First degree atrioventricular block

Introduction to once atrioventricular block First degree atrioventricular block (I°AVB) refers to prolonged atrioventricular conduction time, which exceeds the normal range, but each atrial activation can still be transmitted to the ventricle, also known as atrioventricular conduction delay. On the electrocardiogram, the PR interval reached or exceeded 0.21 s (children under 14 years of age reached or exceeded 0.18 s), and each P wave had a QRS wave. basic knowledge The proportion of illness: 0.003% Susceptible people: no special people Mode of infection: non-infectious Complications: paroxysmal ventricular tachycardia

Once atrioventricular block

(1) Causes of the disease

Once the atrioventricular block can be seen in normal people, some PR interval can exceed 0.24s, the incidence rate of young and middle-aged people is 0.65% to 1.1%, and about 1.3% in normal people over 50 years old, the vagus nerve tension is increased. It is the reason for its occurrence, and the incidence rate of some athletes can reach 8.7%.

Certain drugs such as digitalis, quinidine, procainamide, potassium salts, beta blockers and calcium antagonists, central and peripheral sympathetic blockers such as methyldopa, clonidine, etc. To prolong the PR interval, many scholars often refer to the extension of the PR interval caused by such factors as the atrioventricular conduction delay, not called atrioventricular block, and the prognosis is good.

Once atrioventricular block is common in rheumatic myocarditis, acute or chronic ischemic heart disease, the incidence of acute myocardial infarction in patients with 4% to 15%, especially in patients with acute inferior myocardial infarction, also common in myocarditis Hyperthyroidism or adrenal insufficiency, congenital heart disease, heart surgery, etc., mostly temporary, can disappear quickly or disappear after a period of time, the primary conduction system fibrosis in the elderly is a more common cause , showing long-term progressive conduction block.

(two) pathogenesis

Once atrioventricular block may also be referred to as atrioventricular conduction delay, which may be due to conduction delays in the atria, atrioventricular node, His bundle or Hip-Pulse system, or may be due to a combination of more than one conduction delay However, in most cases, about 90% occur in the atrioventricular node, a few occur in the atria, and some occur in the Xi-Pu system. The conduction delay in the Xi-Pu system often does not cause an abnormally prolonged PR interval. There are exceptions, which occur in the His bundle. This is because the labyrinth structure of the atrioventricular node is conducive to the formation of diminishing conduction, and the conductive fibers of the His bundle are arranged in a longitudinal direction, which is not conducive to the occurrence of diminishing conduction. Ventricular conduction block is due to the extension of the relative refractory period of the atrioventricular junction, leading to prolonged atrioventricular conduction time, but each atrial activation can be transmitted to the ventricle.

Once atrioventricular block prevention

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

Once complicated atrioventricular block Complications paroxysmal ventricular tachycardia

There are no obvious clinical complications. The disease often occurs as a complication of other diseases, such as acute inferior myocardial infarction, hyperthyroidism, pre-excitation syndrome, etc. can cause the disease, the complications caused by this disease are rare, but once it occurs, it is very Danger, such as high atrioventricular block can be complicated by ventricular fibrillation, patients with ventricular fibrillation before electrocardiogram often have frequent ventricular premature beats, ventricular tachycardia, and most patients have fatigue, palpitations, chest tightness, panic, irritability Symptoms, so the patient should be prepared for rescue in the clinic. The rescue of ventricular fibrillation should be divided into seconds. The ventricular fibrillation often has aura. The ventricular tachycardia is a prelude. Immediately after the discovery, antiarrhythmic drugs are given to avoid Serious complications have occurred.

Once atrioventricular block symptoms Common symptoms Crying syncope ECG abnormal fatigue Head stunned short chest tightness heart palpitations fainting convulsions

Once atrioventricular block does not cause obvious symptoms and signs. In the auscultation of myocarditis or other heart disease patients, it can be found that the loud first heart sound suddenly decreases when the block occurs, and the clinical manifestations are mostly the symptoms or signs of the primary disease. .

Once atrioventricular block

ECG features:

1. Typical ECG characteristics of once atrioventricular block

(1) Each sinus P wave can be transmitted to the ventricle and produce a QRS-T wave group.

(2) PR interval > 0.20 s (adult); pediatric (under 14 years) PR interval 0.18 s.

(3) The PR interval is greater than the normal maximum value (depending on the heart rate).

(4) When there is no significant change in heart rate, the PR interval is increased by 0.04 s or more, even if the PR interval is within the normal range.

2. The performance of the block of the atrioventricular block on the ECG

(1) Electrocardiogram characteristics of once atrioventricular block caused by atrial:

1P wave broadens, with notch, prolonged PR interval, but most of the PR segment does not prolong, and the atrioventricular block of the atrioventricular node is prolonged in the PR segment, with or without P-wave broadening, PR Most of the prolonged period (>0.40s) was once blocked in the atrioventricular node, followed by atrial block.

2 Only the PR interval is prolonged, and there is no P wave widening or notch. Severe intra-atrial conduction delay often causes the amplitude of P wave on the surface electrocardiogram to decrease significantly. This type is difficult to distinguish from the atrioventricular node. Only with the His bundle electrogram examination, such as the extension of the PA interval, can be diagnosed. ECG characteristics of one-time atrioventricular block in the atrioventricular node: usually PR interval > 0.40s, mostly caused by one-time conduction block in the atrioventricular node, and the performance of AH in the His bundle beam diagram The period was extended, and there was a report of a delay in the atrioventricular node with an extended AH interval of 900 ms.

(3) There are two manifestations of ECG characteristics that occur in the first-stage atrioventricular block caused by the Xi-Pu system:

1P-R interval prolongation with bundle branch block or branch block: it is likely to be asymmetry of incomplete left and right bundle branch block (ie, one side bundle branch is completely blocked, and the contralateral bundle branch is once blocked Stagnation), the first block of atrioventricular node is not accompanied by bundle branch block, so the atrioventricular node block with one side bundle branch is completely blocked, can not exclude double level block.

2 only the PR interval is prolonged without bundle branch or branch block: this is caused by the symmetry left and right bundle branch once blocked, and can not be distinguished from the atrioventricular node once block on the surface electrocardiogram, according to According to the Histodian beam electrogram, if the PR interval is >0.28s, most of the atrioventricular node block is produced. If the bundle branch pattern is found in the review, it should be determined as a bilateral bundle branch block. As a result, the first block of the atrioventricular node in the His bundle beam diagram is extended by the AH interval, and the bilateral bundle branch block is prolonged in the HV interval. Therefore, it is most reliable to determine the block site by using the His bundle beam diagram. .

3. A detailed description of a typical ECG

(1) The length of the PR interval is related to the heart rate. In the normal heart, when the heart rate increases significantly, the PR interval can be shortened. However, in the case of heart disease, the heart rate increases and the PR interval can be prolonged. What is the heart rate? As long as the adult PR interval is >0.20s, the child is >0.18s, or the normal upper limit of the PR interval when the corresponding heart rate is exceeded, the first degree of atrioventricular block should be diagnosed.

(2) If the heart rate does not change significantly on the electrocardiogram of the same person at different times, and the PR interval increases by more than 0.04s, the possibility of atrioventricular block should be considered, even if the extended PR interval is still upper limit. Within the value, this is because the PR interval usually does not change unless the heart rate is very fast. In addition, when the heart rate increases, the PR interval does not shorten, but it is extended by 0.04 s or more, and the atrioventricular conduction resistance should also be considered. Stagnation.

(3) Usually, the PR interval of one-time atrioventricular block is mostly 0.21 to 0.35 s, but sometimes it can be longer, even 1.0 s. Sometimes the QRS wave occurs late due to the significant extension of the PR interval. The next P wave may overlap in the T wave before it, which is easily misdiagnosed as the heart rhythm of the atrioventricular junction area, which must be carefully observed.

(4) Once atrioventricular block due to delayed conduction in the atria, atrioventricular node or His bundle, often accompanied by a normal QRS complex, accompanied by a wide QRS wave (bilateral bundle branch block) ), the probability of blockage under the His bundle is large, and it is a pattern of one-side bundle branch block, but if the conduction delay in the bilateral bundle branch is equal, the QRS complex can also be normal (narrow 0.10s).

When the atrioventricular block is accompanied by a wide QRS wave, the ECG pattern is helpful in determining the location of the atrioventricular conduction delay. When the right bundle branch block pattern and the normal frontal ECG axis are presented, the prompt is accompanied by the room. Delay in conduction within the ventricular node; and when the right bundle branch block pattern and the frontal gyroscopic axis are left-biased, the conduction delay can be in the atrioventricular node or in the He-Pu system; when the left bundle branch block pattern is present When the frontal surface of the electrocardiogram is right-biased, it is suggested that more than 50% of the patients have a delay in the atrioventricular conduction in the Xi-Pu system.

Once atrioventricular block with double branch block (right bundle branch block and left anterior branch block) should not be considered a three-branch block, especially when the PR interval is long, because once atrioventricular block may Occurred in the atrioventricular node, when the left bundle branch block and the PR interval prolonged coexistence, the possibility of lesions in the His bundle is very large.

(5) Once atrioventricular block can be expressed as a normal electrocardiogram, that is, normal PR interval (0.20s), QRS wave is supraventricular (time limit <0.10s), which can be seen in the following cases: within the His bundle When the blockage (the lesion before the His bundle split), the time limit of the QRS wave is not prolonged, even if the conduction time in the His bundle is doubled, and the conduction time of the proximal end of the atrioventricular conduction system (in the atrium and the atrioventricular node) is In the normal range, the PR interval may not exceed 0.20 s, only when there is a significant delay (>50 ms) in the His bundle, accompanied by a normal upper PA interval value (45 ms) and an AH interval value (130 ms). The PR interval can be prolonged. In addition, there is a slight delay in the atrium (PA interval > 45ms), while the AH interval is at the lower limit of normal (45ms) and the HV interval is also at the lower limit (35ms). The interphase of PR can be normal. The HV interval of His bundle beam is extended to one of the patients with His's bundle arrest. There are a few patients with PR interval that can be in the normal range. Therefore, it is not possible to rely on normal PR interval and normal QRS. The atrioventricular block was completely ruled out.

4. Once atrioventricular block ECG typing

(1) Once type I atrioventricular block: also known as Wen's type atrioventricular block or PR interval, ECG showed a prolonged PR interval, but not followed by leakage, its block level In the atrioventricular node, the Wenshi type once atrioventricular block can be divided into the following three types.

1 Completely concealed Venturi type atrioventricular block: only one degree of atrioventricular block on conventional electrocardiogram, only the period of PR can occur after the artificial pre-stimulation induces a longer compensation period. Phenomenon.

2 Incompletely concealed Venturi type atrioventricular block: more pre-trial contraction after the compensatory period, the PR interval shortened and the exponential prolonged Wen's phenomenon, which is due to the pre-contraction compensation period The posterior AV region is detached from the refractory period and the conduction function is temporarily improved. The insertion ventricular premature contraction is due to the lack of compensation period, which often causes the PR interval to be extended after the pre-systolic contraction to form the inverse Wenshi phenomenon.

3 Completely displayed type of Venturi type atrioventricular block: mainly one-time atrioventricular block combined with second-degree sinus block, sinus block, whether type I or type II can cause PP interval regularly Alternating length and length, long PP interval can restore the conduction function of the AV area, and the PR interval is shortened. Later, due to the shortening of the PP interval, the P wave of the downstream transmission falls on the earlier stage of the relative refractory period of the AV area. The PR interval is prolonged; when the sinus block has a long PP interval, the Venturi period of the PR interval is also terminated, and this type has a chance to be fully displayed when contracted before the contraction.

(2) once type II atrioventricular block: also known as PR interval fixed atrioventricular block, commonly known as one-time atrioventricular block, the most common.

(3) once type III atrioventricular block: also known as PR interval indefinite atrioventricular block, prolonged PR interval varies, PR interval can also change with heart rate, in long RR spacing After that, the PR interval is shorter, and after a short RR interval, the PR interval is longer, which may be related to fluctuations in vagal tone.

Diagnosis of differential diagnosis of atrioventricular block

Diagnosis : ECG performance:

1. Each sinus P wave can be transmitted down to the ventricle and produce a QRS-T wave group.

2. The PR interval is >0.20s (adult), and the PR interval is 0.18s (children under 14 years old).

Differential diagnosis

1. Identification of some special phenomena during one-time atrioventricular block

When the atrioventricular block is accompanied by sinus tachycardia or atrial tachycardia, the occurrence of P wave can occur in the middle of diastole, early diastole, late systole and middle systole, and even early metaphase. Periods vary, and when the PR interval is greater than the PP interval or equal to the PP interval, or slightly less than the PP interval, it is easily misdiagnosed as other arrhythmias.

(1) When the atrioventricular block is accompanied by sinus or atrial tachycardia, if the PR interval is greater than the PP interval, the sinus P wave needs to cross the next P wave to pass the ventricle, which is called trans-conduction. P wave is called "spanning P wave", which is easily misdiagnosed as 2:1 atrioventricular conduction.

(2) When the atrioventricular block is associated with sinus or atrial tachycardia, if the PR interval is equal to the PP interval, then the P wave overlaps in the QRS wave, and only a series of P waves are not found (or P' wave of supraventricular QRS-T wave group, which is easily misdiagnosed as atrioventricular junction tachycardia or supraventricular tachycardia. If the vagus nerve is stimulated, such as compression of the carotid sinus, the heart rate is slowed down, or injection Atropine speeds up the heart rate and allows P waves (P' waves) to be separated from the QRS complex to determine the diagnosis.

(3) When the atrioventricular block is accompanied by sinus or atrial tachycardia, if the PR interval is slightly smaller than the PP interval, then the P wave appears in the early stage of the mid-systole, that is, the P wave is at the J point. The pre-frontal part of the T-wave peak is easily misdiagnosed as supernormal conduction and pseudo-superconducting (void phenomenon). The difference is that supernormal conduction or pseudo-extra conduction is due to the atrial tachycardia based on sinus tachycardia. Pre-contraction, which occurs in the mid-systolic phase and can be accidentally transmitted underground, while sinus tachycardia (or atrial tachycardia) with one-time atrioventricular block has only one P wave (P' wave), and The PR interval (or P'-R interval) is significantly prolonged.

2. Identification of interfering PR intervals

Pre-expansion contraction can lead to prolongation of PR interval, which is due to occult conduction in the retrograde atrioventricular junction in pre-systolic contraction, and the PR interval or consecutive number of sinus rhythm after pre-systolic contraction The heart-like PR interval is prolonged; when the atrial tachycardia is transmitted to the atrioventricular junction area due to atrial agitation, the area is in a physiological relative refractory period, and the P' wave is often in the previous cardiac T The posterior branch of the wave causes the prolongation of the PR interval, and the above two cases, the so-called atrioventricular interference, prolong the PR interval.

3. Identification of prolongation of PR interval caused by conduction of double pathway in the atrioventricular node

Sometimes the "transient" atrioventricular block that occurs in sinus rhythm is actually the performance of the atrioventricular nodal pathway. At this time, the prolongation of the PR (AH) interval is due to the fast path in the atrioventricular node. Blocking, caused by the conduction of the slow path, sometimes the sinus rhythm is transmitted through the fast path in the atrioventricular node, the next time is through the slow path in the atrioventricular node, and the short and long PR on the electrocardiogram Intervals alternate.

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