Chronotropic Incompetence

Chronotropic incompetence (CI) is defined as the inability to proportionally increase HR with increases in metabolic demand. Since cardiac output is dependent on stroke volume (SV) and heart rate (HR) to increase with increasing workload, peak cardiac output and hence exercise capacity are reduced in patients with CI. CI is seen as a blunted HR response as a function of cardiac output in panel 5 of the Wasserman 9-panel along with low peak HR (<85% of age adjusted predicted).

Prevalence

Varies from 3-11% in patients referred for exercise testing and is high as 40% in patients with pacemakers and 60% in atrial fibrillation. 1

Etiology

    1. Medications
    2. Sinus node dysfunction
    3. Ischemic heart disease
    4. Autonomic dysfunction
    5. LV Dysfunction (heart failure)
    6. Atrial fibrillation
    7. Hypothyroidism

Treatment:

The exercise capacity in these patients is reduced due to low peak HR; the other parameters such peak stroke volume and pulmonary function at peak exercise are otherwise normal. The only way to increase exercise capacity in these patients is to improve HR response which will increase peak cardiac output and improve functional capacity thus allowing patients to feel better.

    1. Adjust medications
    2. Identify and treat underlying cause (ischemia, sick sinus syndrome, TSH, etc)
    3. Rate-responsive pacemakers
    4. Theophylline

Prognosis:

Chronotropic Incompetence identifies patients at increased risk for cardiovascular morbidity and mortality. This is thought in part to be due to abnormalities in autonomic regulation. Patients with isolated CI secondary to sick sinus syndrome appear to have more benign clinical course.

1. Gentlesk PJ, MD, Markwood TT and Atwood EJ. Chronotropic incompetence in a young Adult: Case Report and Literature Review. CHEST 2004; 125:297–301.

2. Savonen KP,. Usefulness of chronotropic incompetence in response to exercise as a predictor of myocardial infarction in middle-aged men without cardiovascular disease. Am J Cardiol. 2008 Apr 1;101(7):992-8.

3. Savonen KPKiviniemi V, Laukkanen JA, Lakka TA, Rauramaa R. Chronotropic incompetence and mortality in middle-aged men with known or suspected coronary heart disease. Eur Heart J. 2008 Aug; 29(15):1896-902.

4. Jorde UP, Vittorio TJ, Kasper M, Arezzi E, Colombo PC, Goldsmith RL, Ahuja k, Tseng CH, Hass F, Hirsh DS. Chronotropic incompetence, beta-blockers, and functional capacity in advanced congestive heart failure: time to pace? Eur J Heart Fail. 2008 Jan;10(1):96-101.

5. Oliveira JL, Góes TJ, Santana TA, Travassos TF, Teles LD, Anjos-Andrade FD, Nascimento-Júnior AC, Alves EO, Barreto MA, Barreto-Filho JA, D'Oliveira A Jr, Sousa AC.Chronotropic incompetence and a higher frequency of myocardial ischemia in exercise echocardiography. Cardiovasc Ultrasound. 2007 Nov 2; 5:38.