Objective To assess the effect of thrombus aspiration by optical coherence tomography (OCT) before angioplasty on poststenting tissue protrusion in patients undergoing a primary percutaneous coronary intervention (PCI) for ST-elevation myocardial infarction (STEMI).Methods A total of 106 patients with STEMI who had undergone primary PCI with concurrent OCT were examined in this study,including 69 recipients of thrombus aspiration- PCI and 37 recipients of standard PCI. OCT was performed immediately after primary PCI to assess lesion morphology in the stented segment.Results The minimum stent area was similar between the thrombus aspiration -PCI group and the standard PCI group [7.3 (IQR: 5.8-8.5) vs 7.3 (IQR: 6.0-8.7)mm2, P=0.818]. The maximum tissue protrusion area was[0.6 (IQR: 0.2-1.1) vs 1.2(IQR: 0.8-1.6) mm2, P<0.001], while the mean tissue protrusion area was[0.1 (IQR: 0.1-0.2) vs 0.4 (IQR: 0.2-0.7) mm2,P<0.001], both of which were significantly smaller in the thrombus aspiration -PCI group than in the standard PCI group. The minimum lumen area was significantly greater in the thrombus aspiration - PCI group than in the standard PCI group [7.1 (IQR: 6.2-8.0 vs 5.9 (IQR: 4.9-6.8) mm2, P<0.01].Conclusions Thrombus aspiration before angioplasty in patients with STEMI is associated with significantly smaller tissue protrusion areas and larger lumen poststenting areas than standard PCI. Thrombus aspiration in the primary PCI group favors the lesion morphology in the stent segment and therefore may be a useful adjuvant therapy for primary PCI.