A 56-year-old male diagnosed with ischemic cardiomyopathy, NYHA class IV heart failure, shows left ventricular dilation (EF 0.22) on echocardiogram (ECHO) and frequent ventricular premature contractions on electrocardiogram (ECG). Serum potassium (K) is 4.5 mmol/L and digoxin level is 1.1 ng/mL. The preferred antiarrhythmic drug for this case is: