Assessment of Myocardial Collateral Blood Flow with Contrast Echocardiography

Humans have pre-formed collateral vessels that enlarge with ischemia. In addition, new vessels can be formed within ischemic zones from pre-formed endocardial arcades of vessels providing rich collateral flow. Collateral flow under resting conditions (if >25% of normal) is enough to maintain myocardial viability, but may be insufficient to prevent myocardial ischemia under stress. Coronary angiography is a poor tool for collateral flow assessment. Myocardial contrast echocardiography is arguably the gold standard for experimental and clinical measurement of collateral flow. This review describes several experimental and clinical studies that highlight the importance of the collateral circulation in coronary artery disease.

Intermittent exercise promotes collateral circulation in ischemic myocardial tissue / 中华物理医学与康复杂志

Objective To observe whether appropriate intermittent exercise at the ischemic threshold can safely promote collateral circulation in an ischemic area of the myocardium through the increased expression of vascular endothelial growth factor(VEGF)and its receptor fetal liver kinase-1(Fik-1). Methods A balloon constrictor was surgically implanted in the first obtuse marginal coronary artery(OM1)of miniature pigs.The subjects were divided into 3 groups:a sham-operation group,a pure ischemia group,and an exercise training group.Subjects in the exercise training group performed individualized treadmill programs 30 min daily,5 d per week,for 8 weeks,including 2 two-minute episodes of exercise-induced ischemia.Two pre-exercise episodes of pure ischemia induced by brief OM1 occlusion were also conducted.Only pure ischemia was induced in the pure ischemia group,and the sham-operation group remained sedentary for the experimental period.Relative myocardial blood flow(RMBF)was measured using microspheres.VEGF and Flk-1 expression levels were measured by Western blotting and real time RT-PCR analyses.Cardiac troponin I(ctnI)levels were determined using an enzyme-linked immunosorbent assay(ELISA). Light and electron microscopy were employed to examine myocardia damage in the ischemic area.Results RMBFs in the exercise training group were significantly higher than those in the pure ischemia and sham-operation groups. RMBFs in the pure ischemia group were significantly higher than those in the sham-operation group.The expression of VEGF and Flk-1 proteins and mRNAs in the exercise training group were significantly higher than those in the pure ischemia and sham-operation groups,and the levels in the pure ischemia group were also significantly higher than those in the sham-operation group.After training,no myocardial damage and no ctnI increase was observed in the pure ischemia group.Microscopy revealed no obvious structural changes. Conclusion Intermittent exercise at the isehemia threshold intension can safely promote coronary collateral formation through upregulation of VEGF and Flk-1 expression in the ischemic myocardial area of a porcine model.