Pediatric atrioventricular block
Introduction
Introduction to pediatric atrioventricular block Atrioventricular block, also known as atrioventricular block, refers to conduction delay in the normal conduction pathway between the atrioventricular, partial or total block. Atrioventricular block is divided into one-degree, second- and third-degree (or complete) atrioventricular block. In one-time atrioventricular block, all agitation can be transmitted but the conduction velocity is abnormally delayed. The second degree of atrioventricular block is partially agitated and partial excitatory shedding, and the third degree atrioventricular block is completely without atrioventricular conduction. Cardiac block can occur anywhere on the conduction system, including the sinus node and the atria, the atrial muscle, the atrioventricular junction, the atrioventricular bundle and its left and right bundles, the Purkinje fiber web, and the ventricular muscle. Atrioventricular block is more common in childhood. Atrial agitation is blocked in the atrioventricular junction, atrioventricular bundle and its branches, and cannot be transmitted to the ventricle. The atrioventricular block can be divided into complete and partial. Blocking. Partiality can be divided into first degree and second degree. Completeness is also called third degree atrioventricular block, which is temporary, permanent or intermittent. basic knowledge The proportion of illness: 0.004% Susceptible people: children Mode of infection: non-infectious Complications: syncope, angina pectoris, heart failure, cerebral ischemic disease, sudden death
Cause
Pediatric atrioventricular block
Complete atrioventricular block can be divided into congenital and acquired:
Congenital complete atrioventricular block:
The incidence of live births is 1/22000, 30% of children with congenital heart disease, large blood vessel dislocation, single ventricle more common, 70% isolated, no cardiovascular malformations, because:
Autoimmune disease (27%):
Mothers with autoimmune disease during pregnancy, usually systemic lupus erythematosus, can be in the asymptomatic period; rheumatoid arthritis, dermatomyositis and Sjogren's syndrome are rare, serum has anti-SS-A or anti-SS-B itself Antibody, this kind of antibody is an IgG component, which can enter the fetus through the placenta, causing fibrosis, inflammation, necrosis or calcification and other pathological immune reactions in the fetal atrioventricular junction. Congenital third degree atrioventricular block is 60% to 70% due to It is caused by autoimmune diseases, and the isolated type can be as high as 80%.
Embryonic developmental malformation (25%):
More congenital congenital heart disease, interruption of the atrioventricular conduction system, can occur at the earliest gestational age of 16 weeks, may be due to slow fetal heart, mistaken for intrauterine asphyxia and cesarean section, and some have stillbirth or birth Edema, hepatomegaly, heart failure, clinical symptoms depend on cardiac malformation and slow heart rate, isolated complete atrioventricular block heart rate 60-70 times / min, can be asymptomatic, heart rate below 60 / min , more sleepiness, refusal to milk, weakness, and even A-S syndrome or heart failure, A-S syndrome often due to ventricular tachycardia, ventricular fibrillation, a few due to cardiac arrest, combined with congenital heart disease In children, the atrial rate is below 150 beats/min, the ventricular rate is below 55 beats/min, heart failure can occur in the first week after birth, and those with cardiac malformations are more complicated than infancy due to A-S syndrome. Death or sudden death, 597 cases of congenital complete atrioventricular block patients with natural course, 599 cases of isolated type 418 cases, 2 / 3 follow-up to 10 years old, 92% still survive, another 18l cases of cardiovascular malformations The case fatality rate is 28.7%, another report There were 113 cases of isolated complete congenital atrioventricular block, 56 males and 57 females, all without important cardiac malformations. The maternal serum was anti-SS-A and/or anti-SS-B antibody positive, and the pregnancy record was complete. Of the 87 patients, 71 (82%) were diagnosed for the first time before 30 weeks of gestation (median 23 weeks), 22 (19%) died in 113 cases, occurred in 6 cases in the uterus, and within 3 months after birth 10 For example, 6 cases from 3 months to 6 years old, the mortality rate of births before 34 weeks of pregnancy was significantly higher than that after 34 weeks (52% vs. 9%), of the 107 cases of live birth, 61 cases (62%) required placement pacing. 35 cases were within 9 days after birth, 15 cases within 1 year old, and 17 cases after 1 year old. The heart rate of the physical examination was slow and regular, and the systolic murmurs of the II~III/VI level could be heard on the left sternal border and apex of the sternum. The first heart sound is different. If the atrium and the ventricle contract at the same time, the first heart sound is enhanced like "cannon sound", the systolic blood pressure is increased, the pulse pressure is increased, the peripheral blood vessel sign is positive, and the ventricular diastolic filling is due to bradycardia. Increase, the stroke volume increases, and the heart compensatory increases.
Surgical trauma (15%)
Acquired complete atrioventricular block:
Most occur in intracardiac surgical trauma.
Infection (20%):
Acute infection, viral myocarditis, cardiomyopathy and Kearns-Sayre syndrome (external ophthalmoplegia, pigmented retinal degeneration and mitochondrial myopathy).
Other factors (10%):
Digitalis poisoning, hypokalemia, etc. may also occur atrioventricular block, its clinical manifestations in addition to the primary disease, there are slow heart rate, often fatigue, chest tightness, lethargy, etc., severe cases of A-S syndrome, heart failure Or drowning.
Pathogenesis
1. Pathogenesis and classification
The spread of cardiac activation is the process of excitatory and action potentials of cardiomyocytes in various parts of the cardiac conduction system. In pathological conditions, the electrophysiological properties of cardiomyocytes can be changed, and the Purkinje fiber, atrial muscle, and ventricular muscle react quickly. The membrane potential of the fiber is reduced, and the slow reaction action potential is generated, so that the refractory period is prolonged or even excitable. According to the ECG atrioventricular block, the pathophysiological basis is the myocardial part of the atrioventricular conduction system. The refractory period of the cells is prolonged. The three types of mechanisms are: once the atrioventricular block is due to the extension of the relative refractory period of the myocardial cells in the lesion of the atrioventricular conduction system, and the effective refractory period is still normal, and the second type I atrioventricular conduction Blocking effective refractory period and relative refractory period are prolonged, declining conduction occurs, conduction velocity is slowed down, second degree type II atrioventricular block is mainly effective refractory period is prolonged, and relative refractory period is very short, thus The lesion area of the atrioventricular conduction tissue is in an unstable state, and the arousal of the atrium is reflected in the "all or none" way, ie Normal conduction or heartbeat shedding; third-degree atrioventricular block effective refractory period occupies the entire cardiac cycle, all atrial-induced excitement can not be transmitted, secondary pacing pacing below the block Keeping the ventricular pulsation, the electrocardiogram appears atrioventricular separation. On the electrocardiogram, the effective refractory period of the atrioventricular junction area is roughly equivalent to the apex of the P wave to the apex of the T wave. The relative refractory period is roughly equivalent to the end of the T wave to the end of the U wave. In the relative refractory period, the length of the PR interval is inversely proportional to the RP interval of the previous pulsation. Correct understanding of this point is beneficial to the observation of the PR interval.
2. First degree atrioventricular block
The first degree of atrioventricular block is a common atrioventricular block, which is easy to ignore because it has no clinical manifestations, but it can be an important clue to diagnose certain heart diseases or related diseases.
(1) Clinical manifestations: The first degree of atrioventricular block is more common in children, but usually asymptomatic. At the time of auscultation, the ventricular compartment is overfilled and the S1 intensity is weakened due to prolonged PR interval.
(2) Characteristics of electrocardiogram: The first degree of atrioventricular block is easy to diagnose on the electrocardiogram, but the P-wave should be selected when measuring the PR interval. There are q-wave leads. The characteristics are as follows: 1P-R interval exceeds age, The highest heart rate (Table 1); although the 2P-R interval did not exceed the normal high limit, the PR interval was longer than the original 0.04s when the heart rate did not change or increased; 3 QRS waves after each P wave .
3. Second degree atrioventricular block
At the second degree of atrioventricular block, the impulse of the sinus node can not be transmitted to the ventricle, and there are different degrees of leakage. (1) Clinical manifestations: clinical manifestations depend on basic heart disease and blood flow caused by conduction block Learning changes, mild can be asymptomatic, when the rate of ventricular slow can cause chest tightness, dizziness, fatigue, palpitations and heartbeat leakage, etc., if there is a high degree of atrioventricular block or a slow 2:1 block, There may be symptoms such as dizziness and even syncope. In the second degree of type I atrioventricular block, the first heart sound gradually weakens and there is heart beat. In the second degree type II atrioventricular block, the first heart sound intensity is constant. Interstitial heart beat,
(2) Electrocardiogram diagnosis:
1 Mohs type I (Mobitz type I): The second degree I type atrioventricular block is called Mobitz type I, also known as Wencke type (Wenckebach), the severity is expressed by the ratio of P wave number to QRS wave number. For example, 3:2 means 2 out of 3 P waves; 7:6 means 6 out of 7 P waves are transmitted to the ventricle. It is generally considered that this ECG change is due to decreasing conduction during the relative refractory period. Caused by ECG characteristics: AP-R interval is extended until a QRS wave is blocked, BR-R interval is shortened until a QRS wave falls off, C. The RR interval containing P wave is shorter than 2 PP intervals The sum, but equal to 2 PP intervals minus the total value of PR, the D.QRS wave is generally normal, suggesting that the block is at the atrioventricular node, and the second type I atrioventricular block is due to sinus arrhythmia. , conduction instability in the atrioventricular junction, and the impact of occult conduction, ECG can appear atypical second degree I type atrioventricular block, the following common types: AP-R interval and RR interval changes are not obvious There is no typical Venturi period, only the PR interval is shortened after the ventricular detachment, B. The P wave that has not been transmitted invades the chamber junction area, causing a new one. In the expected period, the PR interval is not shortened after the ventricular detachment, C. The PR interval is equal in the Venturi cycle, and the maximum increment of the DP-R interval does not occur in the first and second PR intervals after ventricular leakage. .
2 Mohs type II (Mobitz II type): the second degree II type atrioventricular block, ECG characteristics: AP-R interval is constant, normal or prolonged, BP wave appears regularly, and the interrupt is blocked, except in P After the wave is transmitted, the first excited PR interval can be slightly shortened, and the PR interval is kept constant. This is important for diagnosing this type of block. The C.QRS wave is often widened by 0.10s, indicating the blockage. Often at or below the His bundle.
3 height atrioventricular block: in the second degree of atrioventricular block, the ratio of atrioventricular conduction is 3:1 or more, such as 4:1, 5:1, etc., and there may be escape, called high atrioventricular conduction resistance Stagnation.
4. Third degree atrioventricular block
The third degree of atrioventricular block is complete atrioventricular block, which is rare for the atrial depolarization wave to pass to the ventricle.
(1) Clinical manifestations: The symptoms of third degree atrioventricular block depend on hemodynamic changes, and hemodynamic changes depend on the site of the block, generally in the more proximal, The hemodynamics and physiological functions are not changed much, and the parasympathetic stimulation is eliminated. The sympathetic excitation can increase the ventricular rate by 10% to 30%. When the block is at the distal end of the atrioventricular bundle, the ventricular rate increases. Often less than 10%.
Clinical manifestations vary, some children can tolerate ventricular rate of 30 ~ 50 times / min without symptoms, but some can have different symptoms including fatigue, dizziness, angina, heart failure, ventricular rate is very slow can cause cerebral ischemia Thus, the loss of consciousness, even convulsions and other Adams-Stokes syndrome performance, severe cases can cause sudden death, if combined with ventricular arrhythmia, patients can feel palpitations.
The physical examination has a slow and regular pulse rate. After exercise, there is only a slight increase or a moderate increase. The pulse is more powerful. The jugular vein can have significant pulsation. The intensity of the first heart sound changes frequently. The second heart sound can be normal or abnormally split. And atrial sound and cannon sound, sometimes can hear the third heart sound or the fourth heart sound, in the absence of other heart disease, about 60% found that the heart is enlarged.
(2) Electrocardiogram diagnosis: The effective refractory period of the third degree atrioventricular block is extremely prolonged, occupying the entire cardiac cycle, so that all P waves fall in the effective refractory period, and the ventricle cannot be transmitted at all. The ventricle is controlled by the low pacing point. The characteristics of ECG are: 1P-P interval and RR interval have their own fixed laws, P wave has nothing to do with QRS wave; 2 atrial rate is greater than ventricular rate, ventricular rhythm is border region or ventricular rhythm, border region frequency is born To 3 years old 60 to 100 times / min, 3 years old and above 50 ~ 70 times / min: ventricular frequency born to 3 years old 40 ~ 60 times / min, 3 years old and above 30 ~ 40 times / min; 3QRS wave morphology: block The QRS wave of the site above the His bundle is the same as that of the normal sinus. It is mostly congenital, and the QRS wave of the block below the His bundle is broadly deformed, often caused by surgery or myocarditis; 4Q-T interval can be Prolonged, but easy to concurrent ventricular tachycardia, poor prognosis.
Prevention
Pediatric atrioventricular block prevention
Active prevention of congenital heart disease; prevention and treatment of electrolyte imbalance and acid-base imbalance, active treatment of primary disease, such as acute infection, viral myocarditis, cardiomyopathy, digitalis poisoning and other arrhythmia, and should continue to improve surgery, reduce surgical trauma, etc. Caused by atrioventricular block.
Complication
Pediatric atrioventricular block complications Complications syncope angina pectoris heart failure cerebral ischemic disease sudden death
Severe cases can cause syncope, angina, heart failure, cerebral ischemia, convulsions, and even sudden death.
Symptom
Pediatric atrioventricular block symptoms Common symptoms Fatigue, dizziness, atrioventricular block, pulse pressure widening, transient fainting, bradycardia, convulsions
The first degree of atrioventricular block is only prolonged atrioventricular conduction time, the ECG is prolonged in the PR interval, and the child has no symptoms. The auscultation may have the first heart sound reduction in the apex, and the second degree atrioventricular block is divided into 2 types. : Type I is also known as Wen's phenomenon, that is, the PR interval is gradually extended, and finally the atrial activation is completely blocked. There is no QRS wave after P wave, causing ventricular leakage, and the first PR interval after ventricular leakage is shortened, showing a periodic change. This type of block is mostly in the atrioventricular junction area, and the prognosis is good. Type II means that some of the atrial agitation is transmitted to the ventricle, while the other part of the agitation is blocked between the atrioventricular compartments. Therefore, ventricular leakage occurs, and the atrioventricular ratio is mostly 3:1 or 2:1, PR interval is fixed, this type of block is mostly in His bundle or below, the prognosis is poor, may develop into complete atrioventricular block, the child may have no symptoms, and the heart rate is slow. At the time, there may be symptoms such as dizziness, fatigue, shortness of breath during labor, and a pause after a few heartbeats during auscultation.
Examine
Pediatric atrioventricular block
Cardiomyocyte assay, blood electrolysis value, pH value and immune function serum antibody should be routinely performed, and electrocardiogram, chest X-ray and echocardiography should be routinely performed.
1.24h dynamic electrocardiogram: observe the degree of slow ventricular rate and whether or not complicated ventricular premature contraction, ventricular tachycardia and other serious arrhythmias.
2. Exercise ECG: Observe the exercise endurance of children, increase the rate of ventricular rate after exercise and whether to induce ventricular arrhythmia, such as increased ventricular rate after exercise for more than 10 times / min, suggesting that the block is above the His bundle.
3. His's beam diagram: Determine the blockage, in the atrioventricular junction, below the His bundle or His bundle.
4. Echocardiography: Congenital complete atrioventricular block for fetal echocardiography, observation of the relationship between atrioventricular contraction, can be diagnosed before birth.
Diagnosis
Diagnostic diagnosis of ventricular block in children
diagnosis
1. History:
The heart rate or heart rate of the congenital complete atrioventricular block is slow. The mother's serum is anti-SS-A or anti-SS-B antibody positive, and the acquired cases have a primary disease history.
2. ECG examination:
Has the following characteristics:
(1) The PP interval and the RR interval have their own fixed laws, and the P wave has no fixed relationship with the QRS wave.
(2) Atrial rate is faster than ventricular rate.
(3) ventricular rhythm is borderline or ventricular self-heart rhythm, borderline frequency is born ~ 3 years old 50 ~ 80 times / min, 3 years old and above 40 ~ 60 times / min; ventricular frequency: newborn ~ 3 years old 40 ~ 50 times /min, 30 to 40 times/min over 3 years old.
(4) The QRS wave boundary heart rhythm is a normal pattern, and the ventricular rhythm is widened, showing a left or right bundle branch block type.
(5) QT interval can be prolonged, and ventricular tachycardia is prone to occur, indicating poor prognosis.
Differential diagnosis
Interfering PR interval prolongation, this is functional atrioventricular block, that is, the interference phenomenon in the atrioventricular junction area. When the atrial agitation is transmitted, the atrioventricular junction area is in a relative refractory period, and the conduction is delayed, so that the PR interval is prolonged. , common in pre-atrial contraction, paroxysmal atrial tachycardia and so on.
1.2:1 or 3:1 atrioventricular block can be a second degree type I or type II atrioventricular block: it is not easy to distinguish, and a long electrocardiogram should be added. If the ratio of atrioventricular conduction is changed, the PR interval is not If it is constant, it may be type I; it is generally considered that the second degree 2:1 atrioventricular block is prolonged in PR interval and is not accompanied by beam-blocking QRS wave, that is, narrow QRS wave is often type I, if PR The period is normal, with the bundle branch block type QRS wave, it is type II.
2. Second degree sinus conduction block: there is no QRS wave in the interval, and there is no P wave, and the P wave appears regularly in the second degree of atrioventricular block, and there is no QRS wave after the P wave.
3. Unsuccessful atrial premature contraction dichotomy: should be differentiated from the second degree of 2:1 atrioventricular block, the former can be seen in the ectopic P' wave in advance, the ectopic P' wave occurs in the former For a drop of T wave, it is necessary to carefully observe the T wave change, and the latter can see the regular sinus P wave.
4. Sinus bradycardia: It should be differentiated from the second degree 2:1 atrioventricular block. Sometimes the P wave and T wave that are not transmitted are heavy or the P wave is very small. The P wave should be checked carefully.
5. Atrial tachycardia: The second rate of 2:1 atrioventricular interference can occur if the room rate is too fast above 250 times/min. This is a functional block.
