Studies in asymptomatic primary hyperlipidaemia. IV. ECG at rest and during exercise and its relation to various lipoprotein classes

Abstract

Among approximately 20,000 apparently healthy subjects whose serum cholesterol and triglyceride (TG) values were screened at a health examination, those with the most pronounced hyperlipidaemia have been selected for further studies. Thus, 188 males and 126 females, aged 30-65 years, with asymptomatic primary hyperlipoproteinaemia (HLP) and 59 male and 69 female controls with non-elevated serum lipids were studied with regard to frequency of ST segment depressions during exercise to near maximal heart rate. Furthermore, the concentrations of cholesterol and TG were determined in the lipoprotein (LP) classes very low (VLDL), low (LDL) and high (HDL) density LP, separated by preparative ultracentrifugation. From the LP analysis each subject's HLP was classified according to the typing system of HLP recommended by the WHO. The frequency of ST depressions (Minnesota code 4.1-4.3 as well as 4.1-4.4) increased with age, was higher in females than in males and was increased in all types of HLP in males. The percentage frequencies of ST depressions 4.1-4.4 in the various types of HLP were (male/female, p against controls): controls 16/36, type IIA 50 (p less than 0.01)/56, type IIB 64 (p less than 0.01)/75 (p less than 0.01)/75 (p less than 0.05), type III 67 (p less than 0.01)/33 and type IV HLP 40 (p less than 0.01/53. There was no significant difference in the frequencies of ST depressions in subjects with "high" and "low" BP (hypertensives were excluded from the study) or in subjects with "high" and "low" k-value for the i.v. glucose tolerance. Non-smokers had a tendency to higher frequencies of ST depressions than smokers. The association between different LPs and other "risk factors" and the occurrence of ST depressions in HLP were studied further with multiple regression analysis. Invariably age was the best predictor of ST depressions. The LP fraction giving the highest correlation coefficient was LDL cholesterol in both sexes. VLDL TG and LDL TG were also positively and significantly associated with ST depressions. HDL cholesterol was negatively but insignificantly correlated to ST depressions. When age and LDL cholesterol had been entered into the multiple regression, the only factor giving further significance was VLDL TG in males. Probability tables for the occurrence of ST depressions considering age and different levels of LDL cholesterol and VLDL TG were given. The importance of simultaneous consideration of both VLDL TG and LDL cholesterol in ST segment depression was evident from the tables. Of other "risk factors" (BP, glucose tollerance, smoking, ESR) entered into the regression together with only age and the LPs, only ESR contributed with borderline significance to ST depressions.