Moderate Ischemic Mitral Regurgitation After Posterolateral Myocardial Infarction in Sheep Alters Left Ventricular Shear but Not Normal Strain in the Infarct and Infarct Borderzone

et al. 2019

Preprint

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Purpose: MitraClip is the sole percutaneous device approved for functional mitral regurgitation (MR; FMR) but MR recurs in over one third of patients. As device-induced mechanical effects are a potential cause for MR recurrence, we tested the hypothesis that MitraClip increases leaflet stress and procedure-related strain in sub-valvular left ventricular (LV) myocardium in FMR associated with coronary disease (FMR-CAD). Methods:Simulations were performed using finite element models of the LV + mitral valve based on MRI of 5 sheep with FMR-CAD. Models were modified to have a 20% increase in LV volume (↑LV_VOLUME) and MitraClip was simulated with contracting beam elements (virtual sutures) placed between nodes in the center edge of the anterior (AL) and posterior (PL) mitral leaflets. Effects of MitraClip on leaflet stress in the peri-MitraClip region of AL and PL, septo-lateral annular diameter (SLAD), and procedurerelated radial strain (Err) in the sub-valvular myocardium were calculated.Results: MitraClip increased peri-MitraClip leaflet stress at end-diastole (ED) by 22.3±7.1 kPa (p<0.0001) in AL and 14.8±1.2 kPa (p<0.0001) in PL. MitraClip decreased SLAD by 6.1±2.2 mm (p<0.0001) and increased Err in the sub-valvular lateral LV myocardium at ED by 0.09±0.04 (p<0.0001)). Furthermore, MitraClip in ↑LV_VOLUME was associated with persistent effects at ED but also at end-systole where peri-MitraClip leaflet stress was increased in AL by 31.9±14.4 kPa (p=0.0268) and in PL by 22.5±23.7 kPa (p=0.0101). Conclusions:MitraClip for FMR-CAD increases mitral leaflet stress and radial strain in LV sub-valvular myocardium. Mechanical effects of MitraClip are augmented by LV enlargement. Abstract Word Count:249 AL P2 Ao MClip A. B. C.

Section: Methodsmentioning

confidence: 99%

Mechanical effects of MitraClip on leaflet stress and myocardial strain in functional mitral regurgitation – A finite element modeling study

Zhang

Wang

et al. 2019

Preprint

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“…[13,14] The LV myocardium was divided into MI, borderzone, and remote regions, where the borderzone-remote boundary was defined as the point where wall thickness is 70% of maximum LV wall thickness. The average area of the infarct zone as a percent of total LV area was 21%, with a range of 14–26%; the method for calculating this area has been previously described [32]. To model the mitral apparatus, the leaflets were constructed from B-spline curves approximating the leaflet contours, edge chords were attached to the free borders of each leaflet, and strut chords attached to the mid-section of each leaflet, as described by Wenk.…”

Section: Methodsmentioning

confidence: 99%

“…recently showed that moderate IMR increases strain in the radial-circumferential direction and may be a trigger for adverse remodeling in the infarct borderzone. [32] Despite a large body of evidence suggesting that strain stimulates adverse remodeling, the contributions of various strain components are not known. As such, the longitudinal strain increase identified in this study may not be the exclusive strain component leading to repair failure.…”

Section: Commentmentioning

confidence: 99%

Undersized Mitral Annuloplasty Increases Strain in the Proximal Lateral Left Ventricular Wall

Pantoja

The Annals of Thoracic Surgery

Jensen

et al. 2017

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Background Recurrence of mitral regurgitation (MR) after undersized mitral annuloplasty (MA) for ischemic MR is as high as 60%, with recurrence rate likely due to continued dilation of the left ventricle (LV). To better understand the causes of recurrent MR, we studied the effect of undersized MA on strain in the LV wall. We hypothesize that the acute change in ventricular shape induced by MA will cause increased strain in regions nearest the mitral valve. Methods Finite element models were previously reported, based on cardiac magnetic resonance images of five sheep with mild to moderate ischemic MR. A 24 mm saddle shaped rigid annuloplasty ring was modeled and used to simulate virtual MA. Longitudinal and myofiber strains were calculated at end-diastole and end-systole, with pre-operative early diastolic geometry as the reference state. Results Undersized MA significantly increased longitudinal strain at end-diastole in the lateral LV wall. The effect was greatest in the proximal-lateral endocardial surface, where longitudinal strain after MA was approximately triple the pre-operative strain (11.17% ± 2.15% vs. 3.45% ± 0.92%, p=0.0057). In contrast, post-operative end-diastolic fiber strain decreased in this same region (2.53% ± 2.14% vs. 7.72% ± 1.79%, p=0.0060). There were no significant changes in either strain type at end-systole. Conclusions Undersized MA increased longitudinal strain in the proximal lateral LV wall at end-diastole. This procedure-related strain at the proximal-lateral LV wall may foster continued LV enlargement and subsequent recurrence of mitral regurgitation.

“…First, in areas of healthy tissue bordering regions of infarct (the MI borderzone), high mechanical load and abnormal contractile protein function decrease the contractility of viable myocardium [26, 27]. Second, after prolonged ischemia, hibernating myocardium may be thinned and hypo- or akinetic, but undergo reverse remodeling and recovery of normal contractile function after revascularization [28].…”

Section: Commentmentioning

confidence: 99%

Ischemic Mitral Regurgitation: Abnormal Strain Overestimates Nonviable Myocardium

The Annals of Thoracic Surgery

Zhang

Tartibi

et al. 2018

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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.