Incidence and significance of chronotropic incompetence in patients with indications for primary pacemaker implantation or pacemaker replacement

This prospective study was undertaken to evaluate the incidence and signifi cance of chronotropic incompetence in 211 patients [age 71.1 6 10.6 years ( mean 6 SD)] by means of maximum exercise test in order to determine the ind ication for rate-responsive pacing before primary pacemaker implantation (1 47 patients) or pacemaker replacement (64 patients). There were 112 (53%) p atients with second- or third-degree AV block, 63 (30%) with sick sinus syn drome, and 36 (17%) with chronic atrial fibrillation. Chronotropic incompet ence tl as defined as maximum heart rate lower than age-adjusted norm calcu lated by the formula: 0.7 x (220 - age) and its significance as the differe nce between the two rates. The overall incidence of chronotropic incompeten ce was 42%. The incidence was significantly higher in patients with atrial fibrillation (67%, P < 0.0005) and sick sinus syndrome (49%, P < 0.012) tha n in those with AV block (30%). The mean difference between maximum heart r ate and the age-adjusted norm was 18% (range 2%-63%). The mean difference w as significantly higher in patients with atrial fibrillation (27%, range 8- 63%) than in those with sick sinus syn drome (19%, range 2%-45%, P < 0.01), or with AV block (12%, range 6%-26%, P < 0.000001). The rate-responsive pa cemakers were implanted in 44% of 211 patients studied and in 43% of 196 pa tients excluded from the study due to the apparent (contra)indication of ra te-responsive pacing (NS). Thus, chronotropic incompetence seems to be comm on in the pacemaker patient population. The highest incidence and significa nce was found in patients with chronic atrial fibrillation. Systematic eval uation of chronotropic competence can double the rate of implantation of ra te-responsive pacemakers; however, fur further studies are needed to clarif y relation between the significance of chronotropic incompetence and functi onal benefit of rate-responsive pacing.