Cardiopulmonary Responses to Exercise in Children with Activity Sensing Rate Responsive Ventricular Pacemakers

The physiological benefits of activity sensing rate responsive ventricular pacing (VVIR) over fixed rate pacing (VVI) were investigated in 14 children during incremental cycle exercise. Based on their heart rhythm response during exercise, children were divided into two groups. Group I patients (13 +/- 4 years) remained in a paced-only rhythm when exercised. Group II patients (16 +/- 7 years) were paced at rest but converted to sinus rhythm with exercise. In Group I patients, the significant physiological benefits of VVIR over VVI pacing were evidenced by a 51% increase in peak heart rate (HRmax) and a 16% increase in exercise duration and maximum oxygen uptake (VO2max). Additionally, a 27% reduction in peak oxygen pulse (O2Pmax) was found, reflecting a similar decrease in stroke volume. The cardiorespiratory responses of Group I and II patients were compared in terms of percent of predicted normal values. Although Group I patients in the VVIR mode attained a better exercise performance than in the VVI mode and a normal O2Pmax (108% pred), their HRmax (62% pred) and VO2max (70% pred) fell far below normal values. In comparison, Group II patients, who went into sinus rhythm, achieved normal values for HRmax (84% pred), VO2max (90% pred), and O2Pmax (97% pred). The higher pacing rates attained by Group I patients in the VVIR mode may have allowed them to reach not only a higher cardiac output but also a more normal stroke volume at peak exercise than in the VVI mode.(ABSTRACT TRUNCATED AT 250 WORDS)