Background and Aim: Recent data suggested that one third of patients meeting conventional electrocardiographic (ECG) criteria for left bundle branch block (LBBB) may be misdiagnosed and new, stricter, ECG criteria for LBBB have been proposed (Strauss's criteria). Accordingly, we used two-dimensional speckle tracking echocardiography (2DSTE), to compare left ventricular (LV) mechanics in patients with LBBB according to conventional versus Strauss's ECG criteria for LBBB.
Methods: We studied 49 asymptomatic patients with incidental LBBB: 16 with conventional (mean age 69 years, 56% were men) and 33 with Strauss's criteria (mean age 66 years, 61% were men), LV ejection fraction (LVEF) 45%, and no significant obstructive coronary artery disease. Three-dimensional echocardiography was performed to measure LV end diastolic (LVEDV) and end systolic (LVESV) volumes, sphericity index (SpI), LV remodelling index (LVRI) and LVEF. 2DSTE was used to measure parameters of LV dyssynchrony: septal to posterior wall time to peak radial strain (SW-PW delay), longitudinal strain delay index (L-SDI), longitudinal strain rate dispersion index (L-SRDI) and LV mechanical dispersion (LVMD). In addition, we also measured LV cardiac work indices: global work efficiency (GWE), global work index (GWI), global constructive work (GCW), and global wasted work (GWW).
Results: Among dyssynchrony parameters; L-SDI was significantly higher in patients with Strauss's criteria than in conventional one (3717% vs 2510%, respectively, p = 0.007). Moreover, GWW tended to be higher in patients with Strauss's criteria than in conventional one (325132% vs 267124% respectively, p = 0.079). In all patients, LVESV index was positively correlated with GWW (r= 0.51, p= 0.001). This correlation may further support the use of LVESV index change as an echocardiographic predictor to assess LV remodelling after cardiac resynchronization therapy (CRT).
Conclusion: Patients in whom LBBB was diagnosed according to stricter (Strauss's) ECG criteria showed significantly higher intraventricular dyssynchrony and tendency for higher LV wasted work than patients with LBBB according to conventional ECG criteria. Further studies are needed to assess if the same occurs in patients with LVEF < 35% considered for CRT and further stratification of patients according to ECG pattern may improve the selection of patients who would benefit from CRT.