high-grade atrioventricular block
Introduction
Introduction to high atrioventricular block High-grade atrioventricular block refers to the atrioventricular block with a ratio of atrioventricular conduction of more than 2:1, which is 3:1, 4:1, 5:1, etc., and the block site can be in the atrioventricular compartment. In the knot, the His bundle and the bundle branch - the Pu's system. High atrioventricular block can be divided into two types according to the block: (1) Type I: mostly occurs at the atrioventricular node level, and a few are blocked at the proximal end of the His bundle. (2) Type II: Both are blocked at the distal end of the His bundle and at the bundle branch. basic knowledge The proportion of illness: 0.14% Susceptible people: no specific population Mode of infection: non-infectious Complications: syncope, angina, hypotension, A-S syndrome, sudden death
Cause
Height atrioventricular block
Many factors can affect the atrioventricular conduction system, the most common being fibrosis and cirrhosis of the conduction system and ischemic heart disease.
Fibrosis hardening of the conduction system (30%):
If the ventricular rate is too slow, especially if the heart has obvious ischemia or other pathological changes, or is complicated by extensive acute myocardial infarction or severe acute myocarditis, the symptoms may be heavier, and heart failure or shock may occur.
Ischemic heart disease (20%):
Or due to lack of blood supply to the brain, the reaction is slow or dizzy, and then develop into syncope (incidence rate of up to 60%), A-S syndrome, due to diastolic ventricular filling and stroke volume increase, pulse pressure may occur Poor widening and mild to moderate heart enlargement.
Pathogenesis:
The blockage of high atrioventricular block can be initially located according to the surface electrocardiogram and clinical features, and the precise positioning depends on the His bundle beam diagram.
1. Characteristics of the block at the atrioventricular node
1 The electrocardiogram shows that the QRS wave of the P-wave can be transmitted to the ventricle is narrow and normal.
2 There is a second-degree I-type Venn phenomenon before the presence of a high degree of atrioventricular block.
3 common in acute inferior myocardial infarction, beta blockers, digitalis poisoning, calcium antagonists caused by high degree of atrioventricular block.
4 High-level conduction block can be converted to 1:1 conduction after intravenous atropine.
2. Characteristics of the block site in the Xi-Pu system
1 The electrocardiogram shows that the QRS wave that can be transmitted is a bundle branch block or a branch block pattern.
2 no history of drug use such as digitalis poisoning, beta blockers and calcium antagonists.
3 Intravenous atropine increased the sinus heart rate, the atrioventricular block was aggravated or unchanged.
Prevention
High degree atrioventricular block prevention
1. Active treatment of the 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 monitoring during cardiac surgery can reduce the incidence of this disease.
3. For patients with high atrioventricular block, different measures are taken according to the block position and the rate of ventricular rate, such as slow ventricular rate, heart rate <40 times / min, and QRS wide and deformed, atrioventricular block Below the His bundle, the drug responds poorly, and an artificial cardiac pacemaker needs to be placed to prevent the occurrence of cardio-cerebral syndrome.
4. Diet has a section, daily life is always, emotional comfort, work and rest, avoiding evil, appropriate physical exercise to enhance physical fitness.
Complication
High atrioventricular block complication Complications, syncope, angina, hypotension, A-S syndrome, sudden death
Patients with high atrioventricular block may have complications such as syncope, angina pectoris, hypotension, A-S syndrome and sudden death due to slow ventricular rate.
Symptom
High degree of atrioventricular block symptoms Common symptoms Fatigue, dizziness, fainting, fainting
Most patients may be asymptomatic or have a feeling of palpitations during rest. During physical activity, they may have palpitations, dizziness, fatigue, chest tightness, shortness of breath, such as ventricular rate is too slow, especially the heart has obvious ischemia or other lesions. Or complicated by extensive acute myocardial infarction or severe acute myocarditis, the symptoms can be heavier, heart failure or shock may occur, or the brain may be unresponsive or confused due to insufficient blood supply to the brain, and then develop into syncope (incidence rate up to 60%) ), A-Syndrome, due to diastolic ventricular filling and stroke volume increase, pulse pressure difference can be widened and mild to moderate heart enlargement.
Examine
Height atrioventricular block
ECG check:
1. Characteristics of electrocardiogram examination of atrioventricular conduction ratio:
(1) There may be various ratios of atrioventricular conduction, generally >2:1, even ratio (such as 4:1, 6:1, 8:1) to odd ratio (such as 3:1, 5:1).
(2) in the presence of arrhythmia: the proportion of the atrioventricular block for the diagnosis of high atrioventricular block should be: A. sinus rhythm, the ratio of atrioventricular conduction should be greater than 2:1; B. atrial tachycardia, room The conduction ratio of the chamber should be above 4:1; C. When the atrial flutter, the ratio of atrioventricular conduction should be above 5:1.
(3) The proportion of the room can be fixed or not fixed: it is rare to be fixed at 6:1 or more.
(4) the proportion of atrioventricular conduction is variable: in the 2:1 atrioventricular conduction or 3:2 Venturi-type atrioventricular block, if there is occult conduction, it can appear in a 3:1 height atrioventricular block. It is indistinguishable from the surface electrocardiogram with a true 3:1 height atrioventricular block caused by a blockade of conduction.
2. The PR interval of the lower transmission: it can be normal or extended, but most of it is fixed or not fixed. This is seen in the P wave appearing in different stages of the relative refractory period (the length of the RP interval is different) and the conduction The degree of delay is different, so that the PR interval is not fixed; the occult conduction or superconducting conduction may not be fixed. In addition, spanning P wave conduction may occur, and even several adjacent transmissions may be seen. The PR interval is gradually extended, similar to the Wen's phenomenon.
3. Can be accompanied or accompanied by escape, escape rhythm:
(1) When there is no escape, the number of P waves is exactly a multiple of the number of QRS complexes, usually 3 or 4 times.
(2) With escape, escape rhythm, escape is mostly atrioventricular junction, ventricular escape is rare, such as continuous escape rhythm, P wave and escape are irrelevant, forming incompleteness Atrioventricular dislocation (Figure 2), ventricular capture or ventricular fusion waves can occur.
4. The RR interval is almost always irregular: because in addition to individual downward pulsations, there is often a crossover or ventricular escape, when there is occult conduction and/or accidental conduction (void phenomenon, Weijinsky phenomenon And superconducting conduction), the RR interval can be unexpectedly irregular, only when the ratio of atrioventricular conduction is constant, and no escape occurs, the RR interval is regular, if different compartment conduction ratios appear alternately (for example, 2 Between 1 and 4:1, there is a pair of beats or pseudo-bi-laws. In addition, ventricular premature contractions also cause ventricular rhythm irregularities.
5. Classification of high atrioventricular block: can be divided into two types according to the block: (1) Type I: mostly occurs at the atrioventricular node level, and a few are blocked at the proximal end of the His bundle. (2) Type II: Both are blocked at the distal end of the His bundle and at the bundle branch.
Diagnosis
High-grade atrioventricular block diagnosis and differentiation
Diagnostic criteria
1. According to clinical history, symptoms and signs.
2. ECG diagnostic criteria
(1) Two or more P-waves that occur in the absence of the ventricle.
(2) Atrioventricular block greater than 2:1.
For the electrocardiogram of the atrioventricular block above the altitude, the P wave should be analyzed one by one, and the phase of the P wave appears. If more than half of the P wave occurs before the ST segment or the T wave peak, the ventricle is not transmitted, and the height can not be diagnosed. Room block, when the ventricular rate is more than 60 times / min, although almost all P waves can not pass down the ventricle, it is not necessarily a high degree of atrioventricular block, because there are often interference factors at work, only in the cardiac cycle During the reaction period, more than half of the P waves were not transmitted, and the diagnosis of high atrioventricular block was confirmed.
Differential diagnosis
1. Identification of high atrioventricular block and complete atrioventricular block: high atrioventricular block has ventricular capture, while third degree atrioventricular block has no ventricular capture.
2. High-level atrioventricular block with supernormal conduction and without abnormal conduction identification: ventricular capture only occurs within a certain range of RR interval, if it is shorter or longer than this range, then P wave Can not be transmitted, this can be determined as a high degree of atrioventricular block with superconducting conduction, and high-ventricular atrioventricular block without superconducting ventricular occlusion is not limited by a certain range of the above RP interval.
3.3:1 high atrioventricular block with 2:1 atrioventricular block or 3:2 ventricle atrioventricular block, 3:1 conduction due to occult conduction identification 2:1 atrioventricular conduction When the block is blocked, the first P wave is transmitted, and the second P wave is blocked at the high position, but the forward occult conduction occurs in the atrioventricular junction area, so that a new one is generated in the upper part of the atrioventricular junction area. Prolonged pathological refractory period, so that the third P wave should be transmitted to the ventricle, but at this time it was not blocked due to obstruction, and it was transformed into a 3:1 atrioventricular block, such as a 3:2 Venturi-type house. The second P wave of the ventricular block should have been transmitted, but because it was not transmitted to the atrioventricular junction at a slow rate, it formed an occult conduction, forming a new refractory period there. The third P wave also failed to be transmitted to the ventricle. Similarly, the second type II 3:2 atrioventricular block can also occur in a 3:1 height atrioventricular block, the above 3:1 conduction due to occult conduction. The 3:1 height atrioventricular block with true blockade of conduction conduction is unrecognizable on the surface electrocardiogram, and it is believed that this 3:1 conduction is less on the same ECG. Health, and mostly second degree atrioventricular block, this 3:1 conduction may be caused by occult conduction, such as 2:1 atrioventricular block with a second degree of lag, should be considered by the second degree Conversion to a 3:1 height atrioventricular block is a true exacerbation of the degree of second block.
4. High atrioventricular block with occult ventricular seizure: although there is no QRS-T wave after a certain P wave, the P wave to the next escape interval (ie, before the escape) is the same as the same time. Other fixed pre-apnea intervals on the electrocardiogram should be prolonged because the P wave fails to pass down the ventricle, but occult conduction is formed in the atrioventricular junction, which causes the latter's escape rhythm to be delayed or inhibited. The next escape is delayed compared to other escapes.
5. Identification of ventricular occlusion with high atrioventricular block with time-differential indoor differential conduction and high atrioventricular block with ventricular premature contraction
(1) The QRS complex of the former is related to the P wave, while the latter is irrelevant.
(2) There is no fixed inter-rational interval between the former, and the latter has a fixed inter-rational interval.
(3) The former QRS wave is a right bundle branch block pattern and has high variability, while the ventricular premature contraction mostly manifests as single-phase or biphasic QRS wave, and the waveform variability is small.
(4) Because the ventricular premature contraction before the escape rhythm of the escape stroke point rhythm, it must also take some time between conduction from the pre-systolic pacing point to the escape stroke point for conduction, so the height of atrioventricular conduction The post-interval of ventricular premature contraction is often slightly longer than an escape cycle, and is incompletely compensated intermittently. However, if the ventricular premature contraction is homologous to ventricular escape, it can be compensated for equal circumference. Intermittently, the interval after capture is often equal to an escape cycle (ie, equal circumference compensation), but the sinus QRS wave may be shifted back due to the prolonged PR interval of the ventricle, and the interval after capture (RR time). Slightly shorter than an escape cycle, this is a sub-perimeter (period) compensation interval.
