To the Editor:

We appreciate the interest in our article shown by Domínguez et al. Their letter correctly describes our current knowledge about the influence of circadian variations in the incidence and success rates of primary (PCI).

Although this aspect is not listed among the principal objectives of our study, it was at least partially analysed. The analysis showed that there were no significant differences in mortality following primary PCI if it is performed within working hours (n=154) or non-working hours (n=229). Indeed, the figures, whether after 30 days or 1 year, were lower during non-working hours (4.8% compared with 8.4%; P=.15, and 7.9% compared with 11.1%; P=.29). There were no significant differences in no-reflow incidence (12.6% for non-working vs 8.9%; P=.28), or in coronary and myocardial flow as evaluated by the TIMI and TMPG flow scales respectively.

These findings appear to be contradictory to that shown by the literature,1 exactly as Domínguez et al describe, and in our opinion they reflect the multi-factorial nature of clinical results following primary PCI. On the one hand, experience and better door-to-balloon times are likely during working hours, while other potential factors, such as circadian variations in platelet aggregability may be acting against us.

In any case, it is worth pointing out that door-to-balloon time, which is a main factor determining the clinical success of primary PCI,2 is normally higher outside of working hours. In our study, it was 22 minutes higher outside of working hours and with no notice, and was reduced to a 14-minute difference only if there was advance warning. The presence of this delay in door-to-balloon time with advance warning could partially explain the good clinical results outside of working hours.