Coronary Steal Via Natural Internal Mammary Artery-To-Coronary Artery Bypasses

Plain-language summary

CORONARY ARTERY DISEASE AND THE BENEFIT OF BYPASSES Despite considerable advances in medicine, cardiovascular diseases remain the number one cause of death globally. In industrialized countries, coronary artery disease (CAD) is the leading cause of death, consequence of myocardial infarction (MI). Artificial - or natural - bypasses exert a protective effect by providing an alternative source of blood flow to a myocardial territory potentially affected by an acute coronary occlusion. Coronary collaterals represent pre-existing inter-arterial anastomoses and as such are the natural counter-part of surgically created bypasses. In patients with chronic CAD, sufficient coronary collaterals have been shown to confer a significant benefits in terms of overall mortality and cardiovascular events. EXTRACARDIAC-TO-CORONARY COLLATERAL SUPPLY Commonly, coronary collaterals are implicitly understood to exist between coronary artery branches. However, the structural existence of coronary collaterals with an extracardiac connection has been confirmed by anatomical investigations. Pathophysiologically and with regard to a potential for arteriogenic stimulation, the connections from the internal mammary arteries, are of special interest. In a recently published work the investigators have investigated the effect of temporary balloon occlusion of the distal IMA on coronary collateral function. There were equivocal findings for the left circumflex coronary artery: CFI was increased by ipsilateral IMA occlusion, but the level of myocardial ischemia was unchanged. MYOCARDIAL STEAL VIA INTERNAL MAMMARY ARTERIES In the investigators' previous study, the coronary occlusion with simultaneous distal IMA occlusion was always performed first as a conservative measure against false-positive detection of internal-mammary-to-coronary artery connections. Repetitive coronary occlusions per se result in higher collateral flow by collateral recruitment and reduced ischemia by ischemic preconditioning and augmented collateral function. Conversely, the sensitivity of the employed method was reduced and might have contributed to the equivocal findings in case of the left circumflex artery. Moreover, the hypothesize d mechanism of localized pressure augmentation was not investigated. This study aims to further characterize the prevalence and function of natural ipsilateral IMA-to-coronary connections, as well as to investigate the hemodynamic mechanisms of coronary collateral function augmentation by distal IMA occlusion. In the investigators' last study, the increased coronary collateral function in response to manipulation of a potential coronary collateral donor (in this case, the IMA) was taken as indirect evidence for the existence of IMA-to-coronary-artery connections. Thus, the employed distal IMA occlusion served as a positive stimulus. Conceptually, additional evaluation with a negative stimulus could heighten the discriminatory power of the investigation. This could be in the form of a hyperemic stimulus affecting the collateral donor, ie in analogy to myocardial or coronary steal (ie, a reduction in coronary collateral supply to a collateral recipient).

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