MacLeod R S, Lux R L, Taccardi B
Nora Eccles Harrison Cardiovascular Research and Training Institute, University of Utah, Salt Lake City, USA.
J Electrocardiol. 1998;30 Suppl:114-21. doi: 10.1016/s0022-0736(98)80053-8.
Despite the widespread use of electrocardiogram (ECG), changes in cardiac activity resulting from ischemia or altered recovery characteristics sometimes remain electrocardiographically "silent" or are first detectable by techniques that measure ventricular contractility, such as ultrasound or blood pressure. Especially local changes in repolarization can go undetected when ECG electrodes do not lie close to the area of the heart affected. Experiments were performed on an isolated, perfused canine heart suspended in a realistically shaped, instrumented, electrolytic torso tank with the goal of determining some mechanisms for these ambiguities. By recording simultaneously both epicardial and torso tank surface potentials, complete descriptions were obtained of the electrical response to interventions such as coronary occlusions and alterations in pacing site and frequency. One hypothesis was that some interventions produce highly variable ECG responses primarily because of differences in their location within the heart. To test this, the effect was measured of repeating the same intervention as the heart's location and orientation in the tank were varied. A numerical forward solution was also used to investigate variation of torso tank potentials with heart location. The resulting changes in tank surface potentials illustrate how, for example, precordial ST-segment shifts following occlusion change from elevation to depression to become almost undetectable as the heart rotates in the tank. The results suggest that some events are electrocardiographically silent because of the complex geometric relationship of the heart, torso, and site of the lesion, as well as the spatial sampling and analysis techniques used in detection.
尽管心电图（ECG）被广泛应用，但由缺血或恢复特性改变引起的心脏活动变化有时在心电图上仍表现为“无异常”，或者最初只能通过测量心室收缩力的技术（如超声或血压）检测到。当心电图电极未靠近受影响的心脏区域时，尤其是复极化的局部变化可能无法被检测到。我们在一个悬浮于形状逼真、配备仪器、充满电解质的躯干模拟槽中的离体灌注犬心脏上进行了实验，目的是确定这些不明确情况的一些机制。通过同时记录心外膜和躯干模拟槽表面电位，完整描述了对诸如冠状动脉闭塞以及起搏部位和频率改变等干预措施的电反应。一种假设是，一些干预措施产生高度可变的心电图反应主要是因为它们在心脏内的位置不同。为了验证这一点，在改变心脏在模拟槽中的位置和方向时，测量了重复相同干预措施的效果。还使用了数值正向求解方法来研究躯干模拟槽电位随心脏位置的变化。由此产生的模拟槽表面电位变化说明了，例如，随着心脏在模拟槽中旋转，闭塞后胸前导联ST段移位如何从抬高变为压低，直至几乎无法检测到。结果表明，由于心脏、躯干和病变部位之间复杂的几何关系，以及检测中使用的空间采样和分析技术，一些事件在心电图上表现为无异常。
