sinoatrial block
Introduction
Introduction to sinus conduction block Sinustrial block (SAB) is referred to as sinus block. The tissue surrounding the sinus node is a lesion that causes the arousal of the sinus node to reach the atrium for prolonged or inability to erupt, resulting in 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). basic knowledge The proportion of illness: 0.006% Susceptible people: no special people Mode of infection: non-infectious Complications: syncope, hypotension
Cause
Sinus block
Organic heart disease (38%):
Most of them are seen in patients with organic heart disease. Coronary heart disease is the most common cause, accounting for about 40%. Due to myocardial ischemia, organic damage around the sinus node, acute inferior myocardial infarction, the incidence of sinus block 3.5%, much less than sinus bradycardia, the cause of which may be secondary to increased vagal tone, and sinus node ischemia or infarction is also common, in addition, also seen in hypertensive heart disease, rheumatic heart Disease, cardiomyopathy, congenital heart disease, chronic inflammation or ischemia-induced sinus node and surrounding tissue lesions.
Drugs (18%):
Many drugs can cause disease: (such as digitalis, quinidine, verapamil, propiamine, amiodarone, beta blockers, etc.) poisoning and high doses of propafenone can also cause, but more For the temporary.
Hyperkalemia and other diseases (15%):
Hyperkalemia, hypercapnia, diphtheria, flu, etc.
1. Degenerative sclerosis, fibrosis, adipose or amyloidosis in the sinus node area.
2. A healthy person who can be seen with increased vagal tone or carotid sinus allergy can be confirmed by atropine test.
3. A few reasons are unknown, and individual can be familial.
4. It is rare to be caused by intravenous bolus injection of magnesium sulfate (cannot be ruled out because the injection speed is too fast), hypokalemia (<2.6mmol / L = can also occur.
5. A small number of atrioventricular block can occur at the same time, showing progressive aggravation, called double knot syndrome.
Pathogenesis
Because the evoked potential of the sinus node is very small, it can not be traced on the surface electrocardiogram. Only the sinus node can be recorded. The sinus node is excited to pass through the sinus junction to the surrounding atrial muscle, making the atrium The muscle depolarization produces atrial wave, ie sinus P wave, in order to indirectly measure the activity of the sinus node. The sinus block is different from the sinus arrest. The sinus node is still on time and regularly excites, but excited. When passing from the sinus junction to the atrial muscle, conduction delay or non-transmission occurs, which is an efferent block. The former shows once and second degree I sinus block, and the latter is a second degree II sinus. Block or third degree sinus block.
Prevention
Sinus block prevention
Prognosis strengthens exercise.
If the sinus block is accidental, the multi-line vagal tone is increased, and the frequent or long-lasting time is mostly caused by organic. The ventricular rate is greater than 50 times / min, the duration is short, no syncope, no A-S syndrome, the general prognosis is good. Such as elderly or advanced heart disease patients with frequent or persistent sinus block, such as no escape rhythm, A-S syndrome can occur, poor prognosis.
Complication
Sinus block complication Complications, syncope, hypotension
If the sinus conduction block is repeated or lasts for a long time, complications such as syncope, hypotension, and A-S syndrome may occur.
Symptom
Sinus block symptoms Common symptoms Fatigue heart beat sinus block block Dizziness conduction block coma Incomplete atrial block sinus 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 leakage, and no escape, there may be dizziness, syncope, coma, A-S syndrome. In addition, there are clinical manifestations of the primary disease.
Once sinus blockade is characterized by prolonged sinus conduction time, difficult to diagnose on the surface electrocardiogram; second degree sinus block can be diagnosed according to history, symptoms and electrocardiogram; third degree sinus block is sinus P The wave disappears and it is difficult to distinguish it from sinus arrest.
Examine
Sinus block
Mainly relying on the diagnosis of electrocardiogram, sinus conduction block can be divided into one degree, second degree, height, and third degree sinus conduction block according to the characteristics of electrocardiogram. It can also be used for routine blood tests, urine routines, and routine examinations.
Once sinus conduction block
Once sinus conduction block is the extension of the conduction time from the sinus node to the heart chamber. Since the potential of the sinus node is too small to be displayed on the electrocardiogram, the sinus conduction time is naturally not measured. It is only possible to make a diagnosis if the moment when the sinus block is suddenly disappeared.
2. Second sinus conduction block
Second-degree sinus block is also known as second-degree sinus block or sinus block-type sinus block. The sinus room phase (SP interval) refers to the time when the sinus node (S) is transmitted to the surrounding atrial muscle (P) through the sinus junction, also known as sinus conduction time (SP conduction time). However, the conduction of the sinus junction can not be compared with the PR interval of the atrioventricular block, and the second degree I sinus block is only analyzed by the PP interval.
3. High sinus conduction block
It means that 2 or more sinus agitation cannot be transmitted to the atria.
4. Third degree sinus block (complete sinus block)
It means that the sinus agitation is blocked in the sinus junction area and cannot be transmitted.
5. Second degree II sinus block combined with first sinus block
Second degree type II sinus block is in complete complete lag. The sinus junction area is improved due to rest. The sinus agitation of the original sinus conduction block was shortened by the time of the sinus junction. The long PP interval of the second degree II sinus block is twice as long as the short PP interval; while the first sinus block is combined, the long PP interval is shorter than 2 times the PP interval. , can be diagnosed as second degree II sinus block combined with first sinus block.
Diagnosis
Diagnosis and identification of sinus conduction block
Once sinus blockade is characterized by prolonged sinus conduction time, difficult to diagnose on the surface electrocardiogram; second sinus block is confirmed according to history, symptoms and electrocardiogram; third degree sinus block is sinus P The wave disappears and it is difficult to distinguish it from sinus arrest.
Differential diagnosis
1. Second degree I sinus block and sinus arrhythmia
Because of the different lengths of PP in the variant Venturi sinus block, it is sometimes difficult to distinguish from sinus arrhythmia, which can be identified according to the following points:
(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) When the sinus arrhythmia is abnormal, the PP interval is related to respiration, which is characterized by gradually shortening and gradually prolonging. However, this type of conduction block PP interval has a certain regularity and is gradually shortened. Short the long interval of the PP interval.
2. Differential diagnosis of second degree II sinus block and 3:2 second degree type I sinus block
Both the short PP interval and the long PP interval may occur alternately, but the long PP interval of the second type I 3:2 sinus block is less than twice the short PP interval; and 3:2 The PP interval of the type 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 PP interval between the sinus pre-contraction and the second interval is not twice as long as the short PP interval, and the PP interval between the 2:2 sinus block and the second-degree II interval is exactly twice that of 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, which was not related to the respiratory cycle. When the sinus arrhythmia was abnormal, the PP interval was gradually shortened and gradually extended, which was related to the respiratory cycle. The gas is short and the exhalation time is long.
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, but in high sinus conduction block, regardless of resistance The degree of stagnation, the long PP interval is always an integral multiple of the short PP interval, and the long PP interval of equal length can be repeated, and the low rhythm is often suppressed during sinus arrest. Under the sinus conduction block, the cardiac arrest is too long, 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, but atrial escape rhythm is not necessarily sinus conduction block, sinus conduction block does not necessarily have atrial escape rhythm, 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 second or second sinus Atrial block is diagnosed as a third degree sinus block.
7. Three-degree sinus conduction block and sinus conduction
There are the following points:
(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.
