Maximum Cardiac Output During Incremental Exercise by First-pass Radionuclide Ventriculography

¹ From the Pulmonary and Critical Care Unit, Massachusetts General Hospital and Harvard Medical School, Boston

David Systrom, MD, Mass General Hospital, Pulmonary and Critical Care Unit, 55 Fruit Street, Boston, MA 02114

Study objective: To validate a noninvasive first-pass radionuclide ventriculographic (FPRV) measurement of maximum cardiac output (Qv) during exercise.

Design: Comparison of Qv to that measured by the Fick principle (Qf) at peak exercise.

Setting: Academic cardiopulmonary exercise laboratory.

Patients: Seventy-eight consecutive patients without a history of septal defect undergoing clinically indicated maximum incremental cardiopulmonary exercise testing with pulmonary arterial catheterization and FPRV.

Measurements and results: Ventilation and gas exchange were measured breath-by-breath or by a mixing chamber/mass spectrometer system. Arterial and mixed venous O₂ content were measured each minute during exercise. When patients without left-to-right ventricular stroke count ratio evidence for left-sided regurgitation were isolated, peak Qv was linearly related to Qf (r=0.75, p=0.0001). To account for a small systematic overestimation (bias) of Qf by Qv, the linear equation for the Qv/Qf relation was derived for patients studied between 1990 and 1993 and applied to those studied subsequently. The resulting corrected peak Qv was tightly related to peak Qf (r=0.90, p<0.001) with confidence intervals for slope and intercept overlapping identity.

Conclusion: FPRV can reasonably estimate maximum cardiac output during incremental exercise in patients for whom the technique has ruled out left-sided cardiac regurgitant lesions.

Key Words: cardiac output • cardiopulmonary exercise testing • first-pass radionuclide ventriculography • pulmonary artery catheter

Submitted on October 17, 1997
Accepted on January 21, 1998