We studied the effects of cardiac resynchronization therapy (CRT) on regional myocardial strain distribution, as determined by echocardiographic strain rate (SR) imaging.
Dilated hearts with left bundle branch block (LBBB) have an abnormal redistribution of myocardial fiber strain. The effects of CRT on such abnormal strain patterns are unknown.
We studied 18 patients (12 males and 6 females; mean age 65 ± 11 years [range 33 to 76 years]) with symptomatic systolic heart failure and LBBB. Doppler myocardial imaging studies were performed to acquire regional longitudinal systolic velocity (cm/s), systolic SR (s−1), and systolic strain (%) data from the basal and mid-segments of the septum and lateral wall before and after CRT. By convention, negative SR and strain values indicate longitudinal shortening.
Before CRT, mid-septal peak SR and peak strain were lower than in the mid-lateral wall (peak SR: −0.79 ± 0.5 [septum] vs. −1.35 ± 0.8 [lateral wall], p < 0.05; peak strain: −7 ± 5 [septum] vs. −11 ± 5 [lateral wall], p < 0.05). This relationship was reversed during CRT (peak SR: −1.35 ± 0.8 [septum] vs. −0.93 ± 0.6 [lateral wall], p < 0.05; peak strain: −11 ± 6 [septum] vs. −7 ± 6 [lateral wall], p < 0.05). Cardiac resynchronization therapy reversed the septal–lateral difference in mid-segmental peak strain from −46 ± 94 ms (LBBB) to 17 ± 92 ms (CRT; p < 0.05).
Left bundle branch block can lead to a significant redistribution of abnormal myocardial fiber strains. These abnormal changes in the extent and timing of septal–lateral strain relationships can be reversed by CRT. The noninvasive identification of specific abnormal but reversible strain patterns should help to improve patient selection for CRT.