The internal thoracic artery as a transitional type of artery: a morphological and morphometric study.

Coronary artery by-pass grafting (CABG) with arterial grafts is widely accepted as the procedure of choice in the treatment of coronary ischemic disease. It brings back focus on morphological studies of arteries used as conduits in this procedure. One of the most frequently used CABG grafts is the internal thoracic artery with an excellent graft prognosis and patency rate. The aim of the study was a detailed morphological and morphometric description of the internal thoracic artery with an emphasis on its basic histological structure and its changes in aging and atherosclerosis. Therefore, 42 full-length arteries were obtained during forensic autopsies from 27 persons, aged between 20 and 81 years, who had died from non-vascular causes. The arteries were classified into three different age groups. Analysis of the serial arterial segments has shown that the internal thoracic artery is an artery of the transitional type whose media is organized into two layers: the internal, muscular layer and the external layer with spirally oriented elastic lamellae and smooth muscle cells in between. The number of elastic lamellae progressively decreases throughout the length of the examined arteries. As opposed to previous assumptions, we have proven that the grade of atherosclerosis is independent of the number of elastic lamellae in the external media. Perfectly formed elastic lamellae are not a persistent feature of the internal thoracic artery, as previously claimed. We have confirmed that the thickness of elastic lamellae decreases, while the number and the size of their fenestrations steadily increase with aging.