Should slow coronary flow be considered as a coronary syndrome?

The concept of slow coronary flow was firstly described in 1972. This phenomenon indicates a coronary slow flow phenomenon in the absence of any known etiology. This phenomenon is not infrequently detected finding during routine coronary angiography, while it is, apparently, quite different from coronary slow flow phenomenon with evident causes. Slow coronary flow, consequently, should be distinguished from occurrence of slow flow in the context of coronary reperfusion therapy such as angioplasty or thrombolysis that is associated with different pathophysiological and clinical implications. Similarly, coronary slow flow associated with coronary spasm, coronary artery ectasia, myocardial dysfunction, valvular heart disease and certain connective tissue disorder involving coronary microvasculature is definitely need to be differentiated in patients with slow coronary flow. In addition, coronary slow flow phenomenon was also found in the situation from inadvertent air-embolism during angioplasty or due to an overlooked ostial lesion. Furthermore, the features of slow coronary flow are not in agreement with cardiac syndrome X. It is not certain, however, whether slow coronary flow phenomenon in the absence of any of known causes represents merely an angiographic curiosity or has special physiologic or therapeutic implications up to now. What kind of factors or etiologic reasons contributes to slow coronary flow? Is slow coronary flow an independent entity of coronary artery disease? All of those answers are still unknown and deserves further investigation. In our opinion, slow coronary flow without evident cause may represent a new entity of coronary heart disease. Therefore, we would like to consider it as a syndrome, and call it as a "slow coronary flow syndrome".