A 47-year-old female with treatment-resistant schizophrenia is being evaluated for a clozapine trial after failing adequate trials of three other antipsychotics. Her current medications include citalopram 40 mg daily for comorbid depression and methadone 80 mg daily for opioid use disorder in sustained remission. A baseline ECG shows a QTc interval of 468 ms using the Bazett correction formula. Her serum potassium is 3.4 mEq/L, and magnesium is 1.7 mg/dL. She has no personal or family history of cardiac arrhythmia, syncope, or sudden cardiac death. Her BMI is 34, and she has a sedentary lifestyle. Which assessment of this patient's QTc prolongation risk profile is most comprehensive and accurate?