Variant pre-excitation syndrome

Introduction to variant pre-excitation syndrome Variant preexcited syndrome (variant preexcitationsyndrome) is also known as Mahaim type pre-excitation syndrome. The traditional Mahaim-type pre-excitation syndrome refers to sinus node stimuli via Mahaim fibers, EK waves appear on the electrocardiogram, and QRS complexes widen and PR A group of syndromes with normal intervals, with or without supraventricular tachycardia. basic knowledge The proportion of patients: the incidence rate of patients with no history of heart disease is about 0.05% Susceptible people: no specific people Mode of infection: non-infectious complication:

Cause of variant pre-excitation syndrome

(1) Causes of the disease

Some people think that Mahaim fiber is a very slender fibrous tissue, which is shorter than Kent bunch. It is more common in children and decreases with age. It is rare in adults and can be seen in normal heart.

(two) pathogenesis

With the advancement of electrophysiological research, it is found that the above-mentioned nodule bypass does not always terminate in the ventricle, and most of them terminate in the right bundle branch, the latter should be called the end bypass, and the end bypass is actually slow. Conductive bundle bypass; the junction bypass that terminates in the ventricle is actually a atrioventricular bypass with slow conduction characteristics. In recent years, Mahaim fibers have been classified into the following types:

1. The end of the bypass starts at the slow junction of the atrioventricular node and ends at the right bundle.

2. The bundle chamber bypass starts at the proximal end of the left and right bundle branches and ends at the ventricular muscle.

3. The junction bypass originates from the atrioventricular node slow path and ends at the right bundle branch.

4. Slow conduction atrioventricular bypass starts at the atria and ends at the ventricular muscle.

5. Slow conduction beam bypass originates from the atrium and ends at the right bundle.

Among the above types, the slow-conducting bundle bypass is the most common. The Mahaim fiber is some extremely fine fibrous tissue. The length is shorter than the kent bundle. It is more common in children and decreases with age. It is rare for adults. Found in the normal heart, the anatomical features of the bundle bypass:

(1) The part of the bundle bypass: the bundle bypass only exists on the right side, between the right atrium and the right ventricle, so it is also called the right atrial bundle bypass. The typical bundle bypass is located in the tricuspid annulus. The side wall is about 78% of the back side wall and 22% of the front side wall. The sub-type is located on the back wall and side wall of the tricuspid annulus.

(2) Length of the bundle bypass: Compared with other normal and abnormal conduction bundles, the right atrial bundle bypass is long and slender. In most cases, the bundle bypass is a single fiber with a length exceeding 4 cm. Its slow conduction rate is related to its slenderness.

(3) Histological characteristics of the bundle bypass: the bundled tricuspid annulus contains cells and structures similar to those of the atrioventricular junction, and its cellular composition includes connective cells, pacemaker cells (ie, typical P cells) and transitional cells (transitional cells), which are very similar to the cells in the normal compartment junction area. Therefore, the tissue in this area has similar self-discipline and compartmental conduction, slower conduction and diminished conduction, gland Glycosides can block or slow down conduction, and the conduction beam below the tricuspid annulus in the bundle bypass has similar structure and conduction characteristics as the bundle branch, but the bundle bypass that has been found so far has no back propagation. Features.

(4) Atrial and ventricular end of the bundle bypass: the bundle bypass is only present on the right side, starting from the right atrium above the tricuspid annulus, forming a right bundle at the side of the tricuspid annulus The special conductive fiber descends from the superficial endocardial surface of the right ventricle to the right ventricular apex. In most cases, the terminal end of the bundle bypass and the terminal end of the right bundle are fused, and a few cases are at the end of the right bundle. The right ventricular free wall is directly inserted near the end. The former is a typical bundle bypass, while the latter is considered to be a special Kent bundle bypass, but because it has the same electrophysiological properties as the bundle bypass. The site of insertion into the ventricle is very close to the end of the right bundle branch, so it is still classified as a bundle bypass, as a typical subtype of the bundle bypass.

1 atrial bypass bypass atrial end: When the tachycardia occurs, the head of the lead is placed on the right atrial appendage or the atrial side of the tricuspid annulus for atrial stimulation, and the timely atrial premature contraction stimulation can take Get the ventricle, can make the tachycardia rhythm reforming, but it does not cause the change of QRS morphology, and does not cause the change of ventricular activation sequence. This method can confirm that the right atrium is an essential component of the reentry loop. The bypass originates from the right atrium, and the above stimulation can be performed at different parts of the tricuspid annulus at 2 to 5 mm, wherein the earliest atrial pacemaker that advances the ventricular QRS is the atrial end of the bundle bypass, except for the above method. On the atrial side, the part of the atrial bypass can be clearly recorded as the atrial end, and the atrial end of the bundle bypass is located in the right atrium free wall, most of which are located on the side wall and a few are located on the front side wall.

Ventricular end of 2 room bundle bypass: When the atrioventricular nodal tachycardia or atrial premature stimulation captures the ventricle, the complete pre-excitation may be obtained, that is, the ventricular activation is bypassed. Under the agitation control of the lower pass, the earliest excitatory point of the ventricle can be analyzed, and then the insertion site of the bypass on the ventricle side is determined. The ventricular end of the bypass bundle is located at the apex of the right ventricle, that is, the free wall of the right ventricle is near. At 1/3 of the apex, the ventricle end of the bypass is inserted directly into the ventricular muscle of the ventricle, or merges with the distal end of the right bundle branch. Because the sheath bundle is wrapped with an insulating sheath, the supraventricular sensation is transmitted. The right ventricular apex is the first to be excited.

(5) Room bundle bypass combined with other abnormalities: 90% of the bundle bypass does not incorporate other abnormalities, and only about 10% of the cases have a double pathway in the atrioventricular node, or a combined atrioventricular bypass.

Variant pre-excitation syndrome prevention

The typical pre-excitation syndrome, also known as WPW syndrome, is the most common type of pre-excitation syndrome, with an incidence of 0.1 to 3.1, 90% of patients mostly under 50 years of age, more men than women. Men account for 60% to 70%, and all age groups can develop disease, but the incidence decreases with age.

Variant pre-excitation syndrome complications Complication

If the instinct is combined with rapid tachycardia, symptoms such as palpitations and chest tightness may occur.

Symptoms of variant pre-excitation syndrome Common symptoms Chest tightness, dyspnea, retrograde atrioventricular reentry... Dizziness and heart block

Similar to the typical pre-excitation syndrome, there is no clinical symptom when there is no tachycardia. For example, when tachycardia is combined, symptoms such as palpitations, dizziness and chest tightness may occur, but patients with Mahaim pre-excitation syndrome are reversed. Type of atrioventricular reentry tachycardia, with left bundle branch block pattern wide QRS complex tachycardia, which brings some difficulties to differential diagnosis, may also affect hemodynamics than forward type atrioventricular reentry The tachycardia is large and the corresponding symptoms may be more pronounced.

Examination of variant pre-excitation syndrome

1. Electrophysiological characteristics of the bundle bypass

(1) Slow conduction velocity: This is the most prominent electrophysiological feature of the bundle bypass. The conduction time of the bundle bypass is mostly >150ms, and the conduction time of the paraventricular bundle (Kent bundle) is 30-40ms. The conduction time of the atrioventricular node (AH period) is <150ms. This slow conduction rate makes the electrocardiogram appear as: normal or prolonged 1P-R interval; 2 with left bundle branch block often accompanied by atrioventricular block 3 When the supraventricular tachycardia occurs, the AV interval is longer.

(2) Only forward conduction: the beam bypass that has been found so far has no back-transmission function, and only the forward conduction between the chambers. This feature makes the supraventricular tachycardia in patients with atrial bypass. It is a retrograde type of atrioventricular node, that is, the QRS wave is a wide deformity with a left bundle branch block pattern, and the right bundle branch block pattern is very rare.

(3) The refractory period is relatively short: compared with the refractory period of the atrioventricular node, the refractory period of the bundle bypass is relatively short, and the ventricular refractory period can be encountered when the premature supraventricular sensation is transmitted. Conduction was blocked, and the excitability was transmitted along the bypass of the refractory period, and the retrograde atrioventricular reentry tachycardia was formed.

(4) There is diminished conduction: the bundle bypass is similar to the atrioventricular node, and there is also diminished conduction. When the supraventricular atrial stimulation with faster frequency is applied, the original bundle bypass is 1:1, which can be changed to The Venturi type is transmitted down and there is a decreasing conduction.

(5) ATP can block its conduction: the injection of ATP can block the conduction of atrioventricular node, but has no effect on the conduction of bypass, which is the result of excitatory vagus nerve. The conduction of AF bypass is affected by ATP. Its only pre-transmission function temporarily disappeared after ATP injection.

(6) Since the end of the bundle bypass is directly fused with the terminal end of the right bundle, the surface electrocardiogram can be free of delta waves, and less waves are seen by the bypass of other Mahaim fibers.

2. The characteristics of the bundle bypass esophageal atrial pacing

(1) With the advance of atrial pre-stimulation: the atrioventricular may enter the refractory period, the supraventricular sexual excitability is transmitted along the bundle bypass, the QRS wave appears similar to the left bundle branch block pattern, and the V1 lead is still rS. type.

(2) The left bundle branch block with frequency dependence of atrial pacing is different: the interval between S2-R2 is not obvious with the shortening of the interval of early stimulation.

3. ECG features

(1) Typical ECG characteristics of traditional variant pre-excitation syndrome:

1P-R interval 0.12s,

2QRS wave widened the deformity, but narrower than the Kent beam pre-excitation syndrome,

The 3QRS wave has a pre-shock ( wave) at the beginning, but it is small.

4 may be associated with secondary ST-T changes, the dominant pre-excitation syndrome caused by Mahaim fiber rarely sees typical ECG patterns.

(2) Electrocardiogram characteristics of the bundle-type bypass type pre-excitation syndrome: In the past, the intracardiac electrophysiological diagnosis of the bundle bypass was considered to be difficult, and the diagnosis of the electrocardiogram was more difficult. Guo Jihong et al. The electrocardiogram performance has high specificity and can provide reliable evidence or clue for diagnosis. The electrocardiogram of the bundle bypass pre-excitation syndrome is similar to the traditional Mahaim fiber pre-excitation syndrome, and its characteristics are as follows:

1QRS wave widening deformity is a left bundle branch block pattern,

The 2 wave may not exist, and if the wave is smaller than the wave of the typical WPW syndrome,

3P-R interval is normal,

4 with supraventricular tachycardia, often a wide QRS tachycardia, with left bundle branch block and electric axis left deviation (generally <-30 ° =.

In the case of atrial bypass bypass pre-excitation syndrome, in addition to the above-mentioned electrocardiogram performance, there are some specific electrocardiograms, which are considered to be helpful for diagnosis.

1 frequency-dependent, intermittent left bundle branch block: the tricuspid annulus of the bundle bypass has the characteristics of atrioventricular nodule conduction, the conduction velocity of the bundle bypass is slower than that of the atrioventricular node, and the sinus is generally Excited along the "fast track" compartment, the surface electrocardiogram is completely normal. When the sinus frequency becomes faster, the "fast track" atrioventricular node enters the refractory period, and the excitement is transmitted along the bundle bypass. Frequency-dependent, intermittent left bundle branch block, due to fusion of the terminal bundle bypass end and the right bundle branch end, the QRS wave appears as incomplete or complete left bundle branch block pattern, when sinus When the excitement slows down, the ECG turns to normal again.

2 compartment conduction can be fast frequency-dependent Venturi conduction or conduction delay, once atrioventricular block: Because of the atrioventricular junction conduction characteristics of the bundle bypass, there may be fast frequency dependent Venturi conduction or Conduction delay, in addition, due to sinus agitation along the bundle bypass, its conduction velocity is slow, the PR interval is often prolonged, forming a degree of atrioventricular block.

3 When the tachycardia occurs, the QRS wave width is the left bundle branch block pattern: because the earliest excitatory point of the ventricle is located at the apex of the ventricle, the ventricular depolarization sequence is from the bottom to the top, and the ventricle is toward the bottom of the heart, thus forming the frontal axis. Left to the left, completely different from idiopathic right ventricular tachycardia.

4 unique ventricular fusion wave: In the WPW syndrome, the conduction velocity of the Kent bundle bypass is faster than that of the atrioventricular node. The pre-excited ventricular depolarization forms a delta wave, forming the first half of the wide deformed QRS wave. The PR interval is <0.12 s, and the ventricular fusion wave formed by the bundle bypass is opposite. Because the conduction velocity is slower than the atrioventricular node, the QRS wave can be formed by the excitatory ventricle muscle depolarization. The posterior part is therefore not pre-excited but "late". This ventricular fusion wave can also have an "accordion effect" due to the difference in the ratio of the atrioventricular node to the atrial tract bypassing the ventricle. The QRS wave pattern Such changes are sometimes mistaken for electrical alternation, intermittent indoor conduction block, and the like.

In summary, some scholars believe that if there is frequency dependence, intermittent left bundle branch block; or left bundle branch block, such as with a rapid frequency-dependent conduction delay or Venturi-type conduction case with PR interval Suspected and there is the possibility of room bundle bypass; if there is a wide QRS tachycardia, and the left bundle branch block pattern with the left axis of the electric axis, should be highly suggestive of the presence of the bundle bypass.

McClelland and Klein have the following diagnostic criteria for electrocardiogram and electrophysiological testing:

A. On the surface ECG, the wave is small, and there is no pre-shock wave performance; the PR interval is normal; often accompanied by wide QRS tachycardia, showing left bundle branch block pattern, with the left axis of the electric axis (general - 30°).

B. When the pre-atrial contraction or atrial rate increases, the bypass may exhibit rapid frequency-dependent decreasing conduction with progressive prolongation of the A- interval.

C. Right atrial pacing can increase the degree of pre-excitation, shorten the S- interval, and there is no significant change in left atrial pacing.

D. Intracardiac electrogram recording: The earliest ventricular activation during pre-excitation is at the apex of the right ventricle, recorded before or at the beginning of the QRS wave of the surface electrocardiogram.

E. The bundle bypass has no back-transfer function: the pre-excitation tachycardia is a retrograde type, which is transmitted through the lateral bundle bypass and reversed through the normal atrioventricular pathway.

F. At the free wall of the right ventricle between the left tricuspid annulus and the right ventricular apex, a Hess bundle potential-like beam bypass potential can be recorded, which is when the catheter is slightly pressurized or intravenously injecting adenosine disappear.

G. Often accompanied by atrioventricular node reentry or other typical Kent atrioventricular bypass conduction.

(3) Characteristics of the bundle bypass subtype ECG: The subtype of the bundle bypass refers to the right ventricular free wall directly inserted into the right bundle branch near the end of the bundle bypass, and the surface ECG performance:

1 similar to type B WPW syndrome;

2QRS wave group broadening, may have delta waves, but smaller than typical WPW syndrome;

3P-R interval is normal;

4 Because of the characteristics of atrioventricular nodal conduction, it is different from the general WPW syndrome, and can be transmitted in the Wenshi type. Therefore, when the surface electrocardiogram is a B-type WPW syndrome pattern, the PR interval is normal and the frequency is fast-dependent. Delayed or Venturi-type conduction, the possibility of suspected and bundle bypass subtypes; if the width of the QRS tachycardia is the same, and the left bundle branch block pattern with the left axis of the electric axis, the height of the beam bypass The existence of subtypes.

Diagnosis and differentiation of variant pre-excitation syndrome

Can be diagnosed according to clinical manifestations and electrocardiogram, electrophysiological characteristics.

The bundle bypass pre-excitation syndrome should be differentiated from the following arrhythmias.

1. Identification of the left bundle branch block with the characteristics of the bundle bundle bypass pre-excitation syndrome is:

1 Most patients are young and have no structural heart disease;

2 can be expressed as frequency-dependent, intermittent left bundle branch block;

3 often accompanied by atrioventricular block;

4 have a history of tachycardia;

When the left bundle branch block is used, the V1 lead is mostly QS waveform, rS type is rare, but when the beam bypass is passed down to form the pattern of the left bundle branch block, the QRS wave of the V1 lead is rS type. Identification with left bundle branch block.

2. The characteristics of the WPW syndrome with the right WPW syndrome are:

1P-R interval <0.12s;

2 has wave, QRS wave width and deformity;

3 Associated tachycardia is mostly cis-type atrioventricular reentry tachycardia, QRS wave is narrow and normal; only a few are retrograde atrioventricular reentry tachycardia with bundle branch block, QRS wave wide deformity, The bundle bypass pre-excitation syndrome does not have the above characteristics, and the supraventricular tachycardia caused by the retrograde atrioventricular reentry tachycardia, QRS wave wide deformity (the bundle bypass, the atrioventricular node) Caused by a reverse pass).

3. Identification of idiopathic right ventricular tachycardia with supraventricular tachycardia caused by supraventricular tachycardia QRS wide deformity, left bundle branch block, easy to idiopathic right ventricular ventricular tachycardia Over-speed confusion, resulting in treatment difficulties (including radiofrequency treatment, etc.), the two points of discrimination are:

1 ventricular tachycardia caused by ventricular tachycardia without compartment separation, the chamber was 1:1 retrograde;

2 atrial stimulation is easy to induce and terminate supraventricular tachycardia caused by atrioventricular bypass, and idiopathic right ventricular tachycardia atrial stimulation is more difficult to induce;

3 When the tachycardia is overspeed, the QRS wave of the electrocardiogram is a left bundle branch block pattern, and the electric axis is left-biased; while the idiopathic right ventricular ventricular tachycardia is right-handed or unbiased.

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