Background: Familial combined hyperlipidemia (FCHL) is a common hereditary disorder of lipoprotein metabolism estimated to cause 10% to 20% of premature coronary heart disease. We investigated whether functional abnormalities exist in coronary reactivity in asymptomatic patients with FCHL.
Methods and results: We studied 21 male FCHL patients (age, 34.8+/-5.4 years) and a matched group of 21 healthy control subjects. Myocardial blood flow (MBF) was measured at baseline and during dipyridamole-induced hyperemia with PET and 15O-labeled water. The baseline MBF was similar in patients and control subjects (0.79+/-0.19 versus 0.88+/-0.20 mL. g-1. min-1, P=NS). An increase in MBF was seen in both groups after dipyridamole infusion, but MBF at maximal vasodilation was lower in FCHL patients (3.54+/-1.59 versus 4.54+/-1.17 mL. g-1. min-1, P=0.025). The difference in coronary flow reserve (CFR) was not statistically significant (4.7+/-2.2 versus 5.3+/-1.6, P=NS, patients versus control subjects). Considerable variability in CFR values was detected within the FCHL group. Patients with phenotype IIB (n=8) had lower flow during hyperemia (2.5+/-1.2 versus 4.2+/-1.5 mL. g-1. min-1, P<0.05) and lower CFR (3.4+/-2.1 versus 5.4+/-2.0, P<0.05) compared with phenotype IIA (n=13).
Conclusions: Abnormalities in coronary flow regulation exist in young asymptomatic FCHL patients expressing phenotype IIB (characterized by abnormalities in both serum cholesterol and triglyceride concentrations). This is in line with previous observations suggesting that the metabolic abnormalities related to the pathophysiology of FCHL are associated with the phenotype IIB.