In human hearts, an extensive pre-existing collateral network is present. This was shown unequivocally some 50 years ago in a series of very detailed post-mortem angiographic studies. In these studies, it was also observed that the pre-existent collateral vessels enlarge upon closure of an epicardial coronary artery, resulting in large collateral conduit arteries, in sharp contrast to earlier claims that human coronary arteries are functional end arteries. These insights still form the basis for the concept of arteriogenesis as positive remodeling of pre-existent arteriolar connections. Subsequent experimental studies disclosed the putative role of circulating cells, especially monocytes, which invade the proliferating vessel wall and secrete growth factors, degrading enzymes and survival factors that are required for the development of a mature collateral circulation. Experimental stimulation of arteriogenesis is feasible but to date a relatively low number of clinical studies, with no or limited success, have been performed. The use of intracoronary derived collateral flow index can increase the sensitivity to detect the effects of pharmacological compounds on arteriogenesis, which is important in first proof-of-principle studies. These invasive measurements also allow the detection of patients with an innate defect in their arteriogenic response to coronary obstruction. In a reversed bedside-to-bench approach, the characterization of ribonucleic acid and protein expression patterns in these patients generated new targets for therapeutic arteriogenesis.

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A disparity often exists between the extent of myocardial damage and the severity of the underlying coronary artery disease. Only where pathological examination has been supplemented by detailed injection studies is it possible to provide satisfactory interpretation of the changes found. From such studies the importance of collateral blood supply through enlarged anastomotic channels within the heart has become better appreciated in recent years.Obliterative disease of the major coronary arteries, together with secondary changes in the smaller vessels, may result in the original coronary tree becoming distorted in a great variety of ways. Nevertheless certain basic trends in anastomotic development may be recognized. When the arterial changes are widespread and of extreme degree a characteristic vascular pattern and pathological picture may appear.From an investigation of coronary artery disease, using a technique that included stereoarteriography, four closely similar cases have been selected for presentation. These cases illustrate the extensive nature of the vascular changes that may be found in the subendocardial plexus of the left ventricle. No reference to the importance of this plexus in disease has so far been found in previous records; nor does the characteristic vascular pattern now to be described appear to have been mentioned hitherto.The clinical and pathological findings broadly correspond to the features described in " acute coronary insufficiency" (Friedberg and Horn, 1939). The characteristic vascular pattern found in these cases is considered in relation to the distribution of focal necrotic lesions in the inner layers of the left ventricle, and also in relation to the freedom from massive myocardial infarction, notwithstanding severe obliterative coronary artery disease. MATERIAL AND METHODSThe four cases to be presented are part of a series of 26 cases of advanced coronary artery disease which have been investigated post-mortem by a special technique. Thirty-six controls were examined of which 18 were patients with cardiac disease other than coronary artery disease; the remainder were cases without cardiac abnormality or with only minor departures from normality.Each case was subjected to an analysis that included injection of the coronary arteries with a radio-opaque medium, followed by stereo-radiography of the intact heart and of the partially dissected heart. It is intended to publish the details of the method, but for the purpose of this presentation it may be pointed out that certain features of the technique were important in revealing

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