Table 5.

Interactions between CI-6MW and treatment assignment on time to first severe acute exacerbation of COPD (requiring hospitalization with or without mechanical ventilation)

	Interaction Term	95% CI	P Value
Interaction between baseline CI-6MW and metoprolol assignment	1.53	1.15–2.03	0.003
Interaction between time-varying CI-6MW and metoprolol assignment	1.40	1.05–1.88	0.02

Definition of abbreviations: 6MW = 6-minute walk; BMI = body mass index; CI = confidence interval; CI-6MW = chronotropic index during a 6MW; COPD = chronic obstructive pulmonary disease; FEV₁ = forced expiratory volume in 1 second; HR = hazard ratio.

Interaction terms represent the ratio of adjusted HRs in the metoprolol group compared with the placebo group. Adjusted HRs are adjusted for age, sex, race, current smoking status, BMI, baseline FEV₁ percent predicted, San Diego Shortness of Breath Questionnaire score, and 6MW distance and were stratified by study center.