Cardiac resynchronization therapy (CRT) has become a common means of treatment in select patients with left ventricular systolic dysfunction and prolonged QRS duration. In an effort to gain a fuller understanding of the patients most likely to benefit from this therapy, a study published Aug. 25 in the Journal of the American College of Cardiology compared patient mortality after CRT defibrillator (CRT-D) implantation by sex, QRS morphology and duration, and found that among patients with left bundle branch block (LBBB) who received CRT-D, mortality is lower in women than in men. "Additionally, longer QRS duration in LBBB is associated with better survival in both sexes. In contrast, there is no sex difference in patients without LBBB, regardless of QRS duration."

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The study was led by Robbert Zusterzeel, MD, Center for Devices and Radiological Health, U.S. Food and Drug Administration, and looked at patients from the ACC's ICD Registry who received a CRT-D device between Jan. 1, 2006 and Sept. 30, 2009. Of the 31,892 CRT-D patients, 11,542 (36 percent) were women and 20,350 (64 percent) were men. Results showed women were more likely to have LBBB (86 percent vs. 70 percent), normal atrioventricular conduction (82 percent vs. 70 percent), and non-ischemic cardiomyopathy (62 percent vs. 33 percent). From an overall standpoint, the majority of both women and men had New York heart Association functional class II heart failure symptoms (84 percent and 82 percent).

In the overall cohort of those with LBBB, women had a 21 percent lower mortality risk than men (HR 0.79; 95 percent CI: 0.74 to 0.84; p < 0.001), though no sex difference was found in non-LBBB (HR 0.95; 95 percent CI: 0.85 to 1.06; p 1⁄4 0.37). Both sexes with longer QRS duration were associated with better survival, but not in patients without LBBB. Between women with LBBB and QRS of 120 to 129 ms, women with LBBB and QRS of 140 to 149 ms had a 27 percent lower mortality (HR 0.73; 95 percent CI: 0.60 to 0.88; p 1⁄4 0.001), a difference that was 18 percent in men (HR 0.82; 95 percent CI: 0.71 to 0.93; p 1⁄4 0.003). Furthermore, the mortality in LBBB and QRS of 150 ms or longer compared with those with LBBB and QRS of 120 to 129 ms was similar between sexes (HR 0.61–0.68; p < 0.001 for women and HR 0.58–0.66; p < 0.001 for men).

Ultimately, Zusterzeel and his colleagues recommend that further studies should include a non-CRT comparator group to confirm their findings.

In a corresponding editorial comment, G. William Dec, MD, FACC, notes that "this report adds to knowledge derived from smaller clinical trials by further identifying patients more (and less) likely to respond to CRT-D treatment." He adds that moving forward, "limiting CRT-D therapy to individuals with LBBB and QRS duration of 150 ms or more may deprive a substantial number of women with shorter QRS duration of this beneficial treatment. Conversely, the appropriate role of CRT-D therapy in both men and women with moderately severe heart failure symptoms who lack LBBB morphology appears to require careful reevaluation."

Keywords: Registries, Defibrillators, United States Food and Drug Administration, Cardiomyopathies, Heart Failure, Bundle-Branch Block, Ventricular Dysfunction, Left, Radiologic Health, Cardiac Resynchronization Therapy, National Cardiovascular Data Registries, ICD Registry

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