A 15-year-old boy presented in an unconscious state and on connecting the ECG electrodes, atrial fibrillation was diagnosed. The relatives told the doctor that the boy had similar episodes of syncope in the past as well. Lab studies revealed normal potassium and calcium levels, normal CK-MB levels. The patient died of cardiac arrest and could not be revived. When the previous records were checked some undue abnormality was noted in the ECGs. There was also a history of sudden cardiac death in the family. What is the most likely defect in the above patient: –