điển hình điện tâm đồ ghi lại từ điện cực kết nối cánh tay. P, quá trình khử cực tâm nhĩ; QRS, khử cực tâm thất; T, tái cực thất. (Dưới) thất thế hoạt động được ghi lại từ một tế bào cơ tâm thất. Lưu ý sự tương ứng của khu phức hợp QRS với quá trình khử cực và thư từ của sóng T với tái cực. | Vander et al. Human Physiology The Mechanism of Body Function Eighth Edition III. Coordinated Body Functions 14. Circulation The McGraw-Hill Companies 2001 394 PART THREE Coordinated Body Functions FIGURE 14-20 Top Typical electrocardiogram recorded from electrodes connecting the arms. P atrial depolarization QRS ventricular depolarization T ventricular repolarization. Bottom Ventricular action potential recorded from a single ventricular muscle cell. Note the correspondence of the QRS complex with depolarization and the correspondence of the T wave with repolarization. 2T Q concerning different areas of the heart. The shapes and sizes of the P wave QRS complex and T wave vary with the electrode locations. To reiterate the ECG is not a direct record of the changes in membrane potential across individual cardiac muscle cells but is rather a measure of the currents generated in the extracellular fluid by the changes occurring simultaneously in many cardiac cells. To emphasize this point the bottom of Figure 14-20 shows the simultaneously occurring changes in membrane potential in a single ventricular cell. Because many myocardial defects alter normal impulse propagation and thereby the shapes and timing of the waves the ECG is a powerful tool for diagnosing certain types of heart disease. Figure 14-21 gives one example. It must be emphasized however that the ECG provides information concerning only the electrical activity of the heart. Thus if something is wrong with the heart s mechanical activity but this defect does not give rise to altered electrical activity then the ECG will not be of diagnostic value. QRS QRS QRS QRS QRS a QRS QRS QRS b p T p p T p T QRS QRS P pTp P P T c FIGURE 14-21 Electrocardiograms from a healthy person and from two persons suffering from atrioventricular block. a A normal ECG. b Partial block. Damage to the AV node permits only one-half of the atrial impulses to be transmitted to the ventricles. Note that every second P wave is not .
