QTc Interval on 24 hour Holter Monitor: To Trust or Not to Trust?

Introduction: QT interval represents the ventricular depolarization and repolarization. Its accurate measurement is critical since prolonged QT can lead to sudden cardiac death. QT is affected by heart rate and is corrected to QTc via several formulae. QTc is commonly calculated on the ECG and not the 24-hour Holter. Methods: 100 patients presenting to our institution were evaluated by an ECG followed by a 24-hour Holter. QTc measurement on both of these platforms using Bazett and Fridreicia formulae was recorded and compared. Results: Mean age was 14.09 years, with the majority being males. Mean heart rate was 125.87. In the ECG, the mean QTc interval via Bazett formula was 0.40 seconds compared to 0.38 seconds using the Fridreicia formula. The mean corrected QT via Bazett formula was 0.45, 0.39 and 0.42 seconds for the shortest RR, longest RR and the average RR respectively. In contrast to Fridreicia formula, the corrected QT interval was 0.40, 0.39, and 0.40 seconds for the shortest RR, longest RR and the average RR respectively. Using Bazett, highest specificity reached during longest RR interval (92.2%) while highest sensitivity was recorded during shortest RR interval (40%). As for Fridreicia, sensitivity always reached 0% while highest specificity was reached during average RR interval. Conclusion: QTc measured during Holter ECG reached a high specificity regardless of RR interval using the Fridreicia and during long and average RR interval for Bazett formula. The consistently low sensitivity reveals that Holter ECG should not be used to rule out prolonged QT.