A 52-year-old man with a history of anterior wall myocardial infarction 6 months ago presents with recurrent episodes of palpitations and syncope. On examination, blood pressure is 110/70 mmHg and heart rate is 140 bpm. A 12-lead ECG shows a wide complex tachycardia with a left axis deviation and concordance in the precordial leads. Which investigation is most appropriate to confirm the diagnosis and assess the substrate for arrhythmia?