Regional myocardial work characterisation in the remodelled left ventricle

Abstract

Left ventricular (LV) remodelling is observed in pathologies with regional inhomogeneous myocardial function and workload such as ischemic disease or conduction delays. Cardiac resynchronization therapy (CRT) with bi-ventricular pacemakers has become an established treatment when conduction delays (e.g. left bundle branch block, LBBB) are present. However, more than 30% of the patients fail to respond to this expensive and invasive therapy. Assessment of the asynchronous LV function by non-invasive imaging is one promising approach for better patient selection. However, previously proposed echocardiographic selection criteria have failed to demonstrate added value in multicentre trials for CRT response prediction. More recent approaches using myocardial strain deformation imaging have shown much more promising results. While deformation imaging provides excellent information on regional myocardial function, it is still depends on the regional wall stress induced by the loading of the heart. In an effort to integrate the effect of the wall stress - which is not measurable in vivo - it was substituted with the LV pressure from pressure-volume loops. Such combination of regional strain deformation and LV pressure has been suggested as an index of regional myocardial workload, and has shown to be of strong predictive value in the response to CRT. However, as the pressure is considered uniform in the entire LV, it also assumes an uniform wall stress distribution. This assumption does not hold true for remodelled hearts with conduction delays, where the septal and lateral wall are remodelled and move in a dyssynchronous manner. Therefore, the wall stress (or LV pressure) should be corrected for a given local wall thickness and radius/curvature, to truly reflect the regional myocardial workload. 18F-fluorodeoxyglucose (FDG), a nuclear radiotracer measured by positron emission tomography (PET), is an established method to investigate regional metabolism, including the myocardium. Regional differences in myocardial FDG-uptake in patients selected for CRT have been observed in the past, together with a relation to pressure-strain loops. The uptake of FDG could in such also be a promising marker of regional myocardial workload. However, the inhomogeneous regional wall thickness in remodelled hearts with conduction delays compromises exact quantification of FDG-uptake. The low spatial resolution of PET does not allow to distinguish a thin myocardial wall with normal metabolism from a thick wall with reduced metabolism. Therefore, our group developed a new method to enhance the spatial resolution of PET by applying motion correction for both the breathing and beating of the heart (i.e. "gating"). Additionally, the metabolic data are registered with exact morphological information from either magnetic resonance imaging (MRI) or computer tomography (CT). This should allow us to obtain correct estimates of regional myocardial energy consumption and, with this, insight in the true distribution of regional myocardial metabolism and workload. Because the complex underlying inhomogeneities in myocardial function, workload and metabolism - as seen in LV remodelling - remain poorly understood, new ways to better characterise the regional workload and metabolism would allow a better understanding of their effect on LV remodelling.status: publishe