The heart is responsible for transporting oxygen and nutrients to all tissues in the body, and it performs this function through the coordinated contraction of muscle cells. When coordination of these contractions occurs, the heart fibrillates, or stops beating. The systems of specialized cells that are responsible for this coordination are the cardiac conducting network, commonly referred to as the Purkinje network. These specialized muscle cells rapidly conduct signals to contract, so that the heart tissue at the base of the heart contracts at nearly the same time as tissue at the apex of the heart. Although we have known about these specialized cells for over a hundred years, the only way we are currently able to see them is if we remove the heart, and examine pieces of it under light microscopy. These current techniques are labor intensive, and result in destruction of tissue. We have developed a non-invasive means to determine the anatomical location of these specialized cells using magnetic resonance microscopy and diffusion imaging. Using magnets at the National High Field Magnet Laboratory in Gainesville, Florida, we have obtained the highest resolution MR images to date of myocardial tissue (7um isotropic resolution), and performed diffusion imaging at resolutions down to 40um. We are able to visualize the atrial-ventricular node, conducting bundle, left and right bundle branches, and subsequent fibers that extend down the ventricular septum of the heart and into the ventricular cavities (as free-running Purkinje fibers). We propose to further improve our ability to discriminate these fibers from cardiac muscle cells, and to construct atlases of the conduction network to aid in future modeling. We will also compare the anatomy of this network in both male and female young adults, since the incidence of sudden cardiac death is dramatically different between the genders at this age.
The heart relies on specialized cardiac muscle cells that conduct electrical impulses faster than normal cardiac muscle cells, and allow the entire heart to contract at almost the same time. We will develop, for the first time, the non-invasive techniques to visualize these cells (using magnetic resonance microscopy and diffusion) and generate atlases of the entire cardiac conduction network. These studies facilitate accurate modeling of cardiac conduction, and will benefit people with cardiac arrhythmias and congenital heart defects, and will permit new investigations into heart disease.