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Cardiac magnetic resonance T1 mapping pre and post contrast characterizes the myocardium in orthotopic heart transplantation recipients without active rejection

Background: Transplant rejection is characterized by interstitial inflammatory infiltrate. This inflammatory reaction is followed by both replacement fibrosis and interstitial fibrosis which in the long term can impair diastolic and systolic ventricular (LV) function.Cardiac magnetic resonance (CMR) with gadolinium quantifies replacement fibrosis and compares well with biopsy in the diagnosis of heart transplant rejection. New T1 mapping sequences are proposed for the quantification of interstitial fibrosis.

Methods: We studied 33 heart transplant patients (Tx) (7 Females), mean time from Tx 112±56 mo (range 2–1288) and 12 normals (N), age 48±13 and 40±11 p=0.04. Absence of active rejection was confirmed by EMB. CMR was performed on a 1.5 Tesla scanner (Siemens). Short axis SSFP cine images covering the LV were acquired; image position was used for T1-mapping and late gadolinium enhancement (LGE). MOLLI T1 maps were generated from 5-7 SSFP images with variable inversion preparation time as described by Messroghli (2007) before and after gadobutrol i.v. (0.15 mmol/kg). Region of interest were drawn on 3 short axis (base,mid,apex) average T1 values pre and post contrast administration (msec) were fitted by a non-linear curve. Data are mean±SD

Results: Systolic function was similar in both groups Tx 65±10 vs N 67±5 p=0.69, LV Mass Index was slightly higher in Tx 76±17 vs 66±8 N p=0.16. In Tx pre -contrast T1 was longer 1020±93 vs 957±45 msec p<0.001, whereas post contrast was shorter 406±46 msec vs 455±35 msec p<0.001. In Tx with cytomegalovirus infection (n=17) T1 mean pre-contrast was significantly higher 1043±15 vs 981±46 p=0.018. T1 post-contrast but not pre-contrast was inversely correlated to time interval from Tx y=4925-0.327x; p<0.05. Patients with LVH (n=7) had a significantly higher T1 both pre (p=0.007) and post contrast (p=0.04). LV mass index was directly correlated to T1 pre P=0.05 and inversely correlated to T1 post (p=0.002). Twentythree out of 33 Tx had patchy LGE distribution mainly in the inferior RV insertion, 2 had a previous myocardial infarction and 8 did not show LGE.

Conclusions: Patient transplanted with no active rejection show a significant increase of interstitial fibrosis which builds up over time. CMR beside anatomo-functional parameters combining LGE and T1 mapping can provide a useful non invasive characterization of the collagen deposition in transplanted hearts and allow a better insight into the progression of restrictive physiology