Extrasystoles, the most common cause of irregularity of the heart's action, were formerly regarded as a symptom of myocardial damage. A valuable part of Sir James Mackenzie's great work was the clinical differentiation between extrasystoles and auricular fibrillation; at the same time he showed the relative unimportance of the former and the importance of the latter. However, to deny any significance to extrasystoles would be to lose a sign which might help in diagnosis and treatment. According to Boas and Levy,1 at least 50 per cent of patients with extrasystoles have normal hearts as far as can be determined. They occur in a large proportion of elderly men and not infrequently in young subjects. Mackenzie2 noted premature beats in a man at the age of 69 in whom they were first discovered at the age of 18. This patient had earned a living at work that entailed great
EXTRASYSTOLES. JAMA. 1936;107(26):2135–2136. doi:10.1001/jama.1936.02770520037014
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