Evaluation of mortality in bundle branch block patients from an electronic cohort: Clinical Outcomes in Digital Electrocardiography (CODE) study

Abstract

Background

Left bundle branch block is recognized as a marker of higher risk of death, but the prognostic value of the right bundle branch block in the general population is still controversial. Our aim is to evaluate the risk of overall and cardiovascular mortality in patients with right (RBBB) and left bundle branch block (LBBB) in a large electronic cohort of Brazilian patients.

Methods

This observational retrospective study was developed with the database of digital ECGs from Telehealth Network of Minas Gerais, Brazil (TNMG). All ECGs performed from 2010 to 2017 in primary care patients over 16 years old were assessed. The electronic cohort was obtained by linking data from ECG exams (name, sex, date of birth, city of residence) and those from national mortality information system, using standard probabilistic linkage methods (FRIL: Fine-grained record linkage software, v.2.1.5, Atlanta, GA). Only the first ECG of each patient was considered. Clinical data were self-reported, and ECGs were interpreted manually by cardiologists and automatically by the Glasgow University Interpreter software. Hazard ratio (HR) for mortality was estimated using Cox regression.

Results

From a dataset of 1,773,689 patients, 1,558,421 primary care patients over 16 years old underwent a valid ECG recording during 2010 to 2017. We excluded 17,359 patients that didn't have a valid QRS measure from the Glasgow program and 11,091 patients from the control group that had QRS equal or above 120 ms and were not RBBB or LBBB. Therefore, 1,529,971 were included (median age 52 [Q1:38; Q3:65] years; 40.2% were male). In a mean follow-up of 3.7 years, the overall mortality rate was 3.34%. RBBB was more frequent (2.42%) than LBBB (1.32%). In multivariate analysis, adjusting for sex, age and comorbidities, both patients with RBBB (HR 1.32; CI 95% 1.27–1.37) and LBBB (HR 1.69; CI 95% 1.62–1.76) had higher risk of overall mortality. Women with RBBB had an increased risk of all-cause death compared to men (p < 0.001). Cardiovascular mortality was higher in patients with LBBB (HR 1.77; CI 95% 1.55–2.01), but not for RBBB.

Conclusions

Patients with RBBB and LBBB had higher risk of overall mortality. Women with RBBB had more risk of all-cause death than men. LBBB was associated with higher risk of cardiovascular mortality.

Introduction

Bundle branch block has been associated with worse prognosis in cardiac disease, especially in heart failure [1]. Left bundle branch block (LBBB) is a known predictor of cardiac events in coronary heart disease [2], heart failure [3] and also in general population [4,5]. However, there are controversial data regarding right bundle branch block (RBBB), considered to be benign in asymptomatic healthy individuals [6]. Although, one study conducted in the general population showed that RBBB was associated with higher risk in all-cause and cardiovascular mortality [7]. For coronary heart disease and heart failure, the prognostic meaning of RBBB also has conflicted findings in the literature [5,8].

Most previous findings came from epidemiological studies or case series. More recently, large databases of digital electrocardiograms (ECG) were linked to mortality databases, what was called an electronic cohort. Big data provided from electronic cohorts with a large amount of information have more reliable and applicable results to the general population [9]. Our aim was to evaluate the overall and cardiovascular mortality in bundle branch block patients from a large electronic cohort composed by primary care patients.