Could exercise unveil the mystery of non-response to cardiac resynchronization therapy?

Abstract

This editorial refers to 'Effects of physical exercise on cardiac dyssynchrony in patients with impaired left ventricular function' by M. Kü hne et al., on page 839.Cardiac resynchronization therapy (CRT) is an established nonpharmacological therapy for patients with advanced heart failure in the last decade. 1 Although the compelling evidence from multiple clinical trials suggests that CRT improves symptoms, exercise capacity, and cardiac function as well as reduces heart failure hospitalization and cardiovascular mortality, poor or no response to CRT is observed in about one-third of patients receiving this therapy. 2,3 It has been suggested that insufficient evidence of mechanical dyssynchrony before device implantation might be one of the major reasons, while others include the presence of transmural scar at posterolateral wall, lack of myocardial contractile reserve, severe mitral regurgitation, suboptimal left ventricular (LV) lead position, and inappropriate device programming. 2,4,5 Left ventricular mechanical dyssynchrony describes the differences in the timing of contraction between different myocardial segments that are commonly observed in patients with congestive heart failure, particularly in those with depressed LV ejection fraction. Its presence varies with not only the methods of assessment, but also characteristics of the study population including the QRS duration, loading condition, severity of coronary artery disease, LV hypertrophy, and LV remodelling. Therefore, the ECG criteria of QRS width ≥120 ms adopted in the current guidelines may not be optimal for identifying patients who will benefit most from CRT or defining the presence of mechanical dyssynchrony. 6 Analysis of LV dyssynchrony is achieved by different imaging modalities such as echocardiography, from conventional M-mode and Doppler echocardiography to more advanced tissue Doppler imaging (TDI), three-dimensional echocardiography, and speckle tracking imaging, and most of the time, performed at rest. Consequently, lack of mechanical dyssynchrony has been found in about one-third of heart failure patients with QRS duration ≥120 ms. On the other hand, mechanical dyssynchrony occurs in 40-50% of patients with a narrow QRS complex defined as ,120 ms. 7 Furthermore, numerous studies have suggested that the presence and the extent of LV mechanical dyssynchrony could be a better predictor of response to CRT than QRS duration per se. 5,8 Not until recently, the contribution of exercise to LV mechanical dyssynchrony has been investigated and exercise-induced dyssynchrony has been found to be associated with exacerbation of heart failure symptoms, an increase in mitral regurgitation, and a reduction in exercise capacity. 9 -12 Therefore, it appears that the assessment of LV mechanical dyssynchrony only at rest may not be sufficient in heart failure patients. The landmark study by Lafitte et al. 9 first described how mechanical dyssynchrony was modified by exercise in 65 consecutive patients with LV ejection fraction of ,35% and New York He...

The role of the fragmented QRS complexes on a routine 12-lead ECG in predicting non-responsiveness to cardiac resynchronization therapy

“…Its presence varies by not only the methods of assessment, but also by characteristics of the study population including the QRS duration, loading condition, severity of coronary artery disease, LV hypertrophy, and LV remodeling. Therefore, the ECG criteria of QRS width ≥120 ms adopted in the current guidelines may not be the optimal tool in identifying the patients who benefit most from CRT or defining the presence of mechanical dyssynchrony (14, 15). …”

Cardiac Contractility Modulation for Heart Failure: A Meta‐Analysis of Randomized Controlled Trials

“…Cardiac resynchronization therapy (CRT) has been shown to be successful in improving clinical status and quality of life and it is indicated for symptomatic HF patients with New York Heart Association (NYHA) functional class III or IV with LVEF of ≤35% and QRS duration of ≥120 ms 7–10 . However, as the selection criteria states, only a small proportion of HF patients are suitable candidates for CRT and approximately one‐third of patients are nonresponders 11 . Therefore, there is a need to identify a widely applicable therapy, especially for those with normal QRS duration and normal ejection fraction (EF).…”