Is magnetic resonance imaging the 'reference standard' for cardiac functional assessment? Factors influencing measurement of left ventricular mass and volumes

Clinical Significance of Papillary Muscles on Left Ventricular Mass Quantification Using Cardiac Magnetic Resonance Imaging: Reproducibility and Prognostic Value in Fabry Disease

PURPOSE

Accurate and reproducible assessment of left ventricular mass (LVM) is important in Fabry disease. However, it is unclear whether papillary muscles should be included in LVM assessed by cardiac magnetic resonance imaging (MRI). The purpose of this study was to evaluate the reproducibility and predictive value of LVM in patients with Fabry disease using different analysis approaches.

MATERIALS AND METHODS

A total of 92 patients (44±15 y, 61 women) with confirmed Fabry disease who had undergone cardiac MRI at a single tertiary referral hospital were included in this retrospective study. LVM was assessed at end-diastole using 2 analysis approaches, including and excluding papillary muscles. Adverse cardiac events were assessed as a composite end point, defined as ventricular tachycardia, bradycardia requiring device implantation, severe heart failure, and cardiac death. Statistical analysis included Cox proportional hazard models, Akaike information criterion, intraclass correlation coefficients, and Bland-Altman analysis.

RESULTS

Left ventricular end-diastolic volume, end-systolic volume, ejection fraction, and LVM all differed significantly between analysis approaches. LVM was significantly higher when papillary muscles were included versus excluded (157±71 vs. 141±62 g, P<0.001). Mean papillary mass was 16±11 g, accounting for 10%±3% of total LVM. LVM with pap illary muscles excluded had slightly better predictive value for the composite end point compared with LVM with papillary muscles included based on the model goodness-of-fit (Akaike information criterion 140 vs. 142). Interobserver agreement was slightly better for LVM with papillary muscles excluded compared with included (intraclass correlation coefficient 0.993 [95% confidence interval: 0.985, 0.996] vs. 0.989 [95% confidence interval: 0.975, 0.995]) with less bias and narrower limits of agreement.

CONCLUSIONS

Inclusion or exclusion of papillary muscles has a significant effect on LVM quantified by cardiac MRI, and therefore, a standardized analysis approach should be used for follow-up. Exclusion of papillary muscles from LVM is a reasonable approach in patients with Fabry disease given slightly better predictive value and reproducibility.

Cardiac Imaging in Heart Failure with Comorbidities

Imaging modalities stand at the frontiers for progress in congestive heart failure (CHF) screening, risk stratification and monitoring. Advancements in echocardiography (ECHO) and Magnetic Resonance Imaging (MRI) have allowed for improved tissue characterizations, cardiac motion analysis, and cardiac performance analysis under stress. Common cardiac comorbidities such as hypertension, metabolic syndromes and chronic renal failure contribute to cardiac remodeling, sharing similar pathophysiological mechanisms starting with interstitial changes, structural changes and finally clinical CHF. These imaging techniques can potentially detect changes earlier. Such information could have clinical benefits for screening, planning preventive therapies and risk stratifying patients. Imaging reports have often focused on traditional measures without factoring these novel parameters. This review is aimed at providing a synopsis on how we can use this information to assess and monitor improvements for CHF with comorbidities.

Objective selection of short-axis slices for automated quantification of left ventricular size and function by cardiovascular magnetic resonance

BACKGROUND

Quantification of left ventricular (LV) volume from cardiovascular magnetic resonance images relies on subjective and often challenging selection of short-axis (SAX) slices. We hypothesized that this could be solved by defining mitral annular (MA) plane and apex in long-axis (LAX) views, which could be combined with automated LV volume analysis that does not rely on manual tracing of the endocardial border.

METHODS

SAX images from 50 subjects were analyzed using custom software. LV apex and insertion points of the mitral leaflets were marked on LAX views and used to approximate MA plane. End-systolic and end-diastolic LV volumes (ESV, EDV) were measured while including only slices or their parts located between MA plane and LV apex. Endocardial borders were automatically detected using our previously validated algorithm and also manually traced to obtain reference values.

RESULTS

Selection of anatomic landmarks in LAX views allowed automated measurement of LV volumes without the need for subjective slice selection. Intertechnique comparisons resulted in high correlations (EDV: r=0.95; ESV: r=0.96) and small biases (1 and 9ml). Combined three-dimensional displays of LAX and SAX views with the MA plane showed that in 7/10 worst cases, intertechnique discordance was due to incorrect manual tracing at LV base that erroneously included part of atrial cavity in LV volume or excluded part of LV cavity, i.e., incorrect reference values.

CONCLUSION

Defining the MA plane and apex in the LAX views obviates the need for subjective slice selection and eliminates errors in LV volume measurements.

LV mass assessed by echocardiography and CMR, cardiovascular outcomes, and medical practice

The authors investigated 3 important areas related to the clinical use of left ventricular mass (LVM): accuracy of assessments by echocardiography and cardiac magnetic resonance (CMR), the ability to predict cardiovascular outcomes, and the comparative value of different indexing methods. The recommended formula for echocardiographic estimation of LVM uses linear measurements and is based on the assumption of the left ventricle (LV) as a prolate ellipsoid of revolution. CMR permits a modeling of the LV free of cardiac geometric assumptions or acoustic window dependency, showing better accuracy and reproducibility. However, echocardiography has lower cost, easier availability, and better tolerability. From the MEDLINE database, 26 longitudinal echocardiographic studies and 5 CMR studies investigating LVM or LV hypertrophy as predictors of death or major cardiovascular outcomes were identified. LVM and LV hypertrophy were reliable cardiovascular risk predictors using both modalities. However, no study directly compared the methods for the ability to predict events, agreement in hypertrophy classification, or performance in cardiovascular risk reclassification. Indexing LVM to body surface area was the earliest normalization process used, but it seems to underestimate the prevalence of hypertrophy in obese and overweight subjects. Dividing LVM by height to the allometric power of 1.7 or 2.7 is the most promising normalization method in terms of practicality and usefulness from a clinical and scientific standpoint for scaling myocardial mass to body size. The measurement of LVM, calculation of LVM index, and classification for LV hypertrophy should be standardized by scientific societies across measurement techniques and adopted by clinicians in risk stratification and therapeutic decision making.

Phase II trials in heart failure: the role of cardiovascular imaging

The development of new therapies for heart failure (HF), especially acute HF, has proven to be quite challenging; and therapies evaluated in HF have greatly outnumbered treatments that are eventually successful in obtaining regulatory approval. Thus, the development of therapies for HF remains a vexing problem for pharmaceutical and device companies, clinical trialists, and health care professionals. Nowhere is this more apparent than in the phase II HF clinical trial, in which the goal is to determine whether an investigational agent should move forward to a phase III trial. Recent advancements in noninvasive cardiovascular imaging have allowed a new era of comprehensive phenotyping of cardiac structure and function in phase II HF trials. Besides using imaging parameters to predict success of subsequent phase III outcome studies, it is essential to also use imaging in phase II HF trials in a way that increases understanding of drug or device mechanism. Determination of the patients who would benefit most from a particular drug or device could decrease heterogeneity of phase III trial participants and lead to more successful HF clinical trials. In this review, we outline advantages and disadvantages of imaging various aspects of cardiac structure and function that are potential targets for therapy in HF, compare and contrast imaging modalities, provide practical advice for the use of cardiovascular imaging in drug development, and conclude with some novel uses of cardiac imaging in phase II HF trials.

Cardiac volumetry in patients with heart failure and reduced ejection fraction: a comparative study correlating multi-slice computed tomography and magnetic resonance tomography. Reasons for intermodal disagreement

BACKGROUND

In humans with normal hearts multi-slice computed tomography (MSCT) based volumetry was shown to correlate well with the gold standard, cardiac magnetic resonance imaging (CMR). We correlated both techniques in patients with various degrees of heart failure and reduced ejection fraction (HFREF) resulting from cardiac dilatation.

METHODS

Twenty-four patients with a left ventricular enddiastolic volume (LV-EDV) of C 150 ml measured by angiography underwent MSCT and CMR scanning for left and right ventricular (LV, RV) volumetry. MSCT based short cardiac axis views were obtained beginning at the cardiac base advancing to the apex. These were reconstructed in 20 different time windows of the RR-interval (0-95%) serving for identification of enddiastole (ED) and end-systole (ES) and for planimetry. ED and ES volumes and the ejection fraction (EF) were calculated for LV and RV. MSCT based volumetry was compared with CMR.

RESULTS

MSCT based LV volumetry significantly correlates with CMR as follows: LV-EDV r = 0.94, LV-ESV r = 0.98 and LV-EF r = 0.93, but significantly overestimates LV-EDV and LV-ESV and underestimates EF (P \ 0.0001). MSCT based RV volumetry significantly correlates with CMR as follows: RV-EDV r = 0.79, RVESV r = 0.78 and RV-EF r = 0.73, but again significantly overestimates RV-EDV and RV-ESV and underestimates RV-EF (P \ 0.0001).

CONCLUSION

When compared with CMR a continuous overestimation of volumes and underestimation of EF needs to be considered when applying MSCT in HFREF patients.

A dual propagation contours technique for semi-automated assessment of systolic and diastolic cardiac function by CMR

BACKGROUND

Although cardiovascular magnetic resonance (CMR) is frequently performed to measure accurate LV volumes and ejection fractions, LV volume-time curves (VTC) derived ejection and filling rates are not routinely calculated due to lack of robust LV segmentation techniques. VTC derived peak filling rates can be used to accurately assess LV diastolic function, an important clinical parameter. We developed a novel geometry-independent dual-contour propagation technique, making use of LV endocardial contours manually drawn at end systole and end diastole, to compute VTC and measured LV ejection and filling rates in hypertensive patients and normal volunteers.

METHODS

39 normal volunteers and 49 hypertensive patients underwent CMR. LV contours were manually drawn on all time frames in 18 normal volunteers. The dual-contour propagation algorithm was used to propagate contours throughout the cardiac cycle. The results were compared to those obtained with single-contour propagation (using either end-diastolic or end-systolic contours) and commercially available software. We then used the dual-contour propagation technique to measure peak ejection rate (PER) and peak early diastolic and late diastolic filling rates (ePFR and aPFR) in all normal volunteers and hypertensive patients.

RESULTS

Compared to single-contour propagation methods and the commercial method, VTC by dual-contour propagation showed significantly better agreement with manually-derived VTC. Ejection and filling rates by dual-contour propagation agreed with manual (dual-contour - manual PER: -0.12 +/- 0.08; ePFR: -0.07 +/- 0.07; aPFR: 0.06 +/- 0.03 EDV/s, all P = NS). However, the time for the manual method was approximately 4 hours per study versus approximately 7 minutes for dual-contour propagation. LV systolic function measured by LVEF and PER did not differ between normal volunteers and hypertensive patients. However, ePFR was lower in hypertensive patients vs. normal volunteers, while aPFR was higher, indicative of altered diastolic filling rates in hypertensive patients.

CONCLUSION

Dual-propagated contours can accurately measure both systolic and diastolic volumetric indices that can be applied in a routine clinical CMR environment. With dual-contour propagation, the user interaction that is routinely performed to measure LVEF is leveraged to obtain additional clinically relevant parameters.

Comparison of MRI, 64-slice MDCT and DSCT in assessing functional cardiac parameters of a moving heart phantom

To compare magnetic resonance imaging (MRI), 64-slice multi-detector computed tomography (MDCT) and dual-source computed tomography (DSCT) in assessing global function parameters using a moving heart phantom. A moving heart phantom with known volumes (215–258 ml) moving at 50–100 beats per minute was examined by three different imaging modalities using clinically implemented scanning protocols. End-diastolic and end-systolic volumes were calculated by two experienced observers using dedicated post-processing tools. Ejection fraction (EF) and cardiac output (CO) were calculated and mutually compared using Bland-Altman plots. MRI underestimated the ejection EF by 16.1% with a Bland-Altman interval (B-A) of [-4.35 (-2.48) -0.60]. Sixty-four-slice MDCT overestimated the EF by 2.6% with a relatively wide B-A interval of [-3.40 (0.40) 4.20]. DSCT deviated the least from the known phantom volumes, underestimating the volumes by 0.8% with a B-A interval of [-1.17 (-0.13) 0.91]. CO analysis showed similar results. Furthermore, a good correlation was found between DSCT and MRI for EF and CO results. MRI systematically underestimates functional cardiac parameters, ejection fraction and cardiac output of a moving heart phantom. Sixty-four-slice MDCT underestimates or overestimates these functional parameters depending on the heart rate because of limited spatial resolution. DSCT deviates the least from these functional parameters compared to MRI, EBT and 64-slice MDCT.

Comparison of the reproducibility of quantitative cardiac left ventricular assessments in healthy volunteers using different MRI scanners: a multicenter simulation

PURPOSE

To derive reproducibility assessments of ejection fraction (EF) and left ventricular mass (LVM) from short-axis cardiac MR images acquired at single and multiple time-points on different 1.5T scanner models.

MATERIALS AND METHODS

Images of 15 healthy volunteers were acquired twice using a Magnetom Avanto scanner (Siemens, Erlangen, Germany) and once using a Signa Excite scanner (General Electric, Milwaukee, WI, USA) over four months, and analyzed using ARGUS and MASS Analysis+ software, respectively. Two physicists independently segmented the myocardial borders in order to derive intra- and interobserver assessments of EF and LVM for single and multiple time-points on the same and different scanners.

RESULTS

For EF, the coefficient of repeatability (CoR) increased as different observers, multiple time-points, and different scanners were introduced. The CoR ranged from 2.8% (intraobserver measurements, single time-point, same scanner) to 10.0% (interobserver measurements, different time-points, different scanners). For LVM, intraobserver CoR parameters were consistently smaller than interobserver values. The CoR ranged from 7.8 g (intraobserver measurements, single time-point, same scanner) to 39.5 g (interobserver measurements, different time-points, different scanners).

CONCLUSION

Reproducible EF data can be obtained at single or multiple time-points using different scanners. However, LVM is notably susceptible to interobserver variation, and this should be carefully considered if similar evaluations are planned as part of multicenter or longitudinal investigations.

Assessment of cardiac volumes by multidetector computed tomography

Quantitative evaluation of cardiac ventricular and atrial chamber sizes, ventricular function, and left ventricular mass is important for prognosis and management. The most common methods for quantitative evaluation have been echocardiography and cardiac magnetic resonance imaging. Recently, multidetector cardiac computed tomography (CCT) technology has evolved to permit imaging of cardiac structure, function, volume, and mass. Potential advantages of CCT over existing methods include 3-dimensional volumetric assessment of cardiac chambers which are free of geometric assumptions and the ability to obtain true, on-axis imaging planes with double-oblique orientations.