Antithrombotic Therapy for Cerebrovascular Disorders: Echocardiographically
Echocardiographically defined subsets of AF patients at high stroke risk are also still ill defined. Studies relating left atrial diameter to stroke risk have yielded conflicting results. These studies usually used single-dimension measurements made from M-mode echocardiography. As the left atrium is a complex geometric structure, 3-dimensional measurements to determine volume and transmitral diastolic flow evaluated by Doppler techniques may more accurately predict thrombus development and embolic potential. Left ventricular dysfunction and segmental wall motion abnormalities have been associated with thromboembolic risk. In summary, within the broad spectrum of patients with nonrheumatic AF, it is likely that high- or low-risk subgroups do exist. Save for the small fraction with lone AF or those who have already suffered stroke, these subsets have not been convincingly identified.
In a recent retrospective study of 134 inpatients with nonrheumatic AF followed up for a mean of 3.3 years, emboli occurred in 5.9%/year in patients who were not given conventional levels of anticoagulants, compared with 0.7%/year in those treated with anticoagulants (the later group experienced major hemorrhage at a rate of 2.1%/year). Potential selection bias in determining which patients were treated with anticoagulants seriously limits the extrapolation of these observations to patient care.
Although the presence of AF identifies patients at increased risk of ischemic stroke, there are no clinical data determining how to prevent these strokes effectively and safely. In younger patients with lone or paroxysmal AF who appear to have a relatively low stroke risk, long-term anticoagulation is not warranted. For the remaining majority of AF patients, preventive therapy is entirely empiric. Low-intensity anticoagulation or platelet-antiaggregating agents are sometimes advocated, although their safety and efficacy are not established at present. If reversion from AF to sinus rhythm is a high-risk period for some AF patients (suggested by studies of electrical cardioversion, but unconfirmed by observations of spontaneous cardioversion in younger patients,) iatrogenic attempts to restore sinus rhythm in the hope of minimizing the long-term risk of embolism should be undertaken with caution and appreciation of the likelihood of recurrent AF. In AF patients with initial stroke, evaluation of stroke mechanism will influence secondary preventive strategies. Anticoagulation is recommended if a cardioembolic source is deemed probable, and such therapy can be safely administered to the individual patient.
Category: Antithrombotic Therapy
Tags: antithrombotic therapy, cardioembolic source, cerebrovascular disorders