Left atrial size and geometry in the intact dog

Area of Science:

• Cardiovascular Physiology
• Cardiac Mechanics
• Hemodynamics

Background:

• The left atrium plays a crucial role in cardiac function, acting as a reservoir and conduit for pulmonary venous return.
• Understanding left atrial size and dynamic changes is essential for assessing cardiac health and disease.
• Variations in ventricular outflow resistance can impact atrial filling and emptying dynamics.

Purpose of the Study:

• To quantify left atrial size, shape, and diameter changes under varying ventricular outflow resistance.
• To investigate the mechanisms driving atrial dimensional alterations, specifically valve ring displacement.
• To determine if atrial emptying is optimized at resting cardiac conditions.

Main Methods:

• Utilized chronic markers on the mitral annulus and valve cusps in anesthetized dogs.
• Performed high-speed (120 frames/s) left atrial angiography following pulmonary artery contrast injection.
• Analyzed angiograms to measure changes in left atrial area and characterize dimensional variations.

Main Results:

• Left atrial size increased with elevated aortic pressure (11.0±3.1 cm² to 12.9±3.7 cm²).
• Increased aortic pressure led to decreased atrial percent emptying.
• Atrial dimensions remained similar to control values during decreased aortic pressure.
• Atrial size changes were primarily driven by symmetrical circumferential and eccentric valve ring displacements.

Conclusions:

• Left atrial emptying appears to be near maximal under normal resting conditions.
• Valve ring displacement is a primary determinant of left atrial dimensional changes.
• Ventricular outflow resistance significantly influences left atrial mechanics and function.