Oxygen Uptake in Cardiopulmonary Exercise Testing as a Diagnostic Marker for Cardiac Ischemia

Background 

In patients with suspected coronary artery disease (CAD), ECG exercise testing is performed for suspicion of cardiac ischemia. Due to low diagnostic power (sensitivity 58%), exercise ECG testing has been downgraded in recent guideline recommendations. Anatomical or functional imaging such as coronary CT, cardiac stress MRI, myocardial scintigraphy and stress echocardiography are more sensitive and specific. 

Cardiopulmonary exercise testing (CPET) is a non-invasive, low-cost examination tool, radiation free and widely available. Prior investigations on patients with CAD showed an additive diagnostic impact through the analysis of gas exchange parameters during exercise that may improve sensitivity and specificity. The aim of our study was to compare CPET with invasive hemodynamic evaluation of coronary stenoses in order to evaluate CPET as a functional noninvasive diagnostic tool. 

Methods 

We included 106 patients (77 male, 29 female, mean 63.6 ±10.1 years) with suspected CAD or suspected progression of known CAD. Patients either had typical angina pectoris and/or dyspnea and a high pre-test probability. In all patients, an invasive assessment was indicated according to the current ESC guidelines. 

At baseline, patients underwent CPET before coronary angiography. Coronary stenoses were evaluated by fractional flow reserve (FFR) and percutaneous coronary intervention with stent implantation was performed when hemodynamically relevant (FFR value <0.8). Four to six weeks after invasive assessment patients underwent a second CPET. The CPET data were evaluated blinded to the invasive measurements.

Results 

76.2% of patients achieved a respiratory exchange rate of > 1.05, indicating maximal patient physiological effort. After hemodynamic evaluation 47 patients (44.3%) had a relevant stenosis and underwent stent implantation. 

Patients with an FFR value <0.8 had a significantly lower peak oxygen uptake (p=0.01). ROC analysis revealed a cut-off at 72% of the expected individual peak oxygen uptake with a sensitivity of 76% for the prediction of relevant CAD. Adding ST-Segment change on exercise ECG and angina pectoris to the analysis improved the sensitivity to 93.6%. 

Oxygen uptake significantly improved at follow-up in all patients (p-value <0.001). Notably, stent implantation had no significant effect on oxygen uptake.

Conclusion

We compared oxygen uptake on CPET with invasive hemodynamic FFR evaluation in coronary angiography. Relevant coronary artery stenoses result in a significant decrease in maximum oxygen uptake on CPET. In combination with changes in ECG and the clinical parameter angina pectoris, CPET significantly improves sensitivity compared to exercise ECG only and may be used as an additional noninvasive diagnostic tool for patients with suspected CAD or progression of known CAD.