Idiopathic dilated cardiomyopathy among Swedish patients with congestive heart failure

Abstract

Idiopathic dilated cardiomyopathy (IDCM) is an exclusion diagnosis. Although it is a prognostically important entity and a common indication for cardiac transplantation, the incidence and age distribution of idiopathic IDCM in a well-defined population today is unknown. The present study intended to estimate the proportion of IDCM among congestive heart failure (CHF) patients, and to evaluate its prognostic implications. The records of all 16–65-year-old patients hospitalized for CHF or IDCM during a 6-year period (n=2711) were evaluated in a defined region of Western Sweden (1.05 million inhabitants 16–65 years of age). Twenty-two percent (584/2711) of these records contained no plausible cause of CHF or IDCM, and among living patients an obvious aetiology was lacking in 27% (411/1516). These 411 patients were subsequently offered a diagnostic investigation including echocardiography, and were compared to a randomly selected healthy control group (n=103). Of 411 patients, 293 accepted the investigation and 286 had acceptable echocardiographic recordings, indicating left ventricular dilatation and systolic dysfunction in 30%. From the hospital records, 170 patients were identified as new cases of IDCM during the 6-year period. Adding another 34 cases revealed by our diagnostic procedures yielded an age-gender standardized incidence rate of 29.2 cases per 10⁶ persons/year. The incidence of IDCM increased considerably with age, although in younger patients its relative contribution to heart failure was greater. The incidence of IDCM was higher in the urban compared to the rural parts of the region (21 vs 32/10⁶; P=0.013). The estimated prevalence was 131/10⁶. The 8-year survival rate was 47%, which was significantly higher than among those with other types of CHF (32%; P=002). Four IDCM patients, and four with other types of CHF had cardiac transplants during the study period. The adjusted incidence of IDCM was lower than in earlier reports, possibly owing to the inclusion of rural areas and an improved ability to disclose aetiological factors.