Abstract
Over the past 50 years, cardiac pacemakers have been used to treat bradycardia such as complete heart block, with single chamber pacing, then dual chamber pacing with the advantage of atrioventricular synchrony and more recently the development of biventricular pacing for heart failure, severely impaired left ventricular function and left bundle branch block. Throughout this pacemaker therapy has been designed to approach normal physiology. Indeed biventriuclar pacing is conceived as resynchronisation therapy, and is commonly referred to as such.Alongside such developments in pacemaker therapy, real-time three-dimensional echocardiography has emerged as a technique to accurately measure left ventricular function and assess dyssynchrony.
This thesis uses this technique in four discrete projects. The first investigated the optimal timing of pacing stimuli compared to impedance and invasive haemodynamics. The second investigated mid-septal as compared to conventional right ventricular pacing. The third investigated the utility of dyssynchrony assessment after biventricular pacing to predict medium term response and the need for optimisation. The final chapter investigated the reliability and reproducibility of novel three-dimensional speckle tracking techniques.
The concordance of impedance, haemodynamic and echocardiographic measurements in selecting the optimum atrioventricular pacing interval was poor. Right ventricular pacing resulted in an acute decrement in left ventricular function, particularly in patients with pre-existing left ventricular dysfunction. In these patients mid-septal pacing caused less of a decline in left ventricular function than apical pacing. The assessment of dyssynchrony after biventricular pacemaker therapy was a powerful predictor of medium term response, as well as identifying a group of patients with a higher probability of acute response to optimisation of timing of pacing stimuli. Novel three-dimensional speckle tracking methods have good reproducibility for calculation of left ventricular volumes, but not for dyssynchrony measurements. After training and with better quality datasets, reproducibility is improved.
Three-dimensional echocardiography is an attractive technique in the evaluation of patients with pacemakers. Some of the changes induced by altering pacemaker settings are near the limit of resolution of the technique. Speckle tracking is attractive and the improvement in software may improve its reliability and utility.
| Date of Award | 2016 |
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| Original language | English |
| Awarding Institution |
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| Supervisor | Mark Monaghan (Supervisor) |