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Integration of cardiac magnetic resonance imaging with three-dimensional electroanatomic mapping to guide left ventricular catheter manipulation

Feasibility in a porcine model of healed myocardial infarction

Vivek Y. Reddy, MD^*,*, Zachary J. Malchano^*, Godtfred Holmvang, MD, Ehud J. Schmidt, PhD, Andre d'Avila, MD^*, Christopher Houghtaling, BS, MS^*, Raymond C. Chan, PhD and Jeremy N. Ruskin, MD^*

^* Cardiac Arrhythmia Service, Massachusetts General Hospital-Harvard Medical School, Boston, Massachusetts
Cardiac MRI Unit, Massachusetts General Hospital-Harvard Medical School, Boston, Massachusetts
Radiology Department, Massachusetts General Hospital-Harvard Medical School, Boston, Massachusetts
G.E. Medical Systems, Waukesha, Wisconsin

View larger version (54K): [in a new window]   Figure 1 In vitro left ventricular (LV) phantom experiments. After filling a hollow plastic model of the heart (A) with a dilute solution of gadolinium, magnetic resonance imaging (MRI) scans were performed. The aorta and LV were manually segmented to generate a three-dimensional (3D) surface reconstruction (B). (C) After electroanatomic mapping of this phantom, the locations of the endoluminal aortic (blue points) and endocavitary LV (white points) points were registered with the 3D MRI. Strategies to register these MRI and magnetic electroanatomical mapping (MEAM) datasets were then evaluated. (D) Image registration was based solely upon registration of the MEAM LV points with the MRI-based LV surface. After a coordinate transformation, each MEAM LV point was sequentially incorporated into the registration process (horizontal axis). The level of accuracy of the registration process (vertical axis) was defined as the mean distance of either: 1) the complete MEAM LV point dataset to the MRI-based LV surface (red lines), or 2) the complete MEAM aorta point dataset to the MRI-based aorta surface (blue lines). Five simulations were performed with each of three separate dataset acquisitions; each line represents an average of each set of five simulations. This reveals that the MEAM LV point to MRI surface distance (red lines) can be minimized to 1 mm error, after only 30 points. However, the high level of inaccuracy in the MEAM aorta point to MRI surface distance (blue lines) demonstrates that the registration was simply a local minimal solution. Videlicet, in the registered image (right), the LV points appear to be well-aligned, but the misalignment of the aorta points indicates that this is an inaccurate solution—apparently as a result of rotation about the LV long axis. (E) Image integration was based upon first registering all of the MEAM aorta points with the MRI surface, followed by sequential incorporation of each MEAM LV point into the registrations process (horizontal axis). The level of accuracy of the registration process (vertical axis) was again defined by the mean distance of the complete MEAM LV point dataset to the MRI-based LV surface (red lines). The results show that after first registering the aorta, the MEAM LV point to MRI surface distance (red lines) can be minimized to 1 mm error after incorporating the first three LV points into the registration process.

View larger version (111K): [in a new window]   Figure 2 In vivo iron oxide injection experiments. (A) As shown in this procedure flow map, a solution of iron oxide particles and tissue dye (either methylene blue or India ink) was injected into the myocardium of normal animals at two to three discrete LV locations (left). Because the iron oxide particles are visible to MRI (middle), these injections served as "targets" (shown by an arrow in B) to test the registration strategy. The animals underwent MRI, and manual segmentation was performed to delineate the endoluminal surface of the aorta, the endocardial border of the LV, and the locations of the iron oxide injections (shown in C; each group of three blue dots represents an injection site). During the subsequent electroanatomic mapping procedure, these 3D datasets were registered with the MEAM system. Because the iron oxide injections do not leave any electrophysiologic signature, the locations of the ablation lesions were entirely based upon the registered MR images.

View larger version (45K): [in a new window]   Figure 3 Accuracy of registration: in vivo evaluation. Datasets using the normal animals were evaluated. The image integration was performed based upon either (A) sequential registration of the MEAM LV points with the MRI-based LV surface, or (B) registering the MEAM aorta points with the MRI surface, followed by sequential incorporation of the MEAM LV points with the MRI-based LV surface. As described in the legend of Figure 1, the registration accuracy was defined as the mean distance of either: 1) the complete MEAM LV point dataset to the MRI-based LV surface (red lines), or 2) the complete MEAM aorta point dataset to the MRI-based aorta surface (blue lines). Congruent with the in vitro phantom data, registration based solely upon the LV (A) resulted in an inaccurate local minimal solution which could be rectified by first registering the aorta points (B). Note that even after proper registration (figure in B), many of the MEAM LV points, but not the aorta points, were located beyond the MRI-defined LV endocardial boundary. Abbreviations as in Figure 1.

View larger version (81K): [in a new window]   Figure 4 MRI-guided in vivo catheter manipulation. The position of the catheter tip (green icon) was visualized in real-time as the catheter was manipulated within the registered 3D MRI construct to the mitral valve annulus (shown in right-posterior oblique and left-lateral views, A and B, respectively). The corresponding MEAM image is shown in left lateral view (C), along with the corresponding intracardiac electrogram (inset) depicting the characteristic electrophysiologic signature of the mitral valve, videlicet, concurrent atrial and ventricular electrograms. Abbreviations as in Figure 1.

View larger version (89K): [in a new window]   Figure 5 Accuracy of image integration based upon the iron oxide injection experiments. (A) As described in the legend of Figure 2, the register magnetic resonance imaging was used to guide movement of the catheter tip (green icon) to the iron oxide injection targets (yellow dot). (B and C) After catheter ablation at this point, the animal was killed and distance from the ablation lesion (blue asterisk) to the injection (arrow) noted.

View larger version (60K): [in a new window]   Figure 6 MRI-guided catheter navigation in vivo to the myocardial infarct borders. (A) The porcine infarct models underwent MRI 4 months after the anterior wall infarction procedure. The gadolinium-enhanced scarred myocardium (yellow arrows) is shown in these long- and short-axis (inset) delayed enhancement magnetic resonance images. (B) The aorta, LV endocardium, and myocardial scars were manually segmented and compiled into 3D datasets. During MEAM, the chamber geometries were constructed without displaying the corresponding electrophysiologic information. Radiofrequency ablation lesions were subsequently targeted to the borders of the scar solely on the basis of the registered MR image. Shown are the re-compiled surface reconstructions of the segmented LV, aorta, and scarred myocardium (in brown). (C) The registered 3D MRI of the porcine infarct model is shown: orange dots = LV points; blue dots = aorta points. (D) The electroanatomic bipolar voltage map depicts the anterior wall myocardial infarct; the color range was set such that the purple color represents normal tissue (i.e., >1.5 mV). The ablation lesions are shown as red dots; the yellow arrow denotes the ablation corresponding to the catheter position shown as a green icon in (E). (F) The corresponding ablation lesion (blue asterisk) was noted upon gross pathologic examination to be situated at the scar border; two other ablation lesions placed near the LV apex (yellow asterisk) were also appropriately localized to the scar borders. Abbreviations as in Figure 1.