Sinus bradycardia

Introduction to sinus bradycardia Sinus rhythm is slower than 60 times per minute called sinus bradycardia. Can be seen in healthy adults, especially athletes, the elderly and when sleeping. Other causes are increased intracranial pressure, hyperkalemia, hypothyroidism, hypothermia, and the use of digitalis, beta blockers, reserpine, guanethidine, methyldopa and other drugs. In organic heart disease, sinus bradycardia is visible. Most of the sinus bradycardia caused by extracardiac factors is accompanied by vagus nerve hyperactivity, which is neurotic and the heart rate is not stable. When the autonomic nervous tension changes, such as deep breathing, exercise, injection of atropine, etc., there is often a change in heart rate, and the PR interval may be slightly prolonged. basic knowledge The proportion of illness: 0.001% Susceptible people: no specific people Mode of infection: non-infectious Complications: syncope, angina

Cause of sinus bradycardia

Extracardiac factor (25%):

Most of them pass the nerve (mainly vagus nerve excitability), the body fluid mechanism acts through the extracardiac nerve, or directly acts on the sinus node to cause sinus bradycardia. The sinus bradycardia caused by extracardiac factors, the vast majority of patients with vagal hyperthyroidism, is neurological, heart rate is not very stable, when the autonomic nervous tension changes, such as deep breathing, exercise, injection of atropine, etc. often have heart rate The change in the PR interval can be slightly extended.

Injury of sinus node function (20%):

Refers to sinus bradycardia caused by damage to the sinus node (such as inflammation, ischemia, poisoning or degenerative damage), in addition, can be seen in myocardial damage, such as myocarditis, pericarditis, endocarditis , cardiomyopathy, myocardial infarction, myocardial sclerosis, etc., may also be caused by transient sinus node inflammation, ischemia and toxic damage.

Acute myocardial infarction (25%):

The incidence of sinus bradycardia is 20% to 40%, and the incidence rate is highest in the early stage of acute myocardial infarction (especially inferior wall infarction).

Vagus nerve excitement (15%):

Most of them act through the nerve (mainly vagus nerve excitability), the body fluid mechanism through the extracardiac nerve, or directly affect the sinus node and cause sinus bradycardia.

Pathogenesis

The occurrence of sinus bradycardia is due to the slowing of the 4-phase rise rate of sinus node pacemaker cells, the increase of the maximum diastolic potential, the increase of the threshold potential level, and the decrease of the sinus node self-discipline intensity.

Sinus bradycardia prevention

1. Active prevention and treatment of primary disease and timely elimination of primary causes and incentives are the key to preventing the occurrence of this disease.

2. Sick sinus syndrome, such as ventricular rate <50 times / minute, and hemodynamic changes are obvious, when the heart, brain and other important organs are insufficient blood supply, artificial heart pacemaker should be placed in time to prevent heart and brain synthesis The occurrence of levy and sudden death.

3. Use drugs that slow heart rate and heart conduction with caution. The application of such drugs should strictly control the indications and doses, avoid excessive and misuse, and disable digitalis preparations for patients with sick sinus and atrioventricular block. Receptor blockers and other antiarrhythmic drugs that significantly slow heart rate.

4. Pay attention to the conditioning of life and emotions. There should be a diet, a regular life, and no work.

Sinus bradycardia complications Complications syncope angina

If the rate of ventricular tachycardia is too slow and there is an organic heart disease, dizziness, syncope, angina and other complications may occur.

Symptoms of sinus bradycardia common symptoms delayed pulse chest tightness vagus nerve tension increased syncope shortness tachycardia dizziness tachycardia fatigue

Most sinus bradycardia, especially those caused by neurological factors (increased vagal tone), are 40 to 60 beats/min. Because hemodynamic changes are not significant, they can be asymptomatic. There is no important clinical significance. If it is not significant sinus bradycardia, the other side of the bradycardia is to reduce myocardial oxygen consumption, increase myocardial rest time, and good ventricular filling, so the cardiac stroke output increases, and the compensatory heart rate decreases. Therefore, the cardiac output per minute is not reduced, but when the heart rate continues to decrease significantly, the heart's stroke output can not increase, the cardiac output per minute is reduced, coronary artery, cerebral artery and kidney Arterial blood flow is reduced, which can manifest shortness of breath, fatigue, dizziness, chest tightness and other symptoms. In severe cases, syncope may occur, and patients with coronary heart disease may have angina pectoris, which is more common in organic heart disease.

Continuous and significant slowing of heart rate also makes ventricular ectopic rhythm easy to produce. Patients with organic heart disease, especially those with acute myocardial infarction, are prone to occur because of the increased potassium concentration of extracellular fluid and negative cell membrane potential during acute myocardial infarction. Decreased, ventricular ectopic pacemaker is prone to auto-diastolic depolarization, prone to ventricular premature contraction or ventricular tachycardia, due to bradycardia, myocardial cell repolarization time is inconsistent, and the potential between adjacent cells is not equal. It is easy to produce a potential difference, which can also cause ectopic rhythm.

1. Sinus P wave: frequency <60 times / min, generally not less than 40 times / min, 24h dynamic electrocardiogram sinus heart rate <80,000 times.

2. PR interval: 0.12 ~ 0.25s.

3. The QRS wave is normal.

Sinus bradycardia check

The characteristics of laboratory tests related to primary disease that cause bradycardia can be seen.

Relying on ECG, there are the following performances:

1. The sinus P wave form sinus bradycardia and sinus tachycardia have a large difference in P wave morphology. This is due to the sinus bradycardia when the sinus node is at the tail of the sinus node. The sinus tachycardia is usually located in the head, and the pacing point of the sinus node is mostly located in the head. The sensation is often transmitted along the anterior internode. Although the head and tail of the sinus node are only 15mm apart. However, due to the characteristics of preferential conduction between the internodes, the sinus P wave morphology of the two is different. The P wave of the II and III leads is slightly lower than the P wave of the normal sinus rhythm.

2. The frequency of sinus P wave should be <60 times/min, usually 40~59 times/min, more than 45

More than /min, there are also slow to 35 times / min or even 20 times / min report, <45 times / min for severe sinus bradycardia, infant heart sinus bradycardia heart rate, in 1 year old or younger should be <100 times/min, 1 to 6 years old should be <80 times/min, and 6 years old or older should be <60 times/min.

3. The PR interval is 0.12 to 0.25 s.

4. QRS wave is followed by a normal QRS wave after each P wave, and the shape and time limit are normal.

5. T wave, u wave sinus bradycardia is normal, but also can show T wave amplitude is low, u wave is often more obvious.

6. The QT interval of QT interval is prolonged proportionally, but the Q-Tc interval after correction is within the normal range. Normal Q-Tc=QT(s)/ should be 0.42s.

Diagnosis and diagnosis of sinus bradycardia

Differential diagnosis

Second degree sinus block

When 2:1, 3:1 sinus block occurs, the heart rate is very slow, similar to sinus bradycardia, both can be identified according to the following methods, after atropine injection or physical activity (can do underarm, get up and exercise) The sinus heart rate of sinus bradycardia can be gradually accelerated, and the increased heart rate is not multiplied by the original heart rate; while the heart rate of sinus block can be suddenly doubled or multiplied, and the sinus block disappears. .

2. Unsuccessful atrial contraction

The pre-atrial contraction P' wave that is not transmitted is generally easier to identify. When the P' wave is superimposed on the T wave, it is not easy to distinguish. It can be mistaken for sinus bradycardia. The identification points are:

(1) Careful observation reveals that the TP' mixed wave is different from the other T waves.

(2) It is possible to find a P' wave that has not been transmitted from the lead of the T wave low level.

(3) When the electrocardiogram is recorded, the voltage (gain) can be increased: the paper feed speed is increased to 50 to 100 ms, and the P' wave superimposed on the T wave can be revealed.

3. 2:1 atrioventricular block

In the case of 2:1 atrioventricular block, since the P wave that has not been transmitted can overlap in the T wave, the T wave shape is broadened, sharpened, notched, inverted, bidirectional, etc., or the P wave is The u wave is ignored, and the sinus bradycardia is mistaken for its discriminating point.

(1) A closer observation reveals that the TP mixed wave is different from the other T waves:

(2) When the electrocardiogram is recorded, the voltage (gain) can be increased, the paper feed speed is increased to 50 to 100 ms, and the P wave superimposed on the T wave can be revealed.

(3) After injecting atropine or changing the heart rate, the P wave overlapping in the T wave can be revealed and can be distinguished from the u wave.

4. Atrial escape rhythm

Atrial rhythm is less common, and its P' wave morphology is significantly different from that of sinus rhythm. However, if the atrial escape point is close to the sinus node, its P' wave and sinus P wave are in the shape. It is not easy to distinguish, the identification points are:

(1) Atrial escape rhythm usually lasts for a short time. Exercise or injection of atropine can accelerate the sinus heart rate, and the atrial escape rhythm disappears.

(2) atrial escape rhythm rules, and sinus bradycardia is often accompanied by sinus arrhythmia.

The material in this site is intended to be of general informational use and is not intended to constitute medical advice, probable diagnosis, or recommended treatments.