In outpatient clinics, emergency departments or online, I often encounter patients with ECGs asking: What is sinus rhythm? Is it normal? What is sinus tachycardia? Is it normal? What should I do? Here are some answers to some common questions. What is sinus rhythm We know that the heart of normal people is constantly working, and most of them are working regularly in accordance with the requirements of the body state, and at the same time working without any feeling. This rhythm of heartbeat, which maintains a normal pattern without any special sensation, is called sinus rhythm. The sinus rhythm is the electrical impulses (electrical activity) issued by the sinus node, which is the supreme commander of the heart beat, and through some special conduction system of the heart, these electrical impulses are transmitted to each corner of the heart in a sequential and regular manner, thus dominating the regular and sequential beating of the whole heart. In normal individuals, the function of the sinus node also includes the ability to regulate its frequency in response to changes in the individual’s physiological activity (e.g., activity, walking, eating, etc.), i.e., the heart rate in sinus rhythm. In current textbooks, the so-called normal sinus rhythm frequency (i.e., the number of heartbeats) is generally 60-100 beats per minute for adults, although clinically most adults are considered to have a heart rate of 50 beats per minute or more. The heartbeat of a child or even an infant is generally faster, and as long as it does not cause significant panic or anything else, it is generally considered normal. Therefore, the so-called sinus rhythm means a normal heartbeat, and once this concept is understood, it is basically not necessary to pay special attention to this problem. What is sinus tachycardia? What should I do? After understanding sinus rhythm and the frequency of normal sinus rhythm, it is relatively easy to understand what sinus tachycardia is. Sinus tachycardia means that the frequency of sinus rhythm exceeds 100 beats per minute in adults. Does sinus tachycardia need to be treated? When does it need to be treated? First of all, we need to know that sinus rhythm is affected by many factors, such as vagus and sympathetic nerves, body position, emotion, physical activity, body temperature, metabolism and medication, etc. Extracardiac diseases and cardiac lesions can affect the frequency of sinus rhythm. As mentioned earlier, the sinus node can regulate its frequency according to the needs of the body. Therefore, if sinus tachycardia is transient or caused by other factors such as activity or excitement, it is not a matter of concern and should only be adjusted gradually. However, if the tachycardia is persistent and not related to physical activity or other factors, i.e. chronic inappropriate sinus tachycardia or chronic non-paroxysmal sinus tachycardia, it may require attention and further treatment. Therefore, the need for treatment of sinus tachycardia requires consideration of various factors and a case-by-case analysis. In some people who are sedentary, inactive, or obese, they often have panic attacks with little or no activity, and sinus tachycardia is the result of an electrocardiogram. In such people, it is generally recommended to increase activity, especially aerobic exercise, and pay attention to weight control, and the decrease of heart rate can be obviously felt within 2-4 weeks after regular increase of activity. In other words, sinus tachycardia can be controlled by some non-pharmacological treatments. Of course, chronic inappropriate sinus tachycardia can be controlled with beta-blockers or certain calcium channel blockers in the context of the aforementioned non-pharmacological treatments, and if necessary, sinus node modification with catheter ablation techniques can be considered. What is sinus arrhythmia? Do I need treatment? Sinus rhythm is relatively regular and neat, but if there is a significant difference in the speed of the sinus rhythm, such as a large difference in the heartbeat time of two adjacent sinus rhythms (more than 120ms), then this kind of irregular sinus rhythm is considered as sinus arrhythmia. There are three types of sinus arrhythmias: 1. Respiratory sinus arrhythmias, where the heartbeat is faster during inspiration and slower during exhalation, and when breathing is suspended the heartbeat becomes more uniform, that is, when the arrhythmia is small, mostly seen in children. 2. 2, non-respiratory sinus arrhythmia, the heart rate is not related to breathing, more common in heart patients or taking some special drugs, such as digitalis drugs. 3. Ventricular phasic sinus arrhythmia, mainly seen in high or complete mode of conduction block. For whether sinus arrhythmia needs treatment, it mainly depends on the underlying cause, that is, what is the cause of sinus arrhythmia, if there is an organic change, then it needs treatment, while if there is no organic disease, or just physiological or extracardiac factors, most of them do not need special treatment.