[Cardiac resynchronisation therapy--how much mechanical dyssynchrony and cardiac imaging is necessary before device implantation?].

Cardiac resynchroinsation therapy (CRT) aims to correct the mechanical dyssynchrony in patients with heart failure and broad QRS complex. Until now, indication for CRT is based mainly on clinical and electrocardiographic criteria. Because QRS width is only weakly correlated to mechanical dyssynchrony, imaging techniques such as echocardiography and magnetic resonance tomography (MRT) seem suitable for analysis of dyssynchrony. Echocardiography has been studied in several studies for identification of suitable CRT candidates. Apart from conventional methods such as M mode-, 2 D-, and Doppler echocardiography other techniques which will be discussed in this article, including tissue Doppler echocardiography, have been used. Despite many positive results in individual studies no single echocardiographic parameter was able to predict positive CRT response in a prospective multicenter trial. Thus, QRS width remains the "gold standard" for CRT patient identification at present. In borderline cases, a combination of several echocardiographic measures of dyssynchrony may prove helpful. The results of studies with new techniques such as 2-dimensional strain analysis or 3D-echocardiography remain to be awaited. In the future, MRT may play a bigger role in this setting.