A 45-year-old man presents with severe central chest pain and sweating. ECG shows ST-segment elevation in leads II, III, and aVF. He is given Aspirin 300mg and transferred for primary PCI. During the procedure, he develops hypotension (BP 80/50 mmHg) and bradycardia (HR 40 bpm). His chest is clear on auscultation. What is the most appropriate immediate management for his haemodynamic instability?