Difference in QT interval measurement on ambulatory ECG compared with standard ECG

Area of Science:

• Cardiology
• Medical Diagnostics

Background:

• The QT interval on standard electrocardiogram (ECG) is crucial for diagnosing congenital long QT syndrome, managing arrhythmias, and assessing ischemic heart disease.
• Ambulatory ECG monitoring (Holter) has been proposed as a tool for assessing QT interval prolongation, similar to standard ECG.

Purpose of the Study:

• To evaluate the agreement between QT interval measurements obtained from standard ECG and ambulatory ECG (Holter) monitoring.
• To determine the clinical utility of Holter monitoring for detecting QT interval prolongation.

Main Methods:

• Simultaneous ECG and Holter tracings were analyzed for 14 patients (age 4-36 years).
• QT intervals were measured in leads V1 and V5 using calipers by two independent observers.
• Comparisons were made between 100 paired ECG and Holter recordings across a QT interval range of 300-620 ms.

Main Results:

• High correlation was observed between standard ECG and Holter measurements for both observers (r values up to 0.988).
• Holter monitoring tended to underestimate the QT interval in lead V1 and overestimate it in lead V5.
• Significant individual variations in measurements were found, with wide 95% confidence intervals, potentially limiting clinical utility.

Conclusions:

• While Holter monitoring shows high correlation with standard ECG for QT interval assessment, significant individual variability exists.
• The magnitude of variability may restrict the clinical usefulness of ambulatory monitoring for diagnosing QT interval prolongation.