A 58-year-old woman with a 10-year history of diabetes mellitus and hypertension presents with acute onset chest pain and dyspnea. On examination, she is hypotensive (BP 85/55 mmHg), tachycardic (HR 115/min), and has bilateral crackles on auscultation. An ECG shows ST elevation in the anterior leads. Which investigation is most appropriate to differentiate between cardiogenic shock and distributive shock in this acute setting?