I. Classification of atrial fibrillation
Atrial fibrillation is a major cause of cerebral embolic events, and 75% of patients with atrial fibrillation are complicated by cerebrovascular events.
There is no uniform opinion on the classification of atrial fibrillation, which is generally divided into paroxysmal (paroxysmal) and chronic (chronic) atrial fibrillation. 7 days is generally recommended as the cut-off point to distinguish paroxysmal from persistent atrial fibrillation.
In paroxysmal AF, if an episode lasts longer than 48 hours, then it is called persistent AF. If AF persists beyond this time limit, formal anticoagulation is necessary before resetting.
Permanent atrial fibrillation refers to the persistence of atrial fibrillation and the ineffectiveness of resetting or recurrence soon after resetting.
Epidemiology of cerebral embolism in atrial fibrillation
The incidence of atrial fibrillation is clearly age-related, and the incidence of atrial fibrillation begins to increase after the age of 40 years and significantly after the age of 65 years, with an incidence of about 7-14% in the elderly. the Framingham study showed that the risk of embolism in non-rheumatic atrial fibrillation was 5.6 times higher than that in controls, while the incidence of rheumatic atrial fibrillation was 17.6 times higher. Nonrheumatic atrial fibrillation accounted for 15 to 20% of ischemic stroke events (see Table 1).
Table 1 Framingham study (1982)
Age
50 to 59 years
80 to 89 years
Incidence of atrial fibrillation
0.5%
8.8%
Incidence of stroke
1.5%
30 %
There is no consensus on the incidence of embolism in chronic AF (6% per year) compared with paroxysmal AF (2-3% per year), although it has been suggested. A pooled analysis of 5 randomized controlled trials showed that the type (paroxysmal or persistent) and duration of AF did not have a significant effect on the risk of embolism. The risk of embolism in atrial fibrillation may be higher early after atrial fibrillation, within 1 year after atrial fibrillation, and early after rhythm resumption.
In the elderly, the incidence of atrial fibrillation-related cerebrovascular events is significantly higher, accounting for 6.7% of all cerebrovascular events in people aged 50 to 59 years and 36.2% in people aged 80 to 89 years. Approximately half of atrial fibrillation-associated embolisms occur in older adults aged 75 years or older.
About 25% of atrial fibrillation-associated strokes are caused by lesions in the cerebral vessels themselves, rather than by thromboembolism or atherosclerotic plaques in the aortic arch.
III. Atrial fibrillation and cerebral embolism
Patients with atrial fibrillation are at increased risk of ischemic stroke, and strokes associated with atrial fibrillation are often severe and have a poor prognosis. A retrospective study showed that 71% of cerebral embolisms died or left severe neurological symptoms within 6 weeks of the observed follow-up. Two prospective studies showed that 63% and 44% of patients with atrial fibrillation had strokes that were fatal or disabling, respectively.
Atrial fibrillation is the most common potential source of emboli for cerebral embolism, with atrial fibrillation causing 20% of all ischemic strokes. Other sources of emboli in cerebral embolism include: left ventricular appendage thrombus; organic mitral valve disorders (including mucinous aneurysm or annular calcification); and atherosclerosis involving cerebral vessels (intracranial or extracranial) or the thoracic aorta.
Some early observational studies showed that the risk of another ischemic stroke within the first 2 weeks after a stroke episode was 10% to 20%. However, these and other studies have also shown a higher incidence of conversion of embolic cerebral infarction to hemorrhage, and some studies have reported symptomatic cerebral hemorrhage associated with heparin anticoagulation. Analysis of the atrial fibrillation subgroup of the International Stroke Trial (ISTT) showed that a fixed dose of subcutaneous plain heparin reduced recurrence of ischemic stroke, but this benefit was offset by a concomitant increase in cerebral hemorrhage.
IV. Oral anticoagulants and their monitoring
The main anticoagulants are coumarins, and the clinically used ones are cotrimoxazole and warfarin.
Chinese people generally start with 3mg daily, and the dosage is reduced appropriately for elderly people >75. The dosage must be adjusted by monitoring the International Normalized Ratio (INR).
(I) International Normalized Ratio
INR is called International Normalized Ratio in Chinese, which is derived from the prothrombin time (PT) and the International Sensitivity Index (ISI) of the measuring reagent, INR = (patient PT/normal control PT) ISI, using I NR to make the PT measured by different laboratories and different reagents comparable and facilitate the unification of medication standards.
(II), adjustment of medication
INR must be measured before drug administration, once in 3~4 days and once in 1 week, once in 1 week in 1 month, and transition to once in 1 month after 2 consecutive INRs in the normal range.
If the INR is below or above the target range for treatment, the dose of cormidine should be increased or decreased appropriately by 0.5~1mg daily for each increase or decrease.
Patients should be instructed to seek medical advice and measure INR if they encounter conditions that can alter INR or if adverse reactions such as bleeding occur.
(iii) Factors affecting INR
Many factors, including travel, diet, environment, physical condition, suffering from other diseases and medication use, can cause changes in INR.
When factors affecting medication are present, such as aspirin in patients with colds, discontinuing medication for any reason or taking medication irregularly, several additional INRs should be done so that the medication dose can be adjusted in a timely manner to maintain the INR within the target range of treatment.
(iv) Effectiveness and safety of oral anticoagulant drugs
If INR monitoring and adjustment of medication is used, oral anticoagulants are very safe, and the incidence of severe bleeding is similar to that of oral aspirin, and bleeding events are associated with increased INR and age at the time of monitoring.
Adjusting the INR at 2.0 to 3.0 ensures antithrombotic effects while minimizing the risk of bleeding.
It has been observed that the antithrombotic effect of INR less than 2.0 is diminished and ischemic stroke increases significantly; if INR is less than 1.5, warfarin is almost ineffective; the target INR should be maintained at 2.5 in most cases (2.0-3.0); if INR is greater than 3.0, bleeding events increase and greater than 5.0 bleeding events increase sharply.
V. Risk factors for cerebral embolism in atrial fibrillation
The occurrence of embolism in patients with atrial fibrillation is related to the presence of associated cardiac disease, the nature of heart disease and its extent, and the presence of other risk factors for thromboembolism. The recurrence rate is significantly higher in patients with a history of cerebral embolism. Other risk factors that increased the risk of cerebral embolism included a history of hypertension, coronary artery disease or congestive heart failure and cardiac enlargement on radiographs, and atrial fibrillation lasting >1 year.
Pooled data from multifactorial analysis showed that independent risk factors for stroke included advanced age, previous stroke or transient ischemic attack, left atrial enlargement, history of hypertension, and diabetes mellitus (Table 2). The risk of embolism is increased by esophageal ultrasound findings of intra-left atrial thrombus, spontaneous ultrasound imaging, slowed left atrial blood flow velocity, and decreased left ventricular function.
Table 2 Clinical factors contributing to stroke in nonrheumatic atrial fibrillation