Using the Appropriate Formula for QT Measurement Can Save Lives.

Area of Science:

• Cardiology
• Oncology
• Pharmacology

Background:

• CDK 4/6 inhibitors combined with endocrine therapy are standard for advanced breast cancer.
• These inhibitors can cause QT prolongation, a risk factor for life-threatening arrhythmias.
• Current guidelines often use the Bazett formula (QTcB), but the Fridericia formula (QTcF) is more accurate at extreme heart rates.

Discussion:

• A study at King Faisal Specialist Hospital and Research Center evaluated QT intervals in 82 advanced breast cancer patients starting ribociclib therapy.
• 19 patients (23%) were initially excluded due to QTc >450ms.
• Recalculation using Fridericia and Framingham formulae allowed 17 of these patients to safely begin treatment.

Key Insights:

• The Fridericia and Framingham formulae are more accurate for QT interval assessment in cancer patients, especially those on CDK 4/6 inhibitors.
• Manual recalculation using these formulae identified patients eligible for ribociclib therapy who were initially excluded.
• No patients in the study experienced QTc exceeding 480ms after treatment initiation, indicating safety.

Outlook:

• Recommend adopting Fridericia or Framingham formulae for QTc measurement in cancer patients receiving QT-prolonging therapies.
• This approach can prevent unnecessary treatment discontinuation and improve patient management.
• Further research should validate these formulae across diverse oncology populations.