Organization and collateralization of a subendocardial plexus in end-stage human heart failure

In the failing myocardium a subendocardial plexus can develop. Detection of the presence or function, however, of such a plexus does not form part of the present diagnostic spectrum for heart failure. This may now change as new methods for high-resolution imaging of myocardial perfusion distribution are being developed. A severely hypertrophic heart was harvested during transplantation and analyzed for morphology of the intramural coronary arterial vasculature. The heart only had one coronary ostium, and the main branches of the coronary artery were cannulated. A fluorescent casting material was infused that was allowed to harden under physiological pressure. The entire heart was frozen and placed in a novel imaging cryomicrotome and sequentially cut in 25-microm slices. High-resolution images of each cutting plane were acquired, allowing a detailed three-dimensional reconstruction of the arterial vasculature. The epicardial layer of the free wall demonstrated a normal vasculature with penetrating branching arteries. The endocardial layer and the septum revealed a highly interconnected vascular plexus with large vessels oriented parallel to the apicobasal axis. An extensive endocardial network with collaterals was detected, forming connections between the main epicardial branches. We conclude that an outward remodeling of transmural vessels did not prevent the generation and growth of subendocardial conduit arteries. The orientation and vascular volume in the plexus provides an opportunity for detection by novel techniques of MRI contrast imaging currently developed. Knowledge of the effect on perfusion studies is required to prevent a misinterpretation of subendocardial perfusion images in heart failure.