The first acute hemodynamic studies that demonstrated the benefits of cardiac resynchronization therapy (CRT) investigated the impact of biventricular pacing in patients with a left bundle branch block (LBBB) and a very wide QRS complex. Subsequent, long-term CRT trials progressively targeted a wider range of patients with heart failure — patients with a less wide QRS complex, non-LBBB QRS patterns, less severe heart failure, and a narrow QRS complex with evidence of mechanical dyssynchrony. Some of these lines of investigation proved that CRT had value in these various heart failure populations; some did not. On one hand, there is clear evidence that patients do not have to have severely advanced heart failure to benefit from CRT. The MADIT-CRT trial provided evidence for that. On the other hand, despite numerous initial publications that advanced imaging techniques could be used to identify patients without a wide QRS complex but with mechanical dyssynchrony who would respond to CRT, patients with a narrower QRS complex or a non-LBBB pattern do not appear to benefit from CRT. These observations were made in RethinQ and others.
Earlier this year, the Heart Failure Society of America modified its guidelines related to CRT.1 This August, the ACC, AHA, and HRS updated their 2008 Joint Guidelines for Device-Based Therapy of Cardiac Rhythm Abnormalities, with a focus on CRT that accounts for the results of the major CRT-related clinical trials published over the past five years.2 The updated major 2012 ACC/AHA/HRS Class I and IIa indications for CRT are listed below. The recommendations are all contingent on the fact that the patient has been treated with guideline-directed medical therapy prior to being considered for CRT.
Class I: CRT is indicated for patients who have:
- LVEF ≤ 35%, sinus rhythm, LBBB with a QRS duration ≥ 150 ms, and NYHA class II, III, or ambulatory IV symptoms.
Class IIa: CRT can be useful for patients who have:
- LVEF ≤ 35%, sinus rhythm, LBBB with a QRS duration 120 to 149 ms, and NYHA class II, III, or ambulatory IV symptoms.
- LVEF ≤ 35%, sinus rhythm, a non-LBBB pattern with a QRS duration ≥ 150 ms, and NYHA class III/ambulatory class IV symptoms.
- Atrial fibrillation and LVEF ≤ 35% if a) the patient requires ventricular pacing or otherwise meets CRT criteria and b) AV nodal ablation or pharmacologic rate control will allow near 100% ventricular pacing with CRT.
- LVEF ≤ 35% and are undergoing new or replacement device placement with anticipated requirement for significant (40%) ventricular pacing.
In summary, the professional society guidelines related to CRT have been updated to reflect recent trial results that demonstrated that CRT should be considered sooner in the course of the heart failure spectrum, but efforts to provide CRT should be focused only on patients with a LBBB pattern and with the widest QRS complexes. It is surprising to see that, after so many preliminary studies from the imaging and pacing community that demonstrated a discord between the degree of mechanical dyssynchrony and electrical dyssynchrony, the only class I indication for CRT in 2012 requires a QRS duration ≥ 150 ms and a pure LBBB. The field of CRT has taken a wide, left turn. It will be important that implanting physicians be aware of this new course and avoid deviating from it too much.
- Stevenson WG, Hernandez AF, Carson PE, et al. Indications for cardiac resynchronization therapy: 2011 update from the Heart Failure Society of America Guideline Committee. J Card Fail 2012;18:94–106.
- Tracy CM, Epstein AE, Darbar D, et al. 2012. ACCF/AHA/HRS focused update of the 2008 guidelines for device-based therapy of cardiac rhythm abnormalities: A report of the American College of Cardiology Foundation/American Heart Association Task Force on Practice Guidelines. J Am Coll Cardiol 2012; doi:10.1016/j.jacc.2012.07.009.