Assessment of infarct-specific cardiac motion dysfunction using modeling and multimodal magnetic resonance merging.

PURPOSE: To propose a cardiac motion tracking model that evaluates wall motion abnormality in postmyocardial infarction patients. Correlation between the motion parameter of the model and left ventricle (LV) function was also determined. MATERIALS AND METHODS: Twelve male patients with post-ST elevation myocardial infarction (post-STEMI) and 10 healthy controls of the same gender were recruited to undergo cardiac magnetic resonance imaging (MRI) using a 1.5T scanner. Using an infarct-specific LV division approach, the late gadolinium enhancement (LGE) MRI images were used to divide the LV on the tagged MRI images into infarct, adjacent, and remote sectors. Motion tracking was performed using the infarct-specific two-parameter empirical deformable model (TPEDM). The match quality was defined as the position error computed using root-mean-square (RMS) distance between the estimated and expert-verified tag intersections. The position errors were compared with the ones from our previously published fixed-sector TPEDM. Cine MRI images were used to calculate regional ejection fraction (REF). Correlation between the end-systolic contraction parameter (αES ) with REF was determined. RESULTS: The position errors in the proposed model were significantly lower than the fixed-sector model (P < 0.01). The median position errors were 0.82 mm versus 1.23 mm. The αES correlates significantly with REF (r = 0.91, P < 0.01). CONCLUSION: The infarct-specific TPEDM combines the morphological and functional information from LGE and tagged MRI images. It was shown to outperform the fixed-sector model in assessing regional LV dysfunction. The significant correlation between αES and REF added prognostic value because it indicated an impairment of cardiac function with the increase of infarct transmurality. LEVEL OF EVIDENCE: 3 J. Magn. Reson. Imaging 2017;45:525-534.

Regional assessment of LV wall in infarcted heart using tagged MRI and cardiac modelling.

A segmental two-parameter empirical deformable model is proposed for evaluating regional motion abnormality of the left ventricle. Short-axis tagged MRI scans were acquired from 10 healthy subjects and 10 postinfarct patients. Two motion parameters, contraction and rotation, were quantified for each cardiac segment by fitting the proposed model using a non-rigid registration algorithm. The accuracy in motion estimation was compared to a global model approach. Motion parameters extracted from patients were correlated to infarct transmurality assessed with delayed-contrast-enhanced MRI. The proposed segmental model allows markedly improved accuracy in regional motion analysis as compared to the global model for both subject groups (1.22-1.40 mm versus 2.31-2.55 mm error). By end-systole, all healthy segments experienced radial displacement by ~25-35% of the epicardial radius, whereas the 3 short-axis planes rotated differently (basal: 3.3°; mid: -1° and apical: -4.6°) to create a twisting motion. While systolic contraction showed clear correspondence to infarct transmurality, rotation was nonspecific to either infarct location or transmurality but could indicate the presence of functional abnormality. Regional contraction and rotation derived using this model could potentially aid in the assessment of severity of regional dysfunction of infarcted myocardium.

Assessment of right pump outflow banding and speed changes on pulmonary hemodynamics during biventricular support with two rotary left ventricular assist devices.

The absence of an effective, easily implantable right ventricular assist device (RVAD) significantly diminishes long-term treatment options for patients with biventricular heart failure. The implantation of a second rotary left ventricular assist device (LVAD) for right heart support is therefore being considered; however, this approach exhibits technical challenges when adapting current devices to produce the lower pressures required of the pulmonary circulation. Hemodynamic adaptation may be achieved by either reducing the rotational speed of the right pump impeller or reducing the diameter of the right outflow cannula by the placement of a restricting band; however, the optimal value and influence of changes to each parameter are not well understood. Hemodynamics were therefore investigated using different banding diameters of the right outflow cannula (3-6.5 mm) and pump speeds (500-4500 rpm), using two identical rotary blood pumps coupled to a pulsatile mock circulation loop. Reducing the speed of the right pump from 4900 rpm (for left ventricle support) to 3500 rpm, or banding the Ø10 mm (area 78.5 mm²) right outflow graft to Ø5.4 mm (22.9 mm²) produced suitable hemodynamics. Pulmonary pressures were most sensitive to banding diameters, especially when RVAD flow exceeded LVAD flow. This occurred between Ø5.3 and Ø6.5 mm (22.05-38.5 mm²) and speeds between 3200 and 4400 rpm, with the flow imbalance potentially leading to pulmonary congestion. Total flow was not affected by banding diameters and speeds below this range, and only increased slightly at higher values. Both right outflow banding or right pump speed reduction were found to be effective techniques to allow a rotary LVAD to be used directly for right heart support. However, the observed sensitivity to diameter and speed indicate that challenges may be presented when setting appropriate values for each patient, and control over these parameters is desirable.