To the Editor:—
We read with great interest the article about myocardial performance index and tissue Doppler imaging in patients with single ventricles, comparing two anesthetic regimens, sevoflurane and fentanyl-midazolam.1
The authors found no change in myocardial performance index, which is a global index of both systolic and diastolic function. However, they describe a significant decrease of both myocardial Doppler imaging systolic (Sm) and early diastolic (Em) wave velocities from baseline to dose 1 and dose 2 with fentanyl-midazolam (table 3 in their article). Nevertheless, both (neo)aortic flow and time-velocity integral decreased significantly.
An important limitation of this study, the preload dependency of both parameters used, was not fully discussed. It has to be speculated that anesthetics, in a setting as used in this study, although not shown, induce major changes in loading conditions.2Assessment of ventricular function implies that load-independent methods should be used. It has been indirectly suggested in the literature that myocardial performance is preload dependent: Broberg et al. 3described a close relation between this index and dP/dtmax, the latter being strongly preload dependent.4Recently, this preload dependency was also suggested by our group when we described a close relation between myocardial performance index and preload adjusted maximal power.5
In addition, the same problem arises with the systolic flow wave velocity of the tissue Doppler imaging. Our group recently showed clearly that this flow wave velocity is load dependent.6Therefore, a decrease in the length of the myocardial fibers due to a decrease in EDV will lead to decreases in stroke volume, the velocity of shortening, and systolic tissue velocity obtained with tissue Doppler imaging.
Echocardiographic parameters as myocardial performance indexes and systolic Doppler myocardial velocity must be used cautiously in view of various physiologic and pathophysiologic interfering factors, in particular when one is assessing hemodynamics in conjunction with various dose regimens of anesthetics.
* Ghent University Hospital, Gent, Belgium. firstname.lastname@example.org