A case report of distal coronary artery spasm overlapping a calcified nodule: a rare mechanism of acute coronary syndrome.

Background: Calcified nodules (CNs) are the least common cause of acute coronary syndrome (ACS) and are distinct from plaque rupture and erosion. Although CNs are increasingly recognized as a unique ACS mechanism, their pathophysiology remains poorly understood. Case summary: A 66-year-old man with a long history of alcohol-related chest discomfort was referred for evaluation of worsening exertional symptoms. The initial electrocardiogram was unremarkable, but coronary computed tomography angiography showed a moderately calcified stenosis in the mid-right coronary artery (RCA), and elective coronary angiography was scheduled. However, on admission for the planned procedure, the patient experienced chest discomfort following binge drinking the night before. The electrocardiogram on admission revealed inferior ST-segment elevation. Emergent coronary angiography and intracoronary imaging identified severe mid-RCA stenosis associated with a CN with an overlying thrombus, while distal flow was preserved (Thrombolysis in Myocardial Infarction grade 3). The subsequent acetylcholine provocation test was positive, confirming coronary spastic angina (CSA). These findings raise the possibility that distal embolization from the surface thrombus on the CN contributed to the ACS presentation, potentially facilitated by CSA-associated flow reduction. Discussion: This case highlights a potential dual mechanism of ACS, in which distal coronary artery spasm may have promoted thrombus formation on a CN by reducing coronary blood flow. The coexistence of CN and CSA may represent a synergistic pathophysiology linking mechanical plaque vulnerability with flow-mediated thrombus formation.