We report a large series of consecutive patients from a single centre. The proportion of female implants matches that of the UK (18%)3
and Danish registries (20%),4
and the results of published clinical trials (AVID, MADIT-1, and MADIT-2). In subjects with CAD, we observed an implant ratio of 8:1 male excess. Framingham originally suggested that the risk of SCD in CAD was a 4:1 male excess.2
The TRACE investigators recently reported a mere 1.4:1 male loading.1
It is concerning that females continue to be under represented in ICD implant activity both from national databases and published trial data.
If females were finding it harder to prove themselves worthy of an ICD at our institution, then we might expect them to have greater baseline markers of arrhythmic risk, more arrhythmia, and poorer survival. Our results showed that male and female subjects were equally matched for baseline co-morbidity, arrhythmia presentation, and VT/VF inducibility at EPS. Females were just as likely to experience appropriate therapy, electrical storm, or death as males on follow up. We concluded that there was no evidence of frank, systematic in-house discrimination against females at ICD prescription.
Sex bias might not be the only explanation for differences in implant practice between males and females. An alternative interpretation might be that female subjects with CAD present at an older age and with more co-morbidity and that it was these subjects who were not receiving an ICD. It was a limitation of our study that we have no data concerning patients assessed for an ICD who were not implanted. The National Health Service has never imposed an upper age limit for ICD implantation. Furthermore, the only co-morbidity that would restrict ICD implantation in our institution is one expected to shorten survival to less than six months.
We were suspicious that the “missing” women were not reaching us from our referring centres. There could be at least four explanations for this: the women were erroneously perceived to be at low risk of SCD; they were not being referred because of increased age and greater co-morbidity; older subjects with co-morbidity were themselves declining to be referred; or they were already dead (women have poorer survival rates following myocardial infarction and SCD). All four explanations are compatible with the observation that our females had less severe CAD. We cannot confirm which explanation is correct because we have no data concerning patients who did not reach our centre. Further studies are required to identify why women are less likely to receive an ICD than men. We suggest that these should be directed towards examining the different outcomes in males and females at risk of arrhythmia before they reach hospital.
We conclude that our data indicate that too few females with CAD are referred for an ICD. The reason for this is unclear.