Noninvasive evaluation of the effects of coronary artery bypass grafting on myocardial function

University dissertation from Stockholm : Karolinska Institutet, Karolinska Institutet, Stockholm Söder Hospital

Abstract: Coronary bypass grafting (CABG) is an effective treatment of patients with coronary artery disease and leads to an improvement in both cardiac symptoms and long-term survival. The effects of CA13G on global left ventricular systolic and diastolic function at rest and during stress, and the long-term effects on right ventricular function and their significance and relation to early graft occlusion and residual myocardial ischemia have however not been fully elucidated. It is known that early graft occlusion depends mainly on thrombotic mechanisms. Thrombosis and inflammation are closely related. However it remains unsettled if preoperative inflammatory activity predicts early graft occlusion and late cardiac events in patients subjected to CABG. The present study comprises 99 patients accepted for CABG because of angina pectoris and significant coronary artery stenosis at angiography. Exclusion criteria were a history of recent myocardial infarction (4 weeks before preoperative angiography), atrial fibrillation, significant valvular heart disease or previous CABG. Eighty-five men and 14 women aged 65±9 years (range 40-82) were included. All patients underwent preoperative blood tests, exercise ECG testing, first pass radionuclide angiography (FPRNA), single photon emission computed tomography (SPECT), echocardiography and a dobutamine stress test before CABG. The same tests and a coronary angiography were repeated 3 months after CABG, and a third echocardiography was performed 12 months after CABG. Of 286 operated grafts 32(11 %) grafts were occluded and 31 % of the patients had at least one occluded graft 3 months after CABG. In patients with a moderately decreased left ventricular ejection fraction (LVEF) CABG improves LVEF under stress (P<0.001) but not at rest. Despite this lack of improvement in resting LVEF, CABG relieves angina, improves myocardial perfusion both at rest (P<0.001) and during stress (P<0.001), and augments the work capacity of the patients as evaluated by a symptom-limited exercise test (P<0.001). CABG also improves the left ventricular diastolic function (P<0.01) as assessed by Doppler tissue imaging (DTI), but not by conventional Doppler echocardiography. The enhancement of diastolic DTI parameters was observed both at rest and during stress. Right ventricular function evaluated by tricuspid annular motion was still decreased 1 year after CABG and septal motion remained paradoxical in the majority of patients, suggesting that these defects might be permanent. This finding was independent of the state of the right coronary artery as well as grafts to this artery. Despite the reduced tricuspid annular motion, exercise performance was improved 3 months after CA13G (P<0.01). Furthermore, we found that elevated preoperative IL-6 levels are predictors of both early graft occlusion (P<0. 1) and late cardiovascular events (P<0.01) after CA13G. Elevated preoperative CRP levels can predict early graft occlusion (P<0.05) after CABG. In conclusion: CABG improves systolic left ventricular function predominantly at stress as well as the diastolic left ventricular function as measured by DTI. The decrease of right systolic ventricular function as evaluated by tricuspid annular motion after CABG was present also at the I -year follow-up and may be permanent. Preoperative inflammatory parameters predict early graft occlusion and late cardiac events after CABG.

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