Ardell J L, Randall W C, Pomeroy G, Lawton M, Kim T
Department of Physiology, University of South Alabama, Mobile 36688.
J Appl Physiol (1985). 1991 Mar;70(3):1175-83. doi: 10.1152/jappl.1991.70.3.1175.
Cardiac responses to graded treadmill exercise were compared in conscious dogs before and after excision of the sinoatrial node (SAN) and adjacent tissue along the sulcus terminalis. The chronotropic and dromotropic responses to dynamic exercise were compared with and without selective muscarinic (atropine) and/or beta-adrenergic (timolol) blockade. With the SAN intact, cardiac acceleration was prompt during onset of exercise and in proportion to work intensity. Immediately after SAN excision (1-7 days), pacemaker activity exhibited marked instability in rate and pacemaker location, with rapid shifts between atrial and junctional foci. Soon thereafter (1-2 wk), subsidiary atrial pacemakers (SAPs) assumed the primary pacemaker function. Although the SAP foci demonstrated stable heart rates and atrioventricular (AV) intervals at rest and during exercise, heart rates at rest and during steady-state exercise were reduced 34% from corresponding levels in the SAN-intact state, both with and without selective autonomic blockade. For control of dromotropic function, animals with SAP foci showed pronounced shortening in AV interval in conjunction with exercise that was further exacerbated by pretreatment with atropine. Eight weeks after excision of the primary SAN pacemakers, direct electrophysiological mapping localized the SAP foci to either the inferior right atrium along the sulcus terminalis or the dorsal cranial right atrium (in or near Bachmann's bundle). Animals with SAPs localized to the inferior right atrium had a more marked suppression in heart rate with a corresponding greater decrease in AV interval during exercise than dogs with SAP foci identified within the dorsal cranial right atrium.
在清醒犬中，比较了沿终沟切除窦房结（SAN）及相邻组织前后，心脏对分级跑步机运动的反应。比较了在有和没有选择性毒蕈碱（阿托品）和/或β-肾上腺素能（噻吗洛尔）阻断的情况下，对动态运动的变时性和变传导性反应。在SAN完整时，运动开始时心脏加速迅速，且与工作强度成比例。SAN切除后立即（1 - 7天），起搏活动在频率和起搏点位置上表现出明显的不稳定性，心房和交界性起搏点之间快速切换。此后不久（1 - 2周），辅助心房起搏点（SAPs）承担主要起搏功能。尽管SAP起搏点在静息和运动时表现出稳定的心率和房室（AV）间期，但无论有无选择性自主神经阻断，静息和稳态运动时的心率均比SAN完整状态下的相应水平降低了34%。为了控制变传导功能，具有SAP起搏点的动物在运动时AV间期明显缩短，阿托品预处理会使其进一步加剧。在切除主要的SAN起搏点8周后，直接电生理标测将SAP起搏点定位到沿终沟的右下心房或背侧颅侧右心房（在巴赫曼束内或附近）。与SAP起搏点位于背侧颅侧右心房的犬相比，SAP起搏点位于右下心房的动物心率抑制更明显，运动时AV间期相应减少更多。
