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. 2020 Oct 22;2(5):e200416. doi: 10.1148/ryct.2020200416

Impact of Myocardial Contouring Method on the Cardiac MRI Assessment of Left Ventricular Mass in Hypertrophied Hearts

William E Moody 1,✉, Ravi Vijapurapu 1, Richard P Steeds 1
PMCID: PMC7977755  PMID: 33778630

Editor:

Dr O’Brien and colleagues should be commended for their important study published in the June 2020 issue of Radiology: Cardiothoracic Imaging which provides novel data highlighting the potential differences in measurements of left ventricular mass (LVM) between transthoracic echocardiography (TTE) and cardiac MRI among patients with Fabry disease (1). The authors conclude that TTE overestimates LVM compared with cardiac MRI. We suggest, however, that the decision not to include papillary muscles in cardiac MRI measurement of LVM will have underestimated the true LVM and significantly contributed to the discrepancy between imaging modalities.

The authors of the current study appear to have used the same methodology as the UK Biobank project, on which their recent publication of normal reference ranges was based. This used ellipsoid “smoothed” contouring of the compacted endocardial border and excluded both papillary muscles and trabeculae from LVM (2). This technique may offer improved reproducibility but sacrifices accuracy (closeness of the measured LVM to the true value). Our opinion is that papillary muscles are myocardial tissue and should routinely be excluded from blood volumes and included in LVM using “detailed” contouring. Use of smoothed contouring can lead to errors in the measurement of derived left ventricular parameters—our data in patients with hypertrophic cardiomyopathy suggest that using smoothed contours misses hyperdynamic function in the presence of large papillary muscles and extensive trabeculations (3). The choice of myocardial contouring technique has potentially even greater importance in phenocopies such as Fabry disease; papillary muscle hypertrophy is an early diagnostic sign and contributes disproportionately to the overall LVM (4).

This issue needs national and international guidance. It is notable that the authors’ analysis conforms with updated 2019 Society for Cardiovascular Magnetic Resonance guidelines (5). These still do not specify whether papillary muscles should be routinely included in measurement of LVM (and excluded from volumes), nor stipulate that any one normal reference range should be adopted, suggesting instead that the reference range is aligned with the reporting technique.

We would be interested to learn from the current authors if intermodality differences in LVM measurements persisted if detailed cardiac MRI contouring was used in this cohort of patients with Fabry disease.

Footnotes

Disclosures of Conflicts of Interest: W.E.M. Activities related to the present article: disclosed no relevant relationships. Activities not related to the present article: author received consultancy fees from Pfizer, Alnylam Pharmaceuticals, and Akcea Therapeutics. Other relationships: disclosed no relevant relationships R.V. Activities related to the present article: disclosed no relevant relationships. Activities not related to the present article: author is consultant for Amicus Therapeutics; author received travel accommodations to WORLD Congress 2018 from Amicus Therapeutics; author receives consultancy fees from Takeda. Other relationships: disclosed no relevant relationships. R.P.S. Activities related to the present article: disclosed no relevant relationships. Activities not related to the present article: author is consultant for Freeline Therapeutics; institution has grant from Takeda Shire for separate project in Fabry disease; author receives payment for educational lecture from Amicus; author receives payment for development of educational presentations from Amicus. Other relationships: disclosed no relevant relationships.

References

  • 1.O’Brien C, Britton I, Karur GR, et al. Left Ventricular Mass and Wall Thickness Measurements Using Echocardiography and Cardiac MRI in Patients with Fabry Disease: Clinical Significance of Discrepant Findings. Radiol Cardiothorac Imaging 2020;2(3):e190149. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 2.Petersen SE, Aung N, Sanghvi MM, et al. Reference ranges for cardiac structure and function using cardiovascular magnetic resonance (CMR) in Caucasians from the UK Biobank population cohort. J Cardiovasc Magn Reson 2017;19(1):18. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 3.Moody WE, Hudsmith LE, Holloway B, et al. Variation in cardiovascular magnetic resonance myocardial contouring: Insights from an international survey. J Magn Reson Imaging 2019;50(4):1336–1338. [DOI] [PMC free article] [PubMed] [Google Scholar]
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Radiol Cardiothorac Imaging. 2020 Oct 22;2(5):e200416. doi: 10.1148/ryct.2020200444

Response

Kate Hanneman *,✉, Robert M Iwanochko †, Paaladinesh Thavendiranathan *,†

We thank Dr Moody and colleagues for their interest in our work. We agree that papillary muscles are myocardial tissue and that inclusion of papillary muscles in LVM should result in a more accurate estimate compared with pathology-weighed explanted hearts (1).

However, it is unclear whether this approach is the most clinically relevant. Any analysis of imaging data has to balance accuracy versus precision. Our group and others have demonstrated that LVM measurements on cardiac MRI are more reproducible when papillary muscles are excluded (2,3). Low inter- and intraobserver variability of LVM measurements are important, as these are used to define the magnitude of change in LVM that is outside accepted measurement error. Furthermore, in patients with Fabry disease, when cardiac MRI is used to evaluate progression of disease, response to treatment, or prognosis, reproducible measurement of LVM is critical (4). Moreover, LVM quantified on cardiac MRI has better predictive value for adverse cardiac events when papillary muscles are excluded (2).

In our cohort of patients with Fabry disease, TTE significantly overestimates LVM compared with MRI even if the papillary muscles are included on MRI (mean difference in LVM indexed to body surface area 21 g/m2, data not published). Notably, the method endorsed by the American Society of Echocardiography for measurement of LVM uses linear measurements of left ventricular wall thickness and internal cavity diameter. The calculated LVM does not include the papillary muscles or trabeculae. Therefore, both MRI and echocardiography estimates of LVM in our study were based on measures with papillary muscles excluded (5). Thus, discrepancies between the two modalities cannot be attributed to disproportionate papillary muscle hypertrophy.

Inclusion or exclusion of papillary muscles has a significant impact on LVM quantified with cardiac MRI. Therefore, it is imperative that the cardiac MRI analysis approach used is clearly specified and that results are interpreted in relation to normal reference ranges based on the same analysis method. We agree with Dr Moody and colleagues that this matter would benefit from clear societal guidelines regarding the optimal analysis approach.

Footnotes

Disclosures of Conflicts of Interest: K.H. Activities related to the present article: disclosed no relevant relationships. Activities not related to the present article: author paid by Sanofi-Genzyme for medical advisory board; author received travel accommodations from Shire Pharmaceutical. Other relationships: disclosed no relevant relationships. R.M.I. disclosed no relevant relationships. P.T. disclosed no relevant relationships.

References

  • 1.Farber NJ, Reddy ST, Doyle M, et al. Ex vivo cardiovascular magnetic resonance measurements of right and left ventricular mass compared with direct mass measurement in excised hearts after transplantation: a first human SSFP comparison. J Cardiovasc Magn Reson 2014;16(1):74. [DOI] [PMC free article] [PubMed] [Google Scholar]
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  • 5.O’Brien C, Britton I, Karur GR, et al. Left Ventricular Mass and Wall Thickness Measurements Using Echocardiography and Cardiac MRI in Patients with Fabry Disease: Clinical Significance of Discrepant Findings. Radiol Cardiothorac Imaging 2020;2(3):e190149. endpoints in clinical research: part I - analytical validation and clinical qualification. J Cardiovasc Magn Reson 2018;20(1):67. [DOI] [PMC free article] [PubMed] [Google Scholar]

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