Role of CMR Mapping Techniques in Cardiac Hypertrophic Phenotype

Abstract

Non-ischemic cardiomyopathies represent a heterogeneous group of myocardial diseases potentially leading to heart failure, life-threatening arrhythmias, and eventually death. Myocardial dysfunction is associated with different underlying pathological processes, ultimately inducing changes in morphological appearance. Thus, classification based on presenting morphological phenotypes has been proposed, i.e., dilated, hypertrophic, restrictive, and right ventricular cardiomyopathies. In light of the key diagnostic and prognostic role of morphological and functional features, cardiovascular imaging has emerged as key element in the clinical workflow of suspected cardiomyopathies, and above all, cardiovascular magnetic resonance (CMR) represents the ideal technique to be used: thanks to its physical principles, besides optimal spatial and temporal resolutions, incomparable contrast resolution allows to assess myocardial tissue abnormalities in detail. Traditionally, weighted images and late enhancement images after gadolinium-based contrast agent administration have been used to perform tissue characterization, but in the last decade quantitative assessment of pre-contrast longitudinal relaxation time (native T1), post-contrast longitudinal relaxation time (post-contrast T1) and transversal relaxation time (T2), all displayed with dedicated pixel-wise color-coded maps (mapping), has contributed to give precious knowledge insight, with positive influence of diagnostic accuracy and prognosis assessment, mostly in the setting of the hypertrophic phenotype. This review aims to describe the available evidence of the role of mapping techniques in the assessment of hypertrophic phenotype, and to suggest their integration in the routine CMR evaluation of newly diagnosed cardiomyopathies with increased wall thickness.

Keywords: ECV mapping; T1 mapping; T2 mapping; cardiovascular magnetic resonance; hypertrophic phenotype; non-ischemic cardiomyopathies.

Figure 1

Normal heart. Basal short axis view (Box A) and 4-chamber long axis view (Box B) balanced steady state free precession images showing normal biventricular size and wall thickness. Normal T1 values at native T1 mapping images (Boxes C and D). Normal T2 values at T2 mapping (Boxes E and F), excluding the presence of oedema. Late gadolinium enhancement (LGE) images show uniform myocardial suppression (Boxes G and H). Normal extracellular volume (ECV) values at ECV mapping (Boxes I and J).

Figure 2

Hypertrophic Cardiomyopathy. Basal short axis view (Box A) and 4-chamber long axis view (Box B) balanced steady state free precession images showing asymmetric myocardial hypertrophy. Diffuse mild increase of T1 values at native T1 mapping images, with highest values at hypertrophied segments (Boxes C and D). Myocardial oedema detected by T2 mapping (Boxes E and F), mostly at septal level. LGE images show mid-wall patchy enhancement at hypertrophic segments (Boxes G and H). Diffuse mild increase of ECV, with highest values at hypertrophied segments (Boxes I and J).

Figure 3

Different biological information provided by native T1 and ECV in Cardiac Amyloidosis (CA). Native myocardial T1 is highly influenced by water content in the tissue, thus significantly raised by oedema, at both intra- and extracellular level in amyloid light chains (AL) CA, or mostly at extracellular level in transthyretin (ATTR) CA. Conversely, ECV values are closely related to amyloid burden, and therefore are usually remarkably high in ATTR as compared to AL. This insight could explain the relatively higher T1 values in AL compared to ATTR, along with the higher ECV values in ATTR compared to AL.

Figure 4

ATTR Cardiac Amyloidosis. Basal short axis view (Box A) and 4-chamber long axis view (Box B) balanced steady state free precession images showing diffuse myocardial hypertrophy and reduced longitudinal systolic function, mostly at basal and mid segments. Native T1 mapping shows diffuse marked increase of T1 values, with granular appearance (Boxes C and D). Myocardial oedema detected by T2 mapping (Boxes E and F), at basal segments. Late gadolinium enhancement (LGE) images show abnormal gadolinium kinetics, coupled with almost transmural enhancement at basal septum, and diffuse subendocardial enhancement at other segments (Boxes G and H). Diffuse severe ECV expansion is noted, up to more than 80% at septal level (Boxes I and J).

Figure 5

Cardiac Sarcoidosis. Basal short axis view (Box A) and 4-chamber long axis view (Box B) balanced steady state free precession images showing asymmetric myocardial hypertrophy at septum. Focal increase of T1 values at native T1 mapping images at septum and inferior wall (Boxes C and D). Myocardial oedema detected by T2-wieghted images (Box E) and T2 mapping (Box F), mostly at septum and inferior wall. LGE images show transmural enhancement at septal level, and subepicardial enhancement at inferior wall (Boxes G and H). Focal increase of ECV, matching native T1 mapping and LGE images abnormalities (Boxes I and J).

Figure 6

Fabry cardiomyopathy. Basal short axis (top row) and 3-chamber long axis (bottom row) cardiovascular magnetic resonance (CMR) images of a patient with Anderson–Fabry cardiomyopathy showing mild ventricular hypertrophy (Boxes A and B), low global native T1 values with normalized values at the basal inferolateral wall (Boxes C and D), mid-wall late gadolinium enhancement at the basal inferolateral wall (Boxes E and F), with matching high ECV values at basal inferolateral wall (Boxes G and H).

Figure 7

Etiological hypotheses of newly diagnosed myocardial hypertrophy according to mapping abnormalities. When informative data provided by mapping sequences are integrated to those delivered by clinical history, cardiovascular magnetic resonance (CMR) morphological analysis and, when possible, LGE assessment, differential diagnoses of Hypertrophic Cardiomyopathy, Cardiac Amyloidosis, Fabry disease or inflammatory cardiomyopathy such as Cardiac Sarcoidosis could be established with the highest degree of confidence.