Rob J. van der Geest

Infarct tissue heterogeneity assessed with contrast-enhanced MRI predicts spontaneous ventricular arrhythmia in patients with ischemic cardiomyopathy and implantable cardioverter-defibrillator.

Background—The relation between infarct tissue heterogeneity on contrast-enhanced MRI and the occurrence of spontaneous ventricular arrhythmia (or sudden cardiac death) is unknown. Therefore, the study purpose was to evaluate the predictive value of infarct tissue heterogeneity assessed with contrast-enhanced MRI on the occurrence of spontaneous ventricular arrhythmia with subsequent implantable cardioverter-defibrillator (ICD) therapy (as surrogate of sudden cardiac death) in patients with previous myocardial infarction. Methods and Results—Ninety-one patients (age, 65±11 years) with previous myocardial infarction scheduled for ICD implantation underwent cine MRI to evaluate left ventricular function and volumes and contrast-enhanced MRI for characterization of scar tissue (infarct gray zone as measure of infarct tissue heterogeneity, infarct core, and total infarct size). Appropriate ICD therapy was documented in 18 patients (20%) during a median follow-up of 8.5 months (interquartile range, 2.1 to 20.3). Multivariable Cox proportional hazards analysis revealed that infarct gray zone was the strongest predictor of the occurrence of spontaneous ventricular arrhythmia with subsequent ICD therapy (hazard ratio, 1.49/10 g; CI, 1.01 to 2.20; &khgr;2=4.0; P=0.04). Conclusions—Infarct tissue heterogeneity on contrast-enhanced MRI is the strongest predictor of spontaneous ventricular arrhythmia with subsequent ICD therapy (as surrogate of sudden cardiac death) among other clinical and MRI variables, that is, total infarct size and left ventricular function and volumes, in patients with previous myocardial infarction.

Infarct Tissue Heterogeneity Assessed with Contrast-Enhanced Magnetic Resonance Imaging Predicts Spontaneous Ventricular Arrhythmia in Patients with Ischemic Cardiomyopathy and Implantable Cardioverter-Defibrillator

Background—The relation between infarct tissue heterogeneity on contrast-enhanced MRI and the occurrence of spontaneous ventricular arrhythmia (or sudden cardiac death) is unknown. Therefore, the study purpose was to evaluate the predictive value of infarct tissue heterogeneity assessed with contrast-enhanced MRI on the occurrence of spontaneous ventricular arrhythmia with subsequent implantable cardioverter-defibrillator (ICD) therapy (as surrogate of sudden cardiac death) in patients with previous myocardial infarction. Methods and Results—Ninety-one patients (age, 65±11 years) with previous myocardial infarction scheduled for ICD implantation underwent cine MRI to evaluate left ventricular function and volumes and contrast-enhanced MRI for characterization of scar tissue (infarct gray zone as measure of infarct tissue heterogeneity, infarct core, and total infarct size). Appropriate ICD therapy was documented in 18 patients (20%) during a median follow-up of 8.5 months (interquartile range, 2.1 to 20.3). Multivariable Cox proportional hazards analysis revealed that infarct gray zone was the strongest predictor of the occurrence of spontaneous ventricular arrhythmia with subsequent ICD therapy (hazard ratio, 1.49/10 g; CI, 1.01 to 2.20; &khgr;2=4.0; P=0.04). Conclusions—Infarct tissue heterogeneity on contrast-enhanced MRI is the strongest predictor of spontaneous ventricular arrhythmia with subsequent ICD therapy (as surrogate of sudden cardiac death) among other clinical and MRI variables, that is, total infarct size and left ventricular function and volumes, in patients with previous myocardial infarction.

Comparison of echocardiographic methods with magnetic resonance imaging for assessment of right ventricular function in children

Assessment of right ventricular (RV) function is clinically relevant in the follow-up of various forms of congenital heart disease. Agreement on the value of different echocardiographic approaches for this purpose is lacking. Magnetic resonance imaging (MRI) provides dimensionally accurate RV volumes and ejection fraction. Transthoracic 2-dimensional echocardiography from 3 different views and gradient-echo tomographic MRI were performed in 16 children with congenital heart disease and 17 age-matched healthy children. RV volumes and ejection fraction were calculated with 5 mono- and biplane area-length and multiple-slice echocardiographic methods. Adequate MRI and echocardiographic apical 4-chamber images could be obtained in all 33 children. The best correlation between MRI and echocardiographic volumes was with the biplane pyramidal approximation method. End-diastolic volume by MRI was 92 +/- 27 ml: systematic difference with echocardiography was +14 +/- 16 ml (r = 0.86). End-systolic volume by MRI was 33 +/- 13 ml: systematic difference with echocardiography was -4 +/- 7 ml (r = 0.82). Ejection fraction by MRI was 65 +/- 8%: systematic difference with echocardiography was +5 +/- 7% (r = 0.72), using monoplane ellipsoid approximation. For all echocardiographic methods, significant effects of RV geometry were noted. Echocardiographic mono- and biplane area-length and multiple-slice calculations demonstrated moderate correlation and significant systematic errors compared with MRI-derived RV volumes. Echocardiographic results were influenced by RV geometry. The relatively simple monoplane area-length method provides ejection fraction results acceptable for clinical practice; results are not improved by more complex biplane and/or multislice methods.

Right Ventricular Diastolic Function in Children With Pulmonary Regurgitation After Repair of Tetralogy of Fallot: Volumetric Evaluation by Magnetic Resonance Velocity Mapping

OBJECTIVES We sought to assess right ventricular diastolic function in young patients with corrected tetralogy of Fallot and pulmonary regurgitation. BACKGROUND Pulmonary regurgitation is an important problem in repair of tetralogy of Fallot. Its effects on right ventricular diastolic function in children are unknown. METHODS Nineteen children with repair of tetralogy of Fallot (mean age [+/- SD] 12 +/- 3 years, mean age at operation 1.5 +/- 1) and 12 healthy children were studied. Summation of magnetic resonance velocity mapping pulmonary and tricuspid volume flow curves provided right ventricular time-volume curves. Ventricular size was assessed with tomographic magnetic resonance imaging (MRI). Graded exercise testing was performed. RESULTS Systematic and random differences (mean +/- SD) of velocity mapping and Doppler tricuspid time to peak velocities (peak E: 1 +/- 26 ms, r = 0.43; peak A: 2 +/- 11 ms, r = 0.76), E/A ratio (0.04 +/- 0.5, r = 0.63) and duration of pulmonary regurgitation (20 +/- 35 ms, r = 0.74) were satisfactory. In 6 patients (group I), late diastolic forward pulmonary artery flow was absent; in 13 patients (group II), this flow contributed 1% to 14% to right ventricular stroke volume. Significant differences were increased deceleration time (315 +/- 91 vs. 168 +/- 28 ms, p < 0.001), decreased filling fraction (44 +/- 11 vs. 55 +/- 16%, p = 0.02) and increased peak early filling rate (378 +/- 124 vs. 286 +/- 112 ml/s, p = 0.018) between control subjects and group I, and increased deceleration time (230 +/- 40, p = 0.03) between control subjects and group II. Pulmonary regurgitation, ventricular size and ejection fraction did not differ significantly between patient groups. Exercise function was diminished with restrictive right ventricular physiology (p < 0.001, group II vs. control subjects). CONCLUSIONS Impaired relaxation and restriction to filling affect right ventricular function in children with repair of tetralogy of Fallot and pulmonary regurgitation. Restrictive right ventricular physiology is associated with decreased exercise function.

Reproducibility of MRI-derived measurements of right ventricular volumes and myocardial mass

Magnetic resonance (MR) imaging has been shown to provide accurate measurements of right ventricular (RV) volumes and myocardial mass. The purpose of this study was to evaluate the reproducibility of MR imaging, which in clinical practice may be as important as its absolute accuracy. The reproducibility of MR imaging measurements of the right ventricle was assessed by analyzing 40 serial functional MR imaging examinations of the right ventricle with variance component analysis. Standard deviations and 95% ranges for change were: for RV myocardial mass, 5.9 and 16 g; and for RV ejection fraction, 6.0% and 16%, respectively. Reproducibility was similar for cine and spin-echo MR imaging. The intraobserver and interobserver errors were especially large, indicating that observer subjectivity is the limiting factor in the interpretation of the MR images. This study suggests that the reproducibility of RV measurements is adequate to detect RV hypertrophy and a low ejection fraction in the individual patient. For accurate follow-up examinations, whereby smaller changes are to be detected, the reproducibility of MR imaging measurements may not be sufficient. More effort is needed to improve the reproducibility of MR imaging measurements.

T1 Mapping in Cardiomyopathy at Cardiac MR: Comparison with Endomyocardial Biopsy

PURPOSE To determine the utility of cardiac magnetic resonance (MR) T1 mapping for quantification of diffuse myocardial fibrosis compared with the standard of endomyocardial biopsy. MATERIALS AND METHODS This HIPAA-compliant study was approved by the institutional review board. Cardiomyopathy patients were retrospectively identified who had undergone endomyocardial biopsy and cardiac MR at one institution during a 5-year period. Forty-seven patients (53% male; mean age, 46.8 years) had undergone diagnostic cardiac MR and endomyocardial biopsy. Thirteen healthy volunteers (54% male; mean age, 38.1 years) underwent cardiac MR as a reference. Myocardial T1 mapping was performed 10.7 minutes ± 2.7 (standard deviation) after bolus injection of 0.2 mmol/kg gadolinium chelate by using an inversion-recovery Look-Locker sequence on a 1.5-T MR imager. Late gadolinium enhancement was assessed by using gradient-echo inversion-recovery sequences. Cardiac MR results were the consensus of two radiologists who were blinded to histopathologic findings. Endomyocardial biopsy fibrosis was quantitatively measured by using automated image analysis software with digital images of specimens stained with Masson trichrome. Histopathologic findings were reported by two pathologists blinded to cardiac MR findings. Statistical analyses included Mann-Whitney U test, analysis of variance, and linear regression. RESULTS Median myocardial fibrosis was 8.5% (interquartile range, 5.7-14.4). T1 times were greater in control subjects than in patients without and in patients with evident late gadolinium enhancement (466 msec ± 14, 406 msec ± 59, and 303 msec ± 53, respectively; P < .001). T1 time and histologic fibrosis were inversely correlated (r = -0.57; 95% confidence interval: -0.74, -0.34; P < .0001). The area under the curve for myocardial T1 time to detect fibrosis of greater than 5% was 0.84 at a cutoff of 383 msec. CONCLUSION Cardiac MR with T1 mapping can provide noninvasive evidence of diffuse myocardial fibrosis in patients referred for evaluation of cardiomyopathy.

Detection and Quantification of Dysfunctional Myocardium by Magnetic Resonance Imaging A New Three-dimensional Method for Quantitative Wall-Thickening Analysis

BACKGROUND Regional left ventricular dysfunction is a major consequence of myocardial ischemia, and its extent determines long-term prognosis. Accurate and reproducible analysis of left ventricular dysfunction is therefore useful for risk stratification and patient management. METHODS AND RESULTS Short-axis cardiac cine magnetic resonance (MR) imaging was performed in 25 patients after anterior myocardial infarction at 21 +/- 2.1 days after the acute onset. The MR images were analyzed with the use of a dedicated analytical software package (MASS version 1.0), which includes a modified centerline method and a new three-dimensional analysis approach. A database of 48 healthy volunteers was constructed to objectively depict myocardial dysfunction in the patients; this database was compared with enzymatically determined infarct size. The mean (+/-SEM) quantity of dysfunctional myocardium and enzymatically calculated infarct size equaled 24.0 +/- 3.0 and 22.3 +/- 2.9 g, respectively (P = .69). Enzymatically determined infarct size correlated strongly with left ventricular dysfunction determined by cine MR imaging (y = 0.90x + .92. P < .0001). Segments related to the distribution of the left anterior descending coronary artery showed a significantly lower percentage wall thickening in patients than did corresponding segments of 48 normal subjects (46.0 +/- 8.22% versus 87.1 +/- mean SEM, respectively; P < .001). The mean (+/-SEM) end diastolic wall thickness of the infarcted segment did not differ from that of corresponding normal segments (7.4 +/- 0.33 versus 7.5 +/- 0.15 mm; P = .75). CONCLUSIONS We conclude that the use of three-dimensional quantitative analysis of cine MR images accurately quantities the extent of regional left ventricular dysfunction in the infarcted heart. This method of analysis may be useful in assessing the effect of interventional therapies.

Quantification in cardiac MRI

Magnetic resonance imaging (MRI) offers several acquisition techniques for precise and highly reproducible assessment of global and regional ventricular function, flow, and perfusion at rest and under pharmacological or physical stress conditions. Recent advances in hardware and software have resulted in strong improvement of image quality and in a significant decrease in the required imaging time for each of these acquisitions. Several aspects of heart disease can be studied by combining multiple MRI techniques in a single examination. Such a comprehensive examination could replace a number of other imaging procedures, such as diagnostic X‐ray angiography, echocardiography, and scintigraphy, which would be beneficial for the patient and cost effective. Despite the advances in MRI, quantitative image analysis often still relies on manual tracing of contours in the images, which is a time‐consuming and tedious procedure that limits the clinical applicability of cardiovascular MRI. Reliable automated or semi‐automated image analysis software would be very helpful to overcome the limitations associated with manual image processing. In this paper the developments directed toward automated quantitative image analysis and semi‐automated contour detection for cardiovascular MR imaging are reviewed. J. Magn. Reson. Imaging 1999; 10:602–608.

Head-to-head comparison of contrast-enhanced magnetic resonance imaging and electroanatomical voltage mapping to assess post-infarct scar characteristics in patients with ventricular tachycardias: real-time image integration and reversed registration

AIMS Substrate-based ablation of ventricular tachycardia (VT) relies on electroanatomical voltage mapping (EAVM). Integration of scar information from contrast-enhanced magnetic resonance imaging (CE-MRI) with EAVM may provide supplementary information. This study assessed the relation between electrogram voltages and CE-MRI scar characteristics using real-time integration and reversed registration. METHODS AND RESULTS Fifteen patients without implantable cardiac defibrillator (14 males, 64 ± 9 years) referred for VT ablation after myocardial infarction underwent CE-MRI. Contours of the CE-MRI were used to create three-dimensional surface meshes of the left ventricle (LV), aortic root, and left main stem (LM). Real-time integration of CE-MRI-derived scar meshes with EAVM of the LV and aortic root was performed using the LM and the CARTO surface registration algorithm. Merging of CE-MRI meshes with EAVM was successful with a registration error of 3.8 ± 0.6 mm. After the procedure, voltage amplitudes of each mapping point were superimposed on the corresponding CE-MRI location using the reversed registration matrix. Infarcts on CE-MRI were categorized by transmurality and signal intensity. Local bipolar and unipolar voltages decreased with increasing scar transmurality and were influenced by scar heterogeneity. Ventricular tachycardia reentry circuit isthmus sites were correlated to CE-MRI scar location. In three patients, VT isthmus sites were located in scar areas not identified by EAVM. CONCLUSION Integration of MRI-derived scar maps with EAVM during VT ablation is feasible and accurate. Contrast-enhanced magnetic resonance imaging identifies non-transmural scars and infarct grey zones not detected by EAVM according to the currently used voltage criteria and may provide important supplementary substrate information in selected patients.

Usefulness of dynamic multislice computed tomography of left ventricular function in unstable angina pectoris and comparison with echocardiography

F efficient cardiac patient management, a comprehensive noninvasive cardiac examination is desirable. Multislice computed tomography (CT) has the potential to assess coronary artery stenosis.1,2 Multislice CT may assess left ventricular (LV) function in addition, without the need for extra acquisitions. The purpose of the present study was to apply dynamic multislice CT for the assessment of regional wall motion and global cardiac function in patients with unstable angina, and to compare the results with conventional 2-dimensional echocardiography. • • • Fifteen patients (mean age 59 11 years) presenting with complaints of unstable angina were included in the present study. Typical electrocardiographic changes (ST-segment depression) were present in 13 patients. Six patients had had a previous infarction ( 3 months before the study), and 1 patient had previously undergone coronary artery bypass graft surgery. All patients had 1 risk factor for coronary artery disease. All patients underwent conventional 2-dimensional echocardiography followed by contrast-enhanced multislice CT on the same day. Informed consent and ethics approval was obtained for all patients. CT studies were performed on a Toshiba MultiSlice Aquilion 0.5 system (Toshiba Medical Systems, Otawara, Japan). Nonionic contrast material (Xenetix, Guerbet, Aulnay S. Bois, France) (140 ml, flow rate 4.0 ml/s) was injected into the antecubital vein. The bolus arrival was automatically detected using peak enhancement detection in the aortic root. Helical CT scanning was begun using simultaneous acquisition of 4 sections with a collimated slice thickness of 2 mm, helical pitch of 1 mm/0.5 second, and 500 ms rotation time. Tube voltage was 120 kV at 250 mA. The heart was imaged from aortic root to diaphragm. Depending on heart rate and heart size, the breath-hold time was 20 to 35 seconds and the temporal resolution was 160 ms. A segmental reconstruction algorithm was used to allow for the inclusion of patients with a range of heart rates without the need for preoxygenation or -blocker therapy. The image data were reconstructed to 1-mm overcontiguous slices. With the recorded electrocardiogram, retrospective reconstruction was performed for the acquisition of phase images starting from early systole (0% of the RR interval) to the end of diastole (95% of the RR interval) using 5% increasing steps, thus obtaining 20 heart phases. Multiplanar reformats were created to obtain 2-chamber, 4-chamber, and short-axis orientations according to previously published methods.3,4 The data were stored in DICOM format and transferred to a dedicated cardiac analysis software utility (CT-MASS, MEDIS Medical Imaging Systems, Leiden, The Netherlands) running on a Linux workstation. Regional wall motion was assessed in a blinded fashion using the multiplanar reformat cinematic loops and the 17-segment model as recently suggested by the Cardiac Imaging Committee of the Council on Clinical Cardiology of the American Heart Association.5 Both inward wall motion and wall thickening were analyzed. Each segment was assigned a wall motion score of 1 to 4: normal 1, hypokinetic 2 (decreased endocardial excursion and systolic wall thickening), akinetic 3 (absence of endocardial excursion and systolic wall thickening), and dyskinetic 4 (paradoxic outward movement in systole). LV ejection fraction was calculated using automated contour detection. The outlined borders of the LV cavity were manually corrected whenever necessary.6,7 As previously described, papillary muscles were regarded as being part of the LV cavity.7 LV end-diastolic and end-systolic volumes were calculated using slice summation and the LV ejection fraction was derived. For 2-dimensional echocardiography, patients were imaged in the left lateral decubitus position using a commercially available system (Vingmed System FiVe, GE-Vingmed, Milwaukee, Wisconsin). Images were obtained using a 3.5-MHz transducer at a depth of 16 cm in the parasternal and apical views (parasternal longand short-axis, apical 2and 4-chamber views), and saved in cine loop format. Regional wall motion of the 2-dimensional echocardiographic data were evaluated using the same 17-segment model and 4-point grading scale as previously described. LV ejection fraction was calculated From the Departments of Radiology and Cardiology, Leiden University Medical Center, Leiden; and the Department of Epidemiology and Statistics, University Hospital Dijkzigt, Rotterdam, The Netherlands. Dr. Dirksen’s address is: Leiden University Medical Center, Albinusdreef 2, 2333 ZA Leiden, The Netherlands. E-mail: M.S.Dirksen@lumc.nl. Manuscript received May 9, 2002; revised manuscript received and accepted July 17, 2002.