Ischemic Mitral Regurgitation: Abnormal Strain Overestimates Nonviable Myocardium

Abstract

Objective Therapy for moderate ischemic mitral regurgitation (IMR) remains unclear. Determination of myocardial viability, a necessary pre-requisite for an improvement in regional contractility, is a likely key factor in determining response to revascularization alone. Myocardial strain has been proposed as a viability measure but has not been compared to late gadolinium enhancement (LGE) cardiac (c)MRI. We hypothesized that abnormal strain overestimates non-viable LV segments measured using LGE and that ischemia and mechanical tethering by adjacent transmural myocardial infarction (TMI) also decreases strain in viable segments. Methods Sixteen patients with ≥ mild IMR and seven healthy volunteers underwent cMRI with non-invasive tags (CSPAMM), LGE and stress perfusion. CSPAMM images were post-processed with HARP and circumferential and longitudinal strains were calculated. Viability was defined as the absence of TMI on LGE (hyperenhancement >50% of wall thickness). The borderzone was defined as any segment bordering TMI. Abnormal strain thresholds (±1–2.5 SD from normal mean) were compared to TMI, ischemia and borderzone. Results 7.4% of LV segments had TMI on LGE while >14.5% of LV segments were non-viable by strain thresholds (p<0.005). In viable segments, ischemia impaired longitudinal strain (least perfused 1/3 of LV segments −.18±.08 vs. most perfused −.22±.1 p=01) and circumferential strain (−.12±.1 vs−.16±.08 p<0.05). In addition, infarct proximity impaired longitudinal strain (−.16±.11 borderzone vs −.18±.09 remote p=.05). Conclusions Impaired LV strain overestimates non-viable myocardium when compared to TMI on LGE. Ischemia and infarct proximity also decrease strain in viable segments.

A Novel MRI-Based Finite Element Modeling Method for Calculation of Myocardial Ischemia Effect in Patients With Functional Mitral Regurgitation

“…CMR was performed with a 3.0 Tesla MRI scanner (General Electric, Waukesha, WI, United States) (Morgan et al, 2018) both before and 3 months after PCI. CMR included 4 pulse sequences.…”

“…The HARmonic Phase (HARP) method developed by Osman et al (2000) was implemented. Implementation in MeVisLab has been previously reported (Morgan et al, 2018). Please note that all the strain presented in this study is LV end-systolic strain.…”

“…The relationship between MI fibrosis, ischemia and function and recovery of function after REVASC in chronically ischemic hibernating myocardium in which myocardial metabolism and contractile function are down-regulated (Wijns et al, 1998) is complex (Canty and Suzuki, 2012). In that regard, we recently measured MI fibrosis, stress perfusion and regional strain with CMR in patients with FMR associated with CAD (Morgan et al, 2018). Briefly, CSPAMM-CMR measured circumferential and longitudinal strain were modestly reduced in sectors without MI or ischemia when compared to volunteers and then decreased in an approximately linearly fashion as the amount of MI fibrosis and ischemia increased (Morgan et al, 2018).…”

“…In that regard, we recently measured MI fibrosis, stress perfusion and regional strain with CMR in patients with FMR associated with CAD (Morgan et al, 2018). Briefly, CSPAMM-CMR measured circumferential and longitudinal strain were modestly reduced in sectors without MI or ischemia when compared to volunteers and then decreased in an approximately linearly fashion as the amount of MI fibrosis and ischemia increased (Morgan et al, 2018). In addition, chronically ischemic hibernating myocardium can partially recover function after surgical or percutaneous REVASC (Kim et al, 2000;Hocum Stone et al, 2017).…”

Fully automatic segmentation of 4D MRI for cardiac functional measurements

“…In this study, the segmentation accuracy was assessed using manual segmentation as the ground-truth. The segmented geometries can be used in biomechanical simulation 66,68–71 . Cardiac functional measurements, including chamber volumes, stroke volume, ejection fraction, cardiac output and myocardial wall thickness, were calculated based on the generated segmentations.…”