Hemodynamics alterations induced by isoproterenol and pacing after aortic valve replacement with the Björk-Shiley or St. Jude medical prosthesis.

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Abstract
Stress evaluation was carried out in 26 patients approximately 7 mo. after aortic valve replacement with Bjork-Shiley valves (13 patients) and St. Jude medical valves (13 patients). During isoproterenol infusion (0.3 .mu.g/kg per min), cardiac output increased by a factor of 1.5 and aortic valve area decreased by 50% for both valve groups. Transvalvular gradients (rest: 7 .+-. 2 vs. 10 .+-. 5 mm Hg, P > 0.05) increased to 42 .+-. 18 vs. 51 .+-. 18 mm Hg (P > 0.05), i.e., to levels of moderate aortic stenosis. During pacing stress, these values progressively decreased with rising heart rates. In other postoperative evaluations that included ergometric stress with isoproterenol and pacing, induced hemodynamic changes after aortic valve replacement were predictable and consistent with regard to direction and magnitude. They differed characteristically according to the stress type used. Apparently, no functional differences between Bjork-Shiley and St. Jude medical valves can be claimed. Standardized evaluation with isoproterenol is a sensitive stress test of prosthetic valvular hemodynamics. Because of the apparent magnification of residual obstruction after aortic valve replacement, it has advantages over pacing.