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Increased exercise capacity after digoxin administration in patients with heart failure
M Sullivan1, J E Atwood, J Myers
1Cardiology Department, Long Beach Veterans Administration Medical Center, California 90822.
Insights
Digoxin improves exercise capacity in patients with chronic heart failure by enhancing oxygen uptake and physiological efficiency. This study clarifies the benefits of digoxin therapy for heart failure patients.
Area of Science:
- Cardiology
- Exercise Physiology
Background:
- Controversy exists regarding digitalis effects on exercise capacity in chronic heart failure.
- Objective assessment is needed to clarify digoxin's role.
Purpose of the Study:
- To objectively assess the effect of digoxin on exercise capacity in patients with chronic heart failure.
Main Methods:
- Maximal treadmill testing with respiratory gas exchange analysis was performed on 11 patients with chronic heart failure.
- Patients were tested both with and without digoxin therapy.
Main Results:
- Digoxin therapy significantly increased ventilatory oxygen uptake at submaximal exercise, anaerobic threshold, and maximal exercise.
- An improvement in the ratio of dead space to tidal volume (VD/VT), indicating enhanced physiological efficiency, was observed during digoxin therapy.
- A significant negative correlation was found between the change in maximal oxygen uptake and the change in maximal estimated VD/VT.
Conclusions:
- Digoxin therapy is associated with significant improvements in exercise capacity in patients with chronic heart failure.
- These improvements are likely due to enhanced ventilation-perfusion matching.
Abstract:
Failure to objectively assess the effect of digitalis on exercise capacity has resulted in controversy regarding its use in patients with chronic congestive heart failure. To clarify this situation, maximal treadmill testing with respiratory gas exchange analysis was performed on 11 patients (mean age 57 +/- 9 years) with chronic congestive heart failure with and without digoxin therapy. Ten of the 11 had a consistent third sound gallop, and the mean ejection fraction of the group was 24 +/- 10%. Rest heart rate was significantly higher (91 +/- 16 versus 102 +/- 16 beats/min; p less than 0.05) and rest systolic blood pressure was significantly reduced in the absence of digoxin (130 +/- 23 versus 121 +/- 15 mm Hg; p less than 0.05). No differences in heart rate or blood pressure were observed during exercise. Significant increases in ventilatory oxygen uptake were observed with digoxin submaximally (3.0 mph, 0% grade), at the gas exchange anaerobic threshold and at maximal exercise (mean increase of 2.6 ml/kg per min; p less than 0.02). An improvement in the estimated ratio of ventilatory dead space to tidal volume (VD/VT), an index of physiologic efficiency, occurred throughout exercise during digoxin therapy, and there was a significant negative correlation between the change in maximal oxygen uptake and change in maximal estimated VD/VT (r = -0.63; p less than 0.05). Thus, digoxin therapy is associated with a significant improvement in exercise capacity in patients with chronic heart failure, most likely due to an improved matching of ventilation to perfusion.