Cardiopulmonary exercise testing: A contemporary and versatile clinical tool
ABSTRACT
Cardiopulmonary exercise testing (CPET) helps in detecting disorders of the cardiovascular, pulmonary, and skeletal muscle systems. It has a class I (indicated) recommendation from the American College of Cardiology and American Heart Association for evaluating exertional dyspnea of uncertain cause and for evaluating cardiac patients being considered for heart transplant. Advances in hardware and software and ease of use have brought its application into the clinical arena to the point that providers should become familiar with it and consider it earlier in the evaluation of their patients.
KEY POINTS
- Technological advances and ease of use have brought CPET out of specialized centers and into the realm of daily clinical practice.
- CPET is a versatile test that has unique ability to assess cardiopulmonary and metabolic responses to exercise that can reflect underlying pathology.
- CPET has established value in assessing patients with exertional dyspnea and can guide clinical decision-making and help streamline patient management by focusing on the cause or excluding pathology.
- CPET has useful prognostic capabilities in patients with heart failure to guide medical treatment or referral for advanced therapies.
Case 3: Systemic sclerosis
A 64-year-old woman with systemic sclerosis, hypertension, diabetes, and sleep apnea is referred for CPET evaluation of dyspnea. Echocardiography 6 months ago showed a normal left ventricular ejection fraction and moderate diastolic dysfunction.
She undergoes screening spirometry. Results are abnormal and suggest restrictive disease, borderline-low breathing reserve, and low peak Vo2 (20 mL/kg/min; 71% of predicted). She also has chronotropic incompetence (peak heart rate 105 beats per minute; 67% of predicted). These findings are thought to be manifestations of her systemic sclerosis. You refer her for both pulmonary and electrophysiology consultation.
Case 4: Mitral valve prolapse
A generally healthy 73-year-old woman undergoes echocardiography because of a murmur. Findings reveal mitral valve prolapse and mitral regurgitation, which is difficult to quantify. She is referred for CPET as a noninvasive means of assessing the hemodynamic significance of her mitral regurgitation.
Her overall peak Vo2 is low (15 mL/kg/min). The Ve/Vco2 slope is elevated at 32 (normal < 30), and end-tidal Pco2 response is also abnormal. The recovery heart rate is also abnormally elevated. Collectively, these findings indicate that her mitral valve regurgitation is hemodynamically significant, and you refer her for mitral valve surgery.
CPET’S ROLE IN HEART FAILURE
Over 2 decades ago, the direct measure of peak Vo2 during exercise was found to be an important prognosticator for patients with advanced heart failure and thus became a conventional measure for stratifying patients most in need of a heart transplant.14 To this day, a peak Vo2 of 14 mL/kg/min remains a prognostic threshold—values this low or less carry a poor prognosis.
Additional CPET variables are prognostically useful, both independently and with each other. Many of them reflect the ventilatory and metabolic inefficiencies that result from the extensive central and peripheral pathophysiology seen in heart failure.7,15–17
An elevated Ve/Vco2 slope is a strong predictor of adverse outcomes for patients with heart failure with either reduced or preserved ejection fraction.18,19 Other recognized prognostic indicators include20–23:
Low end-tidal Pco2
Exercise oscillatory breathing
Low oxygen uptake efficiency slope. All of these are readily provided in the reports of modern CPET systems. Explanations are in Table 1.
Collectively, these variables are strong predictors of outcomes in heart failure patients in terms of survival, adverse cardiac events, or progression to advanced therapy such as a left ventricular assist device or transplant. A multicenter consortium analyzed CPET results from more than 2,600 systolic heart failure patients and devised a scoring system for predicting outcomes (Table 3). This scoring system is a recommended component of the standard evaluation in patients with advanced heart failure.24
EXERCISE TEST REPORTING
Currently there is no universal reporting format for CPET. Using a systematic approach such as the one proposed by Guazzi et al5 can help assure that abnormal values and patterns in all areas will be identified and incorporated in test interpretation. Table 4 lists suggested components of a CPET report and representative examples.
OTHER USES OF EXERCISE TESTING
CPET has also been found useful in several other clinical conditions that are beyond the scope of this review. These include pulmonary hypertension,25 differentiation of pathologic vs physiologic hypertrophy of the left ventricle,26 preclinical diastolic dysfunction,27,28 congenital heart disease in adults,29 prediction of postoperative complications in bariatric surgery,30 preoperative evaluation for lung resection and pectus excavatum,31,32 hemodynamic impact of mitral regurgitation,33 and mitochondrial myopathies.34
COST-EFFECTIVENESS UNKNOWN
The Current Procedural Terminology code for billing for CPET is 94621 (complex pulmonary stress test). The technical fee is $1,605, and the professional fee is $250. The allowable charges vary according to insurer, but under Medicare A and B, the charges are $258.93 and $70.65, respectively, of which patients typically must copay 20%. Total relative value units are 4.60, of which 1.95 are work relative value units.
The cost-effectiveness of CPET has not been studied. As illustrated in the case examples, patients often undergo numerous tests before CPET. While one might infer that CPET could streamline testing and management if done sooner in disease evaluation, this hypothesis has not been adequately studied, and further research is needed to determine if and how doing so will affect overall costs.
IMPLICATIONS FOR PRACTICE
Newer hardware and software have made CPET more available to practicing clinicians.
CPET has proven value in evaluating patients with exertional dyspnea. If first-line evaluation has not revealed an obvious cause of a patient’s dyspnea, CPET should be considered. This may avoid additional testing or streamline subsequent evaluation and management. CPET also has an established role in risk stratification of those with heart failure.
The clinical application of CPET continues to evolve. Future research will continue to refine its diagnostic and prognostic abilities in a variety of diseases. Most major hospitals and medical centers have CPET capabilities, and interested practitioners should seek out those experienced in test interpretation to increase personal familiarity and to foster appropriate patient referrals.
