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Abstract
AimsFragmented QRS complex with visible notching on standard 12-lead electrocardiogram (ECG) is understood to represent depolarization abnormalities and to signify risk of cardiac events. Depolarization abnormalities with similar prognostic implications likely exist beyond visual recognition but no technology is presently suitable for quantification of such invisible ECG abnormalities. We present such a technology.Methods and resultsA signal processing method projects all ECG leads of the QRS complex into optimized three perpendicular dimensions, reconstructs the ECG back from this three-dimensional projection, and quantifies the difference (QRS ‘micro’-fragmentation, QRS-μf) between the original and reconstructed signals. QRS ‘micro’-fragmentation was assessed in three different populations: cardiac patients with automatic implantable cardioverter-defibrillators, cardiac patients with severe abnormalities, and general public. The predictive value of QRS-μf for mortality was investigated both univariably and in multivariable comparisons with other risk factors including visible QRS ‘macro’-fragmentation, QRS-Mf. The analysis was made in a total of 7779 subjects of whom 504 have not survived the first 5 years of follow-up. In all three populations, QRS-μf was strongly predictive of survival (P < 0.001 univariably, and P < 0.001 to P = 0.024 in multivariable regression analyses). A similar strong association with outcome was found when dichotomizing QRS-μf prospectively at 3.5%. When QRS-μf was used in multivariable analyses, QRS-Mf and QRS duration lost their predictive value.ConclusionIn three populations with different clinical characteristics, QRS-μf was a powerful mortality risk factor independent of several previously established risk indices. Electrophysiologic abnormalities that contribute to increased QRS-μf values are likely responsible for the predictive power of visible QRS-Mf.
Highlights
Abnormalities of the electrocardiographic QRS complex reflect intramyocardial conduction pathologies
Electrophysiologic abnormalities that contribute to increased QRS-μf values are likely responsible for the predictive power of visible QRS-Mf
The cardiac risk associated with visually diagnosed QRS fragmentation suggests that important QRS abnormalities might exist below the resolution of visual detection
Summary
Abnormalities of the electrocardiographic QRS complex reflect intramyocardial conduction pathologies. The socalled QRS complex fragmentation, defined by visually detected splits of QRS waves,[3,4] has been found to predict poor outcome in both cardiac patients and other well-defined groups[5–7] including the general population.[4]. This increased risk due to visible QRS fragmentation appears independent of the overall QRS complex duration.[8]. Visual diagnosis of QRS fragmentation leads to a yes/no classification quantitative sums of QRS splits detected in different leads and probabilistic approaches have been proposed.[9] This categorical distinction suggests that important QRS abnormalities might exist below the resolution of visual detection. Spectral analyses of signal-averaged QRS complex were proposed, albeit with variable success, to identify abnormalities hidden within the overall QRS pattern.[10,11] so far, little success has been achieved when trying to detect ‘invisible’ abnormalities of myocardial depolarization in standard clinical 10-s electrocardiograms (ECG)
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