I.CMR technique and classic findings
A. Classic CMR FD semiology
- LV hypertrophy and increased cardiac mass
- During the course of FD, LVH is more frequent in women than in men (7).
- CMR is the gold standard for LVH quantification, LV ejection fraction (LVEF) measurement and thus cardiac mass assessment.
LVH during FD is usually concentric but may be asymmetric.
Steady-state free precession (SSFP) dynamic sequences display the heart movement during the cardiac cycle in the different heart plans':
- 4 chambers long-axis view
- 2 chambers short-axis view
- 3 chambers long-axis view
-Measure the LVH in 2 chambers short-axis during end-diastole
-Cut-offs for LVH:
- LV septal wall thickness >9mm for women and >10mm in men
- LV mass/BSA:>95g/m2 for women and >115g/m2 for men
-hypertrophic papillary muscle accounts for 20% of the total LV mass. In healthy patients, it accounts only for 8% (8).
During the ultimate stages of FD restrictive heart failure, sets-in and LVEF drops.
2.Late gadolinium enhancement (LGE)
- LGE images are inversion recovery sequences (IR) acquired 10 to 20 minutes after gadolinium administration (0,1 to 0,2mmol/Kg). The inversion time (TI) is chosen to null the healthy or normal myocardium.
- A recent study by Nordin et al (9) suggested that LGE in FD may depict myocardial fibrosis and inflammation, consequently the new concept of inflammatory cardiomyopathy in FD.
The classical LGE pattern during FD is mid-wall in the inferior-lateral segment (50%) (10).LGE commonly spears the septum wall (10).
- There is no clear explanation yet for this LGE pattern during FD (11).
B.The use of mapping in the early FD stages
-CMR is a useful diagnostic tool in FD because of :
- high contrast tissue images
- identify globotriaosylsphingosine myocardium accumulation (from decreased T1 relaxation time)
-T1 mapping is the perfect tool to identify fat accumulation: fat=T1 shortening. There is not yet a clear explanation.
Reduced T1 may be a finding in FD cardiomyopathy and even in pre-hypertrophic FD.
- Reduced T1
- T1 mapping is a relatively new MRI technique enabling the measurement of myocardium T1 signal, displayed after processing as a coloured map.
-Reduced T1 mapping has to be interpreted cautiously. Cardiac damage during FD is a progressive process:
- globotriaosylsphingosine myocardium accumulation
- inflammation
- LVH+fibrosis
- T1 mapping may be normal during FD when fibrosis and globotriaosylsphingosine accumulation coexist: pseudo-normalization.
A recent study showed that T1 in FD patients decreased with globotriaosylsphingosine accumulation and also age (12).
- One commonly used technique for T1 mapping is Modified Look-Locker Inversion Recovery (MOLLI) (13). Its advantages are:
- minimize kinetic artefacts
- shortens the sequence time
2. Increased T2 mapping
- T2 is useful during the early stages of FD. It assesses myocardial inflammation, that is known to be more common in the lateral-inferior wall.
T1 and T2 mapping must be performed routinely for diagnosis and monitoring of FD.
II. Differential diagnosis of LVH
-LVH is a key sign during FD.
-LVH can be stabilized with treatment in FD.
-Concentric LVH:
- Hypertensive cardiomyopathy
- hypertrophic cardiomyopathy (HCM)
- Aortic stenosis
- Cardiac amyloidosis
III.Differential diagnosis of reduced T1
1. Pathological
- Intracardiac lipoma (tuberous sclerosis)
- Hemochromatosis
- Fat transformation of myocardial infarction
- Arrhythmogenic right ventricular dysplasia
2.Physiological
- Age: myocardial T1 decreases with age.
- Sexe: myocardial T1 is higher in younger women
- Athlete's heart: myocardial T1 is lower in athlete