These disorders result in a specific alteration in the pattern of electrical activation that impairs the sequence of ventricular contraction in a different manner for each of these disorders. The most common is left bundle branch block (LBBB, 15-47%), followed by right bundle branch block (4-25%) and, less frequently, non-specific intraventricular conduction delay (IVCD) (10). Patients with heart failure on the other hand often present intraventricular conduction disorders. These structures allow for fast distribution of electrical impulses through both ventricles and synchronous ventricular contraction at both the intraventricular and interventricular levels. In the absence of intraventricular conduction disturbances, sinus impulses are conducted via the atrioventricular node, His bundle and its branches and Purkinje fibers. While these indications are clear (Recommendation Class I, Level A), there is less consensus about various sub-populations underrepresented in clinical trials. Subsequent studies have recommended the use of CRT in patients ins sinus rhythm, NYHA functional class II, LVEF ≤ 30% and QRS ≥ 130 ms (9) (figure 1). Several randomised trials have suppported its recommendation in patients in sinus rhythm, NYHA functional class III-IV, left ventricular ejection fraction (LVEF ) ≤ 35% and QRS ≥ 120 ms (1,6,7,8). Therefore, it is essential to make a careful selection of candidates. However, there are still 20-30% of patients who do not respond to therapy (5). Moreover, these benefits occur in a stable and progressive manner. According to a recent meta-analysis of McAlister et al (4), CRT provides significant improvement in functional class, left ventricular ejection fraction (LVEF), the distance walked at 6 minutes, quality of life and a reduction in hospitalisation for heart failure and overall mortality, mainly due to a reduction in mortality from progressive heart failure.
Its aim is to restore electrical synchrony, commonly impaired in these patients, and thus the cardiac function. Since its appearance in the 80's (2) and its clinical application in 90 years(3), cardiac resynchronisation therapy (CRT) has become an essential therapeutic tool in the treatment of heart failure patient today. Despite many advances in its treatment over the past decades, heart failure remains a problem of high prevalence, morbidity and mortality worldwide (1).
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