Clinical significance of the negative inotropic effect of disopyramide

This study determined the extent of the negative inotropic effect of either 200 mg standard release disopyramide given three times daily or 250 mg sustained release disopyramide given twice daily in 10 patients with normal and 10 with abnormal ventricular function. Assessment, by measurement of ejection fraction using 99mTc radionuclide ventriculography, was made 3 h after the first dose and again after 7 days' treatment, both at rest and after exercise. A similar reduction in ejection fraction occurred at rest and after exercise. Patients with an abnormal left ventricular function showed a greater decrease in ejection fraction compared with patients with normal left ventricular function, both at rest and after exercise. The extent of this reduction appeared to be correlated with the extent of left ventricular dysfunction. In no cases were these decreases statistically or clinically significant. No significant changes in heart volume occurred in any patient and none showed impaired clinical status. Plasma concentrations of disopyramide were also similar for both types of disopyramide in both groups of patients on days 1 and 7.