Objectives
Clinical guidelines for asymptomatic patients with chronic MR utilize ejection fraction (EF) to trigger surgical referral. We hypothesize that 1) EF is not sensitive enough to detect the earliest contractile injury in chronic MR and 2) that the injury associated with chronic MR is not global but heterogeneous, occurring regionally and predictably, prior to the onset of global left ventricular (LV) dysfunction.
Methods
Fifteen patients with chronic MR and normal LV EF by echocardiography underwent cardiac MRI with tissue tagging. Point-specific comparisons (at 15,300 LV grid points) of multiple strain parameters to a normal human strain database allowed normalization of patient-specific regional contractile function. Data were mapped over patient-specific 3D geometry, then averaged across six LV regions.
Results
Global LV longitudinal and circumferential myocardial strains were normal for all 15 MR patients when compared to normal controls (p>0.05). Despite preserved global function, the anteroseptum and posteroseptum demonstrated significantly worse contractile function when compared to other regions of the LV (p=0.003 and p=0.035, respectively). Hyper-contractile regions (lateral walls) appeared to compensate (p=0.002) for the reduced septal contractile function thereby masking injury detection by global indices.
Conclusion
The earliest contractile injury seen in MR patients is heterogeneous, and consistently distributed along the LV septum. Compensatory responses include hypercontractility of other regions. These data suggest that rather than relying upon global LV contractile metrics, which do not detect early injury, patients may be better served by undergoing directed surveillance of “sentinel” LV regions (LV septum) with high-resolution metrics of regional contractile function.