Myocardial fibrosis in hypertrophic cardiomyopathy: Accurate reflection of histopathological findings by CMR

Objectives: In this study we sought to explore the relationship between cardiac magnetic resonance (CMR) with late gadolinium enhancement (LGE) and histopathological parameters including interstitial fibrosis and replacement fibrosis (scar) in patients with hypertrophic cardiomyopathy (HCM). Background: CMR-LGE is a well-established tool for the assessment of scar in ischemic heart disease. Its role in HCM has evolved in recent years, and an association with nonsustained ventricular tachycardia has been demonstrated. Methods: HCM patients who underwent septal myectomy during the period 2004 through 2010 and had undergone CMR-LGE no more than 6 months before surgery were selected. Histopathological assessment of the myectomy specimens included quantitative digital analysis (interstitial and replacement fibrosis) and semiquantitative assessment (small intramural coronary arteriole dysplasia and disarray). Correlations between CMR-LGE measured with various techniques, SD above the signal intensity for the normal remote myocardium (2, 4, 5, 6, and 10 SD) and the full width at half maximum (FWHM) technique, at the myectomy site, and interstitial fibrosis, replacement fibrosis (scar), and their sum (fibrosis + scar) were evaluated. Results: Twenty-nine patients were included. Statistically significant correlations between CMR-LGE (at 2, 4, 5, 6, 10 SD and by the FWHM technique), and both interstitial fibrosis and the combined interstitial and replacement fibrosis were found. The strongest correlation was between combined interstitial and replacement fibrosis and CMR-LGE measured at 5 SD (r = 0.78, p < 0.0001). LGE measured at 10 SD demonstrated the best correlation with replacement fibrosis (r = 0.42, p = 0.02). Bland-Altman analysis revealed optimum agreement between the combined interstitial and replacement fibrosis found at pathology and LGE measured at 4 SD. In addition, moderate and severe small intramural coronary artery dysplasia showed a statistically significant correlation with replacement fibrosis (p = 0.01) and CMR-LGE at 10 SD (p = 0.04). Conclusions: CMR-LGE measured at 4 SD and 5 SD yields the closest approximation to the extent of total fibrosis measured by the histopathological standard of reference. These findings have implications for future investigations of CMR-LGE and its association with important clinical endpoints in HCM, including sudden cardiac death.