The impact of coronary bypass surgery on myocardial perfusion and function

Woldman, Simon (2000) The impact of coronary bypass surgery on myocardial perfusion and function. MD thesis, University of Glasgow.

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One hundred and fourteen patients were studied before and after coronary bypass surgery using radionuclide techniques to assess myocardial perfusion and function. At baseline and at follow up visits each patient was assessed by a clinician. Regional and global myocardial perfusion was evaluated at rest and at peak exercise using a total of 60MBq of thallium 201. Rest and exercise thallium scintigraphy was repeated 9 months after CABG (late follow up). In order to assess myocardial hibernation redistribution of rest images were acquired at baseline before the exercise images. Left and right ventricular ejection fractions (LVEF and RVEF) were measured by radionuclide ventriculography performed at baseline on a separate day from the thallium images. Regional ventricular wall motion was assessed on a continuous loop cine display of the 24 frames of the radionuclide ventriculogram with the aid of standard fourier amplitude and phase images. After the completion of the rest radionuclide ventriculogram dobutamine was administered at doses of 5-10mug/kg/min and the effect of the dobutamine on left ventricular regional wall motion was assessed. Radionuclide ventriculography was repeated 6 weeks (early follow up) and approximately 9 months (late follow up) after surgery. Coronary bypass surgery produced a marked improvement in symptoms and exercise tolerance. Before the operation 98% of the patients described symptoms of angina. After bypass surgery 71% were completely angina free (p<0.001). Exercise time using a standardised protocol increased from 296.2 + 87 seconds prior to surgery to 357 +/- 98 seconds after surgery (p<0.001). There was only minor variation in rest LVEF: LVEF at baseline was 32% (+10%). This rose to 34% (+/-11%) at the early follow up study (p=0.02). However by late follow up LVEF had;returned to 33% (p=n.s.d. for change from II baseline). In contrast there was a sharp fall in RVEF: RVEF was 33% (+8%) at baseline; by early follow up RVEF had fallen to 27% (+/-7%), p<0.001. There was no recovery in RVEF at late follow up, 26% (+/- 7%), p<0.001 for change from baseline. This fall in RVEF was not related to the preoperative LVEF, total bypass time, total cross clamp time, or grafting of the right coronary artery. The study confirmed major deterioration in septal function following coronary bypass surgery, previously detailed by other authors. There was also a minor deterioration in anterior and inferior regional function. However, posterolateral regional wall motion improved following CABG. Only 1 of the 25 (4%) septal territories that had impaired regional wall motion demonstrated improved function at early follow up. In comparison, 14 of the 20 (70%) posterolateral territories that had impaired regional wall motion at baseline demonstrated improved function at early follow up (p<0.001). The total exercise myocardial perfusion score derived from the thallium scintigrams improved following CABG. The improved perfusion was most noted in the inferior and posteroseptal regions. There was no change in the mean perfusion score in the anterior, posterolateral and septal territories. Rest redistribution imaging did identify patients that demonstrated an increased LVEF at early follow up. In the group of patients who demonstrated a reversible defect from rest to redistribution, LVEF rose from 32% (+/- 13%) to 36% (+/-13%) at early follow up, p=0.004. However at late follow up this was not sustained and LVEF fell back to (32%), p<0.01 for change from early follow up. In contrast amongst those who did not demonstrate reversibility from the rest to redistribution image there was no change in LVEF; at baseline LVEF was 33% (+/-10%), at early follow up 33% (+/-11%) and at late follow up 33% (+/-12%). Similarly, those patients who demonstrated improvement in regional wall motion with dobutamine also demonstrated an initial rise in LVEF at early follow up with a subsequent return to baseline values. In this group LVEF was 27% (+/-8%) III at baseline and 30% (+/-10%) at early follow up (p<0.01). By late follow up LVEF had fallen back to 28% (+/-13%), p<=0.04). Coronary bypass surgery has little effect on left ventricular ejection fraction. Right ventricular ejection fraction falls sharply, and the fall is sustained at least nine months after the operation. Septal regional function deteriorates after bypass surgery, while posterolateral function seems to improve. Global myocardial perfusion indices improve following CABG, particularly in the inferior and posteroseptal regions. Both rest redistribution thallium scintigraphy and low dose dobutamine radionuclide ventriculography can identify a group of patients whose LVEF improves 6 weeks after operation. However this improvement is not sustained, and by nine months after operation LVEF returns to baseline values.

Item Type: Thesis (MD)
Qualification Level: Doctoral
Additional Information: Adviser: Ian Hutton
Keywords: Medicine, surgery.
Colleges/Schools: College of Medical Veterinary and Life Sciences
Supervisor's Name: Supervisor, not known
Date of Award: 2000
Depositing User: Enlighten Team
Unique ID: glathesis:2000-72626
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 11 Jun 2019 11:06
Last Modified: 19 Aug 2022 08:56

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