Unlocking electrocardiogram secrets: understanding low QRS voltages in limb leads

This editorial refers to ‘Prevalence and clinical significance of low QRS voltages in healthy individuals, athletes, and patients with cardiomyopathy: implications for sports pre-participation cardiovascular screening’, by A. Pelliccia et al., https://doi.org/10.1093/eurjpc/zwae027. The inception of electrocardiography dates back to the early 20th century when Willem Einthoven introduced the first practical electrocardiogram (ECG) machine. His groundbreaking work laid the foundation for a transformative era in cardiology. Since Einthoven’s pioneering contributions, the ECG has evolved from a cumbersome laboratory apparatus to the accessible diagnostic tool that get indispensable in the daily practice. Despite numerous advances in medical technology over the past few decades, ECG is still regarded as a cornerstone in initiating the cardiac evaluation process. Deviation from normal ECG patterns during both depolarization and repolarization may indicate the presence of structural heart diseases and raise a red flag for the diagnosis of underlying cardiac disease in otherwise apparently healthy individuals. Some well-known baseline ECG alterations can be linked with cardiac conditions at risk for sudden cardiac death (SCD), as for example left bundle branch conduction abnormalities or presence of negative T-wave in lateral leads.1 This screening capability is particularly relevant in young athletes, who are at increased risk of SCD.2 Nevertheless, athletes also pose a remarkable challenge. Regular exercise may prompt adaptatory cardiac structural changes, so-called athlete’s heart, which may be reflected in the ECG and occasionally overlap with pathologic features. Differentiating physiological and pathological ECGs is crucial to reliably identify those individuals at risk of heart disease.3 Indeed, over the past two decades, notable strides have been taken to improve the ECG performance to identify those athletes with cardiac conditions. In cardiovascular screening studies employing contemporary ECG interpretation standards, consistent findings indicate that ECG screening outperforms traditional methods such as history-taking and physical examination.4,5,6 Yet, the outcomes of extensive ECG screening for athletes’ participation in competitive sports remain contentious due to imperfect ECG accuracy as some of SCDs during sports activities exhibited completely normal ECGs according to the current standards for interpretation.7 Improving the accuracy of ECG interpretation could be achieved by refining algorithms, as previously attempted with standardized ECG criteria, or by identifying new ECG characteristics indicative of cardiomyopathy. In the current publication,8 Pelliccia et al. seem to be leaning towards exploring this latter option. They publish a narrative review assessing the prevalence and clinical significance of an under-used diagnostic finding on the ECG, the low QRS voltage (LQRSV). While there is some heterogeneity in its definition across the literature,9,10 the first strength of the manuscript is to establish a uniform definition of LQRSV adopting the most frequently used criterion of a QRS amplitude from peak to nadir <0.5 mV in all limb leads. Throughout the manuscript, authors perform an exhaustive revision of the clinical significance of LQRSV. They commenced by conducting a thorough literature review to ascertain the prevalence of this ECG finding. The prevalence seems to vary, ranging from as low as 0.3% in the general population to 3% in competitive athletes, exceeding 40% in certain forms of arrhythmogenic cardiomyopathy, and even higher in some forms of infiltrative cardiac diseases (see Table 1). Of particular significance is the high prevalence of LQRSV in patients with left ventricular (LV) scarring. It is well documented that specific distributions of LV fibrosis, such as the ‘ring-like’ pattern,11 along with certain genetic forms of cardiomyopathy, like those resulting from FLNC mutations,12 are associated with a significantly higher risk of arrhythmogenesis. Low QRS voltage appears to be particularly prevalent in these conditions. This observation could be especially relevant, given that these conditions often present with only slight LV dysfunction and may go unnoticed in the early stages.13 Indeed, the primary theoretical advantage of LQRSV in the screening process lies in its association not only with the presence of myocardial fibrosis but also with larger areas of scarring detected in magnetic resonance imaging (MRI) scans, as described by the authors. It is well established that myocardial fibrosis is the principal determinant of arrhythmogenic risk in patients with structural heart diseases.14 Therefore, having an electrocardiographic index directly linked to scarring could prove valuable in screening for undiagnosed conditions that elevate the risk of SCD. This is particularly pertinent in scenarios such as pre-participation screening for competitive and recreational athletes. Summary of the prevalence, presumed mechanism, and clinical implication of low QRS voltage in different populations 61% higher mortality PVC with atypical patterns Ventricular arrhythmias on sport Risk marker of SCD Marker of left ventricular involvement Larger areas of scarring in MRI More advanced state of the disease Extended myocardial fibrosis Independent predictor of SCD Worsened clinical outcomes Independent predictor of LGE Independent predictor of SCD Marker of systolic and diastolic dysfunction Independent predictor of CV death 61% higher mortality PVC with atypical patterns Ventricular arrhythmias on sport Risk marker of SCD Marker of left ventricular involvement Larger areas of scarring in MRI More advanced state of the disease Extended myocardial fibrosis Independent predictor of SCD Worsened clinical outcomes Independent predictor of LGE Independent predictor of SCD Marker of systolic and diastolic dysfunction Independent predictor of CV death CV, cardiovascular; MRI, magnetic resonance imaging; SCD, sudden cardiac death; PVC, premature ventricular complexes; LGE, late gadolinium enhancement. Summary of the prevalence, presumed mechanism, and clinical implication of low QRS voltage in different populations 61% higher mortality PVC with atypical patterns Ventricular arrhythmias on sport Risk marker of SCD Marker of left ventricular involvement Larger areas of scarring in MRI More advanced state of the disease Extended myocardial fibrosis Independent predictor of SCD Worsened clinical outcomes Independent predictor of LGE Independent predictor of SCD Marker of systolic and diastolic dysfunction Independent predictor of CV death 61% higher mortality PVC with atypical patterns Ventricular arrhythmias on sport Risk marker of SCD Marker of left ventricular involvement Larger areas of scarring in MRI More advanced state of the disease Extended myocardial fibrosis Independent predictor of SCD Worsened clinical outcomes Independent predictor of LGE Independent predictor of SCD Marker of systolic and diastolic dysfunction Independent predictor of CV death CV, cardiovascular; MRI, magnetic resonance imaging; SCD, sudden cardiac death; PVC, premature ventricular complexes; LGE, late gadolinium enhancement. For a thorough interpretation of the Pelliccia et al. article, it is essential to acknowledge certain knowledge gaps. The precise prevalence of the LQRSV pattern in the general population remains poorly defined. The only two articles investigating this matter15,16 employed distinct definitions of LQRSV, resulting in estimated prevalence rates ranging from 0.3 to 1.4% (see Table 1). Second, no prospective studies have yet been conducted to evaluate MRI findings and the burden of scar in a large and consecutive population of apparently healthy individuals exhibiting LQRSV in the baseline ECG. Lastly, there is still a lack of data regarding the temporal evolution pattern of this electrocardiographic finding. It remains uncertain whether a progressive reduction of the QRS voltage in serial ECGs of the same individual could serve as a marker of baseline disease progression. This aspect is especially pertinent in athletic contexts, where decreased QRS voltage may initially be compensated by adaptive changes in myocardial structures due to physical activity. Consequently, additional research examining the impact of athlete detraining on limb lead QRS voltage is warranted. Overall, while solid scientific evidence supports an association between LQRSV and the presence of an underlying cardiomyopathy, from a clinical perspective, its role in pre-participation screening algorithms still needs to be established. Does LQRSV provide additive information to known ECG pathologic markers? Would such information be enough to incorporate LQRSV into consensus criteria? Is LQRSV the next hidden ECG secret? In conclusion, the mounting evidence, as succinctly summarized by the authors in the current issue of the journal, should draw our attention to the QR voltage in limb leads during the evaluation of patients without previously diagnosed cardiac disease. The enhanced significance of incorporating this ECG criterion into the existing recommendations for electrocardiographic interpretation in athletes during pre-participation screening warrants careful consideration. None declared. No new data were generated or analysed in support of this research.