The role of advanced cardiovascular imaging in the management of the new cardiovascular epidemics of old age

\\({Background}\\) The ageing population, greater survival following acute myocardial infarction and a greater prevalence of risk factors have all contributed to the emerging epidemics of Atrial Fibrillation (AF) and Heart Failure with Preserved Ejection Fraction (HFpEF). At the same time, the landscape of cardiovascular imaging has shifted from echocardiography alone to one of multi-modality imaging. The combination of these developments has contributed to an increase in inappropriate use of cardiac investigations which, in its own right is an iatrogenic cardiovascular epidemic. An understanding of how best to utilise these technological advances with respect to optimal management of AF and HFpEF requires an evaluation of literature and experimental evaluation of their respective utilities. \\({Hypothesis}\\) The integration of advances in echocardiography (such as myocardial strain), Cardiac Computed Tomography (CT) and Cardiac Magnetic Resonance (CMR) into current diagnostic pathways will improve our ability to evaluate presence of disease, enable comprehensive characterisation of both AF and HFpEF and also enable prognostication of future events. \\({Aims}\\) I seek to determine the roles of Echocardiography, Cardiac CT and CMR with respect to AF and HFpEF. I also aim to use imaging advances to address the epidemic of inappropriate use. The goal of this thesis is to determine how advances in cardiac imaging can be integrated to improve management of cardiovascular epidemics both clinical (AF and HFpEF) and systemic/iatrogenic (inappropriate use). \\({Method}\\) I have divided my PhD thesis into 3 interconnected parts with each part informing the next. Firstly I present a review of current imaging modalities, recent advancements and their roles in the management of AF and HFpEF. Having reviewed the landscape of current advances and how they may contribute to management of the current epidemics of HFpEF, AF, in part 2, I seek to address some barriers and limitations: 1.) Availability, cost and speed of CMR, 2.) The limitations of CMR in evaluating diastolic function in HFpEF 3.) The need to assess atrial function non-invasively and predict AF using atrial strain Which is currently limited by a.) by a lack of consensus on normal references ranges for atrial strain b.) A lack of understanding about inter vendor and inter modality differences Finally, in part 3, informed by the literature reviews and validation data, I seek to employ 2 advances (namely, atrial strain and Hand Held ultrasonography (HHU)) to demonstrate improved efficiency based on information gained, improved service delivery and reduced cost. All statistical analysis was performed on IBM SPSS Statistics version 24 (SPSS, Chicago, IL, USA), R (The R project) and correlation/ Bland-Altman plots were created on MedCalc¬¨vÜ Version 17.9.7(MedCalc Ostend, Belgium). \\({Results}\\) First: the literature reviews show that in addition to the existing role of echocardiography there is a growing body of evidence for the role of Cardiac CT in the management of AF and an underutilised role for CMR in the diagnosis, phenotyping and management of HFpEF. Furthermore, HHU epitomises efficiency and illustrates that advancement need not involve bigger and more expensive machines but may evolve to small and technically sound devices which are well validated and can be applied to various clinical scenarios. Second: the meta-analysis of left atrial strain demonstrates a normal reference range for 3 components of atrial strain - Reservoir Strain, Conduit Strain and Contractile Strain, despite marked heterogeneity in published studies. It explores the contributors to heterogeneity. The meta-analysis also highlighted a distinct lack of inter vendor comparisons and complete lack of validation studies. Third: left atrial reservoir strain is a robust marker of left atrial function which shows good- excellent intervendor and intermodality correlation. Contractile strain however showed modest to good intervendor and intermodality correlation. Fourth: a rapid CMR protocol utilizing radial spatial encoding and non-linear reconstruction protocols can image the entire left ventricle within 2 breath holds and shows excellent correlation with the current reference standard for left ventricular measures and modest to good correlation for right ventricular measures. Fifth: CMR shows reasonable correlation with echocardiography with respect to the diastolic indices of E/A, e' and E/e', however the results need to be validated against an invasive measure of diastolic function. Sixth: atrial strain is the best echocardiographic predictor for atrial fibrillation following cryptogenic strokes. Furthermore atrial strain adds independent and incremental diagnostic value to the current risk prediction algorithms used to predict AF. Seventh: HHU can be an effective selection strategy which reduces inappropriate echocardiograms performed, reduces cost, improves time to scan and does not compromise diagnostic accuracy. \\({Conclusion}\\) Advances in echocardiography and CMR enable a multi-modality approach to AF and HFpEF. As I have demonstrated, the incorporation of such technologies requires fulfillment of certain steps which include validation (left atrial strain validation), description of normal references ranges (meta-analysis) and experimental evidence demonstrating performance relative to existing modalities and reference standards (diastolic CMR, rapid CMR and atrial strain validation). These advances add to current diagnostic algorithms (atrial strain), expand the functionality of existing modalities (diastolic CMR) and improve the technical efficiency by improving speed of imaging (rapid CMR). Finally, I have experimentally applied 2 imaging advances (atrial strain and HHU) in clinical scenarios in a retrospective observational study and a prospective study with case controls. In both cases the imaging advances provided either independent and incremental diagnostic information over and above existing clinical and imaging pathways (atrial strain for predicting AF) or equivalent diagnostic information at a considerably lower cost and resulted in improvements of resource allocation. These final 2 studies put into practice knowledge from literature reviews and the knowledge gained from part 2 of the thesis to demonstrate technical, productive and allocative efficiency.