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Literature Review

Coronary Artery Bypass Grafting With and Without Manipulation of the Ascending Aorta: A Network Meta-Analysis

Zhao DF, Edelman JJ, Seco M, et al. J Am Coll Cardiol. 2017;69(8):924–936.

Reviewers: Zhenhua Wu, MD1; Yong G. Peng, MD PhD FASE2

  1. Department of Cardiovascular Surgery, Tianjin Thoracic Hospital, Tianjin, China
  2. Department of Anesthesiology, University of Florida College of Medicine, Gainesville, FL
Background

Coronary artery bypass grafting (CABG) is one of the most common and effective surgical approaches in treating multivessel coronary heart diseases. Stroke is a common complication after CABG, particularly in geriatric populations. Some evidence has suggested that eliminating cardiopulmonary bypass (CPB) and minimizing aortic manipulation may significantly reduce the incidence of postoperative complications, including stroke.

Methods

The authors searched six electronic databases and collected the results of 13 studies with
37 720 cases in this network meta-analysis. The incidence rate of stroke and other complications after the operation methods of an anaortic off-pump CABG (anOPCABG), off-pump graft with the clampless HEARTSTRING device (OPCABG-HS), and off-pump graft with a partial clamp (OPCABG-PC) were compared to the conventional method in CPB with aortic cross-clamping and their overall outcomes were analyzed and evaluated.

Results

Comparing the incidence rate of stroke, short-term mortality, renal failure, bleeding complications, and atrial fibrillation after the four above-mentioned operations and the time in the intensive care unit (ICU), the results showed that an OPCABG was the most effective surgical modality for decreasing the risk of postoperative stroke (–78% vs CABG, 95% confidence interval [CI]: 0.14 to 0.33; –66% vs OPCABG-PC, 95% CI: 0.22 to 0.52; –52% vs OPCABG-HS, 95% CI: 0.27 to 0.86), mortality (–50% vs CABG, 95% CI: 0.35 to 0.70; –40% vs OPCABG-HS, 95% CI: 0.38 to 0.94), renal failure (–53% vs CABG, 95% CI: 0.31 to 0.68), bleeding complications (–48% vs OPCABG-HS, 95% CI: 0.31 to 0.87; –36% vs CABG, 95% CI: 0.42 to 0.95), atrial fibrillation (–34% vs OPCABG-HS, 95% CI: 0.49 to 0.89; –29% vs CABG, 95% CI: 0.55 to 0.87; –20% vs OPCABG-PC, 95% CI: 0.68 to 0.97), and shortening the length of the ICU stay (–13.3 h; 95% CI: –19.32 to –7.26; p<.0001).

Conclusion

An OPCABG decreases the risk of postoperative stroke by avoiding aortic manipulation, which is especially beneficial to patients with a high risk of stroke, as well as aging. Compared with CABG, the incidence rates of renal failure, atrial fibrillation, and bleeding complications were evidently decreased, and the in-hospital stay also was significantly shorter with OPCABG.

Comments

Stroke is a common complication after a surgical treatment of coronary heart disease. It is hard to determine the principal factor, and it is believed that the causes of complications are multifactorial. The risk factors such as aging, atherosclerosis, hypertension, cardiopulmonary bypass, and ascending aortic manipulation may all contribute to this outcome.

During the operation of CABG, the heart tissue fragments, exfoliated calcium spots, and gas embolism—especially the vestigial gas within the cardiac chamber and pulmonary vein from cardiac resuscitation and impulse recovery—can all result in cerebral embolism, leading to cerebral injury or functional damage of the brain after the operation. Focal cerebral ischemia, caused by hypoperfusion and embolism during the period of operation, leads to reperfusion injury. However, during surgery, using CPB, which is a nonphysiologic circuit, also can impact cerebral blood flow and microcirculation. Longer cardiopulmonary bypass time can result in release of cytokines, complement activation and systemic inflammatory response syndrome, and ultimately lead to neuronal cell injury. Other factors also may be responsible for neurological deficit, such as direct contact of blood with the surface of a foreign circuit, blood pumping through the oxygenator with different pressure, the cooling and rewarming process that occurs during cardiopulmonary bypass, and anticoagulation, which can result in damage of blood constituent, agglutination of the blood platelet and blood components, and forming of a microthrombus, which could lead to postoperative stroke.

OPCABG can effectively avoid atrial-systole wave, hypoperfusion, temperature variation, and embolism formation, lowering the chance for cerebral complications. However, there are still higher incidence rates of stroke because aeroembolism produced during operation process blood pressure fluctuations due to moving heart or use of side wall clamps to clamp the aorta for proximal vessel anastomosis, resulting in focal brain infarction and then stroke. Meanwhile, more and more study results suggest that inflammatory response caused by CABG plays an important role in the acute injury of neurons due to cerebral ischemia.

There are several limitations in this study. First, the article used network metaanalysis, a popular statistic method that is more likely to be valid when analyzing very similar studies for a homogenous patient population. Because current analyses have extended to combine several different studies, there is a potential for arbitrary factors to impact the results of network meta-analysis. Combining different studies with network meta-analysis may not generate valid study results.

Second, the results presented in this article all come from the individual study’s statistical data from short-term outcomes after surgery. A long-term follow-up prognosis of these patients needs to be further evaluated.

Third, the decision of which of the above surgical approaches to use was at the surgeon’s discretion at different medical institutions. There is an unavoidable variation in surgeons’ preferences and bias in case selection. Since this is not a randomized observational combined analysis, the overall results should be interpreted with caution.

Unadjusted summary of this study cannot eliminate potential confounding factors that may have obscured the conclusion of the study. The results warrant additional prospective study to further address these longtime debatable questions.

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