A priori model independent inverse potential mapping: the impact of electrode positioning

__Introduction:__ In inverse potential mapping, local epicardial potentials are computed from recorded body surface potentials (BSP). When BSP are recorded with only a limited number of electrodes, in general biophysical a priori models are applied to facilitate the inverse computation. This study investigated the possibility of deriving epicardial potential information using only 62 torso electrodes in the absence of an a priori model. __Methods:__ Computer simulations were used to determine the optimal in vivo positioning of 62 torso electrodes. Subsequently, three different electrode configurations, i.e., surrounding the thorax, concentrated precordial (30 mm inter-electrode distance) and super-concentrated precordial (20 mm inter-electrode distance) were used to record BSP from three healthy volunteers. Magnetic resonance imaging (MRI) was performed to register the electrode positions with respect to the anatomy of the patient. Epicardial potentials were inversely computed from the recorded BSP. In order to determine the reconstruction quality, the super-concentrated electrode configuration was applied in four patients with an implanted MRI-conditional pacemaker system. The distance between the position of the ventricular lead tip on MRI and the inversely reconstructed pacing site was determined. __Results:__ The epicardial potential distribution reconstructed using the super-concentrated electrode configuration demonstrated the highest correlation (R = 0.98; p < 0.01) with the original epicardial source model. A mean localization error of 5.3 mm was found in the pacemaker patients. __Conclusion:__ This study demonstrated the feasibility of deriving detailed anterior epicardial potential information using only 62 torso electrodes without the use of an a priori model

Integrated whole-heart computational workflow for inverse potential mapping and personalized simulations

Background: Integration of whole-heart activation simulations and inverse potential mapping (IPM) could benefit the guidance and planning of electrophysiological procedures. Routine clinical application requires a fast and adaptable workflow. These requirements limit clinical translation of existing simulation models. This study proposes a comprehensive finite element model (FEM) based whole-heart computational workflow suitable for IPM and simulations. Methods: Three volunteers and eight patients with premature ventricular contractions underwent body surface potential (BSP) acquisition followed by a cardiac MRI (CMR) scan. The cardiac volumes were segmented from the CMR images using custom written software. The feasibility to integrate tissue-characteristics was assessed by generating meshes with virtual edema and scar. Isochronal activation maps were constructed by identifying the fastest route through the cardiac volume using the Möller-Trumbore and Floyd-Warshall algorithms. IPM's were reconstructed from the BSP's. Results: Whole-heart computational meshes were generated within seconds. The first point of atrial activation on IPM was located near the crista terminalis of the superior vena cave into the right atrium. The IPM demonstrated the ventricular epicardial breakthrough at the attachment of the moderator band with the right ventricular free wall. Simulations of sinus rhythm were successfully performed. The conduction through the virtual edema and scar meshes demonstrated delayed activation or a complete conductional block respectively. Conclusion: The proposed FEM based whole-heart computational workflow offers an integrated platform for cardiac electrical assessment using simulations and IPM. This workflow can incorporate patient-specific electrical parameters, perform whole-heart cardiac activation simulations and accurately reconstruct cardiac activation sequences from BSP's

Non-invasive focus localization, right ventricular epicardial potential mapping in patients with an MRI-conditional pacemaker system ‐ a pilot study

Abstract Background With the advent of magnetic resonance imaging (MRI) conditional pacemaker systems, the possibility of performing MRI in pacemaker patients has been introduced. Besides for the detailed evaluation of atrial and ventricular volumes and function, MRI can be used in combination with body surface potential mapping (BSPM) in a non-invasive inverse potential mapping (IPM) strategy. In non-invasive IPM, epicardial potentials are reconstructed from recorded body surface potentials (BSP). In order to investigate whether an IPM method with a limited number of electrodes could be used for the purpose of non-invasive focus localization, it was applied in patients with implanted pacing devices. Ventricular paced beats were used to simulate ventricular ectopic foci. Methods Ten patients with an MRI-conditional pacemaker system and a structurally normal heart were studied. Patientspecific 3D thorax volume models were reconstructed from the MRI images. BSP were recorded during ventricular pacing. Epicardial potentials were inversely calculated from the BSP. The site of epicardial breakthrough was compared to the position of the ventricular lead tip on MRI and the distance between these points was determined. Results For all patients, the site of earliest epicardial depolarization could be identified. When the tip of the pacing lead was implanted in vicinity to the epicardium, i.e. right ventricular (RV) apex or RV outflow tract, the distance between lead tip position and epicardial breakthrough was 6.0±1.9 mm. Conclusions In conclusion, the combined MRI and IPM method is clinically applicable and can identify sites of earliest depolarization with a clinically useful accuracy

Infantile and juvenile presentations of Alexander's disease: a report of two cases

peer reviewedWe describe 2 new cases of Alexander's disease, the first to be reported in Belgium. The first patient, a 4-year-old girl, presented with progressive megalencephaly, mental retardation, spastic tetraparesis, ataxia and epilepsy: post-mortem examination showed widespread myelin loss with Rosenthal fibers (RFs) accumulation throughout the neuraxis. She was the third of heterozygotic twins, the 2 others having developed normally and being alive at age 5 years. The second patient developed at age 10 years and over a decade spastic paraparesis, palatal myoclonus, nystagmus, thoracic hyperkyphosis and thoraco-lumbar scoliosis with radiological findings of bilateral anterior leukoencephalopathy. Brain stereotactic biopsy at age 16 years demonstrated numerous RFs. With these 2 cases, we review the literature on the various clinico-pathological conditions reported as Alexander's disease. We discuss the nosology of this entity and the pathogeny of RFs formation and dysmyelination. Clues to the diagnosis of this encephalopathy in the living patient are briefly described

Presence of bone marrow edema and structural lesions on magnetic resonance imaging of the sacroiliac joints in young military recruits before and after 6 weeks of intensive physical training

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Effect of mechanical stress on magnetic resonance imaging of the sacroiliac joints : assessment of military recruits by magnetic resonance imaging study

To assess the baseline condition of the SI joints (SIJs) in healthy individuals without symptoms of back pain and to study the effect of mechanical stress caused by intense physical training on MRI of the SIJs. Twenty-two military recruits underwent an MRI of the SIJs before and after 6 weeks of intense standardized physical training. Bone marrow oedema and structural lesions were scored based on the Spondyloarthritis Research Consortium of Canada (SPARCC) method, by three trained readers blinded for time sequence and clinical findings. Additionally, fulfilment of the Assessment of SpondyloArthritis international Society (ASAS) definition of a positive MRI was evaluated. At baseline, 9/22 recruits (40.9%) already presented a SPARCC score a (c) 3/41; this number increased to 11/22 (50.0%) at week 6 (P = 0.625). In these patients, the mean (SD) SPARCC score was 2.4 (0.4) at baseline, compared to 3.7 (1.3) at week 6. Overall, the mean (SD) change in SPARCC score over time in all 22 patients was 0.9 (0.6) (P = 0.109). A positive MRI according to the ASAS definition was present in 5/22 recruits (22.7%) at baseline, which increased to 8/22 (36.4%) at follow-up (P = 0.375). Structural lesions were present in 6/22 subjects (27.3%), both at baseline and after 6 weeks of training. A substantial proportion of healthy active individuals without any symptoms of back pain displayed bone marrow oedema lesions on MRI at baseline. However, MRI lesions did not increase significantly after 6 weeks of intensive physical training. Our study underscores the necessity to interpret MRI findings of the SIJs in the appropriate clinical context, even in a young active population