van den Berg M P, de Langen C D, Crijns H J, Haaksma J, Bel K J, Wesseling H, Lie K I
Department of Cardiology, University of Groningen, The Netherlands.
J Cardiovasc Pharmacol. 1994 May;23(5):846-51. doi: 10.1097/00005344-199405000-00023.
We wished to elucidate the effect of beta-blockade on fibrillatory rate and atrioventricular (AV) nodal concealed conduction during atrial fibrillation (AF). Subsequent to determination of the effect on atrial functional refractoriness with the extrastimulus technique (basic cycle length 400 ms), the effect of metoprolol (0.3 mg/kg) on atrial fibrillatory rate was determined in 8 open-chest pigs with metacholine-facilitated AF. Once stable AF was established, fibrillatory rate was recorded with a bipolar epicardial electrode, together with the ventricular response during 500 ventricular intervals. For each episode of AF, three indexes were calculated to determine the degree of concealed conduction: the ratio of the longest to the shortest ventricular interval, the ratio of the median ventricular interval to the median atrial interval, and the coefficient of variation of the ventricular intervals. Metoprolol decreased fibrillatory rate (571-432 beats/min, p < 0.01), suggesting a proportionate increase (+32%) in atrial functional refractoriness during AF that far exceeded the increase (+7%) during sinus rhythm (217-233 ms, p < 0.05). None of the indexes of concealed conduction was affected by metoprolol. Metoprolol decreases fibrillatory rate in AF, possibly due in part to its class I effect, causing rate-dependent prolongation of atrial refractoriness. Despite reducing fibrillatory rate, metoprolol does not affect AV nodal concealed conduction measurably. Our results support the assumption that the reducing effect of beta-blockers on ventricular rate during AF is due to direct prolongation of AV nodal refractoriness.
我们希望阐明β受体阻滞剂对心房颤动（AF）时的颤动率及房室（AV）结隐匿性传导的影响。在用额外刺激技术（基础周期长度400毫秒）确定对心房功能不应期的影响之后，在8只开胸猪中，用乙酰甲胆碱诱发AF，测定美托洛尔（0.3毫克/千克）对颤动率的影响。一旦建立稳定的AF，用双极心外膜电极记录颤动率，同时记录500个心室间期的心室反应。对于每一次AF发作，计算三个指标以确定隐匿性传导的程度：最长心室间期与最短心室间期的比值、心室间期中位数与心房间期中位数的比值以及心室间期的变异系数。美托洛尔降低了颤动率（从571次/分钟降至432次/分钟，p<0.01），提示AF期间心房功能不应期有相应增加（+32%），这远远超过窦性心律期间的增加幅度（+7%，从217毫秒至233毫秒，p<0.05）。隐匿性传导的各项指标均未受美托洛尔影响。美托洛尔降低AF时的颤动率，可能部分归因于其I类效应，导致心房不应期呈频率依赖性延长。尽管降低了颤动率，但美托洛尔并未显著影响AV结隐匿性传导。我们的结果支持以下假设，即β受体阻滞剂在AF期间对心室率的降低作用是由于直接延长了AV结不应期。
