Diagnostic and prognostic value of MRI in cardiac amyloidosis

Cardiac amyloidosis (CAL) might present as unexplained heart failure symptoms.ECG and advanced echocardiographic techniques such as strain imaging can be used, although the diagnosis should be confirmed by endomyocardial biopsy and histology. Cardiac magnetic resonance imaging (CMR) provide valuable information about amyloid distribution in the heart. Besides increased myocardial mass, atrial structure, function of the atrial and ventricles function and other features of cardiac amyloidosis / restrictive cardiomyopathy, CMR imaging relies on tissue characterization: late gadolinium enhancement (LGE) to identify myocardial damage scar and fibrosis, abnormally prolonged T1 times (pre or post contrast) and an expansion of the extracellular volume. Although these are sensitive to diagnose CAL, they are not specific and pathognomonic for this diagnosis and cannot exclusively obviate the need for a definitive histological diagnosis. 1) Characteristic LGE is the earliest feature of cardiac involvement compared to increased wall. It appears as a ‘zebra pattern’ consisting of entire subendocardial (Ed) and subepicardial (Ep) circumference enhancement(DCE) and a diffuse homogeneous myocardial DCE sometimes with intramural focal regions of higher DCE areas. Although Ed circumferential- DCE has high specificity, the focal pattern cannot be considered specific Occurrence rate of LV LGE in documented CAL based on biopsy is universal. Right ventricular LGE present in all mutant ransthyretin and in 72% of AL patients. Diffuse LGE in the atrial wall and AV valves may be a characteristic feature of CAL. 2) Native T1 mapping (non-contrast) detects CAL even sooner than LGE,indicating diffuse global hyperenhancement and is characteristic of CAL. It can track amyloid deposition. It may be particularly helpful in patients with renal dysfunction.Two min post-gadolinium intramyocardial T1 difference between the Ed and EP predict mortality; particularly, the lower the difference, the worse the prognosis.3) Information about the size of the extracellular space (myocardial interstitial disease) as expansion of ECV based on contrast T1 mapping is demonstrated even in myocardial segments without T1 LGE, suggesting incremental diagnostic value of CAL. It may make an early diagnosis even before overt left ventricular LGE and correlated directly with LV mass, TDI S wave, brain natriuretic peptide (BNP) and troponin levels. 4) T2 W images appears as hypointense areas in CAL. The lower T2 ratio the shorter survival.