Pre-excitation is an abnormality of atrioventricular conduction in which an impulse travels down through an additional channel and excites part or all of the ventricle early, causing premature excitation of part of the ventricular muscle. Pre-excitation is called pre-excitationsyndrome or WPW (Wolf-Parkinson-White) syndrome and is often combined with episodes of supraventricular paroxysmal tachycardia. Preexcitation is a relatively rare arrhythmia and is diagnosed mainly by electrocardiography. Preexcitation is an abnormality of atrioventricular conduction in which an impulse travels down an additional channel and excites part or all of the ventricle early, causing premature excitation of part of the ventricular muscle. Pre-excitation is called pre-excitationsyndrome or WPW (Wolf-Parkinson-White) syndrome and is often combined with episodes of supraventricular paroxysmal tachycardia. Pre-excitations are a relatively rare arrhythmia and are diagnosed mainly by electrocardiogram. Symptoms Preexcitation alone is asymptomatic. Complicated supraventricular tachycardia is similar to general supraventricular tachycardia. In cases with atrial flutter or atrial fibrillation, the ventricular rate is mostly around 200 beats/min. In addition to palpitations and other discomfort, shock, heart failure or even sudden death may occur. If the ventricular rate is very fast, such as 300 beats/min, the auscultatory heart sound may be only half of the ventricular rate on the electrocardiogram, suggesting that half of the ventricular excitation cannot produce effective mechanical contraction. The etiology is the presence of a congenital atrioventricular additional channel (referred to as a bypass) outside the normal atrioventricular conduction system. Most patients do not have organic heart disease. It is also seen in certain congenital and acquired heart diseases, such as tricuspid valve subluxation and obstructive cardiomyopathy. Electrophysiological studies have demonstrated that the conduction velocity of the bypass is fast, and part of the atrial impulse travels rapidly down through the bypass, reaching the ventricular end of the bypass early and exciting the adjacent myocardium, thus causing early ventricular excitation and altering the normal excitation sequence of the ventricular myocardium, with the result that the QRS wave group on the electrocardiogram is distorted, with a preexcitation wave (δ wave) at the beginning. The rest of the atrial impulse may travel down the normal pathway and merge with the bypass-induced ventricular excitation to form a ventricular fusion wave. The morphology of the ventricular fusion wave is determined by the length of the normal versus the bypassed nonstop period. If the normal pathway has a long nonstop period, or if most of the impulse is transmitted along the bypass, the QRS distortion is obvious; if the bypass has a long nonstop period, the ventricular fusion wave is close to normal. The presence of two conduction pathways between the atria and ventricles in patients with preexcitation syndrome predisposes to folding and folding tachycardia. Most of the tachycardia episodes are retrograde via the bypass and down the normal channel, so the QRS wave groups of tachycardia are normal; occasionally, the impulse is retrograde via the bypass and down the normal channel, resulting in a preexcited QRS wave group during tachycardia. Patients with preexcitation may also have episodes of atrial fibrillation or atrial flutter, most of which are caused by retrograde impulses that reach the atria during the atrial vulnerable phase. In atrial flutter and atrial fibrillation, cryptic conduction of the impulse in the tissue at the junction drives most or all of the impulse to the ventricle via the bypass. Atrial flutter or atrial fibrillation with extremely fast ventricular rates and aberrant QRS wave clusters can sometimes develop into ventricular fibrillation. Unidirectional block of the bypass (mostly downward transmission block) may result in an electrocardiogram without preexcitation but with recurrent episodes of supraventricular tachycardia; electrophysiological studies may confirm the involvement of the bypass in the tachycardia fold. A second-degree conduction block of the bypass can lead to intermittent preexcitation manifestations on the ECG. The following bypasses are known, and multiple bypasses can be present in the same patient: ① Atrioventricular bypass (Kent bundle). Mostly located in the left and right atrioventricular sulcus or next to the septum, connecting the atrial and ventricular muscles; ② Atrioventricular node bypass (James pathway). A channel between the atria and the lower part of the AV node or AV bundle, probably formed by some fibers of the posterior inter-nodal bundle; (3) Nodal and bundle ventricular connections (Mahaim fibers). For the pathway connecting the distal AV node or the proximal AV bundle or bundle branch with the ventricular septum. Of the three, the atrioventricular collateral tract is the most common. Clinical diagnosis Preexcitation alone is asymptomatic, and concomitant supraventricular tachycardia is similar to general supraventricular tachycardia, with different bypasses from anatomical, electrocardiographic and histoplasmic manifestations. In cases of concurrent atrial flutter or atrial fibrillation, the ventricular rate is mostly around 200 beats/min. In addition to palpitations and other discomfort, shock, heart failure or even sudden death may occur. If the ventricular rate is extremely fast, such as 300 beats/min, the auscultatory heart sound may be only half of the ventricular rate on the ECG, suggesting that half of the ventricular excitation cannot produce effective mechanical contraction. In addition to ECG features, ECG vectorograms can be used as a diagnostic basis, characterized by a slow, linear start of the QRS loop on all surfaces for up to 0.08 seconds, followed by a sudden turn and continuation of the loop at normal speed. Heath bundle electrograms and epicardial mapping (mapping) are useful in identifying the various types of preexcitation and in localizing the bypass, and play an important role in determining whether the bypass is involved in the tachycardia folding loop. Preexcitation patterns on the ECG should be distinguished from bundle branch block, ventricular hypertrophy, or myocardial infarction, and the presence of a shortened PR interval and preexcitation wave may confirm the diagnosis of preexcitation. When the accelerated ventricular autonomic rhythm is interfering with sinus rhythm with atrial separation (especially when the ventricular rate is similar to the sinus rate), there may be short bursts of PR interval shortening and wide QRS wave group distortion on the ECG, which resembles intermittent preexcitation; however, long recordings often show irregular PR intervals and atrial separation, which are not difficult to distinguish from preexcitation. In case of preexcitation complicated by supraventricular tachycardia, the QRS wave group is often not broadened, but there are characteristic electrocardiographic changes after aborting the attack except for occult preexcitation. Treatment Pre-excitation itself does not require special treatment. If supraventricular tachycardia is present, the treatment is the same as that for general supraventricular tachycardia. In the case of atrial fibrillation or atrial flutter, if the ventricular rate is fast and the circulation is impaired, synchronized direct current resuscitation is recommended as soon as possible. Lidocaine, procainamide, propafenone and amiodarone slow down the conduction of the bypass, which can slow down the ventricular rate or convert atrial fibrillation and atrial flutter to sinus rhythm. Digitalis accelerates bypass conduction, and verapamil and propranolol slow down conduction in the AV node, all of which may significantly increase the ventricular rate and even develop into ventricular fibrillation, and therefore should not be used. If episodes of supraventricular tachycardia or atrial fibrillation or atrial flutter are frequent, it is advisable to apply the above antiarrhythmic drugs for long-term oral prevention of episodes. For those who cannot be controlled by medications, or whose electrophysiological examination determines that the bypass interval is short or shortened during rapid atrial pacing, or whose ventricular rate reaches about 200 beats/min during an episode of atrial fibrillation, there are indications for ablation by electric, radiofrequency, laser or freezing methods after localization, or surgical cutting of the bypass to prevent an attack. If the electrocardiogram shows normal QRS waves, regular P-R interval and heart rate of about 200 beats/min, it should be considered as recurrent tachycardia, and its treatment is the same as that of general supraventricular tachycardia, and isopodine, cardioplegia, ATP or digitalis can be used. If the QRS wave group is abnormal and the R-R interval is significantly irregular, it should be suspected and preexcited combined with If the QRS wave group is abnormal and the R-R interval is significantly irregular, then preexcitation combined with atrial fibrillation should be suspected, then cardioplegia, procainamide, or a combination of quinidine and insulin should be used, while isoprodine, digitalis and ATP are prohibited, because the latter three can shorten the bypass conduction period and accelerate the bypass conduction, and even ventricular fibrillation can occur. For frequent episodes of supraventricular tachycardia with obvious symptoms, electrophysiological examination should be performed to clarify the site of the bypass and then treated with electroablation, radiofrequency ablation, or surgery. Health care The so-called “pre-excitation syndrome” has a kind of rapid arrhythmia, that is, at the onset of the heartbeat is particularly fast, the frequency can be about 180-200 times/minute, mostly seen in young adults, sudden onset, suddenly disappear. Each attack may last for a few minutes or hours or days. In addition to the patient’s feeling of slow heartbeat, there is also chest tightness, chest pain, dizziness, and even syncope, which can be easily controlled with a clear diagnosis, but is extremely difficult to cure. The diagnosis is “pre-excitation syndrome”. The so-called “pre-excitation syndrome” is a diagnostic term on the electrocardiogram. From the above, we know that myocardial contraction is controlled by the electrical signal from the sinus node, and we also know that the conduction pathway between the signals is normally unique, called the atrioventricular node. In patients with preexcitation syndrome, there is an additional pathway or pathways, called additional conduction bundles, between the atria and the ventricles, in addition to the AV node. When the pacing signal from the sinus node excites the ventricles through the AV node, it is transmitted back in the reverse direction through another additional pathway. When the atrial and ventricular contractions are completed, the signal is transferred to the atrium through the AV node, causing the ventricle to contract again, repeating the cycle, just like a donkey grinding bean curd, when there are no soybeans in the mill, the master does not tell it to stop, it keeps circling the mill. The normal heart has a fibrous ring in the middle that divides the heart into two parts, the upper part is called atrium and the lower part is called ventricle, the fibrous ring is non-conductive and there is only one channel in the middle that connects the atrium and ventricle to conduct electrical signals. In patients with preexcitation, there are normal atrial or ventricular myocardial fibers embedded in the hiatus, and they can conduct electrical currents. Therefore, the principle of treating this disease is to block or block the conduction of the additional pathway with drugs to inhibit tachycardia and restore sinus rhythm, in fact, it is not difficult to block the conduction of signals in the additional pathway. Therefore, recently, a catheter was invented to insert from the surface of the body to the additional conduction bundle of the heart and then cauterize it with high-frequency current to block the conduction bundle for the purpose of radical treatment, or the conduction bundle can be cut off directly by surgery for the purpose of radical treatment. However, it should be noted that not all tachycardias are preexcited syndromes. There are many causes and types of tachycardia, and preexcitation syndrome is only one of them. Moreover, the principles of medication for different types of tachycardia are completely different, and some of them are even opposite, so distinguishing the type of tachycardia is a prerequisite for safe and effective treatment. It is very difficult without the help of ECG. The consequences are very different due to the different types, some jump for a few days without danger, while others are fatal in a few minutes and must be rescued in a race against time, so when tachycardia occurs, an ECG examination is needed immediately. On the ECG, the doctor can determine what kind of tachycardia is present, which part of the heart is responsible for the tachycardia, and how dangerous it is, so that effective symptomatic treatment can be achieved and treated accordingly.