Abstract 2715: Chronotropic Incompetence Is Manifest In All Phases Of Exercise In Patients With CHF.
Background: Chronotropic Incompetence (CI) as evidenced by a blunted heart rate response to exercise is often seen in subjects (CHF) and associated with aderse outcomes. Definitions for CI are in principle based on whether or not the subject reaches age-adjusted maximally predicted heart rate with or without accounting for resting heart rate (i.e. heart rate reserve), but it is unknown whether subjects with CI display abnormal heart rate acceleration at earlier phases of exercise, and whether beta blockade effects prevalence and presentation of CI. Such knowledge might have important implication for pacer based modulation of CI.
Methods and Results: Cardiopulmonary exercise tolerance testing data for 278 consecutive patients with systolic CHF was analyzed. CI was defined as the inability to reach 80% of maximally predicted heart rate and was present in 128 of 278 subjects (46%). Subjects with CI had lower peak exercise heart rate (114 vs 152 bpm, p < 0.05), and lower peak VO2 (15.4 vs 19.9 ml/kg/min, p < 0.05), but were equally likely to be on chronic beta-blocker therapy (74% vs. 71%; p = 0.51). To examine whether subjects with CI had lower peak exercise heart rates simply due to shorter exercise times, we compared exercise times and generated two point acceleration slopes for subjects with and without CI (Fig 1⇓). While exercise time was indeed shorter in subjects with CI, heart rate acceleration slopes were less steep (4.5 vs 6.7, p < 0.001) in subjects with CI (irrespective of beta blocker use).
Conclusions: CI is common in subjects with advanced systolic CHF irrespective of beta-blocker use and manifests itself throughout all phases of exercise.