The Frank-Starling law states that the stroke volume of a regular cardiac beat increases in response to an increase in the volume of blood filling the heart. If this law applies in atrial fibrillation (AF) as well as in sinus rhythm (SR) then cardiac function will depend on the duration of diastole in the preceding beat as well as the duration of the indexed beat. Aim: The aim of this thesis was to develop a series of tools which would allow an assessment of the changes in cardiac function from one beat to the next in AF and SR. A secondary aim was to find a means of describing rhythm in a way that reflected possible functional change. Methods: List-mode radionuclide ventriculography, RNVG, acquisitions of 373 patients in AF and a comparative group of 385 patients in SR were made. Software was written which allowed tightly defined preceding and indexed beat selection criteria to be established. Left ventricular ejection fraction (LVEF) and other functional parameters (pre-systolic volume, systolic time, the ratio of pre-systolic to end-diastolic volume, peak filling rate and first third filling fraction) were calculated for images created using different beat selection criteria based on the quartiles of beat length. Assessment used both variable and fixed time formatting and included a comparison of results achieved in the first and second half of the scan. Traditional linear measures of heart rate variability together with descriptors of the Poincar´e plot and cycle length entropy were used to describe rhythm in both AF and SR patients. Results: Substantial variation with indexed and preceding beat length was seen in both SR and AF in all the systolic parameters measured and in particular in LVEF where the standard deviation of LVEF for any one patient was found to be 8.2% in SR and 14.1% in AF. A combination of descriptors of rhythm was found to have good correlation with the range of LVEF measured. Examination of the results for LVEF in several clinical sub-groups suggests that the range of LVEF may have clinical interest. The techniques were applied in a small clinical study which considered the value of radio-frequency ablation in patients with AF and heart failure. In this study, measures of Sample entropy and the range of LVEF appeared to have prognostic value. Conclusion: A tool which allows the investigation of beat-to-beat functional variation in RNVG has been produced. It has been shown that the functional variation depending on beat selection criteria is substantial and may have clinical significance both in patients with underlying pathology and prognostically in patients undergoing radiofrequency ablation (RFA).
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:559992 |
| Date | January 2012 |
| Creators | Small, Alexander |
| Publisher | University of Glasgow |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://theses.gla.ac.uk/3564/ |
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