How does heart rate respond to graded work and orthostatic tests in patients with atrial fibrillation on digitalis?
The graded work test in patients with atrial fibrillation on digitalis shows variable linearity between heart rate and work load, requiring cautious clinical evaluation.
Abstract A group of 195 patients with atrial fibrillation, mostly due to advanced valvular heart disease, have been examined by the graded work test and an orthostatic test when they were on maintenance digitalis therapy. The highest attained work load averaged 275 kpm/min, at an average heart (ventricular) rate of 134 beats/min. This corresponded to a load of 145 at heart rate 110. There was a wide range of work capacity. The individual relationships of heart rate increase to work load increase varied considerably from linearity, but were approximately linear in many cases and the average for groups of patients were also relatively linear. Alinearity was observed especially in patients with a very low work capacity. The increase in heart rate during an orthostatic test was 30 beats/min or more in 8% of the patients. A ‘steady state’ was obtained during the highest work load in 44% of the patients. Our experience is that, in atrial fibrillation, the graded work test must be evaluated with caution but often gives valid clinical information.
Åberg et al. (Sat,) studied this question.