Can magnetic targeting of magnetically labeled circulating cells optimize intramyocardial cell retention?

Therapeutic intracavitary stem cell infusion currently suffers from poor myocardial homing. We examined whether cardiac cell retention could be enhanced by magnetic targeting of endothelial progenitor cells (EPCs) loaded with iron oxide nanoparticles. EPCs were magnetically labeled with citrate-coated iron oxide nanoparticles. Cell proliferation, migration, and CXCR4 chemokine receptor expression were assessed in different labeling conditions and no adverse effects of the magnetic label were observed. The magnetophoretic mobility of labeled EPCs was determined in vitro, with the same magnet as that subsequently used in vivo. Coronary artery occlusion was induced for 30 min in 36 rats (31 survivors), followed by 20 min of reperfusion. The rats were randomized to receive, during brief aortic cross-clamping, direct intraventricular injection of culture medium (n = 7) or magnetically labeled EPCs (n = 24), with (n = 14) or without (n = 10) subcutaneous insertion of a magnet over the chest cavity (n = 14). The hearts were explanted 24 h later and engrafted cells were visualized by magnetic resonance imaging (MRI) of the heart at 1.5 T. Their abundance in the myocardium was also analyzed semiquantitatively by immunofluorescence, and quantitatively by real-time polymerase chain reaction (RT-PCR).Although differences in cell retention between groups failed to be statistically significant using RT-PCR quantification, due to the variability of the animal model, immunostaining showed that the average number of engrafted EPCs was significantly ten times higher with than without magnetic targeting. There was thus a consistent trend favoring the magnet-treated hearts, thereby suggesting magnetic targeting as a potentially new mean of enhancing myocardial homing of intravascularly delivered stem cells. Magnetic targeting has the potential to enhance myocardial retention of intravascularly delivered endothelial progenitor cells.

Aortic biological valve thrombosis in an HIV positive patient.

Biological aortic valve thrombosis is an exceptional complication. A 64-year-old patient positive for human immunodeficiency virus presented for syncope on exertion, 2 years after an aortic bioprosthetic valve replacement and double coronary artery bypass. Transvalvular aortic mean gradient was approximately 50 mm Hg on echocardiogram and catheterization. Cardiac computed tomography scan showed a limited opening of the bioprosthesis cusps. Surgical exploration revealed thrombosis of the three cusps on the aortic side, limiting the opening of the valve. No relation could be established between the patient's human immunodeficiency virus status and valve thrombosis.

Hakki's formula for measurement of aortic valve area by magnetic resonance imaging.

Hakki's formula (simplified Gorlin formula) can be used during cardiac catheterization to calculate the stenosed cardiac valve areas and can also be adapted to magnetic resonance imaging (MRI) to measure the stenosed cardiac valve areas. We evaluated the reliability of this approach to determine the severity of aortic stenosis compared to the continuity equation using transthoracic echocardiography and planimetry using MRI. We included all eligible symptomatic patients with known aortic stenosis referred to our department during a 1-year period. The aortic valve area (AVA) was estimated using Hakki's formula (MRI), planimetry (MRI), and the continuity equation (transthoracic echocardiography). The agreement among the measurement methods was analyzed using the Bland-Altman method. A total of 63 patients were included (mean age 72 +/- 10 years, 35 men [56%]). The mean AVA was 0.70 +/- 0.21 cm(2) using the continuity equation (transthoracic echocardiography), 0.67 +/- 0.18 cm(2) using planimetry (MRI), and 0.64 +/- 0.21 cm(2) using Hakki's formula (MRI). The mean difference was 0.03 cm(2) (95% limits of agreement -0.32 to 0.25) between planimetry and the continuity equation, 0.05 cm(2) (95% limits of agreement -0.40 to 0.29) between Hakki's formula and the continuity equation, 0.02 cm(2) (95% limits of agreement -0.20 to 0.25) between Hakki's formula and planimetry. The inter- and intraobserver reproducibility using Hakki's formula was excellent. In conclusion, measurement of the AVA using Hakki's formula yielded similar results to those obtained using planimetry and slightly different ones from those obtained using the continuity equation. However, Hakki's formula has the advantage of being easy to use, fast, and reproducible and can be used regardless of the status of the valve (in contrast to planimetry).