To assess the prognostic role of coronary collaterals in patients with type 2 diabetes mellitus (T2DM) after successful percutaneous coronary intervention (PCI) for chronic total occlusion (CTO). Methods: Coronary collateralization was graded according to Rentrop scoring system in 198 type 2 diabetic patients and 335 non-diabetics with stable angina undergoing PCI for at least one CTO lesion. Left ventricular ejection fraction (LVEF) was determined and major adverse cardio-cerebral events

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... ) were recorded during follow-up. Results: Poor collateralization was more common in patients with T2DM than in nondiabetics (40% vs 29%, p=0.008). At 13.5±4.1 months, the rate of composite MACCE (17.3% vs 27.6%, p=0.034) and repeat revascularization (15.2% vs 25.5%, p=0.026) was lower and the increase in LVEF (3.10 % vs 1.80%, p=0.024) was greater in patients with good collaterals than in those with poor collaterals for non-diabetic group, but did not differ for T2DM group (35% vs 44%; 30% vs 36%; 2.14% vs 1.65%, respectively, all p>0.05) except for a higher all-cause mortality in diabetic patients with poor collaterals (p=0.034). Multivariable Cox proportional hazards analysis showed that coronary collateralization was an independent factor for time to MACCE (HR 2.155 95%CI 1.290-3.599, P=0.003) and repeat revascularization (HR 2.326, 95%CI 1.357-3.986, p=0.002) in non-diabetic patients, but did not enter the model in those with T2DM. Conclusions: T2DM is associated with reduced coronary collateralization. Successful revascularization of CTO lesions results in a mild improvement in left ventricular function, but t he status of coronary collaterals has no independent effect on long-term clinical outcomes in patients with T2DM.