Cardiomyopathy
Significance of Papillary Muscle Abnormalities Identified by Cardiovascular Magnetic Resonance in Hypertrophic Cardiomyopathy

https://doi.org/10.1016/j.amjcard.2007.10.032Get rights and content

Increased thickness of the left ventricular (LV) wall is the predominant feature of the hypertrophic cardiomyopathy (HC) phenotype. The structural characteristics of the LV papillary muscles (PMs) have received little attention. In this study, cardiovascular magnetic resonance (CMR) was used to characterize PM morphology in a large HC population. Cine and delayed enhancement (DE) CMR images were obtained in 201 patients with HC and 43 control subjects. PM number and mass index were greater in patients with HC compared with controls (2.5 vs 2.1, p <0.001, and 6 ± 2 vs 3 ± 2 g/m2, p <0.001, respectively), including 109 (54%) with PM mass ≥7 g/m2 (≥2 SDs above the mean for controls). Greater LV wall mass index was associated with more substantial PM mass (r = 0.09, p <0.001). Furthermore, 12 patients with HC (19%) had normal LV mass with localized wall thickness but increased PM mass. In patients with HC with LV outflow obstruction at rest, PMs were positioned closer to the ventricular septum (displaced anteriorly: 58% vs 42% for subjects without obstruction, p = 0.02), with more marked hypertrophy (9 ± 5 vs 6 ± 4 g/m2, p <0.001). Preoperative CMR identified 3 patients with accessory, anteriorly displaced PMs judged to contribute to outflow obstruction, which were resected during septal myectomy. DE of the PMs was identified in 13 patients with HC (6%), including 3 with DE confined to PMs. In conclusion, CMR demonstrates LV PMs to be part of the cardiomyopathic process in HC, with increases in number and mass, and not uncommonly associated with remodeling with DE. The identification of accessory PMs may be useful in planning preoperative strategy.

Section snippets

Selection of patients

We prospectively evaluated 201 patients with HC who presented to the Tufts-New England Medical Center (Boston, Massachusetts) or the Minneapolis Heart Institute Foundation (Minneapolis, Minnesota) from November 2001 to November 2006. The diagnosis of HC was based on 2-dimensional echocardiographic demonstration of a hypertrophied nondilated left ventricle in the absence of another cardiac or systemic disease capable of producing a similar magnitude of hypertrophy.2, 3, 14 LV outflow tract

Study group characteristics

The demographics of the patients with HC and control subjects are listed in Table 1. Controls and patients with HC did not differ with respect to body surface area (p = NS; Table 1).

PM morphology

The number of LV PMs in patients with HC was 2.5 ± 0.6 and significantly greater than in controls (2.1 ± 0.4) (p <0.001; Figure 2), with no difference with respect to gender (Table 1). Three or 4 PMs were identified in 97 patients with HC (48%) but in only 6 (14%) of controls (p <0.001; Figure 1).

The mean PM mass

Discussion

The present CMR data demonstrate that the LV PMs are commonly involved in HC disease expression. PM hypertrophy was seen in >50% of patients, with twofold greater muscle mass than controls, including about 20% with marked hypertrophy. These differences persisted after correction for body surface area and were unrelated to gender. In addition, the absolute number of PMs identified in patients with HC significantly exceeded that in controls, with about half of the study group having multiple PMs

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