| Summary: | Cardiac Resynchronisation Therapy (CRT) is an effective treatment for selected patients with heart failure. The left ventricular (LV) lead used to achieve this can be hard to place via the coronary sinus in a proportion of patients, and in addition may not be in an optimal position in others. In this thesis, I initially discuss CRT and its technical limitations. Using a large meta-analysis, I elucidate contemporary rates of LV lead placement failure. An alternative method of LV lead placement is endocardial, and I discuss results to date, again using a meta-analysis to summate prior trials and the technique's risks and benefits. The main subject of the thesis is assessing a novel method of LV endocardial pacing via the interventricular septum. I report a trial of 19 patients in whom conventional CRT was not possible or unsuccessful, showing clinical response to CRT delivered in this manner to be similar to conventional CRT, with acceptable risks. LV lead location in endocardial CRT has been little studied. I go on to investigate optimal LV lead positioning in this group, by assessing acute haemodynamic response (AHR) to CRT with a high-fidelity pressure wire and a multi-level modelling analysis. I show that this technique is reproducible. I compare placement at sites of late mechanical activation and late electrical activation, showing little difference in this cohort or in a parallel study of AHR in 22 patients undergoing conventional CRT. With a multivariate analysis I show that only electrical delay is a consistent predictor of acute response. These results support the use of this novel technique for CRT as a second-line procedure, and I discuss future directions for this. Lead site selection at a site of late electrical activation is supported by my work, and again I summarise the context of this.
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