Table 2.

CRT in patients with heart failure and a narrow QRS

Study	Number of patients with narrow QRS (<120 ms)	Average QRS duration (ms)	NYHA class	End point	Outcomes
Achilli et al. (2003)60	14	110.0±10.9	III–IV	Functional capacity and echocardiographic outcomes	Improvements in NYHA class, LVEF, functional capacity, and reverse remodelling
Yu et al. (2006)61	51	103±13	III–IV	Clinical parameters and echocardiographic outcomes	Improvements in reverse remodelling, mitral regurgitation, NYHA class, exercise capacity, and LVEF
Bleeker et al. (2006)62	33	110±8	III–IV	Clinical parameters and echocardiographic outcomes	Improvements in 6-min walking distance, quality of life, LVEF, and reverse remodelling
RethinQ (2007)63	87	107±12	III	Increase of ≥1 ml/kg/min in peak oxygen consumption during cardiopulmonary exercise	Improvement in NYHA class, but not in peak oxygen consumption, quality-of-life scores, 6-min walking distance, or echocardiographic measures
Williams et al. (2009)65	30	Not reported (all <120)	III–IV	Short-term haemodynamic improvement in catheterization laboratory	Improvements in cardiac index, left ventricular stroke work, dP/dtmax, with increase in left ventricular filling
RESPOND (2011)64	29	91.5±10.6	III–IV	Change in 6-min walking distance	Improvement in 6-min walking distance, NYHA class, quality of life, and a composite clinical score

Abbreviations: CRT, cardiac resynchronization therapy; dP/dt_max, maximum rate of change in left ventricular pressure over time; LVEF, left ventricular ejection fraction.