Objective: Chronic obstructive pulmonary disease (COPD) is a highly prevalent syndrome, deeply affecting the cardiovascular system as well as the lungs. We investigated the prognostic role of the QT interval and QT dispersion (QTD) in predicting all-cause, respiratory and cardiovascular mortality in COPD, and the relationship between these electrocardiographic parameters and pulmonary function in a prospective longitudinal study.
Methods: We studied 246 COPD patients without significant co-morbidities, with a mild to moderate functional impairment, admitted to the Department of Internal Medicine from January 1995 to December 2001, performing a 5-year mean follow-up (5-116 months) up to August 2004. After clinical stabilisation, an electrocardiogram and functional respiratory tests were obtained, allowing measurement of the QT interval and QTD, forced vital capacity (FVC), forced expiratory volume at 1 s (FEV1), inspiratory capacity, FEV1/FVC ratio, partial oxygen pressure and partial carbon dioxide pressure in arterial blood.
Results: At the end of the follow-up period, 81 patients were dead, 165 still alive; 36 died because of respiratory causes, 23 because of cardio-cerebrovascular events, 21 because of cancer (mainly lung cancer). A significant high incidence of sudden cardiac death was observed. QTD and QTcD showed a significant relationship with respiratory functional parameters. Maximal QT interval, QTcD and QTD appear to be independent predictors of all-cause, cardiovascular and respiratory mortality (relative risk 1.94, 3.22, 2.88, respectively). Age > 65 years, partial oxygen pressure < 60 mmHg and inspiratory capacity < 80% of the predicted value were the only other independent predictive parameters.
Conclusions: Maximal QT interval, QTD and QTcD are independent predictors of mortality. A significant incidence of cardiac sudden death was observed. These findings suggest the need for a global and multidisciplinary risk assessment in COPD patients. Intriguing relationships between the QTD and functional respiratory parameters were also observed.