Author + information
- Frank A. Flachskampf, MD, PhD∗ ( and )
- Lutz Klinghammer, MD
- ↵∗Uppsala Universitet, Akademiska sjukhuset, Ingång 40, plan 5, 751 85 Uppsala, Sweden
We thank Dr. Saikrishnan and colleagues for their interest in and attention to our paper (1) and are pleased that they find that it “definitely improves our understanding of this problem” (i.e., “paradoxic” low-gradient aortic stenosis). They raise several issues that we would like to briefly address.
• Cardiac catheterization as a gold standard. Nowhere do we cite catheterization as gold standard in this paper, and we discuss in detail limitations of the Gorlin formula. However, as clinicians, we recognize that catheterization continues to be the most widely used reference standard in cases echocardiography is considered doubtful. It is unclear how, as Dr. Saikrishnan and colleagues propose, “a bench-top in vitro study” would help in such cases.
• Differences between echo and catheterization pressure data due to pressure recovery. We entirely agree that this is an important issue and have thus included the energy loss index as a measure of stenosis severity in our analysis.
• Degree of stenosis in the paradoxic and the conventionally defined aortic stenosis groups. As we stated in our discussion: “...overall there was a higher degree of obstruction, in accordance with lower valve areas, higher gradients, and lower energy loss index in this group (the high-gradient aortic stenosis group) than in the ‘paradoxic’ aortic stenosis group” (1). However, it should be remembered that the original clinical question motivating this study was whether “paradoxic” aortic stenosis is really severe at all. The finding that patients with paradoxic aortic stenosis in our study had mildly less obstruction than high-gradient aortic stenosis does not necessarily predict that the patients with paradoxic aortic stenosis have a more benign variant of aortic stenosis.
• Gorlin equation and contraction coefficient. The Gorlin equation incorporates a constant that—among other tasks, such as conversion of units—is supposed to account for the coefficient of contraction (2,3). The equation aims to provide an anatomic orifice area, not an effective one.
• “The use of stroke volume and mean ΔP is incorrect.” This paragraph refers to a recently published letter from Saikrishnan et al. to another journal (4). The authors there draw attention to the fact that the Gorlin formula uses the square root of the mean pressure difference in the denominator, whereas it would be more precise to use the mean of the square roots of instantaneous pressure differences. This is correct, but the Gorlin formula is universally used in the former version, because taking the square root of the average pressure difference is easier than calculating instantaneous pressure differences, taking the individual square roots, and then averaging them. Hence, the original formula uses this simpler, although not entirely correct, notation (2). However, illustrative data from the letter of Saikrishnan et al. (4) show that, in patients with aortic valve areas <1 cm2, the difference in aortic valve areas calculated by both versions of the Gorlin formula was less than 0.05 cm2. Again, it should be understood that it was our intention to compare echocardiographic findings not with the most precise imaginable way of determining aortic stenosis hemodynamic status, but with the clinical invasive standard approach.
- American College of Cardiology Foundation