Cardiac function by MRI in congenital heart disease: Impact of consensus training on interinstitutional variance

Head-to-head comparison of left ventricular function assessment with 64-row computed tomography, biplane left cineventriculography, and both 2- and 3-dimensional transthoracic echocardiography: comparison with magnetic resonance imaging as the reference standard

OBJECTIVES

This study was designed to compare the accuracy of 64-row contrast computed tomography (CT), invasive cineventriculography (CVG), 2-dimensional echocardiography (2D Echo), and 3-dimensional echocardiography (3D Echo) for left ventricular (LV) function assessment with magnetic resonance imaging (MRI).

BACKGROUND

Cardiac function is an important determinant of therapy and is a major predictor for long-term survival in patients with coronary artery disease. A number of methods are available for assessment of function, but there are limited data on the comparison between these multiple methods in the same patients.

METHODS

A total of 36 patients prospectively underwent 64-row CT, CVG, 2D Echo, 3D Echo, and MRI (as the reference standard). Global and regional LV wall motion and ejection fraction (EF) were measured. In addition, assessment of interobserver agreement was performed.

RESULTS

For the global EF, Bland-Altman analysis showed significantly higher agreement between CT and MRI (p < 0.005, 95% confidence interval: ±14.2%) than for CVG (±20.2%) and 3D Echo (±21.2%). Only CVG (59.5 ± 13.9%, p = 0.03) significantly overestimated EF in comparison with MRI (55.6 ± 16.0%). CT showed significantly better agreement for stroke volume than 2D Echo, 3D Echo, and CVG. In comparison with MRI, CVG-but not CT-significantly overestimated the end-diastolic volume (p < 0.001), whereas 2D Echo and 3D Echo significantly underestimated the EDV (p < 0.05). There was no significant difference in diagnostic accuracy (range: 76% to 88%) for regional LV function assessment between the 4 methods when compared with MRI. Interobserver agreement for EF showed high intraclass correlation for 64-row CT, MRI, 2D Echo, and 3D Echo (intraclass correlation coefficient >0.8), whereas agreement was lower for CVG (intraclass correlation coefficient = 0.58).

CONCLUSIONS

64-row CT may be more accurate than CVG, 2D Echo, and 3D Echo in comparison with MRI as the reference standard for assessment of global LV function.

Right ventricular hypertrophy after atrial switch operation: normal adaptation process or risk factor? A cardiac magnetic resonance study

Background

Systemic right ventricle (RV) hypertrophy and impaired function occur after atrial switch for dextro-transposition of the great arteries (d-TGA). Echocardiography is limited in its ability to assess the RV. We sought to evaluate systemic RV myocardial-mass index (MMI) and function after atrial switch and to analyse the role of hypertrophy for ventricular function with special consideration of the interventricular septal (IVS) movement.

Methods

Thirty-seven consecutive patients (median age 22.9 years) after atrial switch were studied using cardiac magnetic resonance imaging (1.5T Intera, Philips) with a dedicated 5-channel phased-array surface cardiac coil. Cine steady-state free-precession sequences were acquired to obtain myocardial masses and function. The systolic movement of the IVS was defined as positive when moving towards the centroid of the RV and was defined as non-positive otherwise. Patient parameters were compared to controls.

Results

The systemic RVs were significantly larger (p < 0.001) than the left ventricles of the control group, systolic function was significantly impaired (p < 0.001) and MMI including the IVS was comparable (p = n.s.). RV-MMI excluding the IVS and RV ejection fraction (EF) demonstrated a quadratic correlation (r = 0.6, p < 0.001), meaning that patients with RV-MMI ≤29 g/m² and >68 g/m² had a reduced level of systolic function. Positive septal movement improved RV function compared with non-positive septal movement (p = 0.024).

Conclusions

There seems to be a range of beneficial RV hypertrophy after atrial switch in which a sufficient RV-EF can be expected. A positive septal movement, probably the result of hypertrophic septal RV fibres, improves RV function and might be regarded as a beneficial contraction pattern.

Rapid pediatric cardiac assessment of flow and ventricular volume with compressed sensing parallel imaging volumetric cine phase-contrast MRI

OBJECTIVE

The quantification of cardiac flow and ventricular volumes is an essential goal of many congenital heart MRI examinations, often requiring acquisition of multiple 2D phase-contrast and bright-blood cine steady-state free precession (SSFP) planes. Scan acquisition, however, is lengthy and highly reliant on an imager who is well-versed in structural heart disease. Although it can also be lengthy, 3D time-resolved (4D) phase-contrast MRI yields global flow patterns and is simpler to perform. We therefore sought to accelerate 4D phase contrast and to determine whether equivalent flow and volume measurements could be extracted.

MATERIALS AND METHODS

Four-dimensional phase contrast was modified for higher acceleration with compressed sensing. Custom software was developed to process 4D phase-contrast images. We studied 29 patients referred for congenital cardiac MRI who underwent a routine clinical protocol, including cine short-axis stack SSFP and 2D phase contrast, followed by contrast-enhanced 4D phase contrast. To compare quantitative measurements, Bland-Altman analysis, paired Student t tests, and F tests were used.

RESULTS

Ventricular end-diastolic, end-systolic, and stroke volumes obtained from 4D phase contrast and SSFP were well correlated (ρ = 0.91-0.95; r(2) = 0.83-0.90), with no statistically significant difference. Ejection fractions were well correlated in a subpopulation that underwent higher-resolution compressed-sensing 4D phase contrast (ρ = 0.88; r(2) = 0.77). Four-dimensional phase contrast and 2D phase contrast flow rates were also well correlated (ρ = 0.90; r(2) = 0.82). Excluding ventricles with valvular insufficiency, cardiac outputs derived from outlet valve flow and stroke volumes were more consistent by 4D phase contrast than by 2D phase contrast and SSFP.

CONCLUSION

Combined parallel imaging and compressed sensing can be applied to 4D phase contrast. With custom software, flow and ventricular volumes may be extracted with comparable accuracy to SSFP and 2D phase contrast. Furthermore, cardiac outputs were more consistent by 4D phase contrast.

Cardiovascular magnetic resonance myocardial feature tracking detects quantitative wall motion during dobutamine stress

BACKGROUND

Dobutamine stress cardiovascular magnetic resonance (DS-CMR) is an established tool to assess hibernating myocardium and ischemia. Analysis is typically based on visual assessment with considerable operator dependency. CMR myocardial feature tracking (CMR-FT) is a recently introduced technique for tissue voxel motion tracking on standard steady-state free precession (SSFP) images to derive circumferential and radial myocardial mechanics.We sought to determine the feasibility and reproducibility of CMR-FT for quantitative wall motion assessment during intermediate dose DS-CMR.

METHODS

10 healthy subjects were studied at 1.5 Tesla. Myocardial strain parameters were derived from SSFP cine images using dedicated CMR-FT software (Diogenes MRI prototype; Tomtec; Germany). Right ventricular (RV) and left ventricular (LV) longitudinal strain (EllRV and EllLV) and LV long-axis radial strain (ErrLAX) were derived from a 4-chamber view at rest. LV short-axis circumferential strain (EccSAX) and ErrSAX; LV ejection fraction (EF) and volumes were analyzed at rest and during dobutamine stress (10 and 20 μg · kg⁻¹· min⁻¹).

RESULTS

In all volunteers strain parameters could be derived from the SSFP images at rest and stress. EccSAX values showed significantly increased contraction with DSMR (rest: -24.1 ± 6.7; 10 μg: -32.7 ± 11.4; 20 μg: -39.2 ± 15.2; p < 0.05). ErrSAX increased significantly with dobutamine (rest: 19.6 ± 14.6; 10 μg: 31.8 ± 20.9; 20 μg: 42.4 ± 25.5; p < 0.05). In parallel with these changes; EF increased significantly with dobutamine (rest: 56.9 ± 4.4%; 10 μg: 70.7 ± 8.1; 20 μg: 76.8 ± 4.6; p < 0.05). Observer variability was best for LV circumferential strain (EccSAX ) and worst for RV longitudinal strain (EllRV) as determined by 95% confidence intervals of the difference.

CONCLUSIONS

CMR-FT reliably detects quantitative wall motion and strain derived from SSFP cine imaging that corresponds to inotropic stimulation. The current implementation may need improvement to reduce observer-induced variance. Within a given CMR lab; this novel technique holds promise of easy and fast quantification of wall mechanics and strain.

Assessment of right ventricle volumes and function by cardiac MRI: quantification of the regional and global interobserver variability

Reproducibility of the manual assessment of right ventricle volumes by short-axis cine-MRI remains low and is often attributed to the difficulty in separating the right atrium from the ventricle. This study was designed to evaluate the regional interobserver variability of the right ventricle volume assessment to identify segmentation zones with the highest interobserver variability. Short-axis views of 90 right ventricles (30 hypertrophic, 30 dilated, and 30 normal) were acquired with 2D steady-state free precession sequences at 1.5 T and were manually segmented by two observers. The two segmentations were compared and the variations were quantified with a variation score based on the Hausdorff distance between the two segmentations and the interobserver 95% limits of concordance of the global volumes. The right ventricles were semiautomatically split into four subregions: apex, mid-ventricle, tricuspid zone, and infundibulum. These four subregions represented 11%, 34%, 36%, and 19% of the volume but, respectively, yielded variation scores of 8%, 16%, 42%, and 34%. The infundibulum yielded the highest interobserver regional variability although its variation score remained comparable to the tricuspid zone due to its lower volume. These results emphasize the importance of standardizing the segmentation of the infundibulum and the tricuspid zone to improve reproducibility.

Flow-sensitive four-dimensional cine magnetic resonance imaging for offline blood flow quantification in multiple vessels: a validation study

PURPOSE

To further validate the quantitative use of flow-sensitive four-dimensional velocity encoded cine magnetic resonance imaging (4D VEC MRI) for simultaneously acquired venous and arterial blood flow in healthy volunteers and for abnormal flow in patients with congenital heart disease.

MATERIALS AND METHODS

Stroke volumes (SV) obtained in arterial and venous thoracic vessels were compared between standard two-dimensional (2D), 4D VEC MRI with and without respiratory navigator gating (gated/nongated) in volunteers (n = 7). In addition, SV and regurgitation fractions (RF) measured in aorta or pulmonary trunk of patients with malformed and/or insufficient valves (n = 10) were compared between 2D and nongated 4D VEC MRI methods.

RESULTS

In volunteers and patients, Bland-Altman tests showed excellent agreement between 2D, gated, and nongated 4D VEC MRI obtained quantitative blood flow measurements. The bias between 2D and gated 4D VEC MRI was <0.5 mL for SV; between 2D and nongated 4D VEC MRI the bias was <0.7 mL for SV and <1% for RF.

CONCLUSION

Blood flow can be quantified accurately in arterial, venous, and pathological flow conditions using 4D VEC MRI. Nongated 4D VEC MRI has the potential to be suited for clinical use in patients with congenital heart disease who require flow acquisitions in multiple vessels.

Imaging the right ventricle--current state of the art

The right ventricle has long been the 'forgotten ventricle', as it is difficult to image owing to its complex morphology, its thin wall with coarse trabeculations, and its anterior position within the chest. Developments in cardiac magnetic resonance imaging (CMR) and echocardiography have provided new insights into right ventricular (RV) structure and function. RV performance seems to be an important determinant of clinical status and long-term outcome in patients with pulmonary hypertension, cardiomyopathies, and, especially, in patients with congenital heart disease. A variety of different parameters can be measured to assess RV function, but a lot of uncertainty remains on how to assess RV performance in daily clinical practice and which measurements to use in clinical decision-making. CMR is currently considered the reference technique for RV volumetry and calculation of ejection fraction. Various echocardiographic techniques can provide reliable information on RV dimensions and RV systolic and diastolic function that can be used in clinical follow-up. The introduction of newer echocardiographic techniques, such as three-dimensional echocardiography, tissue Doppler ultrasonography, and ultrasound strain imaging, challenge the leading role of CMR in RV functional assessment, but further validation and accumulation of data are required before these techniques can play a key part in clinical decision-making.

Pulmonary vascular resistance, collateral flow, and ventricular function in patients with a Fontan circulation at rest and during dobutamine stress

BACKGROUND

The role, interplay, and relative importance of the multifactorial hemodynamic and myocardial mechanisms causing dysfunction of the Fontan circulation remain incompletely understood.

METHODS AND RESULTS

Using an MRI catheterization technique, we performed a differential analysis of pulmonary vascular resistance and aortopulmonary collateral blood flow in conjunction with global ventricular pump function, myocontractility (end-systolic pressure-volume relation), and diastolic compliance (end-diastolic pressure-volume relation) in 10 patients with a Fontan circulation at rest and during dobutamine stress. Pulmonary and ventricular pressures were measured invasively and synchronized with velocity-encoded MRI-derived pulmonary and aortic blood flows and cine MRI-derived ventricular volumes. Pulmonary vascular resistance and end-systolic and end-diastolic pressure-volume relations were then determined. Aortopulmonary collateral flow was calculated as the difference between aortic and pulmonary flow. Compared to rest, dobutamine caused a small increase in mean pulmonary pressures (P<0.05). Collateral flow was significantly augmented (P<0.001) and contributed importantly to an increase in pulmonary flow (P<0.01). Pulmonary vascular resistance decreased significantly (P<0.01). Dobutamine did not increase stroke volumes significantly despite slightly enhanced contractility (end-systolic pressure-volume relation). Active early relaxation (τ) was inconspicuous, but the end-diastolic pressure-volume relation shifted upward, indicating reduced compliance.

CONCLUSIONS

In patients with a Fontan circulation, aortopulmonary collateral flow contributes substantially to enhanced pulmonary flow during stress. Our data indicate that pulmonary vascular response to augmented cardiac output was adequate, but decreased diastolic compliance was identified as an important component of ventricular dysfunction.

Integrated analysis of atrioventricular interactions in tetralogy of Fallot

The atria play an important role in cardiac performance. We evaluated their function and the atrioventricular interaction in operated patients with tetralogy of Fallot (TOF). Twenty patients who had undergone surgical repair of TOF and seven controls were investigated. Patients had residual pulmonary but no major tricuspid valve insufficiency. Atrial and ventricular strain rates were obtained by echocardiographic speckle tracking. Cine MRI-derived volumetric analysis provided atrial and ventricular time volume and time volume change curves yielding emptying and filling parameters. In addition, at the atrial level, reservoir, conduit and pump function, and cyclic volume change were calculated. At the atrioventricular valve level, tricuspid and mitral annular plane systolic excursion (TAPSE and MAPSE, respectively) were measured by two-dimensional echocardiography. In the patients compared with controls, right ventricular end-diastolic volumes were increased and biventricular ejection fraction was decreased (all P < 0.05). Biventricular measures of early diastolic ventricular filling were at control levels, but in late diastole, right ventricular filling parameters and strain rates were decreased (P < 0.001). The maximal right atrial size was slightly but not significantly diminished, but cyclic volume change was significantly reduced (P < 0.0001). Pump and reservoir function were decreased (P < 0.05), and conduit function was elevated (P < 0.001). The left atrium showed reduced reservoir function and cyclic volume change (P < 0.05). TAPSE and MAPSE were also decreased (P < 0.05). There were statistically significant interdependencies between RV ejection fraction, TAPSE, and right atrial filling and emptying parameters (all P < 0.05). In TOF patients, moderate systolic and diastolic right ventricular dysfunction is associated with clearly impaired right atrial function. The left atrium is affected to a lesser extent.

Sex-specific pediatric percentiles for ventricular size and mass as reference values for cardiac MRI: assessment by steady-state free-precession and phase-contrast MRI flow

BACKGROUND

Cardiac MRI is important in the treatment of children with congenital heart disease, but sufficient normative data are lacking. For ventricular volumes and mass, we sought to deliver reference centiles and to investigate sex effects.

METHODS AND RESULTS

We included 114 healthy children and adolescents, uniformly distributed spanning an age range of 4 to 20 years, as required by the Lambda-Mu-Sigma method to achieve a percentile distribution, thus avoiding arbitrary age categories. Subjects underwent axial volumetry (1.5-T scanner) using standardized 2D steady-state free-precession and flow protocols. Percentiles were computed for age 8 to 20 years (99 subjects) because breath-holds were more consistent in this group. When indexed for body surface area or height, the centile curves of ventricular volumetric parameters showed allometric increase until adolescence, when a plateau was reached, with values comparable to published adult reference data. In contrast, ventricular mass centiles increased without plateau. There was a significant sex difference, with centiles reflecting larger values in boys than in girls (P<0.05) when ventricular volumes were indexed to body surface area or height but not when indexed to weight (exception: mass). There was excellent agreement of axial and short-axis volumetry and of volumetric and flow-derived stroke volumes.

CONCLUSIONS

Percentiles for ventricular volumes and mass in healthy children have been established to serve as reference values in pediatric heart disease. Significant sex differences were noted when indexing volumes to body surface area or height. Unisex centiles related to weight may be considered for chamber volumes albeit not for mass.