Imaging predictive factors and exercise training in CRT patients
Cardiac resynchronization therapy (CRT) is an established treatment for patients with moderate-to-severe chronic heart failure (CHF) and intraventricular conduction delay, which is identified by a QRS interval of 120msec or more on a 12-lead electrocardiogram (ECG). CRT improved functional capacity, reduced hospitalizations for worsening CHF and increased survival. However, about 30-40% of patients who underwent CRT were non-responders with no clinical or echocardiographic improvement. Imaging parameters for prediction of CRT response have been reviewed. Cardiac magnetic resonance (CMR), recognized as the gold standard to assess viability, has shown to obtain good results regarding quantification of scar burden. CMR-derived measures of mechanical dyssynchrony appear to predict the outcome of CRT, however they have not been externally validated. Nuclear imaging techniques, namely single-photon emission cardiac tomography (SPECT) provide data on scar burden and location, left ventricular (LV) function, LV contraction and mechanical dyssynchrony from a single scan. The presence, location and burden of myocardial scar have been shown to affect response to CRT. However, compared to CMR, the low spatial resolution of scintigraphy might overestimate the scar extent. This problem can be overcome by positron emission tomography (PET). SPECT has also been used to quantify dyssynchrony, using phase analysis. Imaging investigation is ongoing, trying to better identifying CRT non-responders. The combination of ExT in CRT has not been well investigated; however some data show different aerobic exercise modes and intensities can further improve CRT benefits. Data available on the effects of ExT in patients with CRT have been reviewed.
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