Abstract
AimTo compare the classical and simplified form of the continuity equation in small Trifecta valves.MethodsThis is a retrospective analysis of post-operative echocardiograms performed for clinical reasons after implantation of Trifecta bioprosthetic valves.ResultsThere were 60 patients aged 74 (range 38–89) years. For the valves of size 19, 21 and 23mm, the mean gradient was 11.3, 10.7 and 9.7mmHg, respectively. The effective orifice areas by the classical form of the continuity equation were 1.4, 1.7 and 1.9cm2, respectively. There was a good correlation between the two forms of the continuity equation, but they were significantly different using a t-test (P<0.00001). Results using the classical form were a mean 0.11 (s.d. 0.18)cm2 larger than those using the simple formula.ConclusionHaemodynamic function of the Trifecta valve in the small aortic root is good. There are significant differences between the classical and simplified forms of the continuity equation.
Highlights
The continuity equation is based on the law of conservation of mass and assumes that the stroke volume through a stenotic orifice is the same as upstream from that orifice
The effective orifice area is classically estimated from the cross-sectional area in the left ventricular (LV) outflow tract multiplied by the ratio of the systolic velocity integrals on the subaortic pulsed Doppler signal and the transaortic continuous wave Doppler signal
We analysed our data for newly implanted, normally functioning aortic Trifecta valves in the 19, 21 and 23 mm sizes using the two forms of the continuity equation. This was a retrospective analysis of post-operative echo cardiograms performed within 1 year after surgery in patients implanted with a size 19, 21 or 23 mm Trifecta valve at one centre (Guy’s and St Thomas’ Hospitals) between 1 March 2013 and 31 January 2015
Summary
The continuity equation is based on the law of conservation of mass and assumes that the stroke volume through a stenotic orifice is the same as upstream from that orifice. The effective orifice area is classically estimated from the cross-sectional area in the left ventricular (LV) outflow tract multiplied by the ratio of the systolic velocity integrals on the subaortic pulsed Doppler signal and the transaortic continuous wave Doppler signal. A simplified modification uses the ratio of subaortic to transaortic peak velocity Both forms of the equation were described and compared in the original study [1] introducing the formula to clinical use and both are described in the most recent guidance [2] on the echocardiography of prosthetic valves. It is possible that the form of the equation used affects the resultant effective orifice area estimate independent of other sources of variability, including the level of measurement of the LV outflow tract diameter
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