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3-Dimensional Echocardiographic Assessment of Left Ventricular Dyssynchrony

An Alternative Viewpoint

They state that determining the nadir of a low-amplitude and frequently noisy regional volume curve is difficult. However, noisy curves are (in our collective experience) rare and occur because of: 1) multiple manual editing of the 3-dimensional endocardial boundaries; 2) low temporospatial smoothing setting on the software; and 3) inclusion of datasets with poor image quality and stitching errors. It is surprising that apparently no patients were excluded from this study because of inadequate image quality or atrial fibrillation/irregular R-R intervals, nor did the authors validate datasets for stitching errors or check the software selected nadir.

The 2 dilated cardiomyopathy (DCM) examples in Figure 3 (1) are not representative and have obviously been chosen to make a point in that they both had much greater SDIs (17.8% and 16.7%) than the quoted means (8.7% and 9.1%) for the groups. In addition, proportional (rather than absolute volume curves, as in Figure 3 [1]) usually are used to validate the position of the nadir, which makes error less likely.

There are no data or statistical analyses presented to support the speculative hypothesis that noise is a source of error in this technique, and we are not told how frequently this issue occurs.

Because the interobserver variability of SDI measurements in most (2–6,12–14) studies is not high, this would also make "noise" an unlikely common phenomenon. The presence of "frequently occurring noise" would clearly increase the variability of measurements. Given that they have chosen examples to illustrate the point from the extreme end of their high SDI spectrum, one must assume that it is not really that common.

This same group have previously validated regional volume curves against cardiac magnetic resonance in a variety of different LV pathologies (15,16), and so it is surprising that they have now chosen to criticize the same basic technique.

The use of standard deviation as a way of deriving SDI also is criticized by the authors. We would agree that it is not a perfect statistical technique for describing the dispersion of timing of events; however, it is widely understood and has been used successfully in other echocardiogram dyssynchrony indexes, where noisy curves are significantly more common.

The most surprising statements are that SDI is not useful for the selection of patients for cardiac resynchronization therapy (CRT) or the follow-up of its effects. However, only 32 patients with DCM were included, none of whom had CRT or follow-up, so it is difficult to understand how this conclusion can be justified, especially because these authors have previously advocated the use of SDI in CRT (8–11).

All patients with DCM apparently had an SDI that was greater than their normality threshold of 4%. This is different to an SDI threshold for response to CRT, which has been shown in several published studies (2,8,12–14) to be much greater than the normality threshold. The equivalent to this would be stating that because a normal LV ejection fraction (EF) is >55%, the LVEF cannot be used as part of the CRT selection criteria because all patients with DCM have an EF <55%, whereas we know that an EF 35% is an important value for CRT selection.

In 2006, this same group (9) stated that "ASI [assynchrony index] (real-time 3-dimensional echocardiography [RT3DE] SDI) should be measured in all patients with DCM and in patients who are candidates for CRT, irrespective of QRS width. The use of RT3DE provides a rapid assessment of LV (dyssynchrony) of the entire ventricle. The QRS width should not be used as a criterion for CRT indication because DCM patients without left bundle branch block have increased assynchrony index in 55% of cases." It is interesting that the authors now state that because 100% of DCM patients have increased SDI, it cannot be used for CRT case selection. How is it that the prevalence of dyssynchrony in DCM patients, investigated by mostly the same authors, could have changed so dramatically during a short period of time?

The RT3DE SDI has been shown in several studies (2,12–14) involving larger groups of patients, who actually had CRT, to be a useful tool that can form part of the selection criteria for this technique. It is not perfect and will be improved. However, we believe that the conclusions drawn by the respected authors in this study are not justified on the basis of the data they have currently or previously presented.

^_* King's College Hospital, Cardiology Department, Denmark Hill, London SE5 9RS, United Kingdom (Email: mark.monaghan{at}kch.nhs.uk).

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				V. Mor-Avi and R. M. Lang Reply J. Am. Coll. Cardiol. Img., November 1, 2009; 2(11): 1335 - 1336. [Full Text] [PDF]

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