What is cardiac preexcitation syndrome? You need to know the pathological cause.

To put it simply, cardiac preexcitation syndrome means that there is an extra channel in the heart, which will cause the atria or ventricles to fibrillate prematurely. If tachycardia does not occur, it is fine. If tachycardia occurs, treatment is required. Let's understand the causes of this disease below.

1. The most common type of preexcitation is ventricular preexcitation with atrioventricular accessory tracts , which are composed of atrial myoid bundles and can exist almost anywhere around the atrioventricular annulus, Wolff-Parkiason-White syndrome.

2. In addition, there are three types of abnormal channels : the atrioventricular node accessory tract, that is, the James fibers connecting the atrium to the lower part of the atrioventricular node or the bundle of His, which includes the Lown-Ganong-Levine syndrome; and the two types of Mahaim fibers, including the fibers from the atrioventricular to the ventricle, called nodal-ventricular fibers, and the fibers originating from the bundle of His or bundle branches and attached to the ventricular muscle, called branch-ventricular fibers. When the nodal-ventricular connection occurs, the PR interval may be normal or shortened, and the QRS complex is a fusion wave. The branch-ventricular connection produces a normal PR interval and a fixed abnormal QRS complex.

3. It is now generally recognized that the cause of preexcitation is the existence of a congenital atrioventricular accessory channel (also known as 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 dysplasia, obstructive cardiomyopathy, etc.

4. Electrophysiological studies have shown that the conduction speed of the bypass is fast, and part of the atrial impulse is quickly transmitted down through the bypass and reaches the ventricular end of the bypass in advance, exciting the adjacent myocardium, thereby causing premature ventricular excitation and changing the normal excitation order of the ventricular muscle. As a result, the QRS complex on the electrocardiogram is deformed, with a pre-excitation wave (δ wave) at the beginning. The rest of the atrial impulse can be transmitted down along the normal pathway and merged with the ventricular excitation caused by the bypass to form a ventricular fusion wave. The shape of the ventricular fusion wave is determined by the length of the refractory period of the normal and bypass pathways. If the refractory period of the normal pathway is long, or most of the impulse is conducted along the bypass pathway, the QRS deformity is obvious; if the refractory period of the bypass is long, the ventricular fusion wave is close to normal.

5. There are two conduction pathways between the atria and ventricles in patients with preexcitation syndrome , which makes reentry and reentrant tachycardia prone to occur. When tachycardia occurs, most of the impulses are retrogradely transmitted through the bypass pathway and transmitted down along the normal channel, so the QRS complex of tachycardia has normal morphology; occasionally, the impulse is transmitted down through the bypass pathway and retrogradely transmitted along the normal channel, causing the QRS complex to be pre-excited during tachycardia. Patients with preexcitation may also have atrial fibrillation or atrial flutter. This attack is mostly caused by retrograde impulses reaching the atria during the vulnerable period of the atria. During atrial flutter and atrial fibrillation, the impulse is latently conducted in the tissue at the junction, causing most or all of the impulse to be transmitted to the ventricles through the bypass pathway, resulting in an extremely fast ventricular rate. Atrial flutter or atrial fibrillation with abnormal QRS complex can sometimes develop into ventricular fibrillation.