Ann Thorac Surg 2008;85:79. doi:10.1016/j.athoracsur.2007.09.026
© 2008 The Society of Thoracic Surgeons
Original Articles: Cardiovascular
Invited commentary
Munir Boodhwani, MD, MMSc
University of Ottawa Heart Institute, H3401, 40 Ruskin St, Ottawa, Ontario K1Y 4W7, Canada
(Email: mboodhwani{at}ottawaheart.ca).
Coronary collaterals are present in the human heart at birth and have been shown to exist in the absence of coronary disease. These vessels, in large part, remain physiologically dormant. However, in the setting of coronary artery disease, they can play a crucial role in limiting the burden of myocardial ischemia, thereby reducing the incidence and magnitude of myocardial injury. Coronary collateral reserve has been shown to be associated with a reduction in myocardial events in patients with chronic stable angina and those undergoing percutaneous coronary interventions [1].
The presence of collaterals also has important implications for patients undergoing off-pump coronary surgery (OPCAB), as these collaterals can provide perfusion to the ischemic myocardium during periods of coronary occlusion. The beneficial effects of coronary collaterals on short-term and mid-term outcome in the setting of OPCAB have been previously suggested [2]. In their study, Caputo and colleagues [3] provide further support for this idea by demonstrating that patients with angiographically visible collaterals undergoing OPCAB had a lower incidence of intraoperative ischemic electrocardiographic changes. However, unlike previous reports, they did not find a difference in the occurrence of clinically or electrocardiographically diagnosed perioperative myocardial infarction. Of note, biochemical markers of myocardial injury were not measured in their study.
In their large cohort of OPCAB patients, they also found that the presence of coronary collaterals was not associated with improved mid-term survival or myocardial events. This is in contrast with previous reports that have repeatedly demonstrated the protective effects of collaterals in patients with nonrevascularized coronary artery disease [1]. The fate of coronary collaterals after surgical revascularization has not been extensively studied. Older studies, involving a small number of patients, suggest that coronary collaterals that are visible prior to coronary bypass surgery disappear in the presence of a patent bypass graft and can reappear if the graft occludes [4]. If this is true, the functional benefits of collateral vessels would only be apparent in the setting of graft failure, and the duration of follow-up in this study (median follow-up, 3.7 years) may be too short to demonstrate such a difference. Another limitation of this study is the use of an angiographic, semiquantitative evaluation of coronary collaterals (Rentrop score). Coronary pressure or Doppler-based methods, although more invasive, provide more sensitive and physiologically relevant measures of collateral flow reserve [5].
Last, significant variability exists in the degree to which individuals form coronary collaterals in response to myocardial ischemia. Consistent with previous reports, the authors found that greater severity of coronary disease was associated with increased presence of collateral vessels. Certain disease states (eg, diabetes [6], as well as molecular [7] and genetic factors [8] have been implicated in the formation of coronary collaterals. A better understanding of these determinants of collateral vessel formation will be critical to the successful development of growth factor or cell-based angiogenesis as viable therapeutic strategies in the treatment of coronary artery disease.
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- Boodhwani M, Sodha NR, Mieno S, et al. Functional, cellular, and molecular characterization of the angiogenic response to chronic myocardial ischemia in diabetes Circulation 2007;116:I-31-I-37.[Medline]
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Related Article
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Coronary Collateral Circulation: Effect on Early and Midterm Outcomes After Off-Pump Coronary Artery Bypass Surgery
- Massimo Caputo, Rafik R. Anis, Chris A. Rogers, Nazir Ahmad, Syed I.A. Rizvi, Andreas Baumbach, Karl R. Karsch, Gianni D. Angelini, and Martin Oberhoff
Ann. Thorac. Surg. 2008 85: 71-79.
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