Differential response of the left and right ventricles to pressure overload revealed with diffusion tensor MRI tractography of the heart in vivo
Journal of Cardiovascular Magnetic Resonance volume 17, Article number: O3 (2015)
The left ventricle (LV) can tolerate pressure overload from hypertension or aortic stenosis for many years. In contrast, the right ventricle (RV) adapts to pulmonary hypertension only if this develops at birth, while in the adult heart severe and often fatal RV failure develops. We hypothesized that i) these divergent responses could be due to differences in myofiber architecture in the free walls of the LV and RV and that ii) adaptive changes to pressure overload would be seen in the LV but not the RV.
Mice subjected to aortic banding (AB), pulmonary artery banding (PB), and healthy controls, (n=6 per group), were imaged in vivo, ensuring that myofiber architecture was imaged under true loading conditions. Diffusion Tensor MRI (DTI) tractography was performed at 9.4T with a 1500 mT/m gradient, a motion-compensated Stejskal-Tanner sequence, 24 gradient directions, b-value of 500 s/mm2, and an isotropic resolution of 156 μm3 . Fiber tracts were color-coded by their helix angle (HA) .
In healthy mice, myofiber organization in the LV was comprised of circumferential myofibers in the midmyocardium, myofibers with a positive HA in the subendocardium, and myofibers with a negative HA in the subepicardium. In contrast, very few circumferential myofibers were present in the RV free wall, which approximated a bilayer. This is illustrated in Figure 1, where fiber architecture in a normal mouse heart is depicted using the supertoroidal model of the diffusion tensor. Marked hypertrophy of the LV/RV myocardium was seen in all banded mice. The LV in all AB mice was hyperdynamic, while in the PB mice the RV was dilated with septal flattening. Fiber architecture in the lateral LV wall of the AB hearts showed a marked rightward shift, transforming myofibers in the subepicardium into a more circumferential orientation (Figure 2A-D). In contrast, the fibers in the RV free wall of the PB mice remained oriented in a near-bilayer with limited change in orientation and few circumferential myofibers (Figure 2E-H).
The LV contains a large number of circumferential myofibers at baseline and undergoes a rightward shift in fiber architecture in response to pressure overload. In contrast, the RV contains few circumferential myofibers, and its architecture remains largely unchanged in response to increased load. These differences may account for the inability of the RV to tolerate acquired pulmonary hypertension in adulthood.
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Mekkaoui, C., Chen, I.Y., Chen, H.H. et al. Differential response of the left and right ventricles to pressure overload revealed with diffusion tensor MRI tractography of the heart in vivo. J Cardiovasc Magn Reson 17 (Suppl 1), O3 (2015). https://doi.org/10.1186/1532-429X-17-S1-O3