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Atrial fibrillation is (AF) the most common sustained cardiac rhythm disorder. Small nerve fibres carry autonomic modalities, somatic pain and temperature sensations. The aim of our study was to assess the role of small A-delta nerve fibres in the peripheral nerves of patients with AF.
The function of small nerve fibers was assessed by cutaneous silent period (CSP) elicited by electrical square pulse stimulation using stimulating ring electrodes on the index finger and recording electrodes over thenar musles. The CSP onset, end latencies and suppression of muscle activity - duration over APB were measured. Patients either with polyneuropathy or drugs that contribute to peripheral nerve involvement were excluded.
In the study 30 patients with paroxysmal AF and 30 aged-matched healthy subjects were comprised. The mean CSP onset latency in patients with AF was significantly longer compared with the control group (86.67 ± 8.19 vs. 68.05 ± 7.81, CI 83.2-90.1 vs. 65.9-70.0), meanwhile CSP duration was markedly shorter in AF patients (45.10 ± 10.96 vs. 60.95 ± 10.14, CI 40.7-49.6 vs. 58.3-63.4). Nerve conduction study of the large motor and sensory fibers did not reveal any difference between patients and healthy subjects.
Fig. 1 Cutaneous silent period in patient with AF
In our study, the main attention was focused on the extrinsic cardiac nervous system using a CSP measurement. The delay of CSP onset latency reflects the impairment of afferent volley of A-delta afferents, efferrent motor axons and synaptic delay, while shortened CSP duration is related to the amount of activated axons and indicates the axonal lesion. Abnormality of CSP in AF patients supports the occurrence of small nerve fiber neuropathy. Our study of small nerve fibres may implay a new aspect in the etiology of AF.