They generally arise when a continuous pressure differential allows blood to flow constantly from a high to a low pressure area, as may occur in a variety of congenital defects, most commonly patent ductus arteriosus, anomalou 一般出现在持续压力差使血液从一高压区不断流向低压区时,也可以出现在一些有先天性缺陷的病,最常见的有动脉导管未闭、冠状动脉起端异常,或冠状静脉动脉瘘。