What can be seen in lead Ⅰ? Lead I of the ECG is the first lead of the ECG and is labeled “I” or “L1”. It records electrical information from red and yellow electrodes attached to the left and right hands (yellow electrodes on the left hand and red electrodes on the right hand). The graphic features in a normal ECG in lead I are: the main peaks of the P wave, the QRS wave cluster, and the T wave should all be predominantly upward. Common abnormalities in the I-lead ECG (if you notice any of the following abnormalities, ask your doctor to assist you in determining whether there is a real problem with your ECG): ① The main peaks of all waveforms in the I-lead ECG are predominantly downward: this implies two problems, one of which is that the left and right hand clicks are tied the other way around, i.e., the yellow electrodes are tied on the right wrist and the red electrodes are tied on the left wrist. This can be corrected immediately by careful identification of the drug. Of course there are other graphic features that can be used to recognize this misconnection, which is a matter for the doctor. The second is a congenital anomaly of the heart, with the presence of a congenital right-sided heart. As long as the electrodes are not connected incorrectly, most cases fall under this diagnosis. (ii) Only the main peak of the QRS wave cluster is downward in lead I: others, such as the P and T waves, are upward and upright, so the most likely scenario is the presence of right ventricular hypertrophy, or the presence of a tiny left posterior branching block within the heart. It can also be seen in preexcitation syndrome, bundle branch block within the ventricle. (iii) P-wave in lead I alone is downward: there may be a problem with the normal order of cardiac pacing, with a temporary change from normal sinoatrial node pacing to atrioventricular node (AV junction area) pacing (at this time, there should be a concomitant P-R interval of <3 bars). This is often due to the effects of disease or medication. Get help from a doctor to analyze it. It can also be caused by a temporary shift of the pacing point to pacing in the lower part of the right atrium. ④ Individual T-wave down in lead Ⅰ: There may be myocardial ischemia, acute or chronic damage to the myocardium, or drug overdose. ⑤ Evolution of ST-segment elevation and T-wave inversion in lead Ⅰ, together with abnormal pathologic Q waves: the same phenomenon is often seen in the aVL lead at the same time. This suggests the presence of myocardial infarction near the left upper wall of the left ventricle.