Cardiac resynchronization therapy: How did consensus guidelines from Europe and the United States evolve in the last 15 years?

Cardiac resynchronization therapy (CRT) was proposed around 20 years ago, and its clinical use rapidly moved from pioneering experiences to randomized controlled trials (RCT). Since 2002 recommendations for CRT have been included in international consensus guidelines that even in an early phase recommended CRT as an effective treatment for improving symptoms, reducing hospitalizations and mortality in well-selected patients with wide QRS, left ventricular dysfunction and moderate to severe heart failure (NYHA classes III-IV), on optimal medical therapy. Subsequently the indications were extended to mild (NYHA class II) heart failure (associated with left ventricular dysfunction and wide QRS) and more recently also to appropriately selected patients with conventional indications for pacing having a left ventricular ejection fraction of 50% or less and NYHA class I-III. While all the guidelines strongly recommend CRT in case of LBBB with QRS duration >150 ms, lower strength of recommendations, with some heterogeneity, appears when QRS duration is 130-150 ms, especially if not associated with LBBB. Of note, according to recent guidelines, CRT is not recommended in case of QRS duration <130 ms, which is now the lower limit for candidacy to CRT, differently from the 120 ms limit used before. Despite consensus guidelines, many data indicate that CRT is still underused, with great heterogeneity in its implementation, both in North America and Europe, thus requiring a more organized patient referral.