Why mechanical dyssynchrony remains relevant to cardiac resynchronization therapy. Letter regarding the article 'Optimized implementation of cardiac resynchronization therapy: a call for action for referral and optimization of care: a joint position statement from the Heart Failure Association (HFA), European Heart Rhythm Association (EHRA), and European Association of Cardiovascular Imaging (EACVI) of the European Society of Cardiology'.

Abstract

We read with interest the position statement of Mullens et al.1 on cardiac resynchronization therapy (CRT). The authors should be applauded for their efforts to increase awareness and utilization of this beneficial procedure. Some of the statements, however, require commentary. First, the authors claim that ‘the absence of pre-implant mechanical dyssynchrony should not defer the implantation of a CRT device in patients with a guideline indication.’ We agree that withholding CRT from patients who are very likely to benefit, in particular those with a wide left bundle branch block, is undesirable. However, deliberately ignoring left ventricular mechanical dyssynchrony (LVMD) is, at best, a misunderstanding of the fundamental pathophysiology of the disease. LVMD is the mechanical result of a delay in activation between the septal and lateral region of the left ventricular wall. The resulting regionally different workload induces a continuous remodelling process that leads to deterioration of myocardial function and poor outcome.2 Correction of this workload imbalance reverses the disease process and restores myocardial function. It is incomprehensible why the authors claim that analysing the underlying pathophysiology would not lead to a more adequate patient selection. To support their claim the authors refer to studies performed a decade ago which used parameters now long considered to be unspecific and poorly reproducible.3 They neglect over 10 years of scientific progress while new parameters have already been successfully tested in large retrospective and prospective studies.4, 5 Second, the authors claim that all patients with a guideline indication benefit from CRT and that ‘using mechanical dyssynchrony for the selection of CRT does not select patients more likely to gain benefit.’ It has been demonstrated that there is no significant difference in survival of CRT patients with different classes of indication, including class III (contraindication). LVMD, however, clearly discerned two patient groups within each class; one with poor and one with excellent long-term survival after implantation.4 This finding should motivate clinicians to treat more patients with a QRS width ≥130 ms who show LVMD regardless of QRS morphology. Third, the claim that CRT should be used more as it is a cost-effective therapy, is made from the perspective of a wealthy country. The referenced incremental cost-effectiveness ratio (ICER) originates from the UK and might by far exceed the willingness and/or ability to pay in a low-to-middle income country. LVMD allows clinicians to select patients who will benefit most, which reduces the ICER. Paradoxically, a more stringent selection – which the authors oppose – could facilitate an increased use of CRT, even in high income countries. It is therefore truly unfortunate that the discussed statements of the authors could: (i) prevent clinicians from exploiting echocardiography to identify additional patients who will benefit from CRT, especially when resources are limited, and (ii) limit interest in further research using echocardiography to identify patients beyond the current guidelines.