Effects of cardiac volume loading on left atrial stiffness estimated by 2-dimensional echocardiography in healthy dogs.

Objective: To elucidate the effect of cardiac volume loading, which should physiologically increase left atrial (LA) stiffness (LASt), on echocardiographically estimated LASt in healthy dogs.

Methods: 6 healthy Beagle dogs were anesthetized. In each dog, a Swan-Ganz catheter was placed to measure the mean pulmonary capillary wedge pressure. Cardiac volume loading was performed by IV infusion with hydroxyethylated starch solution. Echocardiography was transthoracically conducted at the baseline and at mean pulmonary capillary wedge pressures of 10 to 15, 15 to 20, 20 to 25, and 25 to 30 mm Hg. The echocardiographic indicators of LA pressure, including the peak velocity of early diastolic transmitral flow (E), ratio of E to the isovolumic relaxation time (E/IVRT), ratio of E to the peak velocity of early diastolic mitral annular motion (E/E'), and LA reservoir strain, were determined to estimate LASt.

Results: During cardiac volume loading, E, E/IVRT, and LA reservoir strain were increased, and E/E' was decreased, when compared with the baseline. Consequently, LASts estimated by using E, E/IVRT, and E/E' were decreased or remained unchanged during cardiac volume loading.

Conclusions: Echocardiographically estimated LASt may not be increased by cardiac volume loading in healthy dogs.

Clinical relevance: Healthy dogs may not be an appropriate model to elucidate the effect of cardiac volume loading on echocardiographically estimated LASt. This is problematic, especially for dogs with myxomatous mitral valve disease that are older and may have cardiac dysfunction.