Association of smoking with abnormal exercise heart rate responses and long-term prognosis in a healthy, population-based cohort.
BACKGROUND
Cigarette smoking is associated with chronotropic incompetence, defined as an attenuated heart rate response to exercise. The long-term prognostic implications of this association have not been well explored.


METHODS
Adults enrolled in the Lipid Research Clinics' Prevalence Study who had no history of cardiovascular disease and who were not taking beta-blockers were observed for 12 years. Chronotropic incompetence was assessed as the failure to achieve 90% of an age-predicted target heart rate during an exercise test or as a low chronotropic index, a measure of exercise heart rate response adjusted for age, resting heart rate, and physical fitness.


RESULTS
Of the 5,354 eligible participants (mean [+/- SD] age of 44 +/- 10 years; 61% male), 1,931 (36%) smoked cigarettes. Smokers were more likely to have a low chronotropic index (26% versus 16%, odds ratio = 1.8, 95% confidence interval [CI] 1.6 to 2.1) and fail to achieve an age-predicted target heart rate (32% versus 22%, odds ratio = 1.7, 95% CI 1.5 to 2.0). Adjustment for standard cardiac risk factors and physical fitness did not affect these associations. During follow-up, there were 327 deaths. Among subjects without chronotropic incompetence, the relative risk of mortality associated with smoking was moderately increased (hazard ratio = 1.8, 95% CI 1.3 to 2.3); among smokers with chronotropic incompetence, the relative risk of mortality was markedly increased (hazard ratio = 2.7, 95% CI 2.0 to 3.7, P for interaction = 0.02).


CONCLUSIONS
In this large, middle-aged population-based cohort, smoking was associated with chronotropic incompetence, which in turn identified smokers with a particularly high mortality rate.
Srivastava
R
R
Department of Medicine, Cleveland Clinic Foundation, Cleveland, Ohio 44195, USA.
Blackstone
E H
EH
Lauer
M S
MS
D000328:Adult; D002170:Canada / Q000453:epidemiology; D002318:Cardiovascular Diseases / Q000453:epidemiology* / Q000209:etiology / Q000503:physiopathology; D002940:Circadian Rhythm / Q000502:physiology*; D004562:Electrocardiography; D015444:Exercise; D005080:Exercise Test; D005260:Female; D005500:Follow-Up Studies; D006339:Heart Rate / Q000502:physiology*; D006801:Humans; D015994:Incidence; D008297:Male; D008875:Middle Aged; D011379:Prognosis; D012016:Reference Values; D012189:Retrospective Studies; D012307:Risk Factors; D012907:Smoking / Q000009:adverse effects* / Q000453:epidemiology / Q000503:physiopathology; D015996:Survival Rate; D014481:United States / Q000453:epidemiology