Second degree atrioventricular block

Introduction to second degree atrioventricular block Second degree atrioventricular block (II°AVB) is a partial conduction interruption in the process of agitation from the atrium to the ventricle, that is, ventricular leakage, accompanied by atrioventricular conduction delay. basic knowledge The proportion of illness: 0.02% Susceptible people: no special people Mode of infection: non-infectious Complications: angina pectoris

Second degree atrioventricular block

(1) Causes of the disease

1. Common causes of second-degree type I atrioventricular block. Most people with normal atrioventricular conduction function, rapid atrial pacing can induce Ventricular atrioventricular block, and progressive atrial pacing can also cause one degree. 2:1 or a high degree of atrioventricular block, dynamic electrocardiogram found that second-degree type I atrioventricular block, like first-degree atrioventricular block, can occur in normal young people (especially athletes), and more Occurring at night, exercise or the use of atropine can significantly improve the conduction function of the atrioventricular node, so that the second degree I type of atrioventricular block disappears, suggesting that this phenomenon is related to increased vagal tone, however, some children's second degree I room Ventricular conduction block can progress to a high degree of atrioventricular block after several years (the mechanism of occurrence is unclear).

Many drugs can prolong the refractory period of atrioventricular node, such as digitalis drugs, beta blockers, calcium antagonists and central and peripheral sympathetic blockers can cause second-degree type I atrioventricular block, The incidence of second-degree atrioventricular block in patients with acute myocardial infarction was 2% to 10% (Reported at 6.9% in Beijing Foreign Hospital), and second-degree I was more common in patients with inferior myocardial infarction, and most of them were from one-time room. The development of ventricular conduction block is usually caused by abnormal function of atrioventricular node. The mechanism may be related to the increase of vagal tone and adenosine action. The appearance time is short and disappears within 1 week. The second degree I does not occur frequently. The anterior wall myocardial infarction, once it occurs, indicates a wide range of His bundles, Purkinje fiber damage, easy to develop a high degree of atrioventricular block, in addition, rheumatic fever can have varying degrees of atrioventricular block, to a degree of room Ventricular conduction block is common, and myocarditis, cardiomyopathy, etc. are also prone to atrioventricular block.

2. Second-degree type II atrioventricular block common causes of drugs such as digitalis, quinidine, procainamide, propafenone, metoprolol, etc. can occur secondary type II atrioventricular block (However, they are more prone to second-degree type I atrioventricular block), hyperkalemia (potassium potassium 10 ~ 13mmol / L) in electrolyte disturbance can cause atrioventricular block, hypokalemia (blood potassium <2.8mmol / L Can also cause atrioventricular block at all levels, about 26% of patients with rheumatic fever, rheumatic myocarditis may have a degree and / or second degree atrioventricular block, to more than once, patients with viral myocarditis twice And third-degree atrioventricular block is not uncommon, sometimes accompanied by bundle branch block, which indicates extensive lesions, other infections such as Coxsackie B virus, measles, mumps, viral upper respiratory tract infection, infectious mononuclear Cytomegalox, viral hepatitis, typhoid, etc. can cause widespread or partial damage to the conduction system. One, two, or three degrees of atrioventricular block can occur, the degree of damage can be light or heavy, but the block is mostly temporary. Reversible, rarely developed as a permanent chronic atrioventricular block.

Coronary heart disease, the incidence of second degree atrioventricular block in acute myocardial infarction is 2% to 10%, second degree type II atrioventricular block is more common in anterior wall myocardial infarction, the incidence rate is 1% to 2%, more Within 72 hours after the onset, the block is mostly below the His bundle, and the dilated cardiomyopathy is about 4%. Other diseases, such as hypertrophic cardiomyopathy, congenital heart disease, open heart surgery Hyperthyroidism and mucinous edema, calcific aortic stenosis, etc. can be seen in various degrees of atrioventricular block, in recent years, it is found that about half of the chronic inferior atrioventricular block is not arteriosclerosis. Due to myocarditis or drug poisoning, non-specific fibrotic changes occur in the two bundles or the three bundles. Sometimes the lesion can invade the bifurcation of the His bundle, and the atrioventricular node and the His bundle are rarely invaded. The reason is not clear.

(two) pathogenesis

Atrioventricular block induced by excessive vagal tone is usually one or two degrees I, rarely secondary type II, and almost does not produce high or complete atrioventricular block, so second degree II, height Third-degree atrioventricular block is mostly formed by organic damage.

The blockade of second-degree type II atrioventricular block is almost entirely in the He-Pu system. The His-beam electrogram confirms that the block is 35% in the middle or lower part of the His bundle, and the number under the His bundle 65%, Chen Xin et al (1997) pointed out that no blockage of the block at the atrioventricular node or atrium was reported. On the surface electrocardiogram, about 29% of patients had a narrow QRS wave (0.10s), about 71%. The patient's QRS wave is broad (0.12s).

The degree of blockade of second-degree type II atrioventricular block can be light and heavy, and the P wave can occasionally not transmit the ventricle (such as 3:2, 4:3, 5:4 block, etc.) until most P waves are blocked. Hysteresis (3:1, 4:1, 5:1 block), patients with a greater degree of blockade (3:1, 4:1 or more) can see escape or escape from below the block Heart rhythm, 3:1, 4:1 conduction above has been a high degree of atrioventricular block.

Second degree atrioventricular block prevention

1. Active prevention and treatment of primary disease, timely control, elimination of causes and incentives is the key to prevent the occurrence of this disease.

2. Familiar with the anatomy of the conduction system and strict ECG detection during cardiac surgery can reduce the incidence of this disease.

3. Second degree type II atrioventricular block should be based on the block location and the rate of ventricular rate, such as slow ventricular rate, heart rate <40 times / min, and QRS wide and deformed, atrioventricular block The site is below the His bundle and has a poor response to the drug. An artificial cardiac pacemaker needs to be placed to prevent the occurrence of cardio-cerebral syndrome.

Second degree atrioventricular block complication Complications, angina, syncope

Patients with second degree II type atrioventricular block may have syncope, angina pectoris, and severe complications such as A-S syndrome may occur.

Second degree atrioventricular block symptoms Common symptoms Fatigue cerebral ischemia Bradycardia convulsions Dizziness pulse pressure Widening atrioventricular block

The clinical symptoms of second degree atrioventricular block depend on the degree of conduction block and the rate of ventricular rate, and the degree of block is light. When the ventricular leakage is small, the hemodynamics is not affected, and there is no obvious symptom. , or only the feeling of heart palpitations, if the ventricular leakage is more, resulting in a slow heart rate below 50 beats / min, there may be dizziness, weakness, blood pressure and other symptoms of decreased cardiac output.

Signs: The most common is that there is an occasional pause in a series of regular heartbeats. There is no premature beat before the interval. The auscultation may be strong or weak due to changes in the relationship between the atrium and the ventricle. The heart sounds and the pulse have When the leakage is 3:2, the heart sound and pulse can be similar to the two-law formed by pre-systolic contraction, and the 2:1 block is accompanied by a slow and regular heart rate.

Second degree atrioventricular block

Electrocardiogram examination

(1) ECG characteristics of second degree I atrioventricular block:

1 typical ECG features:

The AP-R interval is extended until the P wave cannot be transmitted, and a QRS wave leak occurs (Fig. 1).

The increment of the BP-R interval is reduced by the beat, and in each Venturi period, the increment of the second PR interval is the largest, and then the beat is reduced.

C. The RR interval before the miss is shortened, which is related to the incremental increase of the PR interval.

D. Because the long interval of heartbeat leakage contains the shortest PR interval, the long interval must be equal to or less than the sum of any two shortest RR intervals.

E. The first PR interval after a long interval of leakage is normal or near normal.

2 detailed description of typical ECG features:

A. Characteristics of the Venturi cycle: Since the atrioventricular node itself is the most prone to diminished conduction, this phenomenon can occur when the conduction function of the atrioventricular node is reduced, and the atrioventricular node cannot be completely recovered after each beat. When the first atrial agitation in the Venturi cycle is transmitted, the atrioventricular node conduction is normal or prolonged; the second agitation coincides with the relative refractory period of the atrioventricular node, making the PR interval longer than the first PR interval. When the third excitement is transmitted to the atrioventricular node, the atrioventricular node is at a later stage of the relative refractory period, which makes the PR interval more prolonged. Finally, the atrial agitation finally falls in the absolute refractory period of the atrioventricular node, but not Under the ventricle, a leak occurred, and in the long interval of the leak, the conduction function of the atrioventricular node recovered, so that it was repeated.

Each Venturi period may or may not be fixed, and whether it is fixed or not is related to the ratio of the atrioventricular conduction, that is, the ratio of the P wave and the QRS wave transmitted downstream, which can be expressed by numbers, such as 3:2 block, indicating every 3 P The wave has 2 downcasts and 1 leak, the most common rate of atrioventricular conduction is 3:2, but any ratio of (X 1):X can be seen, such as 4:3, 5:4, 6:5 or 7 : 6, etc., some people use the His bundle beam diagram and atrial pacing to observe, in the natural occurrence of the Venturi block 3:2 conduction, the typical second degree type I block only accounted for 34%, rather than the typical text The cycle (atypical second degree I) accounts for 66%; when the proportion of the atrioventricular system exceeds 6:5, the typical Venturi period only accounts for 14%, so the typical rate of atrioventricular conduction in a typical second degree type I block is 3:2, 4:3 and 5:4; while 6:5, 7:6 are less common (Fig. 2).

B. Typical second degree type I block can be transient, intermittent or long-lasting, paroxysmal, but mostly temporary.

3 second degree type I atrioventricular block ECG special type:

A. Increasing the amount of indefinite Wending phenomenon (variant Venn phenomenon) ECG characteristics:

a. Each Venturi cycle ends with a ventricular leak.

The increment of the bP-R interval is generally gradually decreased first, but the increment before the leakage increases.

c. Generally, the increment of the second and last PR intervals is large, and the increment of the middle PR intervals is small.

The dR-R interval is gradually shorter, longer, and changes in the regularity.

e. The long interval of the leak is shorter than the sum of the two sinus cycles.

f. The first RR interval after the miss is shorter than the last RR interval before the miss, the incidence of the variant Wen's phenomenon is much higher than the typical Wen's phenomenon. Because the increment is uncertain, the performance can be Diverse (Figure 3).

B. Incremental Venturi phenomenon ECG features:

The aP-R interval increment gradually increases, that is, the PP interval gradually decreases, and then ends with a ventricular leak, contrary to a typical Venturi electrocardiogram.

b. The last increment of the last PR interval is the largest.

The cR-R interval is gradually extended and then significantly extended (increasing length).

d. The leak duration is shorter than the sum of the two sinus cycles.

e. The first RR interval after the miss is shorter than the last RR interval before the miss.

C. Incremental fixed Wen's phenomenon ECG features:

a. The first PR interval started to be transmitted is normal, and the subsequent PR interval is extended, but they are all equal.

The bR-R interval is equal and fixed until the P wave cannot be transmitted to the ventricle.

D. Characteristics of the Venturi electrocardiogram with negative PR interval increment before leakage:

a. The PR interval increment before the miss is a negative value, so that the PR interval before the miss is shorter than the PR interval of other downstream beats after the miss.

b. May be caused by supernormal conduction.

E. Venturi phenomenon in which the PR interval after cardiac arrest is not shortened: usually there is a second degree block at the same time in two different parts, and when the distal part is blocked, there is a Venus-type conduction in the proximal part. In another part of the case, this blocked wave (not transmitted to the ventricle) can be explained by the occult conduction that occurs in the atrioventricular junction.

F. Alternating Venturi Cycle: Most alternating Venturi cycles occur at the atrioventricular node, there are two upper and lower block regions, and there are two types of alternating Venturi cycle ECG.

aA-type alternating Venturi cycle: manifested as a 2:1 block in the upper (proximal) of the atrioventricular conduction system and a Venturi-type conduction in the lower (distal) (Fig. 4), due to a blocked P at the end of the Venturi cycle ( Or F) before and after the wave, each has a P (or F) wave blocked by the upper part, and three blocked P (or F) waves occur continuously, that is, the type A alternating Venturi cycle is expressed in the atrioventricular node. The upper part (the node area) is a 2:1 conduction block, and the atrioventricular node area is a Venturi type period. The conduction formula is X=(n:2)-1, or n/2-1, and X is the number of ventricular beats. n is the sum of the number of atrial beats that are transmitted and not transmitted in the Venturi period. Because the upper part of the atrioventricular node (the node area) is 2:1, the proportion of the chamber with X=n:2 is formed; the lower part is the text. The cycle is conducted and then leaked again to form a ratio of X = (n: 2)-1, and finally the Venturi cycle is terminated by three consecutive unintroduced atrial activations, and the atrial flutter (F wave) is 2: When 1 and 4:1 are alternately conducted, most of them are caused by the alternating Venturi cycle of type A, and attention should be paid to identification.

Type bB alternating Venturi cycle: the upper (near) of the atrioventricular conduction system is a Venturi-type block; the lower (distal) is a 2:1 block because a P wave at the end of the Venturi cycle is blocked Excitement disrupts the regularity of the 2:1 block, so that the Venturi cycle ends in two blocked P waves, that is, the B-type alternating Venturi cycle is expressed in the atrioventricular node for the Venturi cycle, the lower part ( The junction area or the distal end of the His bundle is 2:1, and the Venturi conduction formula of the atrioventricular node is: X=n-1 atrioventricular relationship, which is transmitted as 2:1 conduction, so there is X=( The law of n-1):2 eventually ends the Venturi cycle by one or two consecutive unintroduced atrial activations (Fig. 5).

The alternating Venturi cycle is a two-level block in the atrioventricular conduction. Most commonly, the knot region is easy to form Venturi conduction, while the junction region and the node region are easy to form 2:1 conduction in the atrioventricular junction. There are also three levels of block zones, usually 2:1 conduction in the junction region, and the Venturi cycle conduction and the 2:1 block at the junction are present simultaneously, and the compartmental junction zone is 3 levels. Blocking is more common in rapid ectopic atrial rhythm, such as atrial flutter, when the proportion of the atrioventricular will be more complex and variable, the three levels of block instability, when the room rate is slightly slowed down, it can become 2 Blocking at a level.

The double-level atrioventricular block in the atrioventricular junction area is usually a physiological reaction. The type A alternating Venturi cycle is less common, because the refractory period of the upper part of the atrioventricular node is shorter, and it is not easy to form 2:1 conduction. It is easy to occur only when the atrial rate is fast. If there is a 2:1 conduction when the atrial rate is slow, it is considered to be pathological. It is generally considered that the alternating Venturi period is when the atrial rate is 135 times/min. Pathological conduction block, alternating Venturi cycle occurs in the atrioventricular underlying lesions, the prognosis is poor, due to the development of third-degree atrioventricular block, syncope, A-S syndrome.

G. Anti-Wen's cycle: also known as the inverse transformation of Wen's phenomenon, its ECG characteristics: in the 2:1 atrioventricular block, it can be seen that the PR interval is gradually shortened, when the PR interval is gradually shortened to a certain extent The atrial sensation was continued for 2 consecutive times, which became 3:2 conduction and ended a group of cycles. The PR interval was extended after 2 consecutive atrial stimuli, and it was again transmitted 2:1, and repeated (Figure 6). ).

H. Wen's atrial (ventricular) echo (acoustic): During the Venturi-type conduction process, the conduction time of the room-room, room-room, junction area-atrium or junction area-ventricle is prolonged, when extended to To a certain extent, an echo of the atria (or ventricle) occurs, and this echo is blocked in the junction area when it is returned to the ventricle (or atrium), ending the Venturi cycle and causing the Venturi cycle. Atypical, ECG performance is like the typical Venturi phenomenon, the PR interval is prolonged, and finally leaked, but the missing P wave is not a sinus P wave, but an atrial echo (or ventricular echo), also known as Wen. The last ventricular beat in the cycle is transmitted to the ventricle with the longest P'-R interval, and the Venturi cycle ends with an atrial (or ventricular) echo (Figure 7). This arrhythmia is in Venturi resistance. Occasionally appears in the stagnation pattern.

I. Second-degree type I atrioventricular block combined with pre-systolic contraction: the compensatory interval of pre-systolic contraction can disrupt the regular extension of the PR interval. For example, pre-atrial contraction can make a typical second degree I. The type of atrioventricular block is a type I atrioventricular block.

J. Second-degree type I atrioventricular block with escape pulse variation: When the second-degree type I atrioventricular block produces a leaky interval, the escape may occur (atrioventricular junction or ventricular escape) Beat), escape can be transmitted in the first sinus P wave or atrial P' wave after interference in the handover area, and the refractory period formed in the handover area can also disrupt the second PR room. The regularity of the period, the emergence of escape can make the second degree of atrioventricular block to escape - capture the second law.

K. Second-degree type I atrioventricular block combined with sinus block variability: due to atrial leakage caused ventricular leakage can not be manifested, so that second degree I atrioventricular block became a type I atrioventricular block .

L. Second-degree I type atrioventricular block combined with significant sinus arrhythmia variation: can disrupt the regularity of the typical Venturi phenomenon RR interval, when the slow phase of sinus arrhythmia occurs When the pre-leakage period with the smallest increment is used, the shortest RR interval can be made longer, even the longest pre-leakage period, and the leak interval can be longer than the two sinus periods.

(2) ECG characteristics of second degree II type atrioventricular block:

1 typical ECG features:

AP wave is interrupted and interrupted, ventricular leakage.

The BP-R interval is fixed, and in most cases the PR interval is normal, but it can also be extended (Figure 8).

C. The QRS wave transmitted downstream can be normal, the time limit is normal (narrow); it can also be bundle branch block or its branch block pattern, and the QRS time limit is widened (Figure 9).

D. Atrioventricular ratio, the QRS complex is periodically leaked, and the ratio of atrioventricular conduction can be expressed as 2:1, 3:1, 3:2, 4:3, 5:4, 6:5, 7:6, and the like.

Mobitz's definition of the second degree II indicates that the PR interval of all the pulsations before and after the occurrence of the heartbeat is constant, but some authors believe that the PR interval of the pulsation can also be mild. Prolonged, but must be fixed, except for the first beat PR interval after the P wave is blocked, the PR interval can be slightly shortened, and the rest of the PR interval is kept constant. This is due to the improvement of conduction after the block, most scholars believe that The strict diagnostic criteria of Mohs type II should be used.

2 special types of second degree II type atrioventricular block ECG:

A. 2:1 atrioventricular block: it is a special type of second degree atrioventricular block, which may be a second degree type I atrioventricular block, or a second degree type II atrioventricular block The lag is characterized by the following:

a. 2:1 atrioventricular block can occur in the atrioventricular node, can also occur in the Xi-Pu system, 33% of the block at the atrioventricular node (AH level), 17% in the His bundle Inside (H level), 50% under the His bundle (bilateral bundle level, HV level).

b. QRS wave is 47% narrow, 53% is wide, 2:1 block (HI-Pu system) occurs at HV level. ECG QRS wave broadening is bundle branch block pattern; QRS wave is normal (narrow ) usually block the site at the atrioventricular node.

c. For 2:1 atrioventricular block is a problem caused by second degree I or second type II atrioventricular block, surface electrocardiogram shows a fixed 2:1 or 3:1 atrioventricular block At the time, it is often difficult to distinguish the second degree type I or the second degree type II. If the change of the ratio of the atrioventricular conduction can be observed, it is advantageous for typing.

B. If a typical Venturi period and 2:1 conduction block appear alternately or sequentially, this 2:1 block is a second type I block, and in addition, when the Venturi cycle changes from 5:4 to 4. When 3, or 4:3 is converted to 3:2, they can all be converted to 2:1, which is also a 2:1 atrioventricular block of the second degree I.

a. 2:1 atrioventricular block, such as a mild extension of the PR interval, but fixed, with or without bundle branch block is a second type II, but some people think that 2:1 resistance Delayed, prolonged PR interval, fixed and without bundle branch block were second-degree type I atrioventricular block (Figure 10).

b. 2:1 atrioventricular block, such as the normal PR interval, fixed and with bundle branch block is a typical second-degree type II atrioventricular block (Figure 10).

c. When changing from a 2:1 block to a 3:2 block, if the PR interval is constant, a second degree type II atrioventricular block should be considered (Figure 9).

d. After exercise or atropine accelerates the sinus heart rate, if the conduction block is improved, it will change from 2:1 to 3:2, suggesting second degree I; if the block is aggravated, change from 2:1 to 3:1. Degree II, PR fixed 2:1 or 3:1 QRS wave can be normal or wide deformity, 35% of the blockage occurs in the atrioventricular node, and 65% occurs at the subventricular level.

C. Second degree type II atrioventricular block (room ratio of 2:1) with alternating PR interval, alternating RR interval is also alternating: the atrioventricular block shows double-level block There is a high position in the intersection of the room, and a low level in the intersection of the room. The blocked activation is alternately interrupted at these two levels, for example, the high position is 4:3 conduction, and the low position is also 4:3. The conduction alternates with each other, and the result is that the ratio of the atrioventricular is 2:1, accompanied by the alternating length of the PR interval (fixed), and the RR interval also has a corresponding short-length alternating. In addition, the QRS wave of the electrocardiogram is a bundle branch block graph. The short PR interval is unilateral bundle branch block, while the PR interval is incomplete left or right bundle branch block.

D. Second degree type II atrioventricular block with different PR interval (some of which are more fixed): PR interval varies, and is related to different degrees of occult conduction, and some PR interval is fixed. , indicating that the conduction time of the atrioventricular is not affected by occult conduction.

E. Blocked P waves overlap in the second wave of type II atrioventricular block: can resemble sinus bradycardia, second-order type II block rhythm absolute rule or basic rule, and sinus cardiac Sudden arrhythmia is often accompanied by sinus arrhythmia; T wave morphology is abnormal due to overlap with P wave, which makes heart rate increase or heart rate slow down, T and P waves can be separated.

F. Second degree type II atrioventricular block (conduction ratio is 3:2): The blocked P wave resembles U wave or T wave, which can be misdiagnosed as premature contraction dichotomy or atriality in the atrioventricular junction area. Pre-contraction dichotomy.

2. Electrophysiological diagnosis

(1) Characteristics of second-degree type I atrioventricular block electrophysiological examination: According to the block position of second-degree type I atrioventricular block, it can be divided into the following three types, the characteristics are as follows, but Confirmed by Histogram.

1 atrioventricular node II type I atrioventricular block: spontaneous second degree I type atrioventricular block, atrioventricular node is also the most common block site, His bundle beam characteristics: AH interval Prolonged progression until an A wave does not follow the H wave, indicating that this atrial activation is blocked in the atrioventricular node. This is a characteristic performance. In the typical Venturi period, the incremental increase of the AH interval is progressively reduced. Small, while the VV (RR) interval is progressively shortened, but the typical Venturi period is not common, but not typical, when the atrioventricular conduction ratio increases to 5:4 or greater, spontaneous and pacing The induced atypical Venturi cycle increases.

2 second-degree type I block in His bundle: seen in 7% to 9% of patients, His bundle beam characteristics: His bundle potential split, between the proximal H wave and the far end H' wave It is progressively extended until there is no H' wave after H wave. If the bundle branch block is not combined, the QRS wave shape is normal.

The characteristics of the second-degree I-type block under the His bundle are:

The AH-V interval is progressively extended until the AH wave of a sinus beat is not followed by a V wave (ventricular depolarization).

B. QRS wave changes from normal progressive to incomplete bundle branch block graph, and then transforms into complete bundle branch block graph: accompanied by progressive extension of HV interval, second-degree I-type conduction resistance under His bundle It is not uncommon to present an atypical Wen's cycle in the stagnation.

Second-degree type I atrioventricular block in the His bundle and under the His bundle can often progress to a high or third degree atrioventricular block.

4 His bundle beam characteristics: 35% of type II type II atrioventricular block lesions occur in the His bundle, and 65% occur in the distal end of the His bundle (the His bundle).

A. When the His bundle is blocked at the near end, the His bundle beam diagram shows that the AH interval is prolonged, but the HV interval of the downstream transmission is normal, and there is no H wave and no V wave after the A wave that cannot be transmitted.

B. When the His bundle is blocked at the distal end, the His bundle beam diagram shows that the AH interval is normal, the HV interval is prolonged, and there is no V wave after the H wave of the heart beat that cannot be transmitted.

Relationship between 5 second-degree and second-degree type II atrioventricular block: Previously, second-degree type I and type II atrioventricular block had different electrophysiological and clinical significance in myocardial infarction occurred in different sites. For example, type I is seen in the inferior myocardial infarction, which is considered to be caused by reversible ischemia of the atrioventricular node. The prognosis is good. Type II is seen in the anterior wall myocardial infarction. It is often accompanied by bundle necrosis. The prognosis is serious. Degree I and II type II atrioventricular block are not two different electrophysiological processes of different nature, and may be different degrees of performance in an electrophysiological process. The following basis can be explained.

A. In acute myocardial ischemia, it was found that the Greek-Pu system gradually loses its normal fast response characteristics, and gradually begins to exhibit slow response characteristics. In the early stage of deviation from normal, the near-end of the He-Po system can exhibit second-order resistance. Hysteresis, accompanied by an imperceptible or a few milliseconds of conduction delay increment (equivalent to a second degree II block). When further deviating from normal, the proximal end of the Greek-Pu system has a similar compartment before the block occurs. The junction has a significant conduction delay increment (equivalent to a second degree I-type Venturi period).

B. In some patients with acute myocardial infarction, it is found that this similar type II block and the obvious type I block in the proximal segment of the He-Pu system are continuous in time, and the Xi-Pu system can be observed. The evolution of second-degree atrioventricular block caused by acute ischemia, in some patients within the first few hours after the onset of acute myocardial infarction, a second degree of atrioventricular block occurred in the He-Pu system. There is only a small increase in conduction delay before the block occurs. After a few days, the second degree atrioventricular block becomes another form, that is, the increase in conduction delay before the block occurs is very obvious, so In terms of mechanism or structure, there is no reliable basis for subdividing the second degree atrioventricular block into two distinct types, but from a practical point of view, the second degree atrioventricular block is not before the block occurs. With the increase of conduction delay, which is the characteristic of the Xi-Pu system, the two terms of type I and type II atrioventricular block are still used clinically.

Diagnosis and diagnosis of second degree atrioventricular block

Diagnostic criteria

1. According to medical history, symptoms and signs.

2. ECG diagnostic criteria

(1) Second degree type I atrioventricular block: the diagnostic criteria for typical Venturi phenomenon:

The 1P-R interval is gradually extended plus QRS leakage, ending a Venturi period,

2 Venturi cycles repeat,

The 3P-R interval is incrementally decreased.

Diagnostic Criteria for Atypical Venturi Phenomena: Regardless of how the electrocardiogram of atypical and variant Venturi phenomena changes, the basic feature is that the first PR interval after QRS leakage is always more or less shortened, before the leak The PR interval is always more or less prolonged, and these two points are the most basic signs of second-degree type I atrioventricular block.

(2) second degree type II atrioventricular block: the diagnostic criteria for second degree type II atrioventricular block is PR interval fixation plus partial ventricular leakage.

Differential diagnosis

(1) Identification of second-degree type I atrioventricular block and sinus arrhythmia: the PR interval of sinus arrhythmia is not gradually prolonged, the length of PP interval is different, and the phenomenon of venturi is not long and short. The ventricular rate is not uniform.

(2) Discrimination of the retarded Venturi phenomenon and the interfering Venn phenomenon: Blocking Venturi phenomenon P wave occurs in the middle and late stages of diastole, with delayed conduction delay or interruption, and interfering Wen's phenomenon Occurring in atrial tachycardia, the atrial P' wave appears in the systolic or early diastolic, resulting in delayed conduction delay or interruption, but when the atrial rate is slowed down to the ectopic atrial P' wave appears in In the middle of diastole, the ventricular conduction can be restored by 1:1, or the Venturi phenomenon disappears when the sinus rhythm is restored.

(3) Identification of 2:1 atrioventricular block and non-downward atrial premature contraction: 2:1 atrioventricular block all P wave patterns are consistent, PP interval is basically regular, but not The P' wave of the pre-atrial contraction two-law prematurely transmitted is different from the sinus P wave. Because the ectopic P' wave occurs in advance, the PP' interval

2. Second-degree type II atrioventricular block and second-degree sinus block. In the second degree type II atrioventricular block, the P wave is easily overlapped with the T wave of the previous cardiac cycle, which leads to the misunderstanding of P wave leakage. The diagnosis of second sinus block, but if you carefully observe the overlapping T wave morphology, you will find morphological abnormalities, while the sinus block, P wave, QRS wave are missing.

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