Skeletal muscle pathology in chronic heart block.

Skeletal muscle samples, mainly from the deltoid, were studied morphologically and histochemically in 35 patients with chronic heart block and from nine elderly control subject. The average age of the first group was 67-7 (range 11-94) years. Abnormalities were present in 20 cases, no difference being found between patients with idiopathic and secondary heart block. In 15 samples there was increased oxidative enzyme activity in some muscle fibres, and in six there was fibre type grouping. Six had unexplained type 11 fibre atrophy and two had a predominance of type 1 fibres. Tubular aggregates were conspicuous in one biopsy specimen, and in another, rod bodies were found. Minor abnormalities were also seen in the control group. In the absence of any consistent pattern many of these changes were attributed to ageing.