Papillary muscle dyssynchrony: what is the optimal cut-off value?

We appreciate the useful comments by Cabrera-Bueno et al. underscoring the importance of mitral regurgitation (MR) in patients with dilated cardiomyopathy (DCM). Cardiac resynchronization therapy (CRT) improves functional MR during the acute and chronic phase of heart failure by improving the coordination of the left ventricular segments and papillary muscle contractions.1,2. However, MR volumes of the patients with minimal papillary muscle dyssynchrony did not improve following CRT.2 The best echocardiographic cut-off value to predict significant papillary muscle dyssynchrony, which in turn, would help patient selection for CRT is still unknown. The papillary muscles usually get closer to each other in the dilated and spheroidized left ventricles of patients with DCM; therefore, the opposing wall delay value of 65 ms might not be applicable in these patients. Most CRT studies on papillary muscle dyssynchrony have investigated the possible papillary muscle insertion regions on the left ventricle in their strain analysis. In patients with heart failure, usually lateral, posterior, and inferior myocardial segments are the most delayed segments independent of QRS duration.3,4 The papillary muscles are usually localized to the lateral, inferior, and posterior segments, and these segments already activate later than other myocardial regions. The interpretation of delay between already most delayed segments might not be accurate. Most of the studies on this topic reported different cut-off values and the optimal delay time to choose CRT candidates is still unclear. Therefore, appropriate echocardiographic cut-off level for the prediction of papillary muscle dyssynchrony is needed. This information can be useful and indicate the severity of MR. Cabrera-Bueno et al. demonstrated that baseline presence of important MR which was defined as a regurgitant orifice area >0.2 cm2 was associated with a lack of response in reverse remodelling in patients with non-ischaemic DCM although there was significant improvement in MR and intraventricular dyssynchrony.5 In another study, the differences in pre-CRT infero-anterior time-to-peak two-dimensional radial strain of >110 ms and presence of non-severe MR were the significant predictors of MR reduction after CRT.6 It is speculated that the maximum benefit of CRT on MR and the associated left ventricular remodelling seems to be present in patients with at least mild MR, but without severe MR.7 In our study, we found that papillary muscle dyssynchrony ≥30 ms independently predicted the patients with functional MR >20 mL.8 This information can help to determine the patients with DCM who have moderate MR and would benefit from CRT. MR in patients with heart failure impairs prognosis and the surgical treatment of MR is associated with perioperative morbidity and mortality. Improvement of MR following CRT is promising and contributes to the mortality benefit of this therapy. Patients with DCM and narrow QRS complexes are usually overlooked and not referred for CRT. However, Achilli et al.9 demonstrated the improvement in functional MR in 14 narrow QRS patients after CRT. It may be useful to evaluate non-ischaemic DCM patients with narrow QRS intervals for the presence of papillary muscle dyssynchrony, and these patients may benefit from CRT by the improvement of their MR severity.