Cardiac Resynchronisation Therapy (CRT) has been shown to improve cardiac performance and quality of life in specific patients with heart failure. These patients have poor cardiac pumping capacity and their heart chambers contract out of sequence, due to a delay in the natural electrical system across the ventricles. The goal of CRT is to reduce the electrical delay and restore synchronisation between the heart chambers. This can be seen as a narrowing in the QRS duration on the ECG. The extent of QRS narrowing is emerging as a key marker of successful CRT with a growing evidence base of improved response and long-term survival.
However, not all patients respond favourably to CRT and approximately 30% are considered non-responders. Multiple factors can influence response to CRT and research has previously focussed on patient selection and lead placement. Electrical programming has been shown to improve CRT response, but a universal programming strategy may be ineffective as patient specific factors can influence electrical timing within the heart. Moreover, there is little guidance for CRT programming, hence CRT devices are often left at suboptimal settings. Two emerging technologies, fusion pacing (e.g SyncAV) and multipoint pacing (MPP), have been shown to narrow QRS and give acute benefit. It seems intuitive that combining technologies may augment the benefit but there is little evidence available to support this. Accurate measurement of QRS duration is crucial in CRT. Despite this, there is no agreed technique to measure QRS duration and different methods are used in clinical practice. Global QRS duration has been shown to have improved accuracy over individual lead measurement. However, global QRS duration is less easily measured without specialist software, hence it is not routinely used in practice.
This study compares five programming strategies specifically tailored to the individual and optimal CRT will be considered as the maximal reduction in ventricular delay (i.e narrowest QRS). A secondary objective is to compare whether an abbreviated global QRS measurement over 5 leads on the device programmer is comparable to individual lead measurements on the 12 lead ECG. Overall, this study may help guide operators to best optimise CRTs in routine practice.
Although the project remains ongoing, it has already resulted in a change in practice at our hospital. The method for measuring QRS duration has been standardised for CRT, abbreviated global QRS over 5 leads is now used as standard for both CRT implantation and follow-up.