EDITORIAL COMMENT
Hypertrophic CardiomyopathyCardiac Magnetic Resonance Imaging Changes the Paradigm*
Nathaniel Reichek, MD, FACC , ,* and
Dipti Gupta, MD, MPH
Department of Research, St. Francis Hospital, Roslyn, New York
Stony Brook University Hospital, SUNY, Stony Brook, New York.
* Reprint requests and correspondence: Dr. Nathaniel Reichek, DeMatteis Center, Research and Education Foundation, St. Francis Hospital, 100 Port Washington Boulevard, Roslyn, New York 11568. (Email: Nathaniel.Reichek{at}chsli.org).
Key Words: hypertrophic cardiomyopathy • cardiac MRI • left ventricular hypertrophy
Over the past 40 years, progress in understanding hypertrophic cardiomyopathy (HCM) has been driven in large part by echocardiography, beginning with depiction of the mechanism of left ventricular (LV) outflow tract obstruction (1,2). However, application of cardiac magnetic resonance imaging (CMR) to HCM began over 20 years ago, initially for conventional 2-dimensional morphology and function, later for myocardial strain and its relationship to hypertrophy (3–5). Recently, CMR has confirmed early observations made with positron emission tomography on microvascular dysfunction in HCM and its potential prognostic significance (6,7). More importantly, with the application of delayed hyperenhancement (DHE) imaging for detection of fibrosis in HCM, CMR has begun to change the paradigm in our understanding of determinants of HCM outcomes (7–9). In this issue of the Journal, Olivotto et al. (10) add another chapter to this story, demonstrating the impact of CMR 3-dimensional LV volumetric assessment, in this case focused on LV mass index, on the prognosis in HCM (9).
Conventionally, the diagnostic echocardiographic marker for HCM has been an unexplained increase in LV wall thickness, and a markedly increased maximal LV wall thickness has been linked to the risk of sudden death (11). However, in some patients, isolated anterolateral LV free wall or apical hypertrophy eludes transthoracic 2-dimensional echocardiography but is easily detected by CMR (5). More recently, the role of CMR DHE has emerged with Moon et al. (8) demonstrating that the presence and severity of myocardial fibrosis by CMR DHE was related to progressive LV dilation and markers of risk for sudden death, while Adabag et al. (9) showed that DHE was associated with a higher likelihood of ventricular arrhythmias. Further insights into the significance of DHE have surfaced in recent abstract presentations and are likely to appear in full publications in the near future. In addition, microvascular dysfunction demonstrated by CMR first-pass stress perfusion imaging appears to be associated with DHE fibrosis, which may explain, in part, the association of microvascular dysfunction with poor prognosis in HCM (6,7). In contrast, the role of CMR analyses of LV hypertrophy in clinical risk assessment in HCM has received little attention. Olivotto et al. (10) have now rectified this situation by examining the relationship between CMR LV mass index and adverse outcomes, as well as the relative utility of 2-dimensional echocardiographic LV wall thickness and CMR LV mass index as clinical markers and predictors of adverse outcomes in a well-powered multicenter HCM study (9). Two-dimensional echocardiographic LV mass is known to be inaccurate in HCM due to the variability of wall thickness, but this limitation is easily overcome by CMR, which provides accurate and reproducible assessment of 3-dimensional LV mass independent of geometric assumptions.
The 4 participating centers studied 264 HCM patients (age 43 ± 18 years; 197 men) with a mean follow-up of 2.6 ± 0.7 years, while 606 healthy control subjects were provided by the Framingham Heart study. The investigators showed that 56 (21%) of the patients had normal CMR LV mass indexes despite echocardiographic segmental wall thickening diagnostic of HCM. While the relationship between LV wall thickness and LV mass index achieved statistical significance, the correlation was weak. Mortality data demonstrated that a markedly increased LV mass index was a more sensitive correlate of cardiac mortality (100% sensitive vs. 41% for echocardiographic wall thickness) while a markedly increased LV wall thickness had greater specificity for HCM-related mortality (90% vs. 39% for CMR LV mass index). These data indicate that yet another component of the CMR examination may have an important role to play in the evaluation of patients with HCM.
There are a few limitations to the current work. The number of cardiac deaths in the study was small, so that confirmation of the results is needed. Furthermore, the inclusion of several deaths after septal myomectomy is debatable. No core laboratory for CMR quantitation was used, and the comparability of results from various participating centers is unclear. The normal control population was not matched to the HCM population with regards to age and gender, which are known to affect LV structure and function. Finally, like most other reports on CMR in HCM, this one addresses only 1 facet of the multifaceted CMR examination. An integrated CMR appraisal, combining LV structure and function, LV outflow obstruction severity, stress perfusion imaging, and DHE assessment of fibrosis is badly needed so that the contribution of each of these important facets of this complex disorder to outcomes can be better understood.
Nonetheless, this study advances our current understanding of HCM and of the role of CMR in assessing HCM at multiple levels. It makes a compelling argument against the popular belief that global LV hypertrophy is a necessary concomitant of diagnosable HCM and underscores the incremental value of CMR LV mass index in the assessment of HCM over and above conventional 2-dimensional echocardiographic results. Thus, Olivotto et al. (10) have introduced a conceptually strong application of CMR that aids our understanding and can improve our approach to risk stratification in HCM. In the future, larger scale, longer-term prospective trials with well-matched control subjects and comprehensive CMR studies and data analysis will be needed to determine the ultimate role of CMR in HCM assessment.
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Footnotes
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* Editorials published in the Journal of the American College of Cardiology reflect the views of the authors and do not necessarily represent the views of JACC or the American College of Cardiology. 
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References
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1. Moreyra E, Elein JJ, Shimada H, Segal BL. Idiopathic hypertrophic subaortic stenosis diagnosed by reflected ultrasound Am J Cardiol 1969;23:32-37.[CrossRef][Web of Science][Medline]2. Shah PM, Gramiak R, Kramer DH. Ultrasound localization of left ventricular outflow obstruction in hypertrophic obstructive cardiomyopathy Circulation 1969;40:3-11.[Medline] 3. Higgins CB, Byrd 3rd BF, Stark D, et al. Magnetic resonance imaging in hypertrophic cardiomyopathy Am J Cardiol 1985;55:1121-1126.[CrossRef][Web of Science][Medline] 4. Kramer CM, Reichek N, Ferrari VA, Theobald T, Dawson J, Axel L. Regional heterogeneity of function in hypertrophic cardiomyopathy Circulation 1994;90:186-194.[Abstract/Free Full Text] 5. Rickers C, Wilke NM, Jerosch-Herold M. Utility of cardiac magnetic resonance imaging in the diagnosis of hypertrophic cardiomyopathy Circulation 2005;112:855-861.[Abstract/Free Full Text] 6. Cecchi F, Olivotto I, Gistri R, Lorenzoni R, Chiriatti G, Camici PG. Coronary microvascular dysfunction and prognosis in hypertrophic cardiomyopathy N Engl J Med 2003;349:1027-1035.[Abstract/Free Full Text] 7. Petersen SE, Jerosch-Herold M, Hudsmith LE, et al. Evidence of microvascular dysfunction in hypertrophic cardiomyopathy: new insights from multiparametric magnetic resonance imaging Circulation 2007;115:2418-2425.[Abstract/Free Full Text] 8. Moon JC, McKenna WJ, McCrohon JA, et al. Toward clinical risk assessment in hypertrophic cardiomyopathy with gadolinium cardiovascular magnetic resonance J Am Coll Cardiol 2003;41:1561-1567.[Abstract/Free Full Text] 9. Adabag AS, Maron BJ, Appelbaum E, et al. Occurrence and frequency of arrhythmias in hypertrophic cardiomyopathy in relation to delayed enhancement on cardiovascular magnetic resonance J Am Coll Cardiol 2008;51:1369-1374.[Abstract/Free Full Text] 10. Olivotto I, Maron MS, Autore C, et al. Assessment and significance of left ventricular mass by cardiovascular magnetic resonance in hypertrophic cardiomyopathy J Am Coll Cardiol 2008;52:559-566.[Abstract/Free Full Text] 11. Spirito P, Bellone P, Harris KM, Bernabo P, Bruzzi P, Maron BJ. Magnitude of left ventricular hypertrophy and risk of sudden death in hypertrophic cardiomyopathy N Engl J Med 2000;342:1778-1785.[Abstract/Free Full Text]
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