1. ECG characteristics of sinus rhythm Generally, the excitation potential of sinus node cannot be recorded by ECG. The activity of sinus node can be inferred from the P wave characteristics of atrial excitation wave caused by sinus node excitation. The ECG characteristics of sinus rhythm are: P wave appears regularly, and P wave morphology shows that the excitement comes from sinus node (that is, P wave stands upright in leads I, II, aVF, V4~V6, and aVR leads are inverted). The inclination rate of normal sinus rhythm is generally 60~ 100 beats/min (Figure 4- 1-4 1).
2. Sinus tachycardia: The inclination rate of sinus rhythm in adults is > 100 beats/min, which is called sinus tachycardia. During sinus tachycardia, the P-R interval and Q-T time limit are shortened correspondingly, sometimes accompanied by secondary ST segment depression and low T amplitude. Common in exercise, mental stress, fever, hyperthyroidism, anemia, blood loss, myocarditis and the role of adrenocortical drugs.
3. Sinus bradycardia (sinus bradycardia) The frequency of sinus rhythm is less than 60 beats per minute, which is called sinus bradycardia. The heart rate of the elderly and athletes is relatively slow. Increased intracranial pressure, hypothyroidism or the use of beta blockers can lead to sinus bradycardia. Sinus bradycardia below 40 beats/min is rare.
4. Sinus arrhythmia The origin of sinus rhythm has not changed, but the rhythm is irregular. The difference between P-P intervals on the same lead is > > 0. 12s。 Sinus arrhythmia often coexists with sinus bradycardia (Figure 4- 1-42). A more common arrhythmia is related to the respiratory cycle, called respiratory sinus arrhythmia, which is more common in teenagers and generally has no clinical recovery. Other rare sinus arrhythmias have nothing to do with breathing, such as sinus arrhythmia related to ventricular contraction and blood discharge and sinus node wandering arrhythmia.
5. Sinus arrest is also called sinus arrest. In regular sinus rhythm, sometimes due to the increase of vagus nerve tension or the disorder of sinus node, the sinus node stops emitting excitement for a period of time, and the ECG shows that the regular P -P interval suddenly falls off, forming a long P-P interval, which is not a multiple of the normal P-P interval (Figure 4-1-43). Escape or escape rhythm often occurs after sinus arrest.
6. Sick sinus syndrome (SSS) In recent years, it has been found that degenerative diseases of pacing conduction system, coronary heart disease, myocarditis (especially viral myocarditis), cardiomyopathy and other diseases can involve sinus node and its surrounding tissues, resulting in a series of bradyarrhythmias and causing dizziness, amaurosis, syncope and other clinical manifestations, which is called sick sinus syndrome. The main ECG manifestations are: ① persistent sinus bradycardia, heart rate < 50 beats/min, which is difficult to correct with atropine and other drugs; ② Sinus arrest or sinus block; ③ On the basis of sinus bradycardia, supraventricular tachycardia (atrial tachycardia, atrial flutter, atrial fibrillation, etc. ) often occurs, also known as the fast-slow syndrome; ④ If the lesion involves the atrioventricular junction at the same time and sinus arrest occurs, there may be no junctional escape or atrioventricular conduction disorder for a long time, which is called double nodal lesion.