Effects of variations in the strength of left ventricular contraction on aortic valve closure in the dog.

The efficiency of aortic valve closure was studied in five experiments on three normal dogs by simultaneous roentgen videodensitometry, upstream sampling of dye dilution and recording of flow velocity and direction in the ascending aorta using a chronically implanted electromagnetic flowmeter. The aortic valve closed effectively during regular ventricular contractions. However, aortic reflux was observed whenever a weak ventricular contraction produced an opening of the aortic valve that was barely detectable, as evidenced by a minimal aortic pressure pulse and stroke volume. This type of aortic regurgitation was mild and invariably occurred at the end of ventricular ejection, coincident with the aortic incisura. Such regurgitation may be clinically significant in some instances of bigeminal rhythm or rapid atrial fibrillation, and is especially important for the evaluation of aortic angiograms. It further supports the concept that competent aortic valve closure depends on vortex formation in the sinus of Valsalva of sufficient degree to keep the aortic valve leaflets in partial apposition during ejection of blood from the ventricle across the aortic valve.