Value of the Oxygen Pulse Curve for the Diagnosis of Coronary Artery Disease

Cardiopulmonary exercise testing in clinical practice: Principles, applications, and basic interpretation

Cardiopulmonary exercise testing (CPET) provides a noninvasive and integrated assessment of the response of the respiratory, cardiovascular, and musculoskeletal systems to exercise. This information improves the diagnosis, risk stratification, and therapeutic management of several clinical conditions. Additionally, CPET is the gold standard test for cardiorespiratory fitness quantification and exercise prescription, both in patients with cardiopulmonary disease undergoing cardiac or pulmonary rehabilitation programs and in healthy individuals, such as high-level athletes. In this setting, the relevance of practical knowledge about this exam is useful and of interest to several medical specialties other than cardiology. However, despite its multiple established advantages, CPET remains underused. This article aims to increase awareness of the value of CPET in clinical practice and to inform clinicians about its main indications, applications, and basic interpretation.

The association between O2-pulse slope ratio and functional severity of coronary stenosis: A combined cardiopulmonary exercise testing and quantitative flow ratio study

Background

The role of cardiopulmonary exercise testing (CPET) parameters in evaluating the functional severity of coronary disease remains unclear. The aim of this study was to quantify the O2-pulse morphology and investigate its relevance in predicting the functional severity of coronary stenosis, using Murray law-based quantitative flow ratio (μQFR) as the reference.

Methods

CPET and μQFR were analyzed in 138 patients with stable coronary artery disease (CAD). The O2-pulse morphology was quantified through calculating the O2-pulse slope ratio. The presence of O2-pulse plateau was defined according to the best cutoff value of O2-pulse slope ratio for predicting μQFR ≤ 0.8.

Results

The optimal cutoff value of O2-pulse slope ratio for predicting μQFR ≤ 0.8 was 0.4, with area under the curve (AUC) of 0.632 (95 % CI: 0.505-0.759, p = 0.032). The total discordance rate between O2-pulse slope ratio and μQFR was 27.5 %, with 13 patients (9.4 %) being classified as mismatch (O2-pulse slope ratio > 0.4 and μQFR ≤ 0.8) and 25 patients being classified as reverse-mismatch (O2-pulse slope ratio ≤ 0.4 and μQFR > 0.8). Angiography-derived microvascular resistance was independently associated with mismatch (OR 0.07; 95 % CI: 0.01-0.38, p = 0.002) and reverse-mismatch (OR 9.76; 95 % CI: 1.47-64.82, p = 0.018).

Conclusion

Our findings demonstrate the potential of the CPET-derived O2-pulse slope ratio for assessing myocardial ischemia in stable CAD patients.

Inter- and intra-observer reliability and agreement of O2Pulse inflection during cardiopulmonary exercise testing: A comparison of subjective and novel objective methodology

Cardiopulmonary exercise testing (CPET) is the 'gold standard' method for evaluating functional capacity, with oxygen pulse (O2Pulse) inflections serving as a potential indicator of myocardial ischaemia. However, the reliability and agreement of identifying these inflections have not been thoroughly investigated. This study aimed to assess the inter- and intra-observer reliability and agreement of a subjective quantification method for identifying O2Pulse inflections during CPET, and to propose a more robust and objective novel algorithm as an alternative methodology. A retrospective analysis was conducted using baseline data from the HIIT or MISS UK trial. The O2Pulse curves were visually inspected by two independent examiners, and compared against an objective algorithm. Fleiss' Kappa was used to determine the reliability of agreement between the three groups of observations. The results showed almost perfect agreement between the algorithm and both examiners, with a Fleiss' Kappa statistic of 0.89. The algorithm also demonstrated excellent inter-rater reliability (ICC) when compared to both examiners (0.92-0.98). However, a significant level (P ≤0.05) of systematic bias was observed in Bland-Altman analysis for comparisons involving the novice examiner. In conclusion, this study provides evidence for the reliability of both subjective and novel objective methods for identifying inflections in O2Pulse during CPET. These findings suggest that further research into the clinical significance of O2Pulse inflections is warranted, and that the adoption of a novel objective means of quantification may be preferable to ensure equality of outcome for patients.

Cardiopulmonary exercise testing and efficacy of percutaneous coronary intervention: a substudy of the ORBITA trial

AIMS

Oxygen-pulse morphology and gas exchange analysis measured during cardiopulmonary exercise testing (CPET) has been associated with myocardial ischaemia. The aim of this analysis was to examine the relationship between CPET parameters, myocardial ischaemia and anginal symptoms in patients with chronic coronary syndrome and to determine the ability of these parameters to predict the placebo-controlled response to percutaneous coronary intervention (PCI).

METHODS AND RESULTS

Patients with severe single-vessel coronary artery disease (CAD) were randomized 1:1 to PCI or placebo in the ORBITA trial. Subjects underwent pre-randomization treadmill CPET, dobutamine stress echocardiography (DSE) and symptom assessment. These assessments were repeated at the end of a 6-week blinded follow-up period.A total of 195 patients with CPET data were randomized (102 PCI, 93 placebo). Patients in whom an oxygen-pulse plateau was observed during CPET had higher (more ischaemic) DSE score [+0.82 segments; 95% confidence interval (CI): 0.40 to 1.25, P = 0.0068] and lower fractional flow reserve (-0.07; 95% CI: -0.12 to -0.02, P = 0.011) compared with those without. At lower (more abnormal) oxygen-pulse slopes, there was a larger improvement of the placebo-controlled effect of PCI on DSE score [oxygen-pulse plateau presence (Pinteraction = 0.026) and oxygen-pulse gradient (Pinteraction = 0.023)] and Seattle angina physical-limitation score [oxygen-pulse plateau presence (Pinteraction = 0.037)]. Impaired peak VO2, VE/VCO2 slope, peak oxygen-pulse, and oxygen uptake efficacy slope was significantly associated with higher symptom burden but did not relate to severity of ischaemia or predict response to PCI.

CONCLUSION

Although selected CPET parameters relate to severity of angina symptoms and quality of life, only an oxygen-pulse plateau detects the severity of myocardial ischaemia and predicts the placebo-controlled efficacy of PCI in patients with single-vessel CAD.

Temporal Skin Temperature as an Indicator of Cardiorespiratory Fitness Assessed with Selected Methods

The aim of this study was to determine whether there are associations between cardiovascular fitness (and aerobic capacity) and changes in temporal skin temperature during and after a single bout of high-intensity exercise. Twenty-three men with varying levels of physical activity (VO2max: 59.03 ± 11.19 (mL/kg/min), body mass 71.5 ± 10.4 (kg), body height 179 ± 8 (cm)) participated in the study. Each subject performed an incremental test and, after a 48-h interval, a 110%Pmax power test combined with an analysis of the thermal parameters, heart rate recovery and heart rate variability. Thermal radiation density from the body surface (temple) was measured using a Sonel KT384 thermal imaging camera immediately after warm-up (Tb), immediately after exercise (Te) and 120 sec after the end of exercise (Tr). The differences between measurements were then calculated. The correlation analysis between the thermal and cardiovascular function parameters during the recovery period showed strong positive associations between the Tr-Te difference and measures of cardiovascular fitness (50 < r < 69, p < 0.05). For example, the correlation coefficient between Tr-Te and VO2max reached 0.55 and between Tr-Te and Pmax reached 0.68. The results obtained indicate that the measurement of temporal temperature during and after an intense 3-min bout of exercise can be used to assess aerobic physical capacity and cardiovascular fitness.

Utility of the oxygen pulse in the diagnosis of obstructive coronary artery disease in physically fit patients

Cardiopulmonary exercise testing (CPET) guidelines recommend analysis of the oxygen (O₂ ) pulse for a late exercise plateau in evaluation for obstructive coronary artery disease (OCAD). However, whether this O₂ pulse trajectory is within the range of normal has been debated, and the diagnostic performance of the O₂ pulse for OCAD in physically fit individuals, in whom V ˙ O 2 may be more likely to plateau, has not been evaluated. Using prospectively collected data from a sports cardiology program, patients were identified who were free of other cardiac disease and underwent clinically-indicated CPET within 90 days of invasive or computed tomography coronary angiography. The diagnostic performance of quantitative O₂ pulse metrics (late exercise slope, proportional change in slope during late exercise) and qualitative assessment for O₂ pulse plateau to predict OCAD was assessed. Among 104 patients (age:56 ± 12 years, 30% female, peak V ˙ O 2 119 ± 34% predicted), the diagnostic performance for OCAD (n = 24,23%) was poor for both quantitative and qualitative metrics reflecting an O₂ pulse plateau (late exercise slope: AUC = 0.55, sensitivity = 68%, specificity = 41%; proportional change in slope: AUC = 0.55, sensitivity = 91%, specificity = 18%; visual plateau/decline: AUC = 0.51, sensitivity = 33%, specificity = 67%). When O₂ pulse parameters were added to the electrocardiogram, the change in AUC was minimal (-0.01 to +0.02, p ≥ 0.05). Those patients without OCAD with a plateau or decline in O₂ pulse were fitter than those with linear augmentation (peak V ˙ O 2 133 ± 31% vs. 114 ± 36% predicted, p < 0.05) and had a longer exercise ramp time (9.5 ± 3.2 vs. 8.0 ± 2.5 min, p < 0.05). Overall, a plateau in O₂ pulse was not a useful predictor of OCAD in a physically fit population, indicating that the O₂ pulse should be integrated with other CPET parameters and may reflect a physiologic limitation of stroke volume and/or O₂ extraction during intense exercise.

The relationships among the skeletal muscle mass index, cardiorespiratory fitness and the prevalence of coronary artery disease in the elderly population

OBJECTIVE

Few studies have investigated the association between cardiorespiratory fitness (CRF) impairment and coronary artery disease (CAD) and the mediating mechanism. Therefore, we investigated the impact of skeletal muscle mass (SMM) on the relationship between CRF and coronary artery disease (CAD) in elderly people.

METHODS

In this cross-sectional study, 109 elderly patients with coronary artery stenosis ≥50% were included in the CAD group, and 148 patients with coronary artery stenosis <50% were included as controls. Mediation analyses were performed to determine the role of the skeletal muscle index (SMI) in the relationship between CRF and the prevalence of CAD. A receiver operating characteristic (ROC) curve analysis was used to evaluate the predictive value of CRF markers and the SMI.

RESULTS

The oxygen pulse, VO₂ max, and MET max were significantly associated with the SMI. In the multiple logistic regression analyses, the oxygen pulse and SMI were both independently correlated with the prevalence of CAD. The mediation analyses showed that the SMI affects the relationship between CRF markers (oxygen pulse, VO₂ max, and MET max) and the prevalence of CAD. The receiver operating characteristic (ROC) curve analysis showed that when CRF and the SMI are considered together, the predictive power for CAD is stronger than that of the CRF alone.

CONCLUSION

Enhancing CRF can facilitate improvement in SMM and decrease the prevalence of CAD in the elderly population. The addition of the SMI to CRF markers may increase the predictive value of CAD.

Relationship Between the Skin Surface Temperature Changes During Sprint Interval Testing Protocol and the Aerobic Capacity in Well-Trained Cyclists

The study investigated whether changes in body surface temperature in a sprint interval testing protocol (SITP) correlated with aerobic capacity in cyclists. The study involved 21 well-trained cyclists. Maximal aerobic power and maximal oxygen uptake relative to lean body mass (LBM-P(max) and LBM-VO(2max), respectively) were determined by incremental exercise testing on a cycle ergometer. SITP was administered 48 hours later and involved four 30-s maximal sprints interspersed with 90-s active recovery. Body surface temperature was recorded at the temple and arm and the delta difference between baseline temperature and temperature measured immediately after the first sprint (DeltaTt(1) and DeltaTa(1), respectively) and 80 seconds after the fourth sprint (DeltaTt(4) and DeltaTa(4)), respectively) was calculated. Significant correlations were found between DeltaTt4 and LBM-Pmax and LBM-VO(2max) (r=0.63 and r=0.75, respectively) with no significant change in DeltaTa(1) or DeltaTa(4). Body surface temperature, measured at the temple region, can be used to indirectly assess aerobic capacity during maximal sprint exercise.

Women with coronary microvascular dysfunction and no obstructive coronary artery disease have reduced exercise capacity

BACKGROUND

Both coronary microvascular dysfunction (CMD) and reduced exercise capacity are associated with adverse cardiovascular prognosis. The association between CMD and cardiopulmonary exercise testing (CPET) derived exercise capacity in symptomatic individuals without obstructive coronary artery disease (CAD) is not clear. We investigated whether exercise capacity was reduced in women with angina, CMD and no obstructive CAD compared with sex-matched controls. Furthermore, we assessed the association between CMD and other CPET-derived variables.

METHODS

All participants underwent transthoracic Doppler echocardiography of the left anterior descending artery with dipyridamole-induced vasodilation and CPET using ergometer cycle with an incremental test protocol.

RESULTS

We included 99 women with angina and no obstructive CAD (patients) and 27 asymptomatic women (controls), age (mean ± standard deviation) 61 ± 10 and 58 ± 10 years, respectively. Patients had a higher burden of risk factors compared with controls, while the weekly physical activity level was comparable between the groups (p = 0.72). CMD was present in 27 (27%) patients and 5 (19%) controls. Peak VO₂ was significantly reduced in patients with CMD compared with controls with normal coronary microvascular function ((median (IQR) 17.3 (15.5-21.3) vs. 27.3 (21.6-30.8) ml/kg/min; age-adjusted p = 0.001), independent of cardiovascular risk factors (p = 0.041). Presence of CMD in symptomatic women was also associated with diminished heart rate reserve (p < 0.001) and blunted heart rate recovery.

CONCLUSIONS

Women with angina, CMD and no obstructive CAD have markedly reduced exercise capacity compared with sex-matched controls. Moreover, combination of angina and CMD is associated with impaired heart rate response and heart rate recovery.