Heart Sinus Bradycardia

There are many reasons for sinus bradycardia. The internal reason is mainly that the nerves that control the heart are overexcited, resulting in reduced effectiveness. Either the heart function is damaged, there is some problem with the heart function, or there is inflammation inside the heart. Generally, heart patients should keep a good mood and not let some external factors cause emotional agitation. A calm mentality is more conducive to the recovery of the disease.

1. What are the causes of sinus bradycardia?

1. Cardiac factors

(1) Vagus nerve excitement

Most of them act through neural (mainly vagus nerve excitation), humoral mechanisms through extracardiac nerves, or directly act on the sinoatrial node to cause sinus bradycardia.

(2) Impaired sinus node function

Refers to sinus bradycardia caused by damage to the sinoatrial node (such as inflammation, ischemia, poisoning or degenerative damage, etc.). In addition, it can be seen in myocardial damage such as myocarditis, pericarditis, myocardial sclerosis, etc. 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 stages of acute myocardial infarction (especially inferior wall infarction).

2. Extracardiac factors

Sinus bradycardia caused by extracardiac factors is mostly accompanied by vagal hyperactivity, is neurological, and the heart rate is not very stable. When the autonomic nervous tone changes, such as after deep breathing, exercise, and atropine injection, the heart rate often changes and the PR interval may be slightly prolonged.

2. What are the tests for sinus bradycardia?

Electrocardiogram

1. The shape of the sinus P wave

The shape of the sinus P wave

The P wave morphology during sinus bradycardia is quite different from that during sinus tachycardia. This is because the pacemaker of the sinoatrial node is mostly located at the tail during sinus bradycardia, and the excitement it emits is mostly transmitted along the middle interatrial bundle; while during sinus tachycardia, the pacemaker of the sinoatrial node is mostly located at the head, and the excitement is mostly transmitted along the anterior interatrial bundle. Although the head and tail of the sinoatrial node differ by only 15 mm, due to the preferential conduction characteristic of the interatrial bundle, the sinus P wave morphology of the two is different. The P wave in leads II and III is slightly flatter than that in normal sinus rhythm.

2. Frequency of sinus P waves

For adults, the blood pressure should be less than 60 times/minute, usually 40 to 59 times/minute, and mostly above 45 times/minute. There are also reports of rates as slow as 35 beats/minute or even 20 beats/minute. <45 beats/minute is severe sinus bradycardia. The heart rate of sinus bradycardia in infants and young children should be <100 beats/minute under 1 year old, <80 beats/minute between 1 and 6 years old, and <60 beats/minute over 6 years old.

3.PR interval

The PR interval is 0.12 to 0.25 seconds.

4.QRS complex

Each P wave is followed by a normal QRS wave with normal morphology and duration.

5. T wave, U wave

Sinus bradycardia is normal, and the T wave amplitude may be low and the U wave is often 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.

58 Shortened PR interval in sinus rhythm