Relation between aerobic capacity and extent of myocardial ischemia in patients with normal cardiac function

Effects of coronary sinus Reducer implantation on oxygen kinetics in patients with refractory angina

AIMS

Refractory angina is still a major public health problem. The coronary sinus Reducer (CSR) has recently been introduced as an alternative treatment to reduce symptoms in these patients. The aim of this study was to investigate objective improvements in effort tolerance and oxygen kinetics as assessed by cardiopulmonary exercise testing (CPET) in patients suffering from refractory angina undergoing CSR implantation.

METHODS AND RESULTS

In this multicentre prospective study, patients with chronic refractory angina undergoing CSR implantation were scheduled for CPET before the index procedure and at six-month follow-up. The main endpoints of this analysis were improvements in VO2 max and in VO2 at the anaerobic threshold (AT). Clinical events and improvements in symptoms were also recorded. A total of 37 patients formed the study population. The CSR implantation procedure was successful and without complications in all. At follow-up CPET, significant improvement in VO2 max (+0.97 ml/kg/min [+11.3%]; 12.2±3.6 ml/kg/min at baseline vs 13.2±3.7 ml/kg/min, p=0.026), and workload (+12.9 [+34%]; 68±28 W vs 81±49 W, p=0.05) were observed, with non-significant differences in VO2 at the AT (9.84±3.4 ml/kg/min vs 10.74±3.05 ml/kg/min, p=0.06). Canadian Cardiovascular Society (CCS) grade improved from a mean of 3.2±0.5 to 1.6±0.8 (p<0.01), and significant benefits in all Seattle Angina Questionnaire variables were shown.

CONCLUSIONS

In patients with obstructive coronary artery disease suffering from refractory angina, the implantation of a CSR was associated with objective improvement in exercise capacity and oxygen kinetics at CPET, suggesting a possible reduction of myocardial ischaemia.

Importance of compensatory heart rate increase during myocardial ischemia to preserve appropriate oxygen kinetics

BACKGROUND

Myocardial ischemia induces cardiac dysfunction, resulting in insufficient oxygen supply to peripheral tissues and mismatched energy production during exercise. To relieve the insufficient oxygen supply, heart rate (HR) response is augmented; however, beta-adrenergic receptor blockers (BB) restrict HR response. Although BB are essential drugs for angina pectoris, the effect of BB on exercise tolerance in patients with angina has not been studied. The aim of this study was to clarify the importance of HR augmentation to preserve exercise tolerance in patients with angina pectoris.

METHODS

Forty-two subjects who underwent cardiopulmonary exercise testing (CPX) to detect myocardial ischemia were enrolled. CPX was performed until exhaustion or onset of significant myocardial ischemia using a ramp protocol. Subjects were assigned to three groups (Group A: with ST depression during CPX with significant coronary stenosis and taking BB; Group B: with ST depression and not taking BB; Group C: without ST depression and not taking BB). HR response to exercise was evaluated during the following two periods: below and above ischemic threshold (IT). In Group C, it was evaluated during the first 2min and the last 2min of a ramp exercise.

RESULTS

No significant differences were observed among the three groups with regard to patients' basic characteristics. Below IT, there were no differences in oxygen pulse/watt (O₂ pulse increasing rate), HR/watt (ΔHR/ΔWR), and ΔV˙O₂/ΔWR. Above IT, O₂ pulse increasing rate was greater in Group A than in Group B. ΔHR/ΔWR was smaller in Group A than in Group B. ΔV˙O₂/ΔWR became smaller in Group A than in Group B. There was no difference in anaerobic threshold, and peak V˙O₂ was smaller in Group A than in Group B.

CONCLUSIONS

Restriction of HR response by a BB is shown to be one of the important factors in diminished exercise tolerance.

Impact of completeness of revascularization by coronary intervention on exercise capacity early after acute ST-elevation myocardial infarction

Background

The importance of achieving complete revascularization by percutaneous coronary intervention (PCI) in patients with acute myocardial infarction (MI) on exercise capacity remains unclear.

Objective

To compare exercise capacity early after acute ST-elevation myocardial infarction (STEMI), in patients receiving PCI with stenting, between those completely revascularized (CR) and those incompletely revascularized (IR).

Methods

We retrospectively reviewed 326 patients [single-vessel disease (SVD) group, 118 patients; multivessel disease (MVD) with CR group, 112 patients; MVD with IR group, 96 patients] who underwent cardiopulmonary exercise testing 7–30 days after STEMI to measure peak oxygen uptake (VO_2peak), oxygen uptake at anaerobic threshold (VO_2AT), and peak oxygen pulse. Demographic data, presence of concomitant diseases, STEMI characteristics, and echocardiography and angiography findings were evaluated.

Results

Most patients were male (89.0%) and mean age was 55.6 ± 11.2 years. Ischemic ST deviation occurred in 7.1%, with no significant difference between groups. VO_2peak and VO_2AT did not differ significantly between groups, despite a trend to be lower in the CR and IR groups compared with the SVD group. Peak oxygen pulse was significantly higher in the SVD group than in the IR group (p = 0.005). After adjustment for age, gender, body mass index, cardiovascular risk factors, MI characteristics and echocardiography parameters, CR was not an independent predictor of VO_2peak (OR = −0.123, 95% confidence interval [CI] -2.986 to 0.232, p = 0.093), VO_2AT (OR = 0.002, 95% CI 1.735 to 1.773, p = 0.983), or peak oxygen pulse (OR = −0.102, 95% CI −1.435 to 0.105, p = 0.090).

Conclusion

CR in patients with STEMI treated with PCI for multivessel disease might show no benefit on short-term exercise tolerance over IR.

Stability of relative oxygen pulse curve during repeated maximal cardiopulmonary testing in professional soccer players

During cardiopulmonary exercise testing (CPET), stroke volume can be indirectly assessed by O(2) pulse profile. However, for a valid interpretation, the stability of this variable over time should be known. The objective was to analyze the stability of the O(2) pulse curve relative to body mass in elite athletes. VO(2), heart rate (HR), and relative O(2) pulse were compared at every 10% of the running time in two maximal CPETs, from 2005 to 2010, of 49 soccer players. Maximal values of VO(2) (63.4 ± 0.9 vs 63.5 ± 0.9 mL O(2)•kg(-1)•min(-1)), HR (190 ± 1 vs188 ± 1 bpm) and relative O(2) pulse (32.9 ± 0.6 vs 32.6 ± 0.6 mL O(2)•beat(-1)•kg(-1)) were similar for the two CPETs (P > 0.05), while the final treadmill velocity increased from 18.5 ± 0.9 to 18.9 ± 1.0 km/h (P < 0.01). Relative O(2) pulse increased linearly and similarly in both evaluations (r(2) = 0.64 and 0.63) up to 90% of the running time. Between 90 and 100% of the running time, the values were less stable, with up to 50% of the players showing a tendency to a plateau in the relative O(2) pulse. In young healthy men in good to excellent aerobic condition, the morphology of the relative O(2) pulse curve is consistent up to close to the peak effort for a CPET repeated within a 1-year period. No increase in relative O(2)pulse at peak effort could represent a physiologic stroke volume limitation in these athletes.

The Clinical Utility of Cardiopulmonary Exercise Testing in Suspected or Confirmed Myocardial Ischemia

Heart disease is a major cause of morbidity and mortality in the United States, with coronary artery disease (CAD) representing more than half of all cardiovascular events. Stable patients presenting with symptoms suggestive of CAD are likely to undergo an exercise electrocardiogram (ECG) and/ or imaging study as a first-line diagnostic assessment. A cardiopulmonary exercise test (CPX) is an ECG stress test plus ventilatory gas analysis. Recently, CPX has been used to detect exercise-induced myocardial ischemia (EIMI) suggestive of underlying CAD. Two CPX variables, oxygen pulse (VO2/HR) and the slope of oxygen consumption versus work rate (Δ VO2/ Δ WR), have been identified to be especially indicative of EIMI. Currently, there are a number of diagnostic tests available for the identification of CAD, with the most widely used being stress ECG, stress myocardial perfusion imaging (MPI) and echocardiography, and cardiac catheterization. Exercise ECG, although inexpensive, has a number of well-recognized limitations, including low sensitivity resulting in false-negative results. Stress (exercise or pharmaceutically induced) MPI and catheterization are more accurate but also more invasive and expensive. It appears that CPX may improve the diagnostic accuracy of exercise ECG. This review will address the potential utility of CPX in patients with suspected or confirmed myocardial ischemia.

Standards for the use of cardiopulmonary exercise testing for the functional evaluation of cardiac patients: a report from the Exercise Physiology Section of the European Association for Cardiovascular Prevention and Rehabilitation

Cardiopulmonary exercise testing (CPET) is a methodology that has profoundly affected the approach to patients' functional evaluation, linking performance and physiological parameters to the underlying metabolic substratum and providing highly reproducible exercise capacity descriptors. This study provides professionals with an up-to-date review of the rationale sustaining the use of CPET for functional evaluation of cardiac patients in both the clinical and research settings, describing parameters obtainable either from ramp incremental or step constant-power CPET and illustrating the wealth of information obtainable through an experienced use of this powerful tool. The choice of parameters to be measured will depend on the specific goals of functional evaluation in the individual patient, namely, exercise tolerance assessment, training prescription, treatment efficacy evaluation, and/or investigation of exercise-induced adaptations of the oxygen transport/utilization system. The full potentialities of CPET in the clinical and research setting still remain largely underused and strong efforts are recommended to promote a more widespread use of CPET in the functional evaluation of cardiac patients.

Flattening of oxygen pulse during exercise may detect extensive myocardial ischemia

PURPOSE

Flattening of oxygen pulse curve during incremental cardiopulmonary exercise testing has been proposed for the improvement of diagnostic accuracy of exercise-induced myocardial ischemia. In this study, we compare the oxygen pulse response to incremental treadmill exercise in patients with and without ischemia as detected by myocardial perfusion scintigraphy.

METHODS

Eighty-seven patients referred to exercise myocardial perfusion scintigraphy were also evaluated with incremental treadmill cardiopulmonary exercise testing. One investigator prospectively identified patients who presented transient exercise-induced perfusion defects on 99mTc sestamibi myocardial scintigraphies. Another investigator evaluated the response of oxygen pulse to incremental exercise testing without knowledge of electrocardiographic response or scintigraphic findings.

RESULTS

Exercise myocardial perfusion scintigraphy detected transient perfusion defects in 36% of the patients. Compared with patients with normal perfusion studies, patients with exercise-induced ischemia presented similar peak double product, peak oxygen uptake, and anaerobic threshold. Oxygen pulse at 25% of peak (ischemia: 9.7 +/- 2 mL per beat; no ischemia: 9.3 +/- 2 mL per beat), 50% of peak (11.2 +/- 3 vs 10.8 +/- 3 mL per beat), 75% of peak (12.5 +/- 3 vs 11.9 +/- 3 mL per beat), and at peak exercise (13 +/- 4 vs 13 +/- 4 mL per beat) were not different in exercise-induced ischemia and normal groups, respectively. However, patients who presented extensive transient perfusion defects during exercise had a lower peak oxygen pulse (12.8 +/- 3.8 vs 16.4 +/- 4.6 mL per beat; P < 0.05).

CONCLUSION

The analysis of the oxygen pulse response to incremental exercise test does not identify mild myocardial ischemia. Flattening of oxygen pulse response during incremental exercise might be present only with extensive myocardial ischemia.

A basic approach to the interpretation of the exercise test

To interpret the exercise test, the following parameters need to be evaluated: the heart rate and blood pressure response, symptoms, dysrhythmias, aerobic capacity, and evidence for myocardial ischemia. When analyzing the ST segment for ischemia, the amount and type of ST depression and the time of onset and resolution are examined. The exercise test results are best used to determine a post-test probability that the patient has significant coronary disease, predict its severity, and provide a prognosis of the patient. The test allows primary care physicians to decide which patients with coronary artery disease can be safely managed medically and which high-risk patients need further evaluation and consideration for revascularization.