ECG monitoring for drugs known to prolong the QT interval (Guidelines)



  • All NHS Highland
  • Primary and Secondary Care



Some medications can affect the heart and cause QT prolongation. In susceptible individuals this can lead to ventricular arrhythmias and in some cases death. This flow diagram is intended for use by clinical teams who prescribe such drugs, full list found at CredibleMeds (see resources), to allow them to safely manage QT prolongation. QT assessment is not possible if there is QRS prolongation (eg RBBB/LBBB). QT assessment is less accurate at extremes of heart rate.

Quick reference guide

Algorithm for evaluation before initiation and follow-up of patients requiring drugs associated with QT prolongation. 

  • a:
  • b: If strong indication and no alternative treatment, consult a specialist.
  • c: According to the 2020 ESC Guidelines for the diagnosis and management of atrial fibrillation. 

Flowchart replicated from ESC Guidelines.

Criteria for cardiology referral

  • Family or person history of long QT syndrome
  • QTc repeatedly > 500ms
  • Concern about long QT and continuation of drug: for discussion about relative risks


  • ECG:  electrocardiogram
  • LBBB: Left bundle branch block
  • LV: Left ventricular
  • RBBB: Right bundle branch block

Editorial Information

Last reviewed: 27/04/2023

Next review date: 30/04/2026

Author(s): Cardiology Department.

Version: 1

Approved By: TAM subgroup of the ADTC

Reviewer name(s): Prof Steve Leslie, Cardiologist.

Document Id: TAM547

Related resources

Further information for Health Care Professionals


Patient information

  • A list of QT prolonging drugs can be found at CredibleMeds