LETTER TO THE EDITOR
Reply
James D. Thomas, MDa,
Michael S. Firstenberg, MDa,
Pieter M. Vandervoort, MDa,
Neil L. Greenberg, PhDa,
Nicholas G. Smedira, MD, FACCa,
Patrick M. McCarthy, MD, FACCa and
Mario J. Garcia, MD, FACCa
a Director, Cardiovascular Imaging, Department of Cardiology/F-15, Cleveland Clinic Foundation, 9500 Euclid Avenue, Cleveland, Ohio 44195 USA
We appreciate the comments of Tonti et al. regarding our recent publication (1). We agree that transmitral flow is a very complex three-dimensional process that can be approached only as an approximation when the Euler equation is applied to color M-mode images. Nevertheless, previous studies (2) using contrast agents have demonstrated that most of the streamlines of flow follow a unidirectional vector along the long axial dimension of the left ventricle (LV). The validity of this concept is further supported by the accuracy of our results. In fact, we demonstrated that this approach could quite accurately predict the total pressure drop across the normal mitral valve, an impossible task with the simplified Bernoulli equation. Tonti et al. correctly point out that display of pressure differences at just two locations misses the subtlety of the spatiotemporal pressure distribution within the LV inflow tract; our methodology, in fact, provides the full spatiotemporal map from which we extracted pressures at locations corresponding to our multisensor catheter. Tonti et al. state that the convective term should completely cancel out at a 5-cm sensor separation, but this assumes complete pressure recovery across the valve, which may not occur owing to turbulence in the inflow jet and vortices that form at the mitral tips. Indeed, if there were complete pressure recovery, there would be no net pressure drop across even stenotic valves.
The noninvasive calculation of true pressure drop across the normal mitral valve is only one application of quantitative analysis of the color M-mode Doppler image. Even more remarkably, this approach has been shown to be able to quantify the very small (1–4 mm Hg) pressure gradients between the base and apex of the LV that are a manifestation of diastolic suction. This has been validated in a canine model (3), and it was recently used to detect the 1–2-mm Hg increase in diastolic suction that occurs in submaximal exercise (4). Such gradients have been shown to decrease in ischemia (5) and increase with revascularization (6). Thus, digital image processing of color M-mode data may yield new noninvasive quantification of diastolic function that should be widely applicable in the clinical setting.
Although the measurement of the very small pressure gradients is difficult even by (perhaps especially by!) micromanometer catheters, we believe that our data are as accurate as can currently be obtained in patients, and we stand by our analysis as presented. We hope that studies such as ours (1,3,4,6) and by Tonti et al. (7) will stimulate further interest in quantitative color Doppler analysis.
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References
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1. Firstenberg MS, Vandervoort PM, Greenberg NL, et al. Noninvasive estimation of transmitral pressure drop across the normal mitral valve in humans: importance of convective and inertial forces during left ventricular filling. J Am Coll Cardiol. 2000;36:1942–1949[Abstract/Free Full Text]
2. Beppu S, Izumi S, Miyatake K, et al. Abnormal blood pathways in left ventricular cavity in acute myocardial infarction. Experimental observations with special reference to regional wall motion abnormality and hemostasis. Circulation. 1988;78:157–164[Abstract/Free Full Text]
3. Greenberg NI, Vandervoort PM, Firstenberg MS, Garcia MJ, Thomas JD. Estimation of diastolic intraventricular pressure gradients by Doppler M-mode echocardiography. Am J Physiol Heart Circ Physiol. 2001;280:H2507–H2515[Abstract/Free Full Text]
4. Vlassak J, King LM, Greenberg NL, Firstenberg MS, Thomas JD, Garcia MJ. Early apical relaxation increases ventricular suction during exercise in normal volunteers (abstr). J Am Coll Cardiol. 2001;37:442A
5. Courtois MA, Kovacs SJ, Ludbrook PA. Physiologic early diastolic intraventricular pressure gradient is lost during acute myocardial ischemia. Circulation. 1990;81:1688–1696[Abstract/Free Full Text]
6. Firstenberg MS, Smedira NG, Greenberg NI, et al. Relationship between early diastolic intraventricular pressure gradients, an index of elastic recoil, and improvements in systolic and diastolic function (abstr). Circulation. 2000;102:II647
7. Tonti G, Riccardi G, Denaro FM, Trambaiolo P, Salustri A. From digital image processing of colour Doppler M-mode maps to noninvasive evaluation of the left ventricular diastolic function: a dedicated software package. Ultrasound Med Biol 2000;26:603–11.
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References