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Chronotropic incompetence does not contribute to submaximal exercise limitation in patients with chronic heart

Klaus K Witte1, Andrew L Clark

  • 1Leeds Institute of Genetics, Health and Therapeutics, University of Leeds, UK. klauswitte@hotmail.com

International Journal of Cardiology
|June 24, 2008
PubMed

Insights

Chronotropic incompetence is unlikely to cause exercise intolerance in chronic heart failure (CHF) patients. Patients exhibit a lower workload/heart rate ratio, suggesting heart rate limitations are a consequence, not a cause, of their reduced exercise capacity.

Area of Science:

  • Cardiology
  • Exercise Physiology

Background:

  • Chronic heart failure (CHF) patients often experience breathlessness and fatigue during exercise.
  • A traditional hypothesis suggests 'chronotropic incompetence' (limited heart rate increase) contributes to exercise intolerance in CHF.

Purpose of the Study:

  • To investigate the relationship between heart rate and workload in patients with CHF during exercise.
  • To determine if chronotropic incompetence is a cause or consequence of exercise intolerance in CHF.

Main Methods:

  • Calculated workload/heart rate ratios during peak and submaximal (15%, 25%, 50% of peak) exercise tests.
  • Compared these ratios between CHF patients and control subjects.
  • Assessed the relationship between heart rate and workload using correlation analysis.

Main Results:

  • CHF patients had a lower workload/heart rate ratio during peak exercise compared to controls.
  • During submaximal exercise, CHF patients had lower absolute workload and oxygen consumption but similar heart rates to controls, resulting in a lower workload/heart rate ratio.
  • A significant relationship between heart rate and workload was found in controls (r=0.85), but not in CHF patients (r=0.003) during steady-state exercise.

Conclusions:

  • Heart rate limitation is likely a consequence, rather than the primary cause, of exercise intolerance in CHF.
  • CHF patients demonstrate a blunted heart rate response relative to workload during exercise, indicating altered cardiovascular regulation.

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