Left Atrial Receptor Discharge during Atrial Arrhythmias in the Dog

Afferent receptor discharge originating in the atria was recorded from slips of the cervical vagus in the open-chest dog. The activity of two types of atrial receptor endings was identified. Type A receptors exhibited a discharge pattern that was synchronous with the a wave of the atrial pressure pulse in the control recordings, and type B receptors discharged only during the v wave of the atrial pressure pulse in the control recordings. Atrial arrhythmias (flutter or fibrillation) were induced by mechanical stimulation of the area around the sinoatrial node. During atrial arrhythmias, there was a moderate rise in mean left atrial pressure (7.5 ± 0.7 cm H 2 O to 8.6 ± 0.6 cm H 2 O during arrhythmias in which type B receptors were studied, 6.1 ± 0.1 cm H 2 O to 7.8 ± 0.4 cm H 2 O during arrhythmias in which type A receptors were studied), a fall in aortic blood pressure, and a decrease in right atrial force. Atrial contractions were asynchronous and rapid. Type A atrial receptors showed a relatively greater increase in discharge (184.1%) during fibrillation than did type B atrial receptors (27.5%). These experiments demonstrated that both types of atrial receptors increased their discharge rate during atrial arrhythmias, indicating that they might be involved in a reflex diuresis which occurs during these arrhythmias in humans.