Sudden bradycardia

Sinus bradycardia refers to a heart rate of about 60 beats per minute. There are many causes. It may occur in some healthy groups, the most common being the elderly, athletes, and people who are sleeping. Of course, there are also some medical reasons, such as increased intracranial pressure, hypothyroidism, or some organic heart diseases, etc., which may cause sinus bradycardia.

Causes

1. Intracardiac factors (1) Vagal excitation usually acts through neural (mainly vagal excitation), humoral mechanisms, via the extracardiac nerves, or directly acts on the sinoatrial node to cause sinus bradycardia. (2) Impaired sinus node function refers to sinus bradycardia caused by damage to the sinus node (such as inflammation, ischemia, poisoning or degenerative damage). 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) The incidence of sinus bradycardia in acute myocardial infarction is 20% to 40%, with the highest incidence in the early stages of acute myocardial infarction (especially inferior wall infarction).

Clinical manifestations

The severity varies and may occur intermittently. Most of the symptoms are insufficient blood supply to the heart, brain, kidneys and other organs due to a slow heart rate. In mild cases, the symptoms include fatigue, dizziness, poor memory, slow reaction, etc. In severe cases, there may be blackouts, syncope, or attacks of Adams-Stokes syndrome. In some severe patients, in addition to palpitations, the disease may also aggravate existing heart disease symptoms and cause heart failure or angina pectoris. Too low cardiac output seriously affects the perfusion of organs such as the kidneys, and can also cause oliguria, etc.

Prognosis

The prognosis of sinus bradycardia is related to the heart rate and basic heart condition. If the heart rate is 40-60 beats/minute, the hemodynamic changes are not significant, and there is no serious organic heart disease, then there are no obvious symptoms and the prognosis is good. If the heart rate is slow and there is serious organic heart disease, the heart's stroke volume cannot increase compensatorily, and the minute output decreases, and the blood flow to the coronary arteries, brain, and kidneys decreases, causing symptoms such as shortness of breath, precordial pain, and dizziness. In severe cases, syncope may occur. This situation is more common in acute inferior wall myocardial infarction, heart dysfunction, and other conditions with a poor prognosis. If the heart rate is lower than 40 beats/minute, cardiac output will be significantly reduced and the prognosis will be poor. A slow heart rate during acute myocardial infarction may lead to the occurrence of ventricular ectopic rhythm.