QRS Fragmentation Patterns Representing Myocardial Scar Need to Be Separated from Benign Normal Variants: Hypotheses and Proposal for Morphology based Classification

Abstract

The presence of a fragmented QRS complex (fQRS) in two contiguous leads of a standard 12-lead electrocardiogram (ECG) has been shown to be an indicator of myocardial scar in multiple different populations of cardiac patients. QRS fragmentation is also a predictor of adverse prognosis in acute myocardial infarction, coronary artery disease, and ischemic cardiomyopathy and a prognostic tool in structural heart diseases. An increased risk of sudden cardiac death associated with fQRS has been documented in patients with ischemic cardiomyopathy and hypertrophic cardiomyopathy. However, fQRS is also frequently observed in apparently healthy subjects. Thus, a more detailed classification of different QRS fragmentations is needed to identify the pathological fragmentation patterns and refine the role of fQRS as a risk marker of adverse cardiac events and sudden cardiac death. In most studies fQRS has been defined by the presence of an additional R wave (R'), or notching in the nadir of the S wave, or the presence of >1 R' in two contiguous leads corresponding to a major coronary territory. However, this approach does not discriminate between minor and major fragmentations and the location of the fQRS is also neglected. In addition to this, the method is susceptible to large interobserver variability. We suppose that some fQRS subtypes result from conduction delays in the His-Purkinje system, which is a benign finding and thus can weaken the prognostic values of fQRS. The classification of fQRSs to subtypes with unambiguous definitions is needed to overcome the interobserver variability related issues and to separate fQRSs caused by myocardial scarring from benign normal variants. In this paper, we review the anatomic correlates of fQRS and the current knowledge of prognostic significance of fQRS. We also propose a detailed fQRS classification for research purposes which can later be simplified after the truly pathological morphologies have been identified. The research material of our study consist of 15,245 ECGs from the random general population and approximately six thousands (n = 6,241) ECGs from subjects with a known cardiac disease.

Keywords: cardiac arrhythmias; cardiac diseases; diagnosis; electrocardiography; fragmented QRS; myocardial scar; prognosis; sudden cardiac death.

Figure 1

Different morphologies of fQRS on 12-lead ECG describing the fQRS criteria proposed by Das et al. Reprinted from the article “Prevalence and prognostic significance of fragmented QRS complex in middle-aged subjects with and without clinical or electrocardiographic evidence of cardiac disease” (Terho et al., 2014) with permission from Elsevier.

Figure 2

An example of the measurement of amplitude changes and location of the fragmentations in QRS complex. One point is tagged to the fQRS notch, the second to the fQRS peak and the third to the peak of the wave in which fQRS occurs.

Figure 3

The modified fQRS criteria: different morphologies of the fragmented Q wave and a Q-R-borderline-fQRS morphology on the right.

Figure 4

The modified fQRS criteria: different RsR-morphologies.

Figure 5

The modified fQRS criteria: different morphologies of the notched S on the left and an example of the R-S-borderline-fQRS on the right.

Figure 6

The modified fQRS criteria: different RSR-morphologies.

Figure 7

The morphologies of the modified fQRS criteria from left to right: (1) RSr′ (2) rSr′ (3) r′SR.

Figure 8

Other forms of fQRS. On the left the other fragmentation and on the right an example of two separate fQRS morphologies (notched R and notched S) occurring in the same QRS complex.