Is nuclear imaging a viable alternative technique to assess dyssynchrony?

Cardiac resynchronization therapy (CRT) has shown benefits in patients with end-stage heart failure (HF) (NYHA class III or IV), depressed left ventricular (LV) ejection fraction, and prolonged QRS duration (>120 ms). However, at least 30% of the patients who meet the above criteria show no response to CRT. It has shown with echocardiography that the presence of LV mechanical dyssynchrony is an important predictor for response to CRT. However, echocardiography requires expertise to produce reproducible and reliable results. The recent report from the Predictors of Response to Cardiac Resynchronization Therapy trial showed that under 'real-world' conditions the current available echocardiographic techniques including tissue Doppler imaging (TDI) and myocardial strain-rate imaging are not ready for routine clinical practice to assess LV dyssynchrony. It suggested that there is a need for better standardization and refinements of the echocardiographic screening tools currently used for the evaluation of LV dyssynchrony. This article reviews a technique such as phase analysis that allows measuring LV dyssynchrony from conventional electrocardiogram-gated single-photon emission computed tomography myocardial perfusion imaging with no additional procedure. Its advantages over TDI are its automation, repeatability, and reproducibility that are very promising in improving prediction of CRT response in HF patients.