Submitted on June 10, 2008
Revised on January 20, 2009
Accepted on February 24, 2009
Effect of biventricular pacing on ventilatory and perceptual responses to exercise in patients with stable Chronic Heart Failure
Pierantonio Laveneziana1*, Denis E. O'Donnell2, Dror Ofir1, PierGiuseppe Agostoni3, Luigi Padeletti4, Giuseppe Ricciardi4, Paolo Palange5, Roberto Duranti4, and Giorgio Scano4
1 Queen's University
2 Queens University
3 University of Milan
4 University of Florence
5 University of Rome
* To whom correspondence should be addressed. E-mail: pier_lav{at}yahoo.it.
Background: Despite the growing evidence supporting the use of biventricular cardiac resynchronization therapy (CRT) in patients with chronic heart failure (CHF), the mechanisms whereby acute hemodynamic improvements lead to improved exertional dyspnea are not precisely known. We hypothesized that improved cardiac function and ventilation-perfusion relations following CRT would reduce ventilatory demand thereby improving dynamic operating lung volumes and enhancing tidal volume expansion during exercise. This in turn would be expected to reduce perceived exertional dyspnea and contribute to improved exercise performance. Methods: In a randomized, double-blind, crossover study, we compared cardiovascular, metabolic, ventilatory responses (breathing pattern, operating lung volumes, pulmonary gas exchange) and exertional symptoms in 7 stable CHF patients who undertook incremental cardiopulmonary cycle exercise test with CRT switched to the "ON" (CRTon) or "OFF" (CRToff) modality. Results: Following CRTon, peak oxygen uptake was significantly increased by 15% and dyspnea ratings were lower for a given work rate (at work rate of 40 watts, dyspnea = 1±0.4 vs 2.5±0.9 Borg units, P <0.05) and ventilation (at ventilation of 31 l/min, dyspnea = 2±0.7 vs 3.3±1.1 Borg units, P <0.05). CRTon was associated with improvements in ventilatory threshold, oxygen pulse and V'O2/work rate relationships (10.2±1 vs 7.9±1.3 ml/min/watt, P <0.05). CRTon reduced the ventilatory requirement during exercise as well as the steepness of V'E/V'CO2 slope (35±4 vs 45±7, P <0.05). Changes in end-expiratory lung volume during exercise were less with CRTon than with CRToff (0.12 vs 0.37 L, P <0.05) and breathing pattern was correspondingly slower and deeper. Conclusions: Biventricular pacing improved all non-invasive indices of cardiac function and oxygen delivery during exercise. The decreased ventilatory demand, improved dynamic operating lung volumes and the increased ability to expand tidal volume during exercise are potential factors in the reduction of exertional dyspnea.
