Nonsympathetic increased inotropic state early after aortic insufficiency.

Area of Science:

• Cardiovascular Physiology
• Cardiac Mechanics

Background:

• Aortic insufficiency (AI) causes chronic volume overload.
• Early compensatory mechanisms of the left ventricle are not fully understood.

Purpose of the Study:

• To investigate the early left ventricular response to chronic volume overload in AI.
• To differentiate between sympathetic and non-sympathetic influences on contractility.

Main Methods:

• Conscious dogs instrumented for left ventricular pressure, diameter, and wall thickness measurements.
• Comparison of acute volume loading (AVL) with AI-induced volume overload at 24 and 48 hours.
• Assessment of effects with and without beta-blockade.

Main Results:

• Left ventricular systolic shortening increased significantly after AI, even at matched preload.
• Increased shortening and peak velocity of shortening persisted after AI, independent of sympathetic activity (beta-blockade).
• These hyperdynamic responses occurred before observable left ventricular hypertrophy.

Conclusions:

• Early left ventricular hyperfunction in AI is primarily due to increased intrinsic contractility.
• Sustained increased preload may modulate the inotropic state in conscious dogs during early AI.
• Non-sympathetic mechanisms drive early adaptation to volume overload.