Women with QRS of 130 milliseconds or greater see better outcomes than men when using cardiac resynchronization therapy (CRT). A study published online June 23 in JAMA Internal Medicine found that while women receive CRT defibrillation (CRT-D) less often than men, women with left bundle branch block and a QRS of 130 to 149 milliseconds had a 76 percent reduction in mortality and other heart failure-related events.

Previous studies informed guidelines; however, of the patients in those studies only around 20 percent were female. Those studies reported little to no improvements with a QRS of less than 150 in left bundle branch block.

Pooling data from three trials to capture a larger female data set, Robbert Zusterzeel, MD, and colleagues from the FDA found that while men did not see the same improvement, CRT-D had a noticeable effect on outcomes in women. Women treated with CRT-D had a 60 percent relative reduction in heart failure or death and a 55 percent relative reduction in death alone. For men, the relative reductions were more modest, at 26 percent and 15 percent, respectively.

The greatest relative reduction noticed was in potential heart failure events or death for women with a QRS of 130 to 139 milliseconds, of approximately 85 percent. Between 140 and 149 milliseconds, this risk reduction was 69 percent.

Neither men nor women with left bundle branch block benefited from CRT-D at QRS of shorter than 130 milliseconds, however.

“Of note, guidelines do give a class IIa indication to patients with LBBB [left bundle branch block] and QRS of 120 to 149 milliseconds, and thus many of these patients would likely be offered CRT-D. However, considering that women receive CRT-D less often than men, we believe that the current findings are important to communicate,” wrote Zusterzeel et al.

An editorial by C. Noel Bairey Merz, MD, of the Barbra Streisand Women’s Heart Center of the Cedars Sinai Heart Institute in Los Angeles, and Vera Regitz-Zagrosek, MD, of the Institute for Gender in Medicine at the Charite University Medicine in Berlin, noted that sex differences in cardiovascular disease are important to consider at the time of treatment. In particular, women have higher prevalence of heart failure with preserved ejection fraction, stress-induced cardiomyopathy, post-MI depression and coronary microvascular dysfunction.

A difference in the use and efficacy of cardiac devices is only part of the whole. They argued that guidelines based on findings from mostly male populations lead to misdiagnosis and suboptimal treatment of cardiovascular disease in women.

Zusterzeel et al wrote, “The fact that women normally have smaller ventricles and shorter QRS duration than men provides an anatomical and/or physiological explanation for the findings, but the higher rate of nonischemic cardiomyopathy in women compared with men may have also contributed. Overall, this study highlights the importance of sex-specific analysis in medical device clinical studies and the public health value of combining individual-patient data from clinical trials submitted to the FDA.”