Page 161 - Assessing right ventricular function and the pulmonary circulation in pulmonary hypertension Onno Anthonius Spruijt

most likely reflect locally increased focal fibrosis. However, McCann et al. [4] also described edema at the interventricular insertion regions, which also can contribute to an increase in native T1-values [17]. It is suggested that predilection for fibrosis to develop at the interventricular insertion regions is caused by mechanical stress due to the bowing of the interventricular septum into the LV [2] which is often seen in precapillary PH patients. However, late enhancement at the interventricular insertion regions is also described in patients with hypertrophic cardiomyopathy [3, 28] indicating that this phenomenon is not specific for a pressure overloaded RV.
Increased native T1-values of the interventricular insertion regions were moderately, but significantly related to disease severity. This is in line with previous LGE studies showing comparable correlations between the late enhancement of the interventricular insertion regions and RVEF, RV volumes and mPAP [2, 4, 5]. Furthermore, similar correlations were found between native T1-values of the interventricular insertion regions and measures of disease severity [27]. The correlations between native T1-values of the interventricular insertion regions and RV functional measures and NT-proBNP is probably related to the associated increase in RV wall tension. It has been shown that RV wall tension is associated with the delay in time to peak shortening of the RV, causing the leftward shift of the interventricular septum during late RV systole [29]. The right-to-leftward shifting of the interventricular septum probably increases the mechanical shear stress on the interventricular insertion regions.
In a recent study, native T1-values were assessed in the RV of healthy subjects and the authors found increased native T1-values in the RV free wall compared to the LV free wall and suggested that this finding could be due to a higher collagen content of the RV free wall [30]. In the PH patients in our study, native T1-values of the RV free wall were not significantly higher than those of the LV free wall and were in the same range as the native T1-values of the RV free wall in healthy subjects [30]. We could not assess the native T1-values of the RV wall in our control subjects because the wall was too thin. Kawel-Boehm et al. [30] could assess native T1-values of the RV free wall of healthy subjects because they performed native T1-mapping at the end-systolic phase.
Native T1-values of the LV free wall were not significantly different between PH patients and control subjects and were in the same range as native T1-values of the LV free wall conducted in a large cohort of healthy subjects of the same age [11]. This is in line with LGE studies showing no late enhancement in the myocardium of precapillary PH patients apart from the interventricular insertion regions [2-5].
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