The average ventricular response over a 24-hour period should be similar to that in a patient of comparable age without atrial fibrillation. A resting heart rate of 70-90 bpm is generally appropriate. The ventricular response associated with exertion should be appropriate for the level of exercise (i.e., rates of 90-100 bpm for modest activity, 100-120 bpm for more vigorous exertion, and 120-170 bpm for very vigorous exertion).
Many elderly patients are sedentary and may require digoxin only for control of the ventricular response at rest and with modest exertion. However, in more active patients of all ages, a combination of digoxin with a beta blocker or a long-acting calcium channel blocker will result in better 24-hour heart rate control.
What techniques are used to evaluate heart rate in patients with chronic atrial fibrillation?
The heart rate response can be evaluated by two techniques. The use of 24-hour Holter monitoring allows for the assessment of ventricular response during the activities of daily living. The formal graded exercise treadmill test yields information about the rate of rise for the ventricular response as well as peak heart rate at maximal exercise. Both forms of evaluation are helpful in establishing the efficacy of chronic medical therapy.
Can thromboembolic risk in patients with atrial fibrillation be predicted from clinical variables? Echocardiographic variables?
The risk of stroke in patients with chronic atrial fibrillation (nonvalvular) is approximately 4‚ 5% per year. The recent SPAF (Stroke Prevention in Atrial Fibrillation) studies as well as earlier studies (Copenhagen Atrial Fibrillation Trial, AFASAK; Canadian Atrial Fibrillation Anticoagulation Study, CAFA; and Boston Area Anticoagulation Trial in Atrial Fibrillation, BAATAF) suggest that a history of hypertension, congestive heart failure, and previous stroke all are significant clinical predictors of stroke in patients with chronic atrial fibrillation. Additional clinical risk factors may include age 65 years and diabetes mellitus. The SPAF study identified echocardiographic variables, including increased left atrial size and left ventricular dysfunction, as significant risk factors. Additionally, mitral stenosis, prosthetic mitral valves, rheumatic heart disease, and severe mitral regurgitation with marked left atrial enlargement all appear to be associated with increased risk of stroke.