Nonechocardiographic imaging in evaluation for cardiac resynchronization therapy.

TLDR: In patients with heart failure and prolonged QRS duration, randomized clinical trials have shown that cardiac resynchronization therapy (CRT) is associated with improvement in quality of life, left ventricular remodeling, and survival as mentioned in this paper.

Abstract: In patients with heart failure and prolonged QRS duration, randomized clinical trials have shown that cardiac resynchronization therapy (CRT) is associated with improvement in quality of life, left ventricular (LV) remodeling, and survival.1–3 The improvements are believed to be mediated by more effective synchronized contraction in the presence of a wide QRS, but mechanical and electrical dyssynchrony are not equivalent.4,5 Although the concept of CRT response remains problematic,6 20% to 40% of patients who receive CRT based on electrical dyssynchrony criteria (ie, QRS duration) do not derive symptom improvement or demonstrate reverse remodeling.7–10 Scar burden11–13 and failure to place the LV pacing lead at the site of latest onset of contraction14–17 have been linked to a poor response. Thus, optimal clinical decision-making for CRT must include a comprehensive evaluation of all these factors to identify patients with heart failure who will benefit. The standard echocardiographic parameters of LV mechanical dyssynchrony have been extensively reviewed,18 with >600 published articles. Most of this work has been done using tissue Doppler imaging, with more recent work using speckle tracking,19,20 3D echocardiography,21 echocardiographic contrast imaging,22 and intracardiac echocardiography.23 Despite the important benefits of high temporal resolution, success in individual centers, and ability to assess the impact of scar burden and concordance of LV lead with latest activation site,14 fundamental limitations of tissue Doppler imaging include the inability to measure over a sufficient number of cardiac cycles to overcome beat-to-beat variation, poor image quality, and measurement error.24 In the only randomized trial of CRT in patients with wide QRS,25 the failure of 12 different echocardiographic dyssynchrony parameters to improve outcome was most likely related to the large interobserver and …