LETTER TO THE EDITOR
Reply
Liza Thomas, MBBS, FRACP
Westmead Hospital, Cardiology, Darcy Road, Westmead, Sydney, NSW 2145, Australia
Dominic Y. C. Leung, MBBS, FRACP,
Nelson B. Schiller, MD, FACC and
David L. Ross, MBBS, FRACP
lizat{at}westgate.wh.usyd.edu.au
We appreciate the comments that Dr. Rossi expressed concerning our recent study (1) "Compensatory Changes in Atrial Volumes With Normal Aging: Is Atrial Enlargement Inevitable?" We are grateful to be given the chance to respond to the issues raised in the letter.
Our findings demonstrated that, in the younger age group, total left atrial volume change (passive emptying volume + conduit volume + active emptying volume) was approximately 60 ml per cardiac cycle. Thus, one may extrapolate that the left ventricular stroke volume in the absence of valvular regurgitation is approximately 60 ml. For a mean heart rate of 71 beats/min and body surface area (BSA) of 1.8 m2, the cardiac output would be 4.3 l/min or 2.4 l/min/m2, which is a reasonable estimate for the cardiac output of a normal young patient at rest. We agree with Dr. Rossi that correlating the left atrial volume estimation with cardiac output may be useful. However, we elected not to include the data, as insertion of a pulmonary artery catheter for measurement of cardiac output by thermodilution in our normal volunteers was difficult to justify. Estimating stroke volume by measuring the time velocity integral of the left ventricular outflow tract was not included because the main thrust of the present study was on left atrial volume.
Furthermore, we believe that estimation of total left atrial volume change from pulmonary venous flow, which is suggested by Dr. Rossi, would ignore the all-important contribution of active atrial contraction to left ventricular filling, which would lead to an underestimation. However, we would like to emphasize that the potential for volume underestimation is always present with echocardiography. Thus, when estimating atrial volumes echocardiographically, the atrial volume should be maximized by selecting the largest frame, including the curve of the interatrial septum.
Moreover, we would also like to mention that the biplane atrial volumes obtained from transthoracic images do not account for atrial appendage blood volume. This exclusion of left atrial appendage volume may cause the underestimation in total atrial volume. Finally, when imaging at increased depths, the use of a lower frequency transducer may provide greater penetration, thereby optimizing atrial border visualization.
We sincerely hope that the above will adequately address the concern raised in Dr. Rossi’s communication.
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References
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1. Thomas L, Levett K, Boyd A, Leung DYC, Schiller NB, Ross DL. Compensatory changes in atrial volumes with normal aging: is atrial enlargement inevitable? J Am Coll Cardiol. 2002;40:1630–1635[Abstract/Free Full Text]
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