Heart rate variability is associated with haptoglobin phenotype in patients with coronary artery disease

BACKGROUND: Three haptoglobin phenotypes exist called Hp 1-1, Hp 2-2, and Hp 2-1. Patients carrying the haptoglobin 1 allele seem to be partly protected against coronary artery disease. An attenuated heart rate variability is associated with a poor outcome in patients with coronary artery disease. Therefore, we hypothesized that the presence of the haptoglobin 1 allele would be associated with a favourable heart rate variability. DESIGN: A cross-sectional study. METHODS: We included 255 patients who were referred for elective coronary angiography as a result of suspected coronary artery disease, and all underwent 24-h electrocardiogram recordings to assess heart rate variability in the time domain. The haptoglobin phenotype was also determined in each patient. RESULTS: There were 159 patients in the Hp 1-1 and Hp 2-1 groups and 98 patients in the Hp 2-2 group. The two groups were comparable with respect to clinical parameters. However, the Hp 2-2 group had significantly lower 24-h heart rate variability values compared with the other group (RR 882 versus 921 ms, P=0.02; RMSSD 26 versus 30 ms, P<0.01; pNN50 6 versus 9%, P=0.01). Furthermore, Hp 2-2 was independently and negatively associated with heart rate variability (P=0.02). CONCLUSION: Hp 2-2 was associated with an attenuated heart rate variability in patients with coronary artery disease that may help to explain other results reporting a poor prognosis in Hp 2-2 patients.