range of heart rates (90-180 bpm).

CONCLUSION

MRI can provide a reliable, noninvasive measurement of cardiac output that can be carried out without the complications that are inherent with current invasive procedures.

Myocardial first-pass perfusion cardiovascular magnetic resonance: history, theory, and current state of the art

In less than two decades, first-pass perfusion cardiovascular magnetic resonance (CMR) has undergone a wide range of changes with the development and availability of improved hardware, software, and contrast agents, in concert with a better understanding of the mechanisms of contrast enhancement. The following review provides a perspective of the historical development of first-pass CMR, the developments in pulse sequence design and contrast agents, the relevant animal models used in early preclinical studies, the mechanism of artifacts, the differences between 1.5T and 3T scanning, and the relevant clinical applications and protocols. This comprehensive overview includes a summary of the past clinical performance of first-pass perfusion CMR and current clinical applications using state-of-the-art methodologies.

Prediction of myocardial recovery by dobutamine magnetic resonance imaging and delayed enhancement early after reperfused acute myocardial infarction

The purpose was to study dobutamine magnetic resonance cine imaging (DOB-MRI) and delayed myocardial contrast enhancement (DE) early after reperfused acute myocardial infarction (AMI) for the predicion of segmental myocardial recovery and to find the optimal dose of dobutamine. Fifty patients (56+/-12 years, 42 males) with reperfused AMI underwent DOB-MRI and DE studies 3.5 (1-19) days after reperfusion. In DOB-MRI systolic wall thickening (SWT) was measured in 18 segments at rest and during dobutamine at 5, 10 and 20 microg*kg(-1)*min(-1). Dysfunctional segments were identified and the extent of DE was measured for each segment. Segmental recovery was examined after 8 (5-15) months. Two hundred-forty-eight segments were dysfunctional with presence of DE in 193. DOB-MRI showed the best prediction of recovery at 10 microg*kg(-1)*min(-1) of dobutamine with sensitivity of 67%, specificity of 63% and accuracy of 66% using a cut-off value for SWT of 2.0 mm. DE revealed a sensitivity of 68%, specificity of 65% and accuracy of 67% using a cut-off value of 46%. Combined analysis of DOB-MRI and DE did not improve diagnostic performance. Early prediction of segmental myocardial recovery after AMI is possible with DOB-MRI and DE. No improvement is achieved by dobutamine >10 microg*kg(-1)*min(-1) or a combination of DOB-MRI and DE.

Accurate estimation of regional and global cardiac function in old myocardial infarction patients by multidetector-row computed tomography

Recently we can evaluate cardiac function by multidetector-row computed tomography (MDCT) and quantitative gated SPECT(QGS) as well as left ventriculography (LVG). We evaluated regional and global cardiac function using MDCT and QGS, compared to LVG, and also evaluated parameters of left ventricular (LV) diastolic function using MDCT. Regional cardiac function was evaluated using shortening fraction(SF). Global cardiac function was evaluated using ejection fraction(EF). The peak filling rate(PFR) and the ratio of time to peak filling rate to RR interval(tPFR/RR) on MDCT were measured as parameters of LV diastolic function. The SFs by MDCT and LVG were correlated in almost each segment, but those by QGS and LVG were not correlated in some each segment. The SFs by QGS and LVG were not correlated in the myocardial infarcted segments, but those by QGS and LVG were correlated in the non-infarcted segments. Except for patients who had wall motion abnormalities at the ventricular septum or posterolateral wall, the EFs by MDCT and LVG were correlated, but those by QGS and LVG were not correlated. MDCT was more useful in detecting regional and global cardiac function compared to QGS, and parameters of LV diastolic function could be also measured by MDCT.

Influence of positional and angular variation of automatically planned short-axis stacks on quantification of left ventricular dimensions and function with cardiovascular magnetic resonance

PURPOSE

To theoretically and experimentally investigate the influence of the automated cardiovascular magnetic resonance (CMR) scan planning pitfalls, namely inaccurate positioning and tilting of short-axis (SA) imaging planes, on quantification of the left ventricular (LV) dimensions and function.

MATERIALS AND METHODS

Eleven healthy subjects and eight patients underwent CMR. Manually and automatically planned SA sets were acquired. To obtain the quantitative measurements of LV function, one observer performed image analysis twice. The agreement between planning methods, as well as the decomposition of the total variation into interstudy and intraobserver components was measured.

RESULTS

The decomposition of the total variation showed that the interstudy factor accounts for 70-85% of the total variation, while the rest is due to the intraobserver factor. Moreover, the relative contribution of the interstudy factor remains independent from errors in slice positioning and small angular deviation of SA stacks from the optimal orientation. Good agreement between the theoretical and measured variability factors was observed.

CONCLUSION

Global LV function derived from the automatically planned CMR acquisitions yield accurate quantification of the human cardiovascular system. Inaccurate positioning and tilting of SA images does not affect the quantitative measurements of LV function. The computer-aided system for automated CMR has proven clinical applicability.

Intraatrial Repair of Transposition of the Great Arteries: Use of MR Imaging after Exercise to Evaluate Regional Systemic Right Ventricular Function

PURPOSE

To prospectively assess regional systemic right ventricular (RV) function at rest and in response to exercise by using magnetic resonance (MR) imaging in patients who have undergone surgical correction at the atrial level for transposition of the great arteries (TGA).

MATERIALS AND METHODS

Informed consent was obtained, and the medical review board approved this study. In 25 adult patients (mean age, 25.8 years +/- 4.7 [standard deviation]; 13 men) who had undergone correction for TGA (23.4 years +/- 4.9 after surgery) and 11 healthy volunteers (mean age, 27.4 years +/- 2.7; six men), systemic ventricular function was assessed with MR imaging (turbo field echo-planar imaging) at rest and during supine bicycle exercise. Regional wall thickness and wall thickening of the systemic RV were assessed and compared with those of the left ventricle in healthy volunteers by two investigators working together. Regional wall parameters were calculated by using the three-dimensional centerline method. Independent-samples t test and paired-samples t test were used for statistical analysis.

RESULTS

Ejection fraction of the systemic RV did not increase after exercise (56% +/- 8 at rest to 55% +/- 7 after exercise, P = .196). Mean RV wall thickening was impaired in patients with TGA at all levels both at rest and in response to exercise (P < .05). Moreover, the free wall and the anterior wall of the systemic RV had a smaller end-systolic thickness and a diminished thickening at rest and after exercise compared with findings in the normal left ventricle (P < .05).

CONCLUSION

The systemic RV of patients after intraatrial correction for TGA reveals regional functional disturbances at rest and in response to exercise.

Cine and tagged magnetic resonance imaging in short-term stunned versus necrotic myocardium

We investigated the potential of Cine and 2D Tagged Cardiac Magnetic Resonance (CMR) Imaging to distinguish stunned from necrotic left ventricular (LV) myocardium in the early postischemic phase in an open-chest animal model (N = 12). Reversible and permanent occlusion of the LAD coronary artery resulted in global LV dysfunction in both groups without significant differences. LAD perfused segments revealed significant higher values for end systolic wall thickening (ESWT) and percentual systolic wall thickening in animals with stunned myocardium. Analysis of strain parameters showed significant regional differences (maximal principal strain lambda1, deviation angle beta) between postischemic and remote myocardium within both groups, however results were not significantly different comparing animals with stunned myocardium to animals with myocardial necrosis. In conclusion, at rest neither global LV functional nor regional strain parameters derived from Cine and 2D Tagged CMR Imaging can distinguish animals with short-term stunned myocardium from respective animals with necrotic myocardium. Diagnostic value of ESWT is limited due to the spatial resolution of the gradient-echo sequence used.

Accuracy of short-axis cardiac MRI automatically derived from scout acquisitions in free-breathing and breath-holding modes

To qualitatively assess the accuracy of automated cardiovascular magnetic resonance planning procedures devised from scout acquisitions in free-breathing and breath-holding modes, to quantitatively evaluate the accuracy of the derived left ventricular volumes, mass and function and compare these parameters with the ones obtained from the manually planned acquisitions. Ten healthy volunteers underwent cardiovascular MR (CMR) acquisitions for ventricular function assessment. Short-axis data sets of the left ventricle (LV) were manually planned and generated twice in an automatic fashion. Automated planning parameters were derived from gated scout acquisitions in free-breathing and breath-holding modes. End-diastolic volume (EDV), end-systolic volume (ESV), ejection fraction (EF), and left ventricular mass (LVM) were measured. The agreement between the manual and automatic planning methods, as well as the variability of the aforementioned measurements were assessed. The differences between two automated planning methods were also compared. The mean differences between the manual and automated CMR planning derived from gated scouts in free-breathing mode were 8.05 ml (EDV), 1.84 ml (ESV), 0.69% (EF), and 4.72 g (LVM). The comparison between manual and automated CMR planning derived from gated scouts in breath-holding mode yielded the following differences: 4.22 ml (EDV), 0.34 ml (ESV), 0.3% (EF), and -0.72 mg (LVM). The variability coefficients were 3.72 and 3.66 (EDV), 5.6 and 8.19 (ESV), 3.46 and 4.31 (EF), 6.49 and 5.20 (LVM) for the automated CMR planning methods derived from scouts in free-breathing and breath-holding modes, respectively. Automated CMR planning methods can provide accurate measurements of LV dimensions in normal subjects, and therefore may be utilized in the clinical environment to provide a cost-effective solution for functional assessment of the human cardiovascular system.

Ventricular function after coronary artery bypass grafting: Evaluation by magnetic resonance imaging and myocardial strain analysis

OBJECTIVE

Magnetic resonance imaging with radiofrequency tissue tagging permits quantitative assessment of regional systolic myocardial strain. We sought to investigate the utility of this imaging modality to quantitatively determine preoperative impairment and postoperative improvement in ventricular function in patients with ischemic heart disease.

METHODS

Magnetic resonance imaging with radiofrequency tissue tagging was performed on 6 patients (average age 60.2 +/- 13.7 years) with coronary artery disease and 32 control subjects with no known heart disease. Patients with coronary artery disease underwent imaging before and 3 months after coronary artery bypass grafting. The ventricle was divided into 6 segments within a midventricular plane. Regional 2-dimensional left ventricular circumferential strain was calculated from tagged magnetic resonance images throughout systole. Circumferential strain results were compared in patients before and after and 3 months after coronary artery bypass grafting and also in control subjects.

RESULTS

Before the operation circumferential strain identified 100% (10/10) of all regional wall motion abnormalities seen by preoperative ventriculography. Postoperatively, improvements were demonstrated in 56% (20/36) of the regions, and these improvements agreed with viability testing by single-photon emission computed tomography when available. Additionally, preoperative global circumferential strain for the ischemic group was significantly depressed relative to that in control subjects (0.11 +/- 0.05 vs 0.20 +/- 0.03, P <.001). Global circumferential strain correlated with ejection fraction by ventriculography (r = 0.84, P <.01) and improved after coronary artery bypass grafting (0.14 +/- 0.05 vs 0.11 +/- 0.05, P <.01).

CONCLUSIONS

Magnetic resonance imaging with radiofrequency tissue tagging permitted circumferential strain calculation. This technology quantitatively demonstrated improvements in left ventricular wall motion after coronary artery bypass grafting for both individual regions and the entire ventricle. This noninvasive method may prove useful in preoperative evaluation and postoperative serial assessment of left ventricular wall motion.

Absolute concentrations of high-energy phosphate metabolites in normal, hypertrophied, and failing human myocardium measured noninvasively with (31)P-SLOOP magnetic resonance spectroscopy

OBJECTIVE

The purpose of the present study was to measure absolute concentrations of phosphocreatine (PCr) and adenosine triphosphate (ATP) in normal, hypertrophied, and failing human heart.

BACKGROUND

Conflicting evidence exists on the extent of changes of high-energy phosphate metabolites in hypertrophied and failing human heart. Previous reports using phosphorus-31 magnetic resonance spectroscopy ((31)P-MRS) have quantified metabolites in relative terms only. However, this analysis cannot detect simultaneous reductions.

METHODS

Four groups of subjects (n = 10 each), were studied: volunteers and patients with hypertensive heart disease (HHD), aortic stenosis, and dilated cardiomyopathy (DCM). Left ventricular (LV) function and mass were measured by cine magnetic resonance imaging. Absolute and relative concentrations of PCr and ATP were determined by (31)P-MRS with spatial localization with optimum point spread function.

RESULTS

Left ventricular ejection fraction remained normal in HHD and aortic stenosis, but was severely reduced to 18% in DCM; LV mass was increased by 55%, 79%, and 68% respectively. In volunteers, PCr and ATP concentrations were 8.82 +/- 1.30 mmol/kg wet weight and 5.69 +/- 1.02 mmol/kg wet weight, and the PCr/ATP ratio was 1.59 +/- 0.33. High-energy phosphate levels were unaltered in HHD. In aortic stenosis, PCr was decreased by 28%, whereas ATP remained constant. In DCM, PCr was reduced by 51%, ATP by 35%, and reduction of the PCr/ATP ratio by 25% was of borderline significance (p = 0.06). Significant correlations were observed among energetic and functional variables, with the closest relations for PCr.

CONCLUSIONS

In human heart failure due to DCM, both PCr and ATP are significantly reduced. Ratios of PCr to ATP underestimate changes of high-energy phosphate levels.

Magnetic resonance imaging in coronary heart disease

Modern level of cardiac magnetic resonance imaging (MRI) development already allows its routine use (with proper indications) in coronary heart disease patients for studies of heart morphology and functions, performance of stress tests for evaluation of myocardial perfusion and contractile function. Coronary MRA and some other new MR techniques are close to its wide-scale clinical application. It has been shown that cardiac MRI is a valuable tool for detection of postinfarction scars, aneurysms, pseudoaneurysms, septal defects, mural thrombi and valvular regurgitations. Due to intrinsic advantages of the method it is of special value when these pathological conditions cannot be fully confirmed or excluded with echocardiography. MRI is recognized as the best imaging method for quantification of myocardial thickness, myocardial mass, systolic myocardial thickening, chamber volumes, ejection fraction and other parameters of global and regional systolic and diastolic function. MRI is used in studies of cardiac remodeling in postinfarction patients. The most attractive areas for cardiovascular applications of MRI are assessment of myocardial perfusion and non-invasive coronary angiography. Substantial progress has been achieved in these directions. There are some other new developments in studies of coronary artery disease with MRI. High-resolution MR is used for imaging and quantification of atherosclerotic plaque composition in vivo. Intravascular MR devices suitable for performing imaging-guided balloon angioplasty are created. But before MRI will be widely accepted by the medical community as a important cardiovascular imaging modality several important problems have to be solved. Further technical advances are necessary for clinical implementation of all major diagnostic capabilities of cardiac MRI. The subjective obstacles for growth of clinical applications of cardiac MRI are lack of understanding of its possibilities and benefits both by clinicians and radiologists themselves. So proper training of specialists and promotion of this promising modality among the medical community are necessary.

Current awareness

In order to keep subscribers up-to-date with the latest developments in their field, John Wiley & Sons are providing a current awareness service in each issue of the journal. The bibliography contains newly published material in the field of NMR in biomedicine. Each bibliography is divided into 9 sections: 1 Books, Reviews ' Symposia; 2 General; 3 Technology; 4 Brain and Nerves; 5 Neuropathology; 6 Cancer; 7 Cardiac, Vascular and Respiratory Systems; 8 Liver, Kidney and Other Organs; 9 Muscle and Orthopaedic. Within each section, articles are listed in alphabetical order with respect to author. If, in the preceding period, no publications are located relevant to any one of these headings, that section will be omitted.