Standard Electrocardiographic Properties beyond Depolarization and NT-proBNP Associated with Right Bundle Branch Block in the General Population

J. Senftinger (Hamburg)¹, Y. Fakhri (Kopenhagen)², J. L. Isaksen (Kopenhagen)³, G. Ahlberg (Kopenhagen)³, J. Ghouse (Kopenhagen)³, C. Graff (Aalborg)⁴, S. Blankenberg (Hamburg)¹, M. Salling Olesen (Kopenhagen)³, J. Kanters (Kopenhagen)³, P. M. Clemmensen (Hamburg)¹
¹Universitäres Herz- und Gefäßzentrum Hamburg Klinik für Kardiologie Hamburg, Deutschland; ²Rigshospitalet The Heart Center Kopenhagen, Dänemark; ³University of Copenhagen Department of Biomedical Sciences Kopenhagen, Dänemark; ⁴Aalborg University Department of Health Science and Technology Aalborg, Dänemark

Introduction
Complete right bundle branch blocks (cRBBB) are associated with increased cardiovascular morbidity and mortality in general population studies. Data on the morphology of cRBBB and incomplete RBBB (iRBBB) in the general population regarding different electrocardiographic (ECG) parameters like ST-segment deviation and QTc-interval are scarce. The aim of this study was therefore to describe the morphology of cRBBB and iRBBB beyond mere depolarization concerning different ECG parameters in the general population.

Methods and Results
We analyzed sinus rhythm ECGs of 35,397 participants from the UK Biobank, prospectively enrolled between 2006 and 2010 (Age 40-69). The analysis included 1070 participants with iRBBB (2.9%) and 697 with cRBBB (1.9%). cRBBB was defined as Rsr’, rsR’ or rSR’ configuration in leads V1 or V2 and an S-wave duration greater than R-wave duration or greater than 40ms in leads I and V6 and a QRS duration ≥ 120ms. The same criteria with a QRS duration of 100-120ms in adults was defined as iRBBB. Those without BBB constituted the control group. Additionally, we investigated the association between RBBB and NT-proBNP as a non-invasive marker for potentially underlying heart diseases. The results are presented as mean ±standard deviation.

The QRS duration in the control group was 87±10 ms, in iRBBB 103±7 ms and in cRBBB 137±12 ms (p<0.001). We observed a higher S peak amplitude in leads I-III in iRBBB and cRBBB compared to the control group (Lead I in µV: control 54±88, iRBBB 124±135, cRBBB 282±108, p<0.001). Furthermore, we also found higher STJ points in leads V1-3 (Lead V1 in µV: control -8±68, iRBBB 46±37, cRBBB 49±55, p<0.001). There was also a significant prolongation of the QTc-interval, especially in cRBBB: Control 419±21ms, iRBBB 421±21ms, cRBBB 447±21ms, (p <0.001). Regarding the JT-interval we observed a stepwise shortening (Control 331±31ms, iRBBB 319±30ms, cRBBB 308±30ms, p<0.001). Further analyses on the repolarization also showed a T-wave inversion in lead V1 in iRBBB and cRBBB compared to the control group (Control 31±193µV, iRBBB -102±152µV, cRBBB -222±160µV, p <0.001). Additionally, we noted a stepwise increasing ST-segment elevation in leads I and II (Lead I in µV: control 43±5, iRBBB 64±54, cRBBB: 124±88, p<0.001). We also found a surprising significant prolongation of the PR-interval, especially in cRBBB (Control 165±27ms, iRBBB 167±27ms and cRBBB 174±31 ms, p <0.001). Furthermore, the normalized NT-proBNP level was slightly higher in the group with cRBBB (Control -0.13±1.09, iRBBB -0.18±1.02, cRBBB 0.18±1.29, p=0.031).

Conclusions
In conclusion, iRBBB and cRBBB in the general population were associated with hitherto unrevealed alterations in the standard ECG parameters representing different parts of the electrical conductions system, especially concerning the PR-interval and repolarization. Furthermore, we observed a slight increase in the NT-proBNP level in individuals with cRBBB, which may indicate an underlying and previously undiagnosed heart disease.

Figure 1: The morphology of RBBB in the general population and the association with NT-proBNP.

Standard Electrocardiographic Properties beyond Depolarization and NT-proBNP Associated with Right Bundle Branch Block in the General Population

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