London, UK - An index of systolic dyssynchrony derived from real-time 3D echocardiography (RT3DE) and used to assess left ventricular mechanical dyssynchrony can help identify patients who can benefit from cardiac resynchronization therapy (CRT), researchers say [1]. Dr Stamatis Kapetanakis (King's College Hospital, London, UK) and colleagues report that the technology, used with the systolic dyssynchrony index (SDI) they propose, can identify LV dyssynchrony even in chronic heart-failure patients without QRS prolongation.

Their paper appears in the August 9, 2005 issue of Circulation.

"What we show is that the [systolic dyssynchrony] index actually predicts very accurately which patients will remodel and which ones won't," senior author on the study, Dr Mark Monaghan (King's College Hospital), told heartwire. "One of the interesting aspects of this, and this has actually been shown with tissue Doppler data as well, is that 3D measures of dyssynchrony are actually independent of QRS duration."

As reported by heartwire, real-time 3D echo is steadily transforming the way many forms of structural heart disease are diagnosed and managed; the application of the fast-evolving technology to the estimation of LV dyssynchrony requires a practical and reproducible method for quantifying the degree of dyssynchrony.

To this end, Kapetanakis, Monaghan, and colleagues validated their index in 89 healthy volunteers and 174 unselected patients who underwent both 2D echocardiography and RT3DE. The authors report that while healthy participants as well as patients with normal LV systolic function had "highly synchronized segmental function," as indicated by an SDI of 3.5% and 4.5%, those with moderate to severe LV systolic dysfunction had significant dyssynchrony on RT3DE, with SDIs ranging from 10% to 15.6%. Strikingly, 37% of patients with LV systolic dysfunction and dyssynchrony had normal QRS durations.

In a second component of the study, Kapetanakis et al followed 26 patients who had undergone CRT for 10 months, identifying a subset of patients as "responders" (those with symptomatic improvement). Compared with nonresponders, responders had higher baseline SDIs but similar LVEF and NYHA class. At follow-up, SDIs declined significantly in responders, whereas nonresponders had increased dyssynchrony. LVEF and NYHA class improved in responders but did not in nonresponders.

One of our electrophysiologists said to me the other day, I wouldn't understand a tissue Doppler recording if you turned it upside down and back to front.

"We believe that 3D echo will be able to identify a subset of patients who have dyssynchrony but who have a narrow QRS—in other words, the patients who are currently denied CRT because they don't fit the current practical criteria," Monaghan explained. "On the other hand, 20% to 30% of patients in our study and other studies are known to not respond to CRT, and we believe that those are patients who, while they may have a broad QRS and poor EF, don't have very much dyssynchrony at all and therefore they won't benefit from CRT. What this would do is shift the paradigm. It probably won't change the overall numbers of people undergoing CRT, but it will bring in patients who are currently excluded and help us identify patients who are unlikely to benefit."

Monaghan says his group has been working "closely" with companies like Phillips and TomTec on the development of analysis software that would enable people with RT3DE to evaluate dyssynchrony. He believes this software will be available "in the very near future."

In the meantime, he says, it is the electrophysiologists who are among the most eager to have the new application at their disposal. "Tissue Doppler is the gold standard because there are more published data, but it's not very intuitive," Monaghan points out. By contrast, he says, "Electrophysiologists understand real-time 3D echo, when they see the dyssynchronous left ventricle in terms of all the wave forms—for them it's very intuitive, whereas one of our electrophysiologists said to me the other day, I wouldn't understand a tissue Doppler recording if you turned it upside down and back to front."