A 42-year-old woman with acute coronary syndrome complicated by acute anterior wall myocardial infarction undergoes primary percutaneous coronary intervention. Post-PCI angiography shows TIMI 3 flow. However, 2 hours later, she develops hypotension (BP 82/48 mmHg), elevated JVP, clear lung fields on auscultation, and a new holosystolic murmur at the apex. Echocardiography confirms acute mitral regurgitation secondary to papillary muscle rupture. What is the most appropriate immediate next step?