Chronotropic incompetence in patients with an implantable cardioverter defibrillator: prevalence and predicting factors.

Chronotropic incompetence (CI), which has not been systematically examined in the ICD patient population, may have implications for device programming. A total of 123 ICD patients were classified into three groups: single-chamber ICD with sinus rhythm, dual-chamber ICD with sinus rhythm, and single-chamber ICD with permanent atrial fibrillation. Heart rate response, maximum oxygen uptake, and oxygen uptake at the anaerobic threshold were measured during treadmill exercise testing. In addition, clinical variables such as antiarrhythmic drug therapy, underlying heart disease, and left-ventricular (LV) ejection fraction were recorded. Of the patients studied, 38% were chronotropically incompetent (47/123). Significant predictors of CI were as follows: presence of a coronary disease (P = 0.036), prior cardiac surgery (P = 0.037), chronic drug therapy with beta-blockers (P = 0.032), administration of amiodarone (P = 0.025), and a combination of these two forms of treatment (P = 0.01). Spiroergometry revealed reduced exercise capacity (P = 0.041) and lessened VO2max (P = 0.034) among chronotropically incompetent patients. A large percentage of ICD patients demonstrates CI with subsequently reduced physical stress tolerance. In light of the DAVID study, we believe that a closer examination of rate-adaptive modes for ICD patients is warranted under enhanced conditions: (1) optimized AV interval programming; (2) utilization of new algorithms to reduce ventricular pacing in combination with rate-adaptive atrial pacing, with the goal of addressing CI while minimizing ventricular pacing; and (3) an optimized upper heart-rate limit.