Manual versus Automatic Assessment of the QT-Interval and QTc.

BACKGROUND AND AIMS: Sudden cardiac death (SCD) is challenging to predict. Electrocardiogram (ECG) derived, heart rate corrected QT-interval (QTc) is used for SCD-risk assessment. QTc is preferably determined manually, but vendor-provided automatic results from ECG-recorders are convenient. Agreement between manual and automatic assessments is unclear for populations with aberrant QTc. We aimed to systematically assess pairwise agreement of automatic and manual QT-intervals and QTc.

METHODS: A multi-center cohort enriching aberrant QTc comprised ECGs of healthy controls and Long-QT Syndrome (LQTS) patients. Manual QT-intervals and QTc were determined by the tangent and threshold methods and compared to automatically generated, vendor-provided values. We assessed agreement globally by intra-class correlation coefficients and pairwise by Bland-Altman analyses and 95% limits of agreement (LoA). Further, manual results were compared to a novel automatic QT-interval algorithm.

RESULTS: ECGs of 1263 participants (720 LQTS-patients; 543 controls) were available (median age 34 [IQR 35] years, 55% women). Comparing cohort means, automatic and manual QT-intervals and QTc were similar. However, pairwise Bland-Altman-based agreement was highly discrepant. For QT-interval, LoAs spanned 95 ms (tangent) and 92 ms (threshold), respectively. For QTc, the spread was 108 ms and 105 ms, respectively. LQTS-patients exhibited more pronounced differences. For automatic QTc results from 440-540 ms (tangent) and 430-530 ms (threshold), mis-assessment risk was highest. Novel automatic QT-interval algorithms may narrow this range.

CONCLUSION: Pairwise vendor-provided automatic and manual QT-interval and QTc results can be highly discrepant. Novel automatic algorithms may improve agreement. Within the above ranges, automatic QT-interval and QTc results require manual confirmation, particularly if T-wave morphology is challenging.