QT INTERVAL AS A CARDIAC RISK FACTOR IN A MIDDLE-AGED POPULATION

Objective-To evaluate the value of QT interval as a cardiac risk facto r in middle aged people. Methods-The association between QT interval a nd cardiac risk factors and mortality in a middle aged Finnish populat ion of 5598 men and 5119 women was evaluated over a 23 year follow up. To adjust the QT interval confidently for heart rate, a nomogram was constructed from the baseline electrocardiograms separately for men an d women. Results-Nomogram-corrected QT interval (QT(Nc)) prolongation was associated with elevated blood pressure and signs of cardiovascula r disease; QT(Nc) shortening was associated with smoking. Over 10% pro longation of QT(Nc) predicted death in men with heart disease: adjuste d relative risk (RR) was 2.17 (95% confidence interval 0.67-7.45) for sudden death; 2.12 (1.25-3.59) for total cardiovascular mortality; and 1.92 (1.23-3.00) for all cause mortality. In healthy men the increase in RR was not significant: sudden death, 1.48 (0.67-3.25); total card iovascular mortality, 1.25 (0.92-1.70); all cause mortality, 1.21 (0.9 6-1.53). However, healthy men with long QT(Nc) in the lowest heart rat e quartile exhibited an RR of 2.75 (1.00-7.40) for sudden death. Over 10% shortened QT(Nc) predicted cardiovascular death in men with heart disease who smoked; RR 3.72 (1.45-9.54). Non-smoking men with short QT (Nc) had low mortality risks irrespective of possible signs of cardiov ascular disease. The trends in mortality risks were similar but weaker for women. Conclusions-In a middle aged population, prolonged QT inte rval predicts cardiac mortality in men with signs of cardiovascular di sease. In women and healthy men this risk is weak and may reflect subc linical heart disease. A shortened QT interval predicts death in men w ith heart disease who smoke.