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J Thorac Cardiovasc Surg 2003;125:1179-1180
© 2003 The American Association for Thoracic Surgery
Letters to the Editor |
Department of Cardiothoracic Surgery, Yorkshire Heart Center, Leeds General Infirmary, Great George Street, Leeds LS1 3EX, United Kingdom
To the Editor:
Beating heart coronary artery bypass surgery (OPCAB) is gaining wider acceptance because of the potential benefits of eliminating cardiopulmonary bypass and its deleterious effects. The report of Cartier and Robitaille
1 is therefore interesting and adds to the genuine perturbations of this technique. However, some aspects of the study raise concern.
Cartier and Robitaille conducted a retrospective study of the thromboembolic complications after OPCAB and compared it with a selected group of patients who had coronary artery bypass grafting using cardiopulmonary bypass (CABG). They reported the incidence of thrombotic complications as 1% in 500 OPCAB patients in a 4-year period and 0.5% in 1476 CABG patients selected from the latter 2 years of the study period. Admittedly, 3 of the 5 OPCAB patients in whom thrombotic complications developed had predisposing factors. Two had deep vein thrombosis ipsilateral to the leg where a preoperative intra-aortic balloon pump was inserted. The third had chronic renal failure and was being treated by hemodialysis.
No prophylactic regimen for preventing thromboembolism was adopted in the OPCAB patients in this study.
The retrospective study of the prevalence of postoperative thromboembolic complications is hindered by the nature of the investigation. There are many symptom-free patients with thromboembolism (up to 44.8% of patients have deep vein thrombosis after CABG) 2 that will be missed. Also, there are patients with mild symptoms who would not have been investigated appropriately, and yet others who have thromboembolic complications after hospital discharge and receive treatment at a different facility.
The selection of the CABG patients for comparison with the OPCAB group is worrisome. The CABG patients were chosen from a fraction of the study period for the OPCAB patients, and little is known about the patient characteristics and operative and postoperative variables of the two groups. Comparing these unmatched heterogeneous groups of patients who had different surgical myocardial revascularization techniques, operating times, and intraoperative and postoperative management, without controlling for effect modification by these variables, will prejudice the result.
It has been suggested that patients who have leg vein harvest demonstrate circulatory disturbances in the venous system of the donor legs. 3 This, combined with leg wound problems and, sometimes, delayed mobilization, distinguishes the patient with saphenous vein harvest from the patient whose leg veins were not harvested. This also adds to the heterogeneity of the groups.
Thromboembolic prophylaxis is effective in patients undergoing cardiac surgery 4 and is commonplace. The authors eruditely enunciated a formidable and impressive discussion of the hypercoagulability of major tissue trauma and median sternotomy, which are integral to cardiac surgery. It is therefore intriguing that the OPCAB patients did not receive any prophylaxis against thromboembolism. This possibly contributes to the difference in the incidence of thromboembolic complications between the two groups.
This study has not shown compelling evidence in support of its claim. It probably emphasizes the importance of prophylaxis for thromboembolism in high-risk patients undergoing OPCAB.
References
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