Cardiovascular Magnetic Resonance Imaging Assessment of the Acute and Chronic Haemodynamics of Right Ventricular Pacing

Introduction: Right ventricular (RV) pacing is recommended treatment for bradycardia and can normalise life expectancy and restore quality of life. Clinical trials have demonstrated that chronic RV apical pacing may be associated with an adverse prognosis and development of heart failure. Multi-parametric cardiovascular magnetic resonance (CMR) has several clinical and research applications and can quantitatively assess cardiac anatomy, function, intracardiac flow and myocardial tissue characteristics. Aims: To assess 1.) the feasibility of 4D flow and validity of transvalvular flow quantification in pacemaker patients. 2.) haemodynamic response of intrinsic atrioventricular (AV) conduction and forced RV pacing in those with and without focal myocardial fibrosis. 3.) the hypothesis that long term RV pacing in presence of focal myocardial fibrosis leads to adverse cardiac remodelling. Methods: Between November 2017 and August 2019, patients with MRI conditional devices were prospectively recruited from a single centre. Patients underwent multi-parametric CMR at 1.5 Tesla. Patients in Chapters 3 and 4 underwent CMR in two separate pacing modes during a single visit. Patients in Chapter 5 underwent CMR before and 6 months after pacemaker implantation. Results: 1. Flow across aortic, mitral and tricuspid valves was consistent and reproducible in both pacing modes (p>0.05 for all). 2. A greater decline in left ventricular (LV) ejection fraction (p=0.02) was observed during forced RV pacing in patients with myocardial fibrosis compared to patients without fibrosis. 3. Patients with AV block and myocardial fibrosis undergoing pacemaker implantation have greater electromechanical dyssynchrony and a consequent increase in LV end systolic volume (p=0.008) at 6 months compared to those without fibrosis. Conclusions: Right ventricular pacing in patients with myocardial fibrosis, compared to those without, leads to greater deterioration in cardiac function both immediately and after 6 months.