Complete right bundle branch block in young: understanding its clinical significance and the diagnosis implications

This editorial refers to ‘Prevalence and clinical significance of electrocardiographic complete right bundle branch block in young individuals’, by H. MacLachlan et al., https://doi.org/10.1093/eurjpc/zwae082. Complete right bundle branch block (CRBBB) is an electrocardiogram (ECG) finding resulting in a widened QRS and changes of electrocardiographic vector directions, due to the interruption of the normal electrical conduction at the level of the right bundle branch (RBB).1 The electrocardiographic aspect is defined according to the Minnesota Code criteria by a QRS duration of ≥ 120 ms in a majority of beats in any of leads I, II, III, aVL, aVF, plus R′ > R in lead V1 or V2, or; QRS mainly upright, with an R-peak duration of ≥ 60 ms in lead V1or V2 or; S duration > R duration in all beats in lead I or II.2 The prevalence of CRBBB in the general population is between 0.9% and 1.5%, it increases with age, and it is higher in men, in diabetics, and in patients with arterial hypertension.2 This electrocardiographic pattern is frequently found in the general healthy population, but it can also be the expression of diseases affecting the RBB or the myocardial region where the RBB is located, such as trauma, structural changes, infiltrative diseases (e.g. sarcoidosis), myocarditis, and myocardial infarction. CRBBB could also be the result of the stretch of RBB, due to right ventricular pressure and/or volume acute or chronic overload. Lenegre and/or Lev disease (progressive cardiac conduction system diseases-PCCD) can cause CRBBB, especially in elderly patients; while in patients with the degeneration of the conduction pathway caused by an underlying heart disease, a tachycardia-dependent CRBBB can be seen.3 Among asymptomatic individuals with no prior heart disease, CRBBB has been traditionally considered a benign anomaly; however, this conclusion was derived from data of small cohort studies.4–6 On the other hand, evidence derived from larger population studies conducted predominantly on middle-aged adults, showed an increased cardiovascular (CV) risk and all-cause mortality in asymptomatic individuals with CRBBB, suggesting alert to the evaluation of CV risk in these subjects.2,7 As regards young (age ≤ 35 years), the few available data are coming mainly from studies on athletes, in the majority cross-sectional and analysing CRBBB in the context of other ECG abnormalities, suggesting a prevalence of CRBBB ranging from 0.5% to 3.1%, higher compared with healthy members of the general population.8–10 Moreover, there is uncertainty about the clinical significance of CRBBB in this group of subjects, as demonstrated by the international recommendations for electrocardiographic interpretation in athletes.11 According to this document, CRBB is considered among the borderline ECG findings, patterns ECG that may represent normal variants or the result of physiological cardiac remodelling in athletes.11 The presence of CRBB or any of the other borderline ECG findings in isolation does not warrant further assessment in asymptomatic athletes without a family history of premature cardiac disease or sudden cardiac death (SCD). On the other hand, the presence of CRBB together with one of the other borderline findings and/or with a QRS complex duration of ≥ 140 msec, suggest the need for further evaluations to investigate pathological disorders.11 These recommendations are based on a small single study in which CRBBB was due to sports-related cardiac remodelling.12 On the other hand, important information comes from the Italian document (Comitato Organizzativo Cardiologico per l’Idoneità allo Sport- COCIS 2023) which regulates the cardiological protocols for suitability for competitive sports. This document responds to the medical-legal needs arising from the application, unique in the world, in Italy, of the 1982 law on health protection of competitive sporting activity.13 According to the experts of COCIS, CRBB is not a common ECG finding in athletes, and it is not related to physical training, requiring further diagnostic investigation with transthoracic echocardiography (TTE), maximal exercise test, and 24-Holter-monitoring.13 In the manuscript, ‘Prevalence and clinical significance of electrocardiographic CRBBB in young individuals’,14 MacLachlan et al. investigated the prevalence and significance of CRBBB among young individuals (14–35 years old) evaluated in a nationwide cardiac screening program in the UK on a voluntary basis. Between 2007 and 2018, 104 369 consecutive young individuals were evaluated. The mean age was 20.2 ± 6.2 years, the majority were male (n = 64 708; 62%) and white (n = 92 708; 89%). The cohort included 9745 (9%) competitive athletes. The screening team includes a doctor, cardiac physiologists, and additional support staff. Cardiac screening consists of a health questionnaire and a 12-lead ECG followed by clinical consultation. TTE was offered selectively on the day to individuals with concerning symptoms, family history, abnormal physical signs, or ECG abnormalities; moreover, secondary cardiac evaluation was also recommended for individuals with abnormal findings, at the discretion of the consulting physician. CRBBB was classified as ‘isolated’ or ‘non-isolated’ based on the absence or the presence, respectively, of concomitant CV symptoms (typically syncope, chest pain, palpitation, and/or dyspnoea), relevant family history of inherited cardiac conditions or young (aged <50 years) SCD, and other ECG abnormalities. Anterior T wave inversion was considered discordant if confined between V1 and V3, but not V4. At baseline CRBBB was reported in 154 (0.1%) individuals: the prevalence was lower compared with that reported in studies in general population, probably due to the age (mean age 21 years) of subjects of this cohort, younger compared with those of the large population studies (mean age > 50 years). CRBBB was more prevalent in males compared with females (0.20% vs. 0.06%, P < 0.05) and in athletes compared with non-athletes (0.25% vs. 0.14%, P < 0.05). There was no significant difference in terms of age (0.11% for <16 years vs. 0.16% for ≥16 years; P > 0.05) or ethnicity (0.15% for white vs. 0.09% for non-white, P > 0.05). Of the 154 individuals with CRBBB, follow-up was available in 149 (97%). During the follow-up period (mean of 7.3 ± 2.7 years), seven (5%) individuals were identified with a CRBBB-related condition: four with an atrial septal defect (ASD), one with Brugada syndrome, one with PCCD and one with atrial fibrillation; only one of these subjects was an athlete. An additional two individuals were identified with other cardiac conditions, considered as incidental findings: one with mitral valve prolapse, and one with coarctation of the aorta. Five (3%) individuals required cardiac intervention: three underwent percutaneous ASD closure, one individual was implanted with a primary prevention implantable cardioverter defibrillator for a diagnosis of Brugada syndrome and one individual was implanted with a permanent pacemaker for PCCD. The prevalence of CRBBB-related cardiac conditions was significantly greater in individuals with non-isolated CRBBB compared to individuals with isolated CRBBB (14% vs. 1%; P < 0.05), and in individuals with a QRS duration of ≥ 130 ms compared to those with a QRS of < 130 ms (10% vs. 1%; P < 0.05) Concomitant anterior T wave inversion did not correlate with pathology. The results of this study suggest that CRBBB is a rare finding in young (0.1% of prevalence in this large population), and it is often (5% of subjects) associated with CV disease, including conditions associated with SCD. These findings showed the utility of secondary cardiac evaluation with at least a TTE for young individuals with CRBBB, both athletes and non-athletes, with symptoms, concerning family history, additional electrocardiographic anomalies and a QRS duration ≥130 ms, suggesting the need to update ongoing international recommendations. None declared.