Sinoatrial block

Introduction Sinus block is abbreviated as sinus block, which is caused by tissue lesions around the sinus node. The time when the sinus node is excited to reach the atrium is prolonged or cannot be transmitted, leading to atrial ventricular arrest. Sinus block can occur temporarily and can persist or recur. Patients with sinus block are often asymptomatic, but also have mild palpitations, fatigue, and "leakage". Cardiac auscultation can detect arrhythmia, bradycardia, and "leakage" (long interval). If repeated episodes or prolonged blockade, continuous heartbeat skipping can occur, and there is no escape (when the high heart pacemaker delays or stops issuing impulses, the low pacing point instead triggers the impulse and excites the heart) , can appear dizziness, syncope, coma, A-S syndrome. In addition, there are clinical manifestations of the primary disease.

Cause

Increased vagal tone and carotid sinus allergy, acute inferior myocardial infarction, cardiomyopathy, digitalis or quinidine poisoning, hyperkalemia and other even and objective sinus block.

1. Most of the patients with organic heart disease are the most common cause of coronary heart disease, accounting for about 40%, due to myocardial ischemia leading to organic damage around the sinus node. Acute inferior myocardial infarction, the incidence of sinus block is 3.5%, much less than sinus bradycardia, the cause of which may be secondary to increased vagal tone, and sinus node ischemia or infarction common. In addition, it is also seen in hypertensive heart disease, rheumatic heart disease, cardiomyopathy, congenital heart disease, chronic inflammation or ischemic sinus node and its surrounding tissue lesions.

2. Hyperkalemia, hypercapnia, diphtheria, flu, etc.

3. Degenerative sclerosis, fibrosis, adipose or amyloidosis in the sinus node area.

4. Drugs (such as digitalis, quinidine, verapamil, propiamine, amiodarone, beta blockers, etc.) poisoning and high doses of propafenone can also be caused, but mostly temporary of.

5. A healthy person who can be seen with increased vagal tone or carotid sinus allergy can be confirmed by atropine test.

6. A few reasons are unknown, and individual can be familial.

7. It is rare to be caused by intravenous bolus injection of magnesium sulfate (cannot be ruled out because the injection speed is too fast), and hypokalemia (<2.6mmol/L) can also occur.

8. A small number of atrioventricular block can occur at the same time, showing progressive aggravation, called double knot syndrome.

an examination

Mainly rely on the diagnosis of electrocardiogram. According to the characteristics of electrocardiogram, sinus conduction block can be divided into first degree, second degree, height and third degree sinus conduction block.

Because the surface electrocardiogram does not show sinus node electrical activity, the diagnosis of first sinus block is not established. The third degree of sinus conduction block is difficult to distinguish from sinus arrest, especially when sinus arrhythmia occurs. The second degree of sinus conduction block is divided into two types: Mohs type I, ie, Wen's block, which shows that the PP interval is progressively shortened until a long PP interval occurs, which is shorter than the basic PP interval. At twice the duration, this type of sinus block should be differentiated from sinus arrhythmia. In the case of Mohs type II block, the long PP interval is an integral multiple of the basic PP interval. The sinus conduction resistance lag can occur with escape or escape rhythm.

Differential diagnosis

Differential diagnosis of sinus conduction block :

1. Second degree I sinus block and sinus arrhythmia identification Because of the different lengths of PP in the variant Venturi sinus block, sometimes it is difficult to distinguish from sinus arrhythmia. According to the following points can be identified:

(1) It must be the sinus agitation cycle calculated by the Venturi period: the ladder diagram of the PP period similar to the Venturi period that occurs in each lead of the ECG is roughly consistent with the diagnosis. This type of sinus conduction block.

(2) The Venturi cycle begins and ends.

(3) During the sinus arrhythmia, the PP interval is related to respiration, and it is gradually shortened and gradually extended. However, this type of conduction block PP interval change has a certain regularity, which is gradually shortened. Finally, there is a long interval of nearly 2 times short PP interval.

2. The second degree II sinus block and the 3:2 second degree type I sinus block can be identified as short PP interval and long PP interval alternately, but second degree I 3: 2 The long PP interval of sinus conduction block is less than 2 times of the short PP interval; and the PP interval of 3:2 second degree II sinus block is twice as long as the short PP interval. .

3. Identification of second degree II sinus block and sinus premature contraction

The sinus pre-contraction dichotomous length PP interval is not twice as long as the short PP interval. The 3:2 sinus block 2nd type II long interval PP interval is exactly twice the sinus PP interval.

4. Differential diagnosis of second degree III sinus block and sinus arrhythmia

The difference was that the PP interval of the second degree III sinus block was suddenly shortened and suddenly prolonged, regardless of the respiratory cycle. When the sinus arrhythmia is irregular, the PP interval is gradually shortened and gradually extended, which is related to the respiratory cycle, short in inhalation, and long in exhalation.

5. High sinus conduction block and sinus arrest

There is no obvious regularity in sinus arrest. There is no fold relationship between the length and length of the PP interval, and sinus arrest with equal interval between strokes is rare in an electrocardiogram. In the case of high sinus conduction block, the long PP interval is always a multiple of the short PP interval regardless of the degree of block. Moreover, long PP intervals of equal length can be repeated. In the sinus arrest, the low rhythm is often suppressed, and it is generally not easy to escape. In the case of high sinus conduction block, the cardiac arrest is too long, and it is often prone to atrioventricular transitional escape and escape rhythm or ventricular escape, ventricular escape rhythm.

6. Identification of third degree sinus block and persistent sinus arrest

Third-degree sinus conduction block sometimes has atrial escape rhythm or escape; sinus arrest has more atrial escape or escape rhythm, which is a pathological factor that inhibits the autonomicity of sinus node and inhibits Atrial ectopic pacemaker. However, those with atrial pacing rhythm are not necessarily sinus conduction blocks. Sinus conduction block does not necessarily have atrial escape rhythm, and identification is very difficult at this time. In dynamic electrocardiogram or ECG monitoring, if a transient or longer sinus arrest occurs before the P wave is seen for a long time, it can be diagnosed as sinus arrest; if there has been a first or second sinus Conduction block can be diagnosed as a third degree sinus block.

7. The third degree of sinus conduction block and sinus conduction are identified as follows:

(1) Sinus block can have atrial escape rhythm, while the latter does not.

(2) The sinus block is mostly based on the heart rhythm of the atrioventricular junction, so the QRS wave is mostly supraventricular, while the latter is more wide and deformed.

(3) The latter is often accompanied by high-point T waves caused by hyperkalemia, while the former is absent.

(4) If there is an increase in serum potassium, or clinically known to cause hyperkalemia, the formation of diffuse complete intraventricular block often leads to sinus conduction, but less on the sinus node.

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