Left Bundle Branch Associated with Greater Survival in Women than Men

Gender matters when it comes to overall survival after receiving a cardiac resynchronization therapy defibrillator (CRT-D), according to a study published June 3 in the JACC: Heart Failure.  The findings suggests that left bundle branch block (LBBB) diagnosis is associated with greater survival in women than in men following CRT-D implantation.

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The finding comes from a new retrospective analysis of seven years of Medicare data. The study followed 144,642 individuals who received CRT-D therapy between 2002 and 2008. Patients were followed for a median of 28 months after implantation. After adjustment for comorbidities and other factors, LBBB was associated with a 26 percent reduction in the mortality rate for women compared to a 15 percent reduction in the mortality rate for men. After accounting for other factors, LBBB was associated with lower mortality in women than in men (p<0.0001).

"A significant interaction between sex and LBBB confirmed that the LBBB diagnosis in and of itself carries a different prognosis for female and male CRT-D recipients," said lead author Zak Loring, BS, Center for Devices and Radiological Health, U.S. Food and Drug Administration, Silver Spring, Md. "These findings suggest that the sex differences in LBBB mortality rates is independent of differences in baseline risk profiles."

The authors note that it is not clear why LBBB is associated with better outcomes for women than for men following CRT-D implantation. One explanation may be that LBBB carries a different prognostic significance for women compared to men. Another explanation may be that a false-positive LBBB diagnosis is more common in men than in women due to anatomic differences or other factors.

"To our knowledge, this is the first time that LBBB has been shown to portend significantly better long-term survival benefit in women than men receiving CRT-D," the authors concluded. "Future studies should investigate appropriate QRS duration thresholds in men and women that best identify CRT-D candidates."

"LBBB diagnosis is associated with greater survival in women than in men receiving CRT, and this discrepancy is not explained by differences in measured comorbidities," notes Peter C. Block, MD, FACC.

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