Age is an important factor affecting the incidence of heart block, especially in elderly patients with organic heart disease. Gender itself has little effect on heart block, and a few congenital atrioventricular block have family genetic tendency. Sinus atrial block is more common in elderly patients with organic heart disease, sinus and coronary heart disease. Atrioventricular block is mainly seen in left atrial hypertrophy or enlargement caused by various reasons, such as rheumatic mitral stenosis, primary cardiomyopathy, etc. It is also common in acute and chronic ischemic atrial infarction of atrial muscle, hyperkalemia or quinidine and other drugs. In addition, atrial muscle is blocked by degenerative diseases such as fibrosis, fat infiltration or amyloidosis, especially coronary heart disease.

pathogenesis

1. Sick sinus syndrome related sick sinus syndrome See arrhythmia in the elderly.

2. Intra-atrial conduction block refers to the extension or interruption of impulse conduction time from atrial sinoatrial node, which can be divided into two types: incomplete conduction block and complete conduction block.

(1) Incomplete atrial block: It is mainly seen in left atrial hypertrophy or enlargement caused by various reasons, such as rheumatic mitral stenosis and primary cardiomyopathy. It is also common in acute and chronic ischemic atrial infarction, hyperkalemia or quinidine of atrial muscle. In addition, atrial muscle can also lead to prolonged atrial conduction time due to degenerative diseases such as fibrosis, fat infiltration or amyloidosis.

(2) Complete intra-atrial conduction block (atrial separation): refers to complete conduction block between left and right atria or between one part of atria and other parts. At this time, both sides of the atrium or two parts of an atrium are controlled by a pacing point respectively.

In heart block, atrioventricular block (AVB) is the most common one. It refers to the phenomenon that when the atrium enters the ventricle under excitation, the atrial conduction is delayed or partially or even completely unable to descend due to pathological conduction disorder in one or more parts of the atrioventricular conduction system. There are also some functional atrioventricular block with transient changes, which do not belong to the category of pathological conduction disorder.

3. Pathological basis of atrioventricular block Most atrioventricular block has the pathological basis of organic heart, which is generally divided into two categories:

(1) Congenital atrioventricular block: This type is more common in children. It is pointed out that conduction block found at birth or shortly after birth can be mild to onset in old age, and the symptoms are aggravated by aging of conduction tissue. The blocking site is mostly in the atrioventricular junction. The normal ventricular rate of QRS syndrome is 45 ~ 80 beats/min, which is mostly caused by congenital heart disease or conduction system dysplasia.

(2) Acquired atrioventricular block: acute and chronic atrioventricular block.

① Acute atrioventricular block: The common diseases are acute myocardial infarction and myocarditis. Inferior myocardial infarction is easy to be complicated with atrioventricular block due to anatomical reasons. It is transient and can recover on its own. The atrioventricular block caused by anterior myocardial infarction is mostly low-level block, and the mechanism of atrioventricular block caused by inferior myocardial infarction may be related to the following comprehensive factors:

A. temporary ischemia and hypoxia of atrioventricular node

B. local potassium ion accumulation.

C. increased vagal tone.

D atrioventricular node edema and inflammatory infiltration after infarction lead to conduction block.

E negative conduction of ischemic metabolites leads to heart block, and atrioventricular block caused by viral myocarditis is not easy to disappear.

② Chronic atrioventricular block: The most common causes are idiopathic bundle branch fibrosis, chronic myocardial ischemia, cardiomyopathy and calcification of conduction system. The essence of idiopathic bundle branch fibrosis is the gradual fibrosis of conduction system. Although many patients have left ventricular hypertrophy or focal scar, their myocardium is basically unaffected. So this disease is characterized by atrioventricular conduction disorder rather than heart failure.

9 Clinical manifestations

symptom

The symptoms of patients with atrioventricular block are not only affected by the original heart disease and cardiac function, but also depend on the degree and location of block.

(1) Asymptomatic: This type of atrioventricular block has a good prognosis. Second degree type I atrioventricular block or some chronic intermittent atrioventricular block.

(2) Symptoms: In second-degree type II atrioventricular block, if the proportion of blocked atrial waves is large (such as atrioventricular 3∶2 conduction), especially in high-degree atrioventricular block, the symptoms of third-degree atrioventricular block, such as bradycardia, dizziness, chest tightness, shortness of breath and decreased cardiac function, are obvious due to the decrease of ventricular rate, and its hemodynamic impact depends on the speed of escape frequency of the third-degree atrioventricular block above the bifurcation of His bundle, which has a negative impact on blood flow. The low third degree atrioventricular block below his bundle bifurcation has a significant effect on hemodynamics. Patients may have syncope, cardiogenic hypoxia syndrome and even sudden death.

(3) The symptoms are atypical. Some patients have some atypical symptoms, such as general weakness or hypotension. Further examination is needed to confirm the diagnosis.

Pathology/physical signs

(1) Some patients with first degree atrioventricular block may have no signs.

(2) First degree atrioventricular block: Physical examination showed that the first heart sound at apex was weakened. This is due to the delay of ventricular contraction, which makes the blood of the heart more full. Before closing, the atrioventricular valve has floated near the closing point, so the tension of the valve leaves is low when closing, and the vibration caused by closing is small.

(3) Second degree atrioventricular block: Venn's second degree atrioventricular block, the auscultation of the heart was intermittent, but there was no premature beat before the interval. The intensity of the first heart sound can change with the change of PR. The second degree Ⅱ atrioventricular block may have intermittent missed beats, but when the intensity of the first heart sound is constant and the atrioventricular conduction is 3∶2, auscultation can be similar to the binary law of the formation of paired premature beats.

(4) Third-degree atrioventricular block: Its specific sign is that the ventricular rate is slow and regular, accompanied by the unequal strength of the first heart sound, especially the sudden increase of the first heart sound, that is, "guns". The second heart sound can be divided into normal or abnormal, such as atrial contraction and ventricular contraction at the same time, and a huge "A" wave appears in jugular vein.

Electrocardiogram and its clinical significance

(1) Sinus-atrial block: Because the tissues around the sinus node can't make the excitement of the sinus node spread outward as usual, the time for the excitement to reach the atrium is prolonged or can't reach the atrium, resulting in atrial-ventricular arrest, which is called sinus-atrial block, with one or two degrees.

① First degree atrioventricular block: The surface electrocardiogram can't show the sinus node potential, and the diagnosis of first degree atrioventricular block can't be established.

② Second degree atrioventricular block:

A.I type, namely Venn's block, is characterized by progressive shortening of P-P until a long P-P interval appears, which is twice as short as the basic P-P interval.

B. Type II conduction block: This type is characterized by no gradual prolongation of the conduction time of the sinus node. The ECG shows that the P-P interval before atrial leakage is constant, and the long P-P interval including atrial leakage is just a multiple of the short P-P interval.

③ Third-degree sinus block: All the excitement of sinus node can't be transmitted to atrial electrocardiogram without sinus P wave.

Clinical manifestations: Sinus atrial block is more common in organic heart disease. The most common causes of the elderly are sick sinus node and coronary heart disease. First degree sinus atrial block has no clinical symptoms. The severity of clinical symptoms depends on the influence on hemodynamics. If there is no escape rhythm in the third degree sinus atrial block, cardiac arrest may occur.

(2) Intra-atrial conduction block: When the excitation of sinoatrial node is conducted to the atrium, the conduction delay will widen and increase the P wave.

① Incomplete intra-atrial block:

A. The broadening time of P-wave is ≥0. 12s, and the notch is obviously often manifested as frustration and towering of P-wave.

B. Intermittent high-pitched P waves at regular P-P intervals have nothing to do with breathing, and there is no cause of lung disease, which is mostly caused by right atrial block.

② Complete intra-atrial block:

A.p wave disappears, QRS complex is widely deformed, and T wave is symmetrical and towering.

B. The ventricular rate is slow, about 60 beats/min.

C. seen in hyperkalemia

Atrioventricular block

Atrioventricular block refers to the conduction disorder between atrioventricular conduction systems, which is a pathological phenomenon.

① First degree atrioventricular block (atrioventricular conduction delay): A.P-R interval ≥0.2 1s (adult). B. The dynamic change of P-R interval in the same patient is ≥0.04s (the heart rate has no obvious change). C. P'-R interval connecting heart rate >; 0. 16 seconds. D.P-R interval exceeds the normal maximum of corresponding heart rate (Figure 1).

Characteristics of electrophysiological examination:

② In patients with first-degree atrioventricular block, QRS wave does not widen, and conduction delay mostly occurs when A-H time or even H-V time of atrioventricular node electrophysiological examination is prolonged, and it can also be manifested as first-degree atrioventricular block. If patients have atrioventricular block and bundle branch block at the same time, any part of the conduction system will be blocked, but H-V prolongation is more common in left bundle branch block.

③ Second degree atrioventricular block can be divided into second degree type I and second degree type II atrioventricular block:

Second degree type I atrioventricular block (Venturi phenomenon);

Electrocardiogram: a.P-R interval is gradually prolonged until ventricular leakage occurs; B. the gradual decrease of P-R P-R interval leads to the gradual shortening of P-R interval; C. The first P-R interval was normal after ventricular leakage, and the second P-R interval increased the most; D the long P-R interval with ventricular leakage is less than 2 times of the short P-R interval.

B second degree type ⅱ conduction block (also known as Mohs type ⅱ): it is less common than Venn's phenomenon. Electrocardiogram showed that P wave could not be transmitted periodically and suddenly, resulting in ventricular leakage, and all P-R intervals before and after shedding were constant, which could be normal or prolonged. The long P-R interval with ventricular leakage is only a multiple of the short P-R interval.

Electrophysiological examination: In patients with type I atrioventricular block of degree II, if QRS wave is not widened, the block usually occurs in atrioventricular node, and the AH time is gradually prolonged until a long gap appears, and occasionally his bundle block occurs. You can see that the H-wave splitting gradually extends and falls off. At this time, the first part of A wave can distinguish whether the block occurs in atrioventricular node or his bundle without the second part of H wave. After atropine injection, his conduction block will be more serious. However, after massaging the carotid sinus, the block in his nerve bundle was relieved. If it happens above the block of atrioventricular node, the stimulation result is just the opposite. If atrioventricular block is combined with bundle branch block, the block may occur in atrioventricular node, 75% of cases occur in atrioventricular node, and 25% occur in atrioventricular node (Figure 2).

④ Third degree atrioventricular block (complete atrioventricular block).

Electrocardiogram manifestations: ① uniform atrial rate, uniform ventricular rate (P wave) > ventricular rate (QRS wave) is usually lower than 60 beats/min. P wave has nothing to do with QRS wave. ② The shape of ②QRS complex is related to the blocking position, and the ventricular rhythm point is generally not widened, and the performance is stable, with a frequency of 40 ~ 60 beats/min. The QRS complex wave in the ventricle is wide and deformed, with a low frequency of 30 ~ 40 beats/min. The performance is unstable (Figure 3).

Complications: The elderly with severe heart block may have syncope, cardiogenic syndrome and even sudden death.

10 diagnosis

It is not difficult to make a diagnosis according to the typical ECG changes and clinical manifestations. In order to estimate the prognosis and determine the treatment plan, it is necessary to distinguish between physiological and pathological atrioventricular block, atrioventricular bundle branch block, three-branch block and block degree.

Differential diagnosis:

Prolonged PR interval of individual or a few heartbeats or ventricular leakage are mostly caused by physiological conduction block, such as premature escape of atrial intercourse, junctional premature beats of bidirectional block, ventricular capture, repeated heartbeat and other hidden conduction of ventricular premature beats (impulses return to atrioventricular node but not to atrium, so there is no reverse P wave); The atrioventricular node tissue is in refractory period due to conduction impulse, so the next impulse block is also physiological conduction block. In addition, when the atrial rate of supraventricular tachycardia exceeds 180 beats/min, it is accompanied by atrioventricular block, and atrial fibrillation is another manifestation of physiological block. Interference atrioventricular separation should be carefully distinguished from atrioventricular separation caused by complete atrioventricular block, and the ventricular rate is mostly slightly higher than the atrial rate. The latter ventricular rate is slower than atrial rate.

1 1 case study

Intravenous application of cimetidine is a common method to treat duodenal ulcer complicated with upper gastrointestinal bleeding, but it may cause heart block, which should be paid attention to.

clinical data

There were 3 males and 0 females, ranging in age from 54 to 73 years, with an average of 63 years. Have a history of coronary heart disease for 3 ~ 7 years. It's all because of black manure. After admission, fecal occult blood (++) ~ (++++), gastroscopy report showed duodenal ulcer activity, electrocardiogram showed sinus rhythm, and S-T segment was depressed by about 0.5 millivolts. There is no discomfort such as chest tightness, palpitation and dizziness in clinic, and blood pressure is normal. Cimetidine 0.8g each time, plus 500ml liquid intravenous drip, 1 time/day. 1 case experienced chest tightness, palpitation and dizziness during exercise three days later. Two cases developed similar symptoms five days later. 1 case felt chest tightness, palpitation and headache after seven days. The symptoms of 4 cases were relieved when they were lying flat, and their blood pressure was basically the same as when they were admitted to hospital. Electrocardiogram showed that there was no significant change in S-T after I degree atrioventricular block. The symptoms disappeared within two to three days after stopping cimetidine rehydration and taking Losec orally, and the atrioventricular block of ECG disappeared for a time.

discuss

Cimetidine is the first generation of H2 receptor blocker, which has been used for intravenous injection to treat upper gastrointestinal bleeding caused by ulcer for many years and achieved good results. Common cardiovascular complications include bradycardia, atrioventricular block and blood pressure drop. According to FDA statistics, about10.6 cases of serious cardiovascular adverse reactions were found in10.00 million prescriptions. I-degree atrioventricular block in hospital is not a serious arrhythmia, but the incidence is high, accounting for nearly 1% of patients taking drugs at the same time, which may be due to the existence of coronary heart disease. In the same period, more than 400 patients without coronary heart disease did not have atrioventricular block. Dreal et al. reported that 7 patients with conduction system disorder showed headache, palpitation and dizziness after treatment with cimetidine. The information in our hospital is similar. According to Liu Fuyuan's observation and research, it is considered that after cimetidine treatment, the cardiac H2 receptor is blocked, and the activity of H 1 receptor is increased, which prolongs the atrioventricular conduction time and leads to atrioventricular block.

conclusion

Intravenous use of cimetidine can cause complications of heart block, which rarely occur in patients without heart disease basis, but the incidence rate is significantly increased in patients with heart disease basis (such as coronary heart disease). If the drug is stopped immediately after I-degree atrioventricular block is found in time, no special treatment is needed, the symptoms will disappear automatically within two to three days, and the electrocardiogram will turn normal.

12 Prognostic prevention

prognosis

The first and second degree type I atrioventricular block is asymptomatic and generally has a good prognosis. The heart rate of third degree atrioventricular block is slow and unstable, which is prone to ventricular arrest. Therefore, the mortality rate is high and the prognosis is poor.

prevent

The causes of cardiac block in the elderly should be clearly defined and actively treated. For severe symptoms related to syncope, bradycardia or cardiac arrest, pacemakers must be installed immediately.