Novel techniques for quantifying oxygen pulse curve characteristics during cardiopulmonary exercise testing in tetralogy of fallot

Background

Cardiopulmonary exercise testing (CPET) is used in evaluation of repaired tetralogy of Fallot (rTOF), particularly for pulmonary valve replacement need. Oxygen pulse (O₂P) is the CPET surrogate for stroke volume and peripheral oxygen extraction.

Objectives

This study assessed O₂P curve properties against non-invasive cardiac output monitoring (NICOM) and clinical testing.

Methods

This cross-sectional study included 44 rTOF patients and 10 controls. Three new evaluations for O₂P curve analysis during CPET were developed. Best fit early and late regression slopes of the O₂P curve were used to calculate: 1) the early to late ratio, or “O₂ pulse response ratio” (O₂PRR); 2) the portion of exercise until slope inflection, or “flattening fraction” (FF); 3) the area under the O₂P response curve, or “O₂P curve area”.

Results

rTOF patients (median age 35.2 (27.6–39.4); 61% female) had a lower VO₂ max (23.4 vs 45.6 ml/kg/min; p < 0.001) and O₂P max (11.5 vs 19.1 ml/beat; p < 0.001) compared to controls. Those with a FF occurring <50% through exercise had a lower peak cardiac index and stroke volume, but not VO₂ max, compared to those >50%. FF and O₂P curve area significantly correlated with peak cardiac index, stroke volume, left and right ventricular ejection fraction, and right ventricular systolic pressure.

Conclusion

CPET remains an integral part in the evaluation of rTOF. We introduce three non-invasive methods to assess exercise hemodynamics using the O₂P curve data. These evaluations demonstrated significant correlations with stroke volume, cardiac output, and right ventricular pressure.