Self-inflicted thoracoabdominal nail-gun injury presenting as STEMI: diagnostic challenges in a time-critical care pathway.

A 60-year-old male with a history of depression and a prior nail-gun thoracic injury was found in shock at home, with inferior ST-segment elevation on the paramedic electrocardiogram prompting pre-hospital ST-elevation myocardial infarction pathway activation. Initial high-sensitivity troponin was elevated, consistent with the presumed diagnosis. Normal coronary angiography and preserved ventricular function were discordant with the patient's ongoing haemodynamic instability. Four small anterior chest puncture wounds and radiopaque foreign bodies demonstrated on chest radiograph and angiographic imaging did not initially prompt consideration of penetrating injury. Computed tomography pulmonary angiography, performed to exclude pulmonary embolism, identified four nail-gun projectiles penetrating the heart and stomach. The patient underwent sternotomy and laparotomy with repair of cardiac, diaphragmatic, and gastric injuries. The case illustrates the challenges of situation awareness and diagnostic reassessment within time-critical, protocol-driven care.