Introduction: Accurate measurement of QRS duration is crucial in CRT to identify eligible patients. Furthermore, QRS narrowing is emerging as a key marker of successful CRT with a growing evidence base of improved response and long-term survival. Despite this, there is no agreed technique to measure QRS duration and different methods are used in clinical practice. Global QRS duration has been shown to have improved accuracy over individual lead measurement (1). However, global QRS duration is less easily measured without specialist software, hence it is not routinely used in practice. This study compared whether an abbreviated global QRS measurement over 5 leads on the device programmer was comparable to individual lead measurements on the 12 lead ECG.
Methods: Comparison of ECG data for patients undergoing CRT implantation with standard indications. All were implanted with an Abbott CRT device. Individual lead QRS duration from the 12 Lead ECG was compared to abbreviated global QRS duration measured on the Abbott programmer. Up to 6 sets of ECGs were measured per patient. Abbreviated global QRS duration was measured using digital calipers in leads I, II, III, aVF and V5 ‘from the earliest onset to the latest offset of the waveform in all leads’. Individual lead QRS duration in all 12 leads was measured using digital calipers on the 12 Lead ECG via the Phillips haemodynamic system, together with the maximum (QRS_Max) and Mean (QRS_Mean) of the individual leads. 50mm/sec sweep speed was used as standard and gain optimised to improve measurement accuracy. Each measurement technique was applied by a blinded operator and verified by a third independent operator. Bland Altman analysis was used for comparison.
Results: In total, 158 sets of ECG data were compared. Importantly, there was considerable variation in QRS duration between the individual leads on the 12 Lead ECG, likely due to isoelectric segments specific to ECG vector. Compared to GlobalQRS, QRS_Mean averaged 8.4ms shorter with 95% confidence interval for the observed differences ± 21.7ms. This is shown as a Bland-Altman plot (Figure). Greater levels of variation were observed between GlobalQRS and individual lead measurements, e.g. GlobalQRS vs Lead I showed an average difference of 14.2ms with 95% confidence interval ±35.6ms.
Discussion: Accurate measurement of QRS duration is critical for electrical optimisation of CRT. This study found substantial variation between different methods of assessing the QRS duration. We recommend further research and development of practical guidelines to standardise clinical practice. Where single lead measurement is used, the target ECG lead should be specified to avoid inaccuracies that may affect device programming. We also recommend consistency of measurement technique between implantation and follow-up. The device programmer is commonly used in both settings and could be used to measure abbreviated global QRS duration to standardise measurement throughout the patient’s journey.
- De Pooter J, El Haddad M, Timmers L, et al. Different methods to measure QRS duration in CRT patients: Impact on the predictive value of QRS duration parameters. Ann Noninvasive Electrocardiol. 2016;21:305–15.