Background Fragmented QRS (fQRS) complexes are defined as various RSR' patterns (>= 1 R' or notching of S wave or R wave) in two contiguous leads corresponding to a major coronary artery territory. In previous studies, fQRS has been associated with increased morbidity and mortality, sudden cardiac death and recurrent cardiovascular events (CVEs). The causative relationship between fQRS and cardiac fibrosis has been shown in prior studies. The association between inadequate (poor) coronary collaterals and presence of fQRS has not comprehensively been studied in patients with chronic total occlusion (CTO) until now. We tested the hypothesis that the presence of fQRS is associated with inadequate coronary collateral growth.