Compensatory increase of left atrial external work to left ventricular dysfunction caused by afterload increase

Area of Science:

• Cardiology
• Physiology
• Echocardiography

Background:

• Afterload mismatch is a known cause of acute decompensation and acute heart failure.
• The compensatory mechanisms of the left atrium (LA) in response to acute increases in afterload are not fully understood.

Purpose of the Study:

• To investigate the reactive changes in LA and left ventricular (LV) function using speckle tracking echocardiography (STE) during acute increases in afterload.
• To quantify LA strain and work during different phases of the cardiac cycle under conditions of increased afterload.

Main Methods:

• 10 dogs underwent banding of the descending aorta (AoB) to induce acute afterload increase.
• Left atrial (LA) strain and volume were measured using STE.
• LA pressure was measured invasively.
• LA longitudinal strain-volume curves were used to derive peak negative strain, early reservoir strain, and late reservoir strain.
• Pressure-strain loops were used to calculate active contraction/relaxation work (A-work) and passive filling/emptying work (V-work).

Main Results:

• Aortic banding significantly increased LV systolic pressure and mean LA pressure.
• LV global circumferential strain decreased, but LV stroke volume was maintained.
• LA peak negative strain and early reservoir strain increased significantly, indicating enhanced atrial contraction and early filling.
• LA external work during active contraction and relaxation (A-work) significantly increased, while passive filling/emptying work (V-work) remained unchanged.

Conclusions:

• The LA increases its external work during active contraction and relaxation to compensate for acute LV dysfunction caused by increased afterload.
• Failure of this compensatory atrial mechanism may precipitate hemodynamic decompensation and acute heart failure.