Big Hearts, Little Reserve: Coronary Flow Velocity Reserve After Bypass Grafting in Patients With Left Ventricular Hypertrophy

摘要

In this issue of Seminars, Honda et al evaluate myocardial microvascular function in patients with severe left ventricular hypertrophy (LVH) after myocardial revascularization with CABG. The authors used coronary flow velocity reserve (CFVR), measured by transthoracic echocardiography Doppler of the LAD, to assess microvascular function before and after LIMA to LAD CABG. CFVR represents the ratio between maximal (stimulated) coronary blood flow, induced by a coronary vasodilator, and baseline (resting) blood flow. As an inexpensive, radiation-free and noninvasive modality, CFVR is useful to confirm graft patency and evaluate for functional changes of myocardial ischemia. The authors found that although CFVR improves postoperatively in all patients, it does not reach expected normal values in patients with LVH even with a patent LIMA graft. The findings highlight the effects of microvascular dysfunction. Coronary microvascular dysfunction is increasingly recognized as a source of persistent ischemia in patients with ischemic heart disease and is associated with poor prognosis. It can result in an impaired ability to increase coronary blood flow in response to increased oxygen demand (equivalent to flow limiting epicardial coronary stenosis), or it can result in microvascular spasm. In patients with LVH, the increased oxygen demand is further hindered by adverse hemodynamic changes including high left ventricular pressures, relative low coronary perfusion pressure compared to intracavitary pressures, and increased extravascular compres-sive forces.