Ventilatory response and peak circulatory power: New functional markers of response after cardiac resynchronization therapy

Abstract

The minute ventilation/carbon dioxide production (VE/VCO(2)) slope and peak circulatory power, like peak oxygen consumption (VO(2)), possess strong prognostic values in heart failure but have not been studied after ventricular resynchronization. In this retrospective study, we evaluated the evolution of ventilatory response, effort capacity, functional status, peak circulatory power and echocardiographic variables, 6 months after cardiac resynchronization therapy (CRT). Thirty subjects (mean age, 60+/-12 years) underwent symptom-limited exercise testing (CPX) with ventilatory expired gas analysis before and 6 months after CRT. The VE/VCO(2) slope was measured from rest to the end of exercise. Echocardiography was performed in stable clinical and pharmacological conditions. Mean New York Heart Association (NYHA) status improved significantly from 2.9 to 1.8 (p<0.001). Significant improvements were seen in exercise tolerance (evaluated by peak VO(2); from 13.1+/-3.1 to 15.3+/-5.6 mL/kg/min, p=0.02), VE/VCO(2) slope (from 44.4+/-19.2 to 39.6+/-13.8, p=0.003) and maximal workload (from 74+/-24 to 82+/-26 W, p=0.02). Mean peak circulatory power improved from 1663+/-494 to 2125+/-1014 mmHgmL/kg/min (p=0.009). Mean left ventricular ejection fraction increased from 25% to 29% (p=0.01). Mean end-systolic and end-diastolic left ventricular volumes decreased significantly from 155 to 128 mL and from 203 to 179 mL, respectively (p<0.05). Mean mitral regurgitation grade improved from 1.4+/-1.0 to 1.1+/-0.9 (p=0.1). No strong correlation was found between echocardiographic changes and improvement in ventilatory efficiency (VE/VCO(2) slope; all r=0.15-0.24). Patients with narrow QRS complexes (<130 ms) did not show significant improvement in functional or echocardiographic variables other than NYHA status. Cardiac resynchronization therapy improved ventilatory and haemodynamic responses. Our results highlight the potential value of new functional variables such as ventilatory response and peak circulatory power as better markers for identifying responders to CRT.