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 (OP) is the CPET surrogate for stroke volume and peripheral oxygen extraction.

Objectives: This study assessed OP 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 OP curve analysis during CPET were developed. Best fit early and late regression slopes of the OP curve were used to calculate: 1) the early to late ratio, or "O pulse response ratio" (OPRR); 2) the portion of exercise until slope inflection, or "flattening fraction" (FF); 3) the area under the OP response curve, or "OP curve area".

Results: rTOF patients (median age 35.2 (27.6-39.4); 61% female) had a lower VO max (23.4 vs 45.6 ml/kg/min; p < 0.001) and OP 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 VO max, compared to those >50%. FF and OP 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 OP curve data. These evaluations demonstrated significant correlations with stroke volume, cardiac output, and right ventricular pressure.