The efficacy of pharmacological β-blockade in decreasing cardiac death in patients after myocardial infarction suggests the existence of sympathetic overactivity and indicates the importance of assessing its magnitude. The paper by Graham and co-workers in this issue of Clinical Science has attempted to address this issue by measuring muscle sympathetic nerve activity (MSNA) in various groups of patients and control subjects. It was found that, after myocardial infarction, there was sympathetic overactivity, which was more marked and more long-lasting than after unstable angina, whereas, in the presence of simple coronary artery disease, sympathetic activity did not differ from that in control subjects. Clear signs of sympathetic overactivity lasting for months after an acute myocardial infarction have already been reported using quite different methodology, i.e. spectral analysis of heart period and systolic arterial pressure variability. The soundest hypothesis to explain such a sympathetic overactivity appears to be based on the well-demonstrated finding that the ischaemic heart is a powerful site of origin of both excitatory and/or inhibitory reflexes, which may be of paramount clinical importance.

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