Page 58 - Simplicity is Key in CRT

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Introduction
Cardiac resynchronization therapy (CRT) improves symptoms, quality of life, and survival in patients with reduced left ventricular (LV) ejection fraction, heart failure symptoms, and prolonged QRS duration. The randomized clinical trials that lead to the initial widespread adoption of CRT used only QRS duration of more than 120ms as entry criteria [1-4]. Ever since, multiple subanalyses of large randomized trials showed QRS morphology to be associated to the measured benefit by CRT [5]. Where the benefit in patients presenting with left bundle branch block (LBBB) on their baseline ECG was shown to be very robust [6,7], in non-LBBB patients the benefit is still controversial [6,7]. Moreover, the specific criteria that should be used to classify LBBB are not properly indicated in clinical practice guidelines [7,8].
Currently, there are multiple ECG definitions for LBBB proposed by scientific organizations [6,9-11] and research groups [12]. Moreover, the European Society of Cardiology (ESC) has changed the definition of LBBB a few times over the last decade [6,10,11]. While initially these ECG criteria were used to classify the conduction abnormality per se, the more recent ones implicitly assume that LBBB represents the most important substrate for CRT. The lack of uniformity of LBBB definitions and uncertainty about the differences in association with outcomes to CRT can contribute to the still remaining group of patients not experiencing benefit from CRT.
Therefore, we aimed to evaluate a population of patients implanted with a CRT for (1) the consistency of a CRT patient to be classified as having LBBB, and (2) the association of the different LBBB definitions with both reverse remodelling and HF hospitalization and all-cause mortality.
Methods
Study population.
All consecutive patients who received a CRT at two different European centres (Cardiocentro Ticino, Lugano, Switzerland and Maastricht University Medical Centre, Maastricht, The Netherlands) from 2006 to 2016 were retrospectively analysed for the inclusion in the study. Patients were indicated for CRT according to European guidelines indications available at time of CRT implantation. All patients underwent implantation of a CRT system, with or without implantable cardioverter- defibrillator capabilities based upon clinical and patient decision. Exclusion criteria were unavailability or poor quality of the baseline ECG, baseline right ventricular pacing, incomplete follow-up data and inadequate biventricular pacing after implantation (≤95% biventricular pacing). The study protocol was approved by the locally appointed ethics committee and complied with the Declaration of Helsinki. Written informed consent has been obtained from all subjects (or their legally authorized representative).