Prognostic Role of Metabolic Exercise Testing in Heart Failure

Abstract

Heart failure is a clinical syndrome with significant heterogeneity in presentation and severity. Serial risk-stratification and prognostication can guide management decisions, particularly in advanced heart failure, when progression toward advanced therapies or end-of-life care is warranted. Each currently utilized prognostic marker carries its own set of challenges in acquisition, reproducibility, accuracy, and significance. Left ventricular ejection fraction is foundational for heart failure syndrome classification after clinical diagnosis and remains the primary parameter for inclusion in most clinical trials; however, it does not consistently correlate with symptoms and functional capacity, which are also independently prognostic in this patient population. Utilizing the left ventricular ejection fraction as the sole basis of prognostication provides an incomplete characterization of this condition and is prone to misguide medical decision-making when used in isolation. In this review article, we survey and exposit the important role of metabolic exercise testing across the heart failure spectrum, as a complementary diagnostic and prognostic modality. Metabolic exercise testing, also known as cardiopulmonary exercise testing, provides a comprehensive evaluation of the multisystem (i.e., neurological, respiratory, circulatory, and musculoskeletal) response to exercise performance. These differential responses can help identify the predominant contributors to exercise intolerance and exercise symptoms. Additionally, the aerobic exercise capacity (i.e., oxygen consumption during exercise) is directly correlated with overall life expectancy and prognosis in many disease states. Specifically in heart failure patients, metabolic exercise testing provides an accurate, objective, and reproducible assessment of the overall circulatory sufficiency and circulatory reserve during physical stress, being able to isolate the concurrent chronotropic and stroke volume responses for a reliable depiction of the circulatory flow rate in real time.

Keywords: cardiopulmonary exercise testing; diagnosis; functional capacity; heart failure; metabolic exercise testing; oxygen consumption; prognosis.

Figure 1

Prognostic Markers for Heart Failure. * Acute Decompensated Heart Failure National Registry-ADHERE [10]; AHA Get With The Guidelines Score [11]; Candesartan in Heart failure-Assessment of Reduction in Mortality and morbidity-CHARM Risk Score [12]; Controlled Rosuvastatin Multinational Trial in Heart Failure-CORONA Risk Score [13]; Enhanced Feedback for Effective Cardiac Treatment-EFFECT Risk Score [14]; Evaluation Study of Congestive Heart Failure and Pulmonary Artery Catheterization Effectiveness-ESCAPE Risk Model and Discharge Score [15]; Guiding Evidence-Based Therapy Using Biomarker Intensified Treatment-GUIDE-IT [16]; Heart Failure Survival Score [17]; Heart Failure: A Controlled Trial Investigating Outcomes of Exercise Training-HF-ACTION [18]; Meta-analysis Global Group in Chronic Heart Failure-MAGGIC [19]; Irbesartan in Heart Failure with Preserved Ejection Fraction-I-PRESERVE Score [20]; PARADIGM-HF [21]; Seattle Heart Failure Model [22]; Treatment of Preserved Cardiac Function Heart Failure with an Aldosterone Antagonist trial-TOPCAT [23].

Figure 2

Metabolic Exercise Test Component Threshold.