The combination of history, physical exam (including orthostatic vital signs), and ECG has a diagnostic yield of over 80%, with orthostatic blood pressure being the highest yield and most cost-effective intervention. The addition of cardiac enzymes, EEG, and carotid ultrasound have a 1% yield. TTE has an additional yield of only 2%, and inpatient telemetry may be helpful in only up to 5% of cases. The current ACC/AHA guidelines take into account many of these factors, and the only Class I recommendation in the evaluation of suspected syncope is to obtain history/physical and ECG. Beyond that, the algorithm will differ based on risk factors and clinical suspicion. In patients with suspected cardiovascular abnormalities based on the initial basic evaluation, you can consider more prolonged cardiac monitoring. Check out the useful algorithms in the full guidelines.
References: 2017 ACC/AHA/HRS Guideline for the Evaluation and Management of Patients With Syncope