Answer- A. Synchronised CardioversionThe next best step of management in this patient is synchronized cardioversion.The ECG is suggestive of paroxysmal supraventricular tachycardia (PSVT) at a rate of 150/min. In this case, carotid massage and IV adenosine have failed to control PSVT and the patient continues to have hemodynamic instability (B.P. - 60/30 mmHg). In this condition, synchronized direct current cardioversion (and not just DC shock) should be initiated with the staing dose of 50-100J.