To the Editors:
In a recent issue of the European Respiratory Journal, Gabor et al. 1 reported the effects of standard cardiac resynchronisation therapy (CRT) on nocturnal central sleep apnoea (Cheyne–Stokes respiration). CRT was shown to reduce Cheyne–Stokes respiration significantly in six out of 10 patients.
The study was performed in Canada between 1999 and 2002, which is the same era as when new generations of beta-blockers (e.g. metoprolol, carvedilol) were introduced into the market. The authors declare that the medication remained unchanged during the study, but that might be true for substance classes only and not for the type of beta-blocker. Substitution of beta-blockers had been a routine measure at that time in many industrialised countries 2.
According to our own data (currently unpublished), there seems to be a statistically significant and clinically relevant effect of high-dose beta-blocker treatment on the prevalence and severity of nocturnal central apnoeas and hypopnoeas. It could be demonstrated in three well-matched cohorts (no beta-blocker n = 16; metoprolol n = 16; carvedilol n = 13) of chronic heart failure patients (New York Heart Association II and III) that both beta-blockers, i.e. metoprolol and carvedilol, could significantly reduce the combined apnoea–hypopnoea index (19.5±14.4 versus 7.4±8.5 versus 8.7±8.1 per hour of sleep, respectively).
We suggest that the results of the study by Gabor et al. 1 should be related to the presence, dosage and type of beta-blocking medication in order to discriminate between the effects of cardiac resynchronisation therapy and potential pharmacological influences.
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