Invited Commentary

 

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The present study focuses on the unique design feature of the Mitroflow bioprosthesis, making it suitable especially for small aortic roots, and concludes that even small sizes can be implanted safely and with good hemodynamic results without the need for root enlargement procedures.

On the contrary today’s cardiac surgeons are told that implantation of small valves is dangerous for the patient because of the (somewhat arbitrarily defined) problem called patient-prosthesis mismatch (PPM). PPM is suspected when a high transprosthetic gradient is ascertained echocardiographically. This gradient is accused to prevent appropriate left ventricular muscle mass regression, resulting in less functional recovery and decreased short- and long-term survival.

The problem with PPM is that the echocardiographic (Doppler) gradient is a poor measure of the hemodynamic workload of prosthetic aortic valves because a significant amount of pressure recovery is not being considered. For clarification: the hemodynamic impact of a native aortic stenosis with a gradient of, for example, 30 mm Hg is completely different than that of a biological or mechanical heart valve prosthesis exhibiting exactly the same gradient. This does not mean that the Doppler gradient is incorrect. It is a true measurement of the pressure drop across the orifice, but even with the same calculated orifice area a calcified aortic valve has a higher energy loss than a smooth mechanical or biological prosthesis.

This might be the reason why, apart from theoretical works on PPM mainly by the group from Quebec,[1] [2] [3] [4] the vast majority of clinical studies fails to demonstrate a negative impact.

In most studies left ventricular muscle mass regression after aortic valve replacement for aortic stenosis takes place irrespective of the degree of PPM,[5] [6] [7] and even if not, there is no impact on functional recovery[5] [6] [7] [8] and mortality.[5] [9] [10] [11] [12] Only for patients with impaired left ventricular function a significant effect of PPM on survival could be demonstrated in some studies,[13] [14] while others again found no impact.[15] Lastly, even if PPM would be assumed to cause increased mortality, aortic root enlargement might be of no benefit, as has been suggested by Kulik et al.[16] [17]

The data of the present study obtained from an everyday patient collective demonstrate that 19-mm Mitroflow valves can be implanted in small aortic roots with good results. This is in line with similar studies on other small mechanical and biological aortic valve prostheses.[5] [8] [18] [19] This knowledge may prevent complex surgery with “scientific justification” in the hand of the less experienced surgeon.

To prevent misunderstanding: The larger the valve, the easier left ventricular ejection. But as long as PPM is determined solely by the Doppler gradient and its consequences according to the current literature remain inconsistent and vague, we should be cautious to recommend a more complex surgical procedure implicitly in patients exhibiting a small aortic annulus. A more radical approach may be justified in the young and active patient (who rarely has a small annulus), but here again, scientific data are insufficient.

• References

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