Patient presents with complaints suggestive of prolonged QT interval syndrome.  Presenting symptoms include palpitations, syncope, presyncope, or family history of sudden cardiac death.  Electrocardiogram (ECG, EKG) reveals a corrected QT interval (QTc) greater than 470 ms for males or 480 ms for females, using Bazett's formula or other appropriate correction methods such as Fridericia's correction.  Differential diagnoses considered include congenital long QT syndrome (LQTS), acquired long QT syndrome, electrolyte imbalances such as hypokalemia and hypomagnesemia, and drug-induced long QT interval.  Evaluation includes a thorough review of medications, family history, and cardiac history.  Further investigations may include genetic testing for congenital LQTS, electrolyte panels, and potentially an echocardiogram to assess cardiac structure and function.  Management is focused on risk stratification for sudden cardiac death and may involve lifestyle modifications, beta-blockers, avoidance of QT-prolonging drugs, and in some cases, implantable cardioverter-defibrillator (ICD) placement.  Patient education regarding symptom recognition and emergency response is crucial.  ICD-10 code I45.9 for Long QT syndrome is assigned, and medical billing will reflect the complexity of evaluation and management.  Follow-up is scheduled to monitor QTc interval response to therapy and adjust management as necessary.  Patient advised to report any recurrence or worsening of symptoms immediately.