Blood flow to the heart from noncoronary arteries: an intriguing but challenging research field

Abstract

It has been proven that blood supply to the heart can include blood from noncoronary collateral circulation. Whether this network can somehow be augmented to provide an alternative therapy for ischemic patients is an intriguing hypothesis with no clear answer yet due to the challenging nature of this research field. In an attempt to enhance noncoronary collateral blood flow, we experimented with left internal thoracic artery ligature and angiogenic growth factors in a canine model. Eight dogs weighing between 20 and 29 kg were scheduled for three operations each. Neutron-activated microspheres were used for blood flow measurement throughout the study. The first operation was a left thoracotomy for ameroid constrictor positioning at the proximal segment of the circumflex coronary artery. Three weeks later the left internal thoracic artery was ligatured distally. A micro-pump was positioned in the mediastinum, connected with a small catheter inserted in the proximal segment of the left internal thoracic artery for slow delivery of vascular endothelial growth factor. The protocol called for a coronary angiography 4 weeks later, sacrifice of the animals, and explantation of the heart for microsphere analysis. Four of the dogs failed to tolerate ameroid constrictor positioning by thoracotomy and died after the first operation. The remaining four dogs underwent a second operation to ligate their left internal thoracic arteries and implant micro-pumps with catheters. The implant was a success, but only one dog survived in the postoperative period. When the last dog was voluntarily sacrificed after a third operation, coronary angiography showed no neovascularization, nor did heart slice analysis reveal microspheres. Despite the technical challenge of building research protocols to exactly quantify blood from noncoronary arteries, there are many historical, anatomical, physiopathological, clinical, radiological, and surgical indications suggesting that blood flow from extracardiac structures may play an important role in ischemic heart disease. Our preliminary investigation combining internal thoracic artery occlusion and angiogenic growth factors was unsuccessful for several reasons, the main one being it was too heavy a protocol for the dogs. Despite this, we think that noncoronary collateral blood flow represents an intriguing research field worthy of debate and further study.