Ablation of ligament of Marshall attenuates atrial vulnerability to fibrillation induced by inferior left atrial fat pad stimulation in dogs.

BACKGROUND: The role of ligament of Marshall (LOM) in the mechanism of "vagal" atrial fibrillation (AF) is still unknown. OBJECTIVE: To investigate the impact of LOM ablation on atrial vulnerability to AF induced by inferior left atrial fat pad (ILAFP) stimulation in dogs. METHODS: AF inducibility and atrial effective refractory period (ERP) were elevated before and after LOM ablation in 8 of 14 dogs (the ablation group). Same protocol but without LOM ablation was conducted in the remaining 6 dogs (the control group). The activation patterns of LOM and left pulmonary veins (LPVs) during sustained AF were analyzed. The distribution of epicardial cholinergic nerve fibers between LOM and ILAFP was investigated in the control group. RESULTS: Ablation of LOM significantly attenuated AF inducibility (87.5% vs 33.3%, P < 0.001) and prolonged ERPs of the structures in contiguity with LOM (P < 0.05) in the ablation group. In contrast, there was no significant change in ERPs and AF inducibility in the control group. During sustained AF, fractionated atrial electrograms were more common in the LOM area than the LPVs (84% vs 18% of the analyzed episodes, P < 0.001). In 46.7% of the episodes with identifiable LOM spikes, atrial potentials, and LOM spikes were related in 2:1 or 3:2 pattern during the intermittent organized activity. Acetylcholinesterase staining revealed a close cholinergic nerved relationship between LOM and ILAFP. CONCLUSIONS: LOM plays a critical role in maintaining AF induced by stimulation of ILAFP. Ablation of LOM can markedly attenuate AF inducibility in this model.

Extrinsic and intrinsic innervation of the guinea pig knee joint: toward an animal model for manipulative therapy.

OBJECTIVES: Besides spinal conditions, knee joint problems are one of the most common ailments of the musculoskeletal system. Problems with the knee can be classified into (1) poor mechanics, (2) traumatic injury, and (3) arthritic changes. All these problems can produce pain. Conservative treatment such as chiropractic manipulative therapy can be helpful in alleviating some of the pain. The present study was carried out to investigate the extrinsic and intrinsic innervation of the knee joint of the guinea pig in the hope of shedding light on future study of the underlying mechanism of chiropractic manipulative therapy on knee joint pain conditions. METHODS: A total of 16 guinea pigs were used in the present study. Microdissection was performed to reveal the gross anatomy of nerve innervation. Histology and immunohistochemistry were also performed to identify nerve endings and immunoreactive fibers in different articular tissues. RESULTS: Gross dissection revealed the general pattern of guinea pig knee joint innervation. By using gold chloride preparations, various kinds of nerves and terminals or endings were identified in these tissues. Immunohistochemistry also revealed immunoreactivities in nerve fibers in different joint tissues. CONCLUSIONS: The distribution of the different nerve endings showed a characteristic pattern in different articular tissues. They were considered to be mechanoreceptors (types I, II, and III) and pain receptors (type IV). The structural characteristics and distribution patterns of the different types of nerve endings suggest that the roles of the different nerve endings vary in different parts of the articular tissues.