What Is Junctional Bradycardia?

Sinus rhythm is slower than 60 times per minute and is called sinus bradycardia. It 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.

Basic Information

English name: sinus bradycardia
Visiting department: Cardiology
Multiple groups: Athletes, seniors

Common causes: Onset factors include intracardiac and extracardiac factors
Common symptoms: Insufficient blood supply to the heart, brain, kidney and other organs caused by slow heart rate
Contagious: no

Causes of sinus bradycardia

Intracardiac factor

(1) Vaginal nerve excitability Mostly act through nerves (mainly vagal nerve excitement), humoral mechanisms through the extracardiac nerve, or directly affect the sinoatrial node and cause sinus bradycardia.

(2) Impaired sinus node function refers to sinus bradycardia caused by damaged sinus node (such as inflammation, ischemia, poisoning or degenerative damage, etc.). In addition, it can be seen in myocardial damage such as myocarditis, pericarditis, and myocardial sclerosis. It may also be caused by transient sinus node inflammation, ischemia, and toxic damage.

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

2. Extra-cardiac factors

Sinus bradycardia caused by extracardiac factors, most of which are accompanied by vagus nerve hyperactivity, are neurological and the heart rate is not very stable. When the autonomic nerve tension changes, such as deep breathing, exercise, atropine injection, etc., there is often a change in heart rate, and the PR interval can be slightly extended.

Clinical manifestations of sinus bradycardia

The severity varies and can occur intermittently. The main symptoms are insufficient blood supply to the heart, brain, kidney and other organs caused by slow heart rate. Mild persons have fatigue, dizziness, poor memory, and unresponsiveness, while severe patients may have blackout, syncope, or Alzheimer's syndrome. In addition to palpitations, some severe patients can aggravate existing heart disease symptoms and cause heart failure or angina. Cardiac blood output is too low, which seriously affects perfusion of organs such as the kidney, and can cause oliguria.

Sinus bradycardia

Electrocardiogram

1. The shape of sinus P wave

Sinus bradycardia and P wave morphology during sinus tachycardia are significantly different. This is because the sinus node's pacing point in the sinus bradycardia is mostly at the tail. The sinus tachycardia is mostly transmitted along the middle node and the pacing point of the sinoatrial node is mostly on the head. The excitability is mostly transmitted along the anterior node. Although the difference between the head and tail of the sinoatrial node is only 15 mm, However, due to the characteristic of preferential transmission of internodal bundles, the morphology of sinus P waves in the two is different. The P waves in leads II and III are slightly lower than those in normal sinus rhythm.

2. Frequency of sinus P wave

Adults should be <60 beats / minute, usually 40 to 59 beats / minute, and more than 45 beats / minute. There are also reports of as slow as about 35 beats per minute or even 20 beats per minute, with <45 beats per minute as severe sinus bradycardia. The heart rate of sinus bradycardia in infants and young children should be <100 times / minute under 1 year old, <80 times / minute between 1 and 6 years old, and <60 times / minute over 6 years old.

3.PR interval 0.12 0.25 seconds

4.QRS wave

Each P wave is followed by a normal QRS wave, with normal shape and time limit.

5.T wave, U wave

Sinus bradycardia is normal when T wave amplitude is low and U wave is usually more obvious.

6.QT interval

The QT interval was prolonged proportionally, but the corrected Q-Tc interval was within the normal range. Normal Q-Tc = QT (s) / should be 0.42 seconds.

Sinus bradycardia diagnosis

1. Sinus P wave frequency <60 times / minute, generally no less than 40 times / minute, 24-hour dynamic electrocardiogram sinus beat <80,000 times.

2. PR interval is 0.12 0.25s.

3. The QRS wave is normal.

Differential diagnosis of sinus bradycardia

1. Second degree sinoatrial block When a 2: 13: 1 sinoatrial block occurs, the heart rate is very slow, similar to sinus bradycardia. The two can be identified according to the following methods. After atropine injection or physical activity (can do squats and get up), sinus bradycardia can gradually increase in heart rate, and the increased heart rate is not multiples of the original heart rate Heart rate can be suddenly doubled or doubled in sinoatrial blockers.

2. Pre-atrial contraction without downloading the pre-atrial contraction P 'wave without downloading the dual law is generally easier to identify. The value can be mistaken for sinus bradycardia when the P wave is superimposed on the T wave and it is difficult to distinguish.

3. Atrial escape rhythm is rare, and its P wave shape is significantly different from that of sinus rhythm. It is not easy to distinguish in morphology. The identification points are:

(1) Atrial escape rhythm usually does not last long. Exercise or injection of atropine can accelerate sinus heart rate and atrial escape rhythm disappear.

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

Sinus bradycardia treatment

Treatment principle

(1) Sinus bradycardia such as a heart rate of not less than 50 beats per minute. Asymptomatic patients do not need treatment.

(2) If the heart rate is less than 50 times per minute and symptoms occur, you can use a heart rate increasing drug (such as atropine, ephedrine or isoprenaline), or you can consider installing a pacemaker.

(3) Patients with significant sinus bradycardia with sinus arrest and syncope should be fitted with an artificial pacemaker.

(4) Treatment of primary disease.

(5) Symptomatic and supportive treatment.

2. General treatment

(1) People with sinus bradycardia should pay attention to finding the cause. Most sinus bradycardia has no clinical significance and does not need treatment.

(2) In patients with organic heart disease (especially acute myocardial infarction), because the heart rate is very slow, the cardiac output can be significantly reduced, which affects the blood supply to important organs such as the heart, brain and kidney. Atropine should be used (injected or orally) and even intravenous infusion of isoproterenol to increase heart rate. Aminophylline can also be taken orally.

(3) For patients with severe sinus bradycardia caused by impaired sinus node function, the heart rate is very slow, the symptoms are obvious, even syncope occurs, and those with poor drug treatment need to install a permanent artificial pacemaker. In case of sudden sinus arrest.

(4) For organic heart disease with sinus bradycardia combined with sinus arrest or long-term recurrent sinus block without recurring rhythm, syncope or Alzheimer's syndrome, medication Ineffective, a permanent artificial pacemaker should be installed.

(5) Sinus bradycardia caused by increased intracranial pressure, drugs, and bile duct obstruction should first be treated with the cause, combined with the slowness of heart rate and whether it has caused a decrease in cardiac output. Appropriate use of drugs to increase heart rate.

Prognosis of sinus bradycardia

The prognosis of sinus bradycardia is related to the heart rate and the underlying heart state. If the heart rate is 40 to 60 beats per minute, the hemodynamic changes are not great, and there is no serious organic heart disease, then it has no obvious symptoms and the prognosis is good; Stroke volume cannot be compensated to increase, and the volume per minute decreases. Coronary, cerebral, and renal blood flow decreases. Shortness of breath, pain in the precardiac area, dizziness, and so on. More common in acute inferior myocardial infarction, poor heart function and other poor prognosis. If the heart rate is less than 40 beats / minute, the cardiac output is significantly reduced, and the prognosis is poor. Slow heart rate during acute myocardial infarction can cause ventricular ectopic rhythms.

Sinus bradycardia prevention

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

2. Sick sinus node syndrome, such as ventricular rate <50 times / minute, and obvious changes in hemodynamics, when there is insufficient blood supply to important organs such as the heart and brain, timely placement of artificial cardiac pacemakers to prevent cardio-brain synthesis Signs and sudden death occur.

3. Use drugs that slow heart rate and cardiac conduction with caution. The application of such drugs should be strictly controlled with indications and dosages to avoid overuse and misuse. Digitalis preparations, should be disabled for patients with diseased sinus and atrioventricular block. Blockers and other antiarrhythmic drugs that significantly slow heart rate.

4. Pay attention to the conditioning of life and emotions. You should have a moderate diet, live a regular life, and don't do rash work.