What is the role of CPX in determining the prognosis of dilated cardiomyopathy?

Updated: Nov 28, 2018
  • Author: Vinh Q Nguyen, MD, FACC; Chief Editor: Gyanendra K Sharma, MD, FACC, FASE  more...
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Answer

Cardiopulmonary exercise testing in determining prognosis

An important determinant of prognosis is peak VO2 (oxygen consumption) obtained with cardiopulmonary exercise testing (CPX). It is known that an inverse relationship exists between exercise duration and mortality. Because exercise capacity is variable among individuals and reproducibility is not always achieved, exercise testing with respiratory gas analysis provides a standardized method for heart transplant selection. [69] Peak VO2 reflects functional capacity and cardiac reserve. [70] It is a good predictor of mortality, as its decline precedes cardiac decompensation. [71]

Cardiac transplantation appears to have the potential to be deferred in a subset of ambulatory patients with heart failure. In a study that assessed mortality in 116 patients with chronic heart failure stratified into 3 groups, Mancini et al found that peak VO2 was the best predictor for survival, with supporting prognostic information from pulmonary capillary wedge pressure. [70] Group 1 had a peak VO2 below 14 mL/kg/min and was accepted for transplantation; the survival rate at 1 year was 48%. Group 2 had a peak VO2 above 14 mL/kg/min, with patients deemed too well for transplantation; the survival rate at 1 year was 94%, which was comparable to that of their counterparts who underwent transplantation. Group 3 had a peak VO2 below 14 mL/kg/min, along with comorbidities that precluded transplantation; the survival rate at 1 year was 47%. [70]

The three groups had comparable NYHA functional class, cardiac index, and ejection fraction. Thus, based on these findings on mortality, patients with intact exercise capacity (peak VO2 >14 ml/kg/min) can be medically managed. That is, deferring cardiac transplantation may be safe in ambulatory patients with severe left ventricular dysfunction and a peak exercise VO2 above 14 mL/min/kg. [70] Similarly, Stelken et al showed that a peak VO2 below 50% of the predicted was a strong predictor of 12-month survival in ambulatory patients with heart failure with an ischemic or dilated etiology. [72]

Ventilatory anaerobic threshold (VAT) is a parameter of CPX that provides an index of submaximal exercise capacity, independent of patient motivation. It is the point when aerobic metabolism transitions to aerobic plus anaerobic metabolism in which lactate increases. Inability to achieve VAT suggests noncardiovascular limitations of exercise tolerance or poor motivation. [73]  In individuals with VAT identified, the reported cardiac event rate was 59% in those with a peak VO2 of 10 mL/kg/min or lower, and 15% in those with a peak VO2 above 18 mL/kg/min. [74]  In patients in whom VAT was not detected, the cardiac event rate was 46% in those with peak VO2 of 10 mL/kg/min or below, but for those with a peak VO2 above 10 mL/kg/min, the risk stratification was inconclusive. [74]

Additionally, ventilatory expired gas parameters (VE/VCO2 slope [minute ventilation/carbon dioxide output]) also carry prognostic capability. [69, 75] VE/VCO2 is a ratio relating liters of inspired air to remove 1 L of CO2. A high ratio or slope carries a worse prognosis. Patients with VE/VCO2 slope of 35 or higher had a higher mortality compared to those with a slope below 35 (30% vs 10%, respectively). [75]


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