Cardiac pacing in patients with heart failure and right bundle branch block

The electromechanical substrate for response to cardiac resynchronization therapy in patients with right bundle branch block

BACKGROUND

Some patients with RBBB may respond to cardiac resynchronization therapy (CRT). However, little is known regarding the electromechanical substrate for CRT and whether this is the optimal pacing strategy.

METHODS

This was a pilot prospective double crossover randomized controlled clinical study comparing ventricular back up pacing (VVI-40), RV fusion pacing (DDD-40, RV only), and biventricular (BIV) pacing (DDD-40 BIV) in nine patients with RBBB and depressed EF. The study compared the frequency of dyssynchrony on baseline echocardiogram in patients with RBBB (n = 4), RBBB + anterior MI (RBBB with left axis deviation + left ventricular (LV) anterior wall thinning, n = 3), and RBBB + LAFB (RBBB with left axis deviation without LV anterior wall thinning n = 2). Echocardiographic assessment of LV dyssynchrony, LV size, and LV function was repeated after 6 months in each pacing mode.

RESULTS

Patients with RBBB + LAFB demonstrated baseline echocardiographic dyssynchrony between the LV anterior and inferior wall. Both DDD-40 RV-only pacing and DDD-40 BIV pacing resulted in improved LV function and clinical status compared to VVI-40 back up pacing. Patients with RBBB alone and RBBB with anterior MI had no baseline dyssynchrony and CRT using either RV only or BIV pacing resulted in LV dilation, worsened left ventricular ejection fraction and worsened clinical status compared to VVI-40 back up pacing.

CONCLUSION

Patients with RBBB, left axis deviation, and no prior anterior MI may have LV dyssynchrony between the anterior and inferior walls that is correctable with CRT.

Left ventricular regional contraction abnormalities by echocardiographic speckle tracking in combined right bundle branch with left anterior fascicular block compared to left bundle branch block

BACKGROUND

In contrast to LBBB patients less is known about patients with RBBB+LAFB regarding LV contractile abnormalities and the potential role of CRT. This study investigated whether patients with RBBB+LAFB morphology have echocardiographic mechanical strain abnormalities between the inferior and anterior LV walls, similar to abnormalities between septal and lateral walls in LBBB.

METHODS AND RESULTS

Ten healthy volunteers with no-BBB, 28 LBBB and 28 RBBB+LAFB heart failure patients were included in this retrospective study. Two-dimensional regional-strains were obtained by speckle-tracking. Scar was assessed by CMR. Response on echo was defined as normal, classical, borderline or other pattern. The number of classical patterns in LBBB was significantly higher than in RBBB+LAFB and no-BBB groups (p<0.001 for both). Contrary, the RBBB+LAFB group showed a significantly higher number of borderline patterns compared to other groups (LBBB: p=0.042, no-block: p=0.012). In addition, RBBB+LAFB patients had more scar than LBBB patients (9.9% vs 3.4%, p=0.041), and the average amount of scar in each wall was also higher in RBBB+LAFB (<5% in LBBB and <16% in RBBB+LAFB).

CONCLUSIONS

Patients with RBBB+LAFB on ECG and clinical HF demonstrate echocardiographic wall motion abnormalities between inferior and anterior LV walls, similar to abnormalities found between septal and lateral LV walls in patients with LBBB and HF. Fewer patients with RBBB+LAFB showed a classical pattern of opposing wall motion compared to LBBB. Factors that might alter strain patterns in RBBB+LAFB, including the detailed presence or absence of LV scar and coexisting block of the central fascicle, should be assessed in future studies.