ECG measurements in end QRS notching and slurring Peter W. Macfarlane, DSc, FRCP, ⁎ Elaine N. Clark, MA Institute of Cardiovascular and Medical Sciences, University of Glasgow, Glasgow, United Kingdom Introduction There has been a significant interest in recent times in the detection of end QRS slurring and notching, at least from a visual point of view. This is linked with a resurgence of interest in an ECG pattern identified some time ago 1 and subsequently called early repolarization 2 which in turn, has more recently been associated with life threatening cardiac arrhythmias. 3,4 The definition of early repolarization in recent papers 3,4 refers to the presence of end QRS slurring or notching in an imprecise way. On the other hand, as far as is known, there are no recommendations on the definition of end QRS notching and slurring that could easily be applied to automated ECG interpretation. This is of considerable importance given the millions of ECGs reported annually worldwide using computer assisted techniques. A number of manufacturers have ECG interpretative software which includes a statement on early repolarization but in all probability, such an interpretation is more likely to be based on the presence of ST elevation than on the occurrence of QRS notching or slurring. The seminal paper on ECG wave measurement was prepared by the working party of the European Project entitled Common Standards in Quantitative Electrocardiog- raphy (CSE). 5 That paper gave many examples of QRS termination or offset but did not specify in detail rules for measurement of slurs or notches. The paper stated that “a deflection is slurred when it displays a distinctive change in slope”. It also said that “a notch is an abrupt change in the direction of a limb of a wave or deflection. A notch has at least 2 turning points located on the same side of the reference level regardless of their distance, amplitude or duration”. These definitions lack precision opening the door for software developers to interpret them in whatever way they wish. The CSE Working Party also recommended that for routine electrocardiography “a wave in a QRS complex is present if it has an amplitude of at least 20 μV and a duration of at least 6 ms”. These values were chosen following a study of ECGs in the CSE library, which had been reviewed by a group of European Cardiologists using enlarged conven- tional ECG recordings. The 20 μV amplitude was somewhat arbitrary in the sense that the Working Party felt that a wave of lesser amplitude could be due to somatic tremor, even in an average beat. What is an end QRS slur? While it may be straightforward to refer to a slur as a distinct change in slope, in turn this requires to be defined. It would be reasonable to consider a line from QRS peak based on the slope of, for example, the first 10–15 ms following the peak and measure the angle of the intercept with the baseline. A moving window from which the slope was measured could then be used to form a continuous assessment of R wave downslope angle with the baseline and when this deviated from the initial assessment by more than X°, then a slur could be defined (Fig. 1). The value of X requires to be specified. This is effectively the reverse of a technique for finding a delta wave in the WPW pattern as used in the Glasgow program 6 for many years. There are mathematical techniques for defining curvature but in the event that the measurement of a slur requires manual calculation, the slope or tangent method is probably the most useful to consider. One danger with this approach is that a more non specific (insignificant, perhaps technical) slurring towards the end of a QRS complex might be reported as a slur and so it is suggested that the onset of a slur should have a minimum amplitude with respect to QRS onset or should not begin less than perhaps 10ms, for example, from ST onset. What is an end QRS notch? A notch can certainly be detected in an automated way and has been within our own software for over 20 years. 6 This could be on the initial upslope of an R wave or initial downslope of a Q wave or S wave. Similarly, it could be Available online at www.sciencedirect.com ScienceDirect Journal of Electrocardiology 46 (2013) 385 – 389 www.jecgonline.com ⁎ Corresponding author. University of Glasgow, Inst of Cardiovascular and Medical Sciences, Electrocardiology Group, Level 1 QEB, Royal Infirmary, Glasgow G31 2ER. E-mail address: peter.w.macfarlane@glasgow.ac.uk 0022-0736/$ – see front matter © 2013 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.jelectrocard.2013.06.011