Background

Depending on the population investigated, the prevalence of complete right bundle branch blocks (RBBB) ranges from 0.2-3.2%. The prevalence of incomplete RBBB (iRBBB) is even higher at 4.5 – 13.5%.  Recent studies like the Copenhagen City Heart Study revealed an increased cardiovascular morbidity and mortality in patients with RBBB without clinically overt cardiac disease. Data on the morphology of RBBB and iRBBB in the general population regarding different electrocardiographic (ECG) parameters like ST-segment deviation and QTc-interval are scarce. The aim of this study is therefore to describe the morphology of RBBB and iRBBB beyond mere depolarization concerning different ECG parameters in the general population.

Methods and Results

We analyzed ECGs of 37,512 participants of the UK Biobank, prospectively enrolled between 2006 and 2010 (Age 40-69). The analysis includes 1098 iRBBB (2.9%) and 734 RBBB (1.9%) in sinus rhythm, excluding complete and incomplete left bundle branch blocks. The following criteria must be fulfilled for the diagnosis of a complete RBBB: a QRS duration equal or greater than 120ms, Rsr’, rsR’ or rSR’ configuration in leads V1 or V2 and an S-wave with a greater duration than R or greater than 40ms in leads I and V6. The same criteria with a QRS duration of 110-120ms in adults was defined as iRBBB. 

The mean QRS duration in control was 88 ms (SD 12), iRBBB 103ms (SD 7) and in RBBB 134ms (SD 12). There was a significant stepwise prolongation of the QTc-interval, especially in RBBB (Mean (SD) in ms: Control 419 (23), iRBBB 422 (22), RBBB 446 (22), p <0,01).  Furthermore, we observed significant stepwise increasing ST-segment elevations in leads I and II (Lead I, mean (SD) in mV: Control 43 (51), iRBBB 64 (54), RBBB 124 (88), p<0,01). Further analyses on the repolarization also showed a T-wave inversion in V1 with a peak amplitude of 34 mV (SD 200 mV) in controls, -102mV (SD 151mV) in iRBBB and -223mV (SD 157mV) in RBBB. We also found a significant prolongation of the PR-interval, especially in RBBB (Mean (SD) in ms: Control 164 (27), iRBBB 167 (SD 27), and RBBB 174 (31), p <0,001). 

Conclusions

In conclusion, iRBBB and RBBB in the general population are associated with hitherto unrevealed alterations in the standard ECG parameters representing different parts of the electrical conductions system, especially concerning repolarization. Knowing the morphology of complete and incomplete RBBB in the general population might help to distinguish healthy individuals from those with underlying structural heart disease causing further alterations in the ECG.