RESUMO
The aim of this study was to compare respiratory gas exchanges during exercise during VVI and DDD modes of cardiac pacing, the latter offering the possibility of preserving the atrio-ventricular sequence and of increasing the heart rate during exercise. Ten patients with normal systolic function (6 men, 4 women; average age 51 years), complete atrioventricular block and no acceleration of the heart rate during exercise, undergoing implantation of a dual-chamber pacemaker, performed maximal exercise stress testing after programming VVI or DDD modes successively with a one hour interval between the two investigations. The parameters recorded at peak exercise capacity were compared according to the pacing mode. Exercise duration (8 +/- 2 mn), maximal heart rate (133 +/- 10 bpm), systolic blood pressure (175 +/- 24 mmHg), work load (104 +/- 20 watts) were significantly higher in the DDD than in the VVI mode (6 +/- 2 mn, 73 +/- 8 bpm, 147 +/- 22 mmHg, 84 +/- 17 watts respectively, p < 0.001 for each parameter). Above all, peak oxygen uptake in the DDD mode was 23.2 +/- 6 ml/kg/mn compared to 19.2 +/- 5.1 ml/kg/mn in the VVI mode (p < 0.001). The increased heart rate obtained with DDD pacing seems to be the main factor which explains the differences observed. At lower exercise levels, there was no significant difference in ventilatory threshold between VVI and DDD pacing. The absence of underlying cardiac disease and a single, fixed atrioventricular delay may reduce the value of maintaining the atrioventricular sequence at more moderate exercise levels. This study shows that dual-chamber pacing increases maximal exercise capacity. These observations may be useful when considering the choice of a cardiac pacemaker.
