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Objective-Off-Pump Coronary Artery Bypass (OPCAB) surgery is gaining more popularity worldwide. The aim of this United Kingdom (UK) multi-center study was to assess the early clinical outcome of the OPCAB technique and perform a risk-stratified comparison with the conventional Coronary Artery Bypass Grafting (CABG) using the Cardio-Pulmonary Bypass (CPB) technique. Methods-Data were collected on 5,163 CPB patients from the database of the National Heart and Lung institute, Imperial College, University of London, and on 2,223 OPCAB patients from eight UK cardiac surgical centers, which run established OPCAB surgery programs. All patients had undergone primary isolated CABG for multi-vessel disease through a midline sternotomy approach, between January 1997 and April 2001. Postoperative morbidity and mortality were compared between the CPB and OPCAB patients after adjusting for case-mix. The mortality of the OPCAB patients was also compared, using risk stratification, to the mortality figures reported by the Society of Cardiothoracic Surgeons of Great Britain and Ireland (SCTS) based on 28,018 patients in the national database who were operated on between January 1996 and December 1999. Results-Morbidity and mortality were significantly lower in the OPCAB patients compared with the CPB patients and the UK national database of CABG patients, over the same period of time, after adjusting for case-mix. Conclusion-This study demonstrates that risk stratified morbidity and mortality are significantly lower in OPCAB patients than CPB patients and patients in the UK national database. (Circulation. 2003;108[suppl II]:II-1-II-8.) Key Words: coronary surgery ischemic heart disease coronary heart disease cardiopulmonary bypass O ff-Pump Coronary Artery Bypass (OPCAB) surgery is gaining more popularity worldwide. 1 The theoretical and proven disadvantages of the use of the Cardio-Pulmonary Bypass (CPB) for multi-vessel Coronary Artery Bypass Grafting (CABG) has prompted many cardiac surgeons in the United Kingdom (UK) to convert to OPCAB practice in their units. 2 To date, no collective data on the initial OPCAB experience in UK is available. The aim of this UK multi-center study was to assess the early clinical outcome of the OPCAB technique and perform a risk-stratified comparison with the established CPB technique.

The timing and amplitude of reflected arterial waves in the ascending aorta were studied by analysis of the aortic pressure waveform and were compared with those derived using wave intensity analysis. Wave intensity analysis considers aortic pressure changes to be the result of forward and backward wavelets carrying energy. Wave intensity (dI = dPdU) is calculated from changes in pressure (dP) and flow velocity (dU), and its sign indicates the direction of travel of propagating wavelets (positive for forward-traveling waves and vice versa). We measured aortic pressure and flow velocity in 14 patients, mean age 60+/-9 years, with three-vessel coronary artery disease at the time of surgical revascularization. The travel time of the reflected wave derived from analysis of the aortic pressure waveform (tp) was measured from the foot of the aortic pressure waveform to the inflection point of the aortic pressure (derived objectively from the zero of second derivative of aortic pressure). From wave intensity analysis, the travel time of the reflected wave was measured to the onset of the wave intensity of the backward-traveling wave dI_ (t(i)), and to the onset of the separated backward pressure wave (t(b)). All patients showed an aortic pressure waveform characterized by an inflection point on the rising limb of the aortic pressure, followed by a secondary rise in pressure, representing the return of reflected waves. Wave intensity analysis consistently showed a negative peak in mid systole, the timing of its onset corresponding closely to the inflection point of the aortic pressure. The travel time of the reflected wave derived from the analysis of the aortic pressure waveform (t(p)) was 121+/-21ms and showed close agreement with ti (118+/-28 ms) and t(b) (115+/-29ms), with mean differences of 4 and 6ms, and 95% confidence intervals of difference (-2 to 7 ms) and (1 to 12ms), respectively. The augmentation index, a measure of the secondary increase in aortic pressure due to reflected waves, was significantly correlated with the magnitude of dI_ (r = 0.63, P < 0.001). Wave intensity is a quantity that indicates the rate of energy flux due to wave travel and since its value is positive for forward-traveling waves and negative for backward-traveling waves, its calculation allows the timing of reflected waves to be accurately predicted. Furthermore, the magnitude of wave intensity in backward-traveling waves (dI_) is related to the augmentation index and may provide a measure of the amplitude of the reflected wave. This analysis of the arterial system is done in the time domain and therefore can be easily applied to assess temporal changes in arterial characteristics.