Introduction: Response to cardiac resynchronization therapy (CRT) is well established in patients with LBBB pattern and modest or even worse in the presence of interventricular conduction delay (IVCD) or RBBB. Consequently only typical LBBB pattern is considered class I indication for CRT implantation. However, IVCD pattern is heterogeneous and little is known about response rates in various IVCD patterns.
Methods: ECGs prior to CRT implantation were analyzed in 197 consecutive patients. ECGs were calcified into 3 groups: A) typical LBBB according to the 2009 AHA guidelines; B) "Atypical LBBB" defined as IVCD with QS/rS in V1, broad R wave in 1, AVL but with QS or rS in V5-V6; C) all other patterns. In all cases QRS> 120 msec. Clinical response was defined as composite score using NYHA functional class, 6-minute walk test, and quality of life questionnaire. Echocardiographic response was defined as a reduction in LV end systolic volume (LVESV) of > 10%.
Results: Baseline clinical characteristics were similar between all 3 patient groups. Patients with "Atypical LBBB" had a similar clinical response and echocardiographic response compared to patients with typical LBBB (71.4% and 47.6 % respectively; p=NS). The clinical (77.6 % vs 52.1% ; p= 0.005) and echocardiographic (59.2 % vs 37.3%; p= 0.02) response rates were significantly superior among patients with "pseudo LBBB" pattern compared to other IVCD patterns (group C patients). There was also a tendency to improved survival at 5 years survival (59% vs. 50% in groups B and C respectively; p=0.01).
Conclusion: Not all IVCD patients respond equally to CRT. Those with "Atypical LBBB" have a favorable response to CRT at least as typical LBBB patients. A larger prospective study should be performed in order to assess the utility of CRT in this population.
