Computerized Interpretation of ECGs

Abstract

Estes III Computerized Interpretation of ECGs 3prolonged QT diagnostic statement. 14 The authors note that such prolonged QT under-reporting was manifest across all patient environments, and reflected algorithmic suppression of the diagnosis.14 This was because of ECG waveform-based criteria in 52.5% of ECGs with prolonged QTc.14 Of the latter ECGs with prolonged QT diagnosis suppression, the computer declared 42.1% as normal, despite QTc prolongation.14 The authors concluded that in evaluating an adult patient, whose ECG-C lacks a prolonged QT diagnostic statement, physicians should examine the actual QTc value displayed on the report before concluding that this parameter is normal.14 They also conclude that assessment of the clinical impact of prolonged QT diagnosis suppression by ECG waveform-based criteria is warranted.14 It is evident that automated evaluation of the QT interval is one of the particularly important functions of any ECG-C. Identification of a prolonged heart rate corrected QT interval (QTc) may identify an individual with an inherited LQTS atrisk for sudden cardiac death because of torsade de point. 3,[7][8][9][10][11][12][13] The QTc also serves as a marker of risk for individuals with a prolonged QT interval, acquired from electrolyte abnormalities or drugs.3,7-13 Specific technical and clinical recommendations for measurement of the QT and QTc intervals on the ECG have been made in a American Heart Association consensus document written to standardize the interpretation of ECGs.3 It is recommended that, in addition to rate, an adjustment for sex and age be incorporated into QTc measurement. As practical clinical limits for considering the QT interval as abnormal, this document recommends that the adjusted QT of 460 ms or longer in women and 450 ms or longer in men be considered a prolonged QT interval, and that QT of 390 ms and shorter be considered a short QT interval.3 It is recommended that linear regression functions rather than the Bazett formula be used for QT-rate correction, and that the method used for rate correction be identified in ECG analysis reports.3 It is further recommended that rate correction of the QT interval should not be attempted when RR interval variability is large, as often occurs with atrial fibrillation, or when identification of the end of the T-wave is unreliable. 3 In view of the clinical importance of the QT-interval prolongation, it is essential to validate QT-interval prolongation reported by a computer algorithm visually.3 In addition to administration of QT-prolonging cardioactive drugs, a number of conditions can induce QT prolongation.3 It is often possible to identify a specific cause of QT prolongation, when appropriate clinical information is available.3 Electrolyte disturbances, including hypokalemia, hypomagnesemia, and hypocalcemia, can prolong phase 2 and phase 3 of the action potential and prolong the QT interval.3 A comprehensive and current list of all possible causes of QT prolongation is readily available. 15 It is evident that presence...

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