An ambulatory electrocardiogram (Holter), which continuously records the electrocardiogram shape of each heartbeat over a 24-hour period, contains a great deal of information about the electrical activity of the heart. How to get valuable information about the disease and condition from it? Generally speaking, in the face of a formal 24-hour ambulatory ECG report, the following aspects should be read and analyzed: 1. Heart rate The 24-hour heart rate of a normal person is 59~87 beats/min. It is high during the day and can reach 180 beats/min during strenuous activities. Usually the highest heart rate increases with age and decreases, and the highest heart rate in the elderly generally does not exceed 130 beats/min, and is higher in women than in men. It is low at night during sleep, about 50 beats/min, or even 40 beats/min. In contrast, if the average heart rate is less than 60 beats/min and the heart rate rises less than 90 beats/min after activity, we should pay attention to the sinus node and other conduction system to see if there is a lesion. 2. Premature beats First of all, it is important to clarify the concept that premature beats do not necessarily mean heart disease; all types of premature beats can occur in normal people. A group of 183 normal people with dynamic ECG monitoring data showed that the incidence of supraventricular premature beats and ventricular premature beats was 46.0% and 28.4%, respectively. Thus, a small number of premature beats (<100 beats = in 24 hours. Generally speaking, supraventricular premature beats have less impact on cardiac function and do not develop into fatal malignant arrhythmias, and can be left untreated if there are no clinical symptoms. 3. The relationship between arrhythmia and clinical symptoms Dynamic ECG can capture transient ECG changes, which has unparalleled advantages over conventional ECG for determining whether there is arrhythmia and the duration of arrhythmia. The detection rate of supraventricular arrhythmias is 50% to 70% in normal adults, and increases with age. Short bursts of supraventricular tachycardia account for 20% in older adults over 60 years of age, while the presence of ventricular arrhythmias often indicates serious cardiac disorders. Observe whether the ECG traced when the patient has palpitations, shortness of breath, dizziness and other discomfort is normal, which can clarify whether the above symptoms are caused by cardiac disorders. 4. Myocardial ischemia and its pattern Monitoring patients with coronary heart disease can understand the number of episodes of myocardial ischemia, their duration, and the pattern of diurnal episodes, which can be of great help to better understand the condition. Most of the episodes increase significantly when the patient is awake or after light activity. The reason is caused by the acceleration of heart rate and the change of coronary diastole, as well as the increase of catecholamine secretion in the body after activity and the increase of myocardial oxygen consumption. In contrast, bradycardia occurs due to high vagal tone, slowed heart rate, decreased cardiac output, reduced sympathetic excitation, peripheral vasodilation, reduced return blood volume, slow blood flow, and insufficient coronary artery blood supply. When the coronary artery oxygen supply cannot meet the myocardial oxygen demand, corresponding clinical symptoms and ECG manifestations may appear. There are many factors affecting myocardial oxygen consumption, among which heart rate, mean arterial pressure, and myocardial contractility are three important factors. Usually, the variation of two parameters, mean arterial pressure and myocardial contractility, is small, so the heart rate alone can be used to indicate the threshold of myocardial ischemia in clinical practice. Myocardial ischemia has a similar diurnal pattern to that of long-proven acute myocardial infarction and sudden cardiac death. The susceptibility of patients with coronary artery disease to myocardial ischemia in the morning may be related to the increased secretion of catecholamines and corticosteroids, elevated platelet aggregation, decreased fibrinolytic activity, and decreased antithrombin III levels at this time.