Background and ObjectivesLeft atrial (LA) fibrosis is a main determinant of LA remodeling and development of atrial fibrillation. However, non-invasive prediction of LA fibrosis is challenging. We investigated whether preoperative LA strain as measured by speckle tracking echocardiography could predict the degree of LA fibrosis and LA reverse remodeling after mitral valve (MV) surgery.Subjects and MethodsSpeckle tracking echocardiography and LA volume measurements were performed in 50 patients one day before MV surgery. LA tissues were obtained during the surgery, and the degrees of their interstitial fibroses were measured. LA volume measurements were repeated within 30 days after surgery (n=50) and 1-year later (n=39).ResultsLeft atrial global strain was significantly correlated with the degree of LA fibrosis (r=-0.55, p<0.001), and its correlation was independent of age, underlying rhythm, presence of rheumatic heart disease and type of predominant MV disease (B=-1.37, 95% confidence interval -2.32 - -0.41, p=0.006). The degree of LA fibrosis was significantly correlated with early (r=-0.337, p=0.017) and 1-year (r=-0.477, p=0.002) percent LA volume reduction after MV surgery, but LA global strain was not significant.ConclusionLeft atrial strain as measured by speckle tracking echocardiography might be helpful for predicting the degree of LA fibrosis in patients with MV disease.

Background-During maximal hyperemia, capillaries provide the greatest resistance to flow. A major determinant of capillary resistance is viscosity. We, therefore, hypothesized that abnormal coronary blood flow (CBF) reserve observed during hyperlipidemia is secondary to increased blood viscosity and not abnormal coronary vasomotion. Methods and Results-Maximal hyperemia was induced in 9 dogs using adenosine. Serum triglyceride levels were increased by incremental doses of Intralipid. A good correlation was noted between serum triglyceride levels and blood viscosity (rϭ0.82). Neither total coronary blood volume nor myocardial blood volume changed with increasing serum triglyceride levels, indicating lack of vasomotion. Myocardial vascular resistance (MVR) increased with increasing triglyceride levels (rϭ0.84), while hyperemic myocardial blood flow (MBF) decreased (rϭϪ0.64). The decrease in hyperemic MBF was associated with a decrease in blood velocity (rϭϪ0.56). These findings were confirmed with direct intravital microscopic observations in the mice cremaster muscle. Conclusions-Increasing lipid levels in a fully dilated normal coronary bed causes no change in large or small vessel dimensions. Instead, the increase in blood viscosity causes capillary resistance to rise, which attenuates hyperemic CBF. Therefore, the abnormal CBF reserve associated with hyperlipidemia is due to increase blood viscosity and not abnormal vascular function. Key Words: risk factors Ⅲ lipids Ⅲ microcirculation A bnormal coronary blood flow (CBF) reserve has been associated with hyperlipidemia even in the absence of structural changes in coronary arteries. [1][2][3][4] It is generally thought that this phenomenon is secondary to endothelial dysfunction that affects the ability of coronary vessels to dilate. 5,6 At rest, maximal resistance to CBF is offered by the coronary arterioles with only a small portion offered by the capillaries and venules. 7 During hyperemia, however, coronary arterial and venular resistances decrease significantly, but capillary resistance remains unaffected. Consequently, capillaries offer the most resistance to CBF during hyperemia and thus determine the maximal possible increase in hyperemic CBF. 8 According to Hagen-Poiseuille's equation, resistance to flow within a tube depends on the dimensions of the tube and the viscosity of the fluid in it. In large vessels, resistance is determined mainly by the dimensions of the vessels with viscosity playing a negligible role. In vessels with Ͻ30 m diameter, however, an abrupt increase in viscosity is seen with an inverse relation between vessel size and effective viscosity. 9 Increased whole blood and plasma viscosity are observed in patients with hyperlipoproteinemia. 10 -12 A major factor affecting capillary resistance is blood viscosity. Because capillaries play a dominant role in limiting maximal hyperemic CBF, we hypothesized that abnormal CBF reserve observed during hyperlipidemia in the absence of coronary stenosis is secondary to increased blood viscosity ...

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