Brown M D, Davies M K, Hudlicka O, Townsend P
University of Birmingham, School of Sport and Exercise Science, United Kingdom.
Cardiovasc Res. 1994 Dec;28(12):1774-9. doi: 10.1093/cvr/28.12.1774.
The aim was to develop a method of inducing bradycardia on a chronic basis by electrical pacing and to study its effect upon myocardial capillarity in pigs.
Farm pigs were instrumented with Medtronic dual chamber telemetric pacemakers and two leads, either both atrial or one atrial and one ventricular. Bradycardia was achieved by linking pacing stimuli to endogenous atrial or ventricular events for the different electrode positions respectively, and monitored postoperatively for 4-5 weeks by implanted telemetric ECG devices. Myocardial capillary supply (lectin staining) and myocyte cross sectional areas were then estimated in sections of the left ventricle.
Heart rates were reduced by 40-50 beats.min-1 at operation from a resting rate of 110(SEM 3) beats.min-1 in eight animals and bradycardia maintained upon recovery from anaesthesia for up to five weeks, with no obvious limitations for the animals. After this time, heart rates measured under anaesthesia were found to remain low for up to 2 h after pacing had been switched off. There was no evidence of myocyte hypertrophy, yet mean capillary density.mm-2 was significantly increased by pacing, from 1470(50) to 1734(82), p < 0.02.
It is possible to produce primary heart rate reduction in the pig by a novel means of pacing on a chronic basis, leading to increased myocardial capillary supply without myocyte hypertrophy. This method can provide a basis for future investigations of the beneficial effects of heart rate reduction in the vascularly compromised heart.
旨在开发一种通过电起搏长期诱导心动过缓的方法，并研究其对猪心肌毛细血管的影响。
给农场猪植入美敦力双腔遥测起搏器和两根导线，两根均为心房导线或一根心房导线和一根心室导线。分别针对不同电极位置，将起搏刺激与内源性心房或心室事件相关联以实现心动过缓，并通过植入的遥测心电图设备在术后监测4至5周。然后估计左心室切片中的心肌毛细血管供应（凝集素染色）和心肌细胞横截面积。
八只动物的心率在手术时从静息心率110（标准误3）次/分钟降低了40 - 50次/分钟，并且在从麻醉中恢复后心动过缓维持长达五周，对动物没有明显限制。在此之后，发现麻醉下测量的心率在起搏关闭后长达2小时仍保持较低水平。没有心肌细胞肥大的证据，但起搏使平均毛细血管密度（每平方毫米）显著增加，从1470（50）增加到1734（82），p < 0.02。
通过一种新型的长期起搏方法可以使猪的心率原发性降低，从而在不引起心肌细胞肥大的情况下增加心肌毛细血管供应。该方法可为未来研究心率降低对血管受损心脏的有益作用提供基础。
