Assessing risk of a prolonged QT interval-a survey of emergency physicians

Although QT prolongation is associated with an increased risk of torsades de pointes (TdP), it is unclear how clinicians determine risk in individual patients with prolonged QT.

To investigate physicians' interpretation of electrocardiogram (ECG) values in patients with a prolonged QT in reference to risk of TdP.

A survey was sent to Australasian emergency physicians (EPs) to investigate interpretation of ECG data in risk assessment for TdP. The survey contained three sections: demographic information, questions on heart rate correction and six sets of ECG data which the clinician ranked from low to high risk. Risk analysis for ECG values was performed by producing histograms of the distribution of responses for each of the six sets of ECG parameters. These distributions were compared to predicted distributions based on Bazett's corrected QT > 500 ms and the QT nomogram. The QT nomogram is a recently developed method for assessing whether QT-HR pairs are associated with increased risk of TdP by plotting them to determine if they are above an at risk line-the nomogram.

Of 720 surveys sent out, 249 were returned (35%). A heart rate correction was used by 90% of respondents and the median "at risk" QTc judged by EPs was 450 ms [interquartile range (IQR): 440-500 ms]. Respondents were divided as to whether bradycardia increased the risk of TdP, with equal numbers responding "no change" and "more caution". In four of the six sets of ECG parameters, EPs had a similar risk distribution to that predicted by Bazett. For one point predicted to be high risk by the QT nomogram, there was a uniform (undecided) risk distribution by EPs.

EPs mainly relied on Bazett's correction as their method of TdP risk assessment, which may be problematic for bradycardic patients.